Aftmast rigs???

[jdardozzi]

Can anyone comment on aftmast rigs. I read some of Brian Eiland's stuff and recently saw a motorsailer with a aftmast bipod flying a hugh genoa. I liked it a lot and want to rerig my 48 steel yawl this way if I can. Any help would be appreciated.

[tspeer]

Before considering an aftmast rig, I'd ask the designer to show you the numerical trade studies he's done concerning the drag of the mast (especially a bipod) and rigging vs the expected gains in sail efficiency. "Show me the numbers."

[jdardozzi]

Now you sound a little skeptical...which is good. I would like to hear more of your opinion if you have more. I am looking for a designer who would be interested in this project. What I've read and seen comes from some fairly respected designers like McGurdy & Rhodes, Phil Bolger, etc.

[tspeer]

Any study of rig effectivness points out that on a per-area basis, jibs are more effective than mainsails. That leads to the conclusion that rigs would better if they were all jib - hence the mast aft rig. What these studies often fail to point out is the effectiveness of the jib comes from its interaction with the main. On its own, it doesn't perform as well. And theoretically the main suffers in the exchange, making it look worse. But the combination is more than either sail acting in isolation.

The finest article I've ever read on the interaction of multiple lifting surfaces is A.M.O. Smith's 1975 Wright Brother's Lecture, "High Lift Aerodynamics" (AIAA Journal of Aircraft, Vol. 12, No. 6, June 1975, pp. 501-530.). He goes into great detail on the five primary effects of slotted airfoils and how they contribute to high lift. Very illuminating with regard to the main/jib interaction.


Then there's the problem of the mast. It's almost impossible to fair an isolated mast because of the range in apparent wind angles. The apparent wind will meet the mast from 20 - 30 degrees either direction. No section shape for the mast will avoid massive separation under these conditions, causing a lot of drag. The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer - with drag coefficients based greater than one. In other words, the drag of an isolated mast can be almost as much per square foot as the sail produces in lift per square foot! When you add up the frontal area of the mast plus any struts and rigging, you get a lot of windage.

The mainsail acts as a splitter plate behind the mast on a conventional rig, preventing the formation of a Karman vortex street in the wake of mast, and the favorable pressure gradient in the slot allows the flow to reattach to the mainsail, minimizing the separation behind the mast. Finally, the jib channels the airflow so that it hits the mast from a much narrower range of angles, making it feasible to reduce its drag by elongating its cross section. So the drag of the mast in a conventional rig is much less than the same mast standing by itself in a mast-aft rig.

Lastly there're the structural considerations. A mast aft rig, especially one that is inclined forward, makes it very difficult to maintain adequate tension in the forestay, leading to lots of sag. The forestay is longer, and the angle between forestay and mast is larger than the angle between backstay and mast. This means the loads on the backstay are far higher than the loads on the forestay, and the mast compression is much greater to achieve a forestay tension anywhere near that of the conventional rig. Making the mast larger, heavier, and needing additional reinforcement to stiffen the boat. You could mitigate some of these problems by mounting the mast more midships and raking it steeply aft to put the hounds at the same location. This would shift the mechanical advantage of the forestay and backstay.

That said, the mast aft rig may still make sense, especially if there are other considerations than pure aerodynamic performance. I've pointed out the downsides because you've already heard the advantages, but I don't mean to sound completely negative on the subject. You have to analyze the entire rig as a system and look at the tradeoffs in quantitative terms. Don't just look at one factor and ignore the drag penalties of others. And qualitative arguments are fine, but they need to be backed up with quantitative estimates so that you can see the relative importance of conflicting influences.

Like I said, ask your designer to walk you through the numbers. I'd take the existence or absence of those trade studies as a pretty good indicator of reliability of the designer's claims.

[jdardozzi]

thanks for the education. Assuming you could resolve the engineering issues with the mast and forestay sag, wouldn't a cutter-style rig give you the same results with regards to the slot-effect as a headsail/mailsail?

[tspeer]

I suppose so, but I've not tried to analyze it. And the cutter rig gives you the option of sailing on the staysail alone, which should present a fairly balanced sailplan in heavy conditions.

The question still remains, what's the drag of the mast(s)? And do you get a net gain?

SUBJECT: Mast-Aft Sailing Rig (single-mast ketch)


Contrary to what one might suppose, I actually enjoy receiving some of the criticisms I get on my mast-aft sailing rig concept……particularly when they come from a knowledgeable, intellectual source such as Mr. Tom Speer. He forces me to work harder at justifying the viability of this concept, as obviously his grasp of the theoretical and mathematical aspects of the aerodynamics exceeds my capabilities. I was never a professional in aerodynamics, but I’ve done some studying.

I think Tom Speer & I are both in agreement as to the superiority of the genoa sail from an aerodynamic viewpoint. And we are in agreement that much of its superiority is gained as a result of its interaction with the mainsail. (We had previous discussions of this interactivity under the subject headings, “The Slot Effect” and “How Sails Work”. Where we probably come to differ a bit is the extent of this superiority of the headsail. I give it greater creditability than he does……and particularly as I have it designed.

We know that the restriction presented by the ‘slot’ tends to divert more air around the two sides of the slot, i.e. the windward side of the main and the leeward side of the genoa. This higher flow rate on the lee side of the headsail increases its effectiveness. Now if we also overlap the mainsail with the trailing edge of the headsail, we further increase the effectiveness of the headsail, as it is able to carry this increased flow rate much further aft along its span than if it was to have to dump its flow at free stream velocities up at the leading edge of the mainsail. This overlap is important.

Now imagine looking down on the sailing rigs from directly overhead and evaluating the cross-sections at various vertical levels ( I probably should draw a diagram of this view and post it on my website). You would discover that my two parallel headstays present uniformity in both the slot between the two sails, as well as the overlap of these two sails. And this uniformity is consistent from the foot of the sails up to the hounds.

Significantly this is no-where near the case with the traditional Bermudan rig, either fractional or masthead configured. In both of these cases the throat of the slot is decreasing in size as we move vertically up the mast, while the wind velocity is increasing with this height……sort of a reverse of what we might desire. And the overlap of the necessarily hollow-leached headsail is at best really only effective at the bottom 1/3 of the sailplan. Seems there are many more questions of the compatible interactivity of the main and the headsail of the Bermudan configuration than with my twin headsail arrangement. In this comparison I think my rig configuration will prove significantly superior.

Note also that this nice uniform genoa overlap is attained while utilizing only what amounts to a 110-120% genoa rather than a radical 150-180% sail (Bermuda rig designations). And the foot areas are fully compatible, unlike the raised boom region of the Bermuda rig. Above the hounds the natural twist in apparent wind should help to make this upper portion of my genoa be a more productive sail area, certainly more productive than the thin strip of Bermudan mainsail hidden behind a mast structure on a fractional rig vessel. Just possibly the slot formed between my bare mast and the genoa sail in this upper region may create an upwash that could assist this productive task.

One might equate the twin headsail portion of my rig to the old ‘cutter’ arrangements. In fact the old cutter rigs many times demonstrated a superiority to the standard sloop when a reasonable open slot was designed between the two sails (too close a slot was an Achilles heel of the cutter arrangement). I also find it interesting that the latest ‘state-of-the-art’ Volvo 60’s appear to be evolving from their fractional rig plans to a masthead arrangement with their new flat cambered Code Zero sails (large genoas?) for close reaching work. I think this speaks to the superiority of the masthead verses fractional rig. Just when we thought evolution was favoring a smaller jib/larger main, things re-adjust. Evolution doesn’t always follow mother nature’s preferred path, it can get skewed off- -course a bit following rules put in place by handicappers.

While on this flow subject, I wish to bring up one other matter. Almost no one including the textbooks addresses the triangular nature of the slot (throat of the slot) in the traditional Bermudan rig, and how this might redirect (divert) some portions of the airflow up or down vertically (3 dimensions)? Everything is treated in a 2 dimensional manner, in a plane parallel to the water’s surface. Wouldn’t this more restrictive slot at the upper regions combined with an increased flow velocity, tend to deflect some airflow in a vertical manner? I’ve certainly seen it with my telltails…..and if my Bermudan mainsail is diverting wind upwards it must be pushing back downward on my mainsail (for every action there is an opposite and equal reaction). Or how about that ‘lift’ I seem to experience with some headsails. Where is the theoretical data to suggest and/or collaborate these observations? Things in nature don’t always follow our assumed calculated rules.

As Tom noted “then there’s the problem of the mast”. Believe me I have always been concerned about the drag of my ‘bare’ mast. I’m acutely aware of those dramatic statistics that implicate round cylindrical sections (mast or wire rigging) with creating a drag force that is somewhat larger than would even be suggested by just their cross-sectional areas. For this reason alone I would not even consider using a round-sectioned mast. Rather my mast is a foil-section for both drag purposes and strength purposes. The significant fore-to-aft forces imposed on my rig (particularly at the hounds), in combination with the necessity to keep the mast in column under significant compression loads, dictates an asymmetrical (elongated) mast section. The ideal sectional shape would be determined in the tests that I hope to conduct prior to building this rig, and may be different yet from that of a conventional rig. The aero configuration of this section will be of prime consideration, both its own drag and its affect on the mizzen sail. In any case I don’t feel it will have anything near to a ‘ten times’ affect hinted at in Tom’s posting. In fact if my sailing rig is really doing its job properly, that of smoothly redirecting the air flow so that my vessel benefits from the reactionary push, then my twin headsails will be directing that airflow over the mast located in their wakes…..and in this case my mast may actually experience smaller angles of apparent wind incidence than a mast sitting up front exposed to the much more variable incoming airflow. This coupled with the airfoil shape should help minimize some of the separation behind the mast. Then there is always the possibility of adding a small flexible piece to the rear of the mast to act as a flow stabilizer (splitter plate, per Tom’s reference).

Per Tom’s comments, “when you add up the frontal area of the mast plus any struts and all the rigging, you get a lot of windage”. How true! I once added up all the frontal area of a sailing rig on a traditional 50’ boat and came up with something like the equivalency of almost a 6’x 8’ sheet of plywood. Wow! Imagine sailing to windward holding up a sheet of drag producing board like this. Sure would be nice to have some wire covers of some sort, that could swivel around to the airflow and fair out these trailing edges. Actually some of the newer wire rigging substitutes (kevlar, zylon, PBO, etc) are of such a strength that their required diameters are much smaller.

Lets compare the frontal area drag of my rig with a traditional rigid-masted Bermuda rig and a modern 3 point stayed, rotating mast rig. In the case of a twin spreader, rigid mast, sloop rig, the required spreaders, diamonds, shrouds, forestays, backstays are just about the same rigging as required for my rig, except I have one extra rear jumper strut at the hounds, one wishbone boom on the mizzen, and a ‘bare’ mast…. However, I also have a rig that’s about 25% shorter in height for the same sail area. Net result, I probably have a slight bit more drag area, but I’m betting tests will show I have more drive per same sail area…..so my drive to drag ratio is similar or better. Close call.

I’ll concede that my rig has considerable more drag than a 3 point stayed, rotating mast rig…...and for that reason it very well may not be a candidate for a ‘RACE’ boat. Believe me, I’ve surely experienced the dramatic improvements in sail propulsion offered by rotating wing-mast rigs compared to rigid rigs. But wait a minute, what if the boat lengths increase for the next ‘RACE’…..and surely they will! I wrote of this subject in a letter/proposal to Paul Cayard (copy available). If the boat lengths increase (*note), then surely the sail driving areas must also, and yet, can it be done with a sloop rig?? Mr. Ollier has carried out EXTENSIVE tests and determined that the size of the mainsails carried on the boats of this past ‘RACE’ were the maximum size that could be handled by man-power alone (unassisted by power). If this is so, then what can be done to increase the sail areas….a multiple mast rig…..a ketch, schooner, etc?? Now, I just might be tempted to challenge a double-masted rig with my ‘single-masted ketch’. I think I might have less frontal area in this case.

Frontal area drag is not really as prime a concern, induced drag is far more critical. I expect much less off the bottom of my rig than the traditional low jib/high boom configuration of most Bermudan rigs. But at the top, I’m unsure as to all the factors, particularly with as many as 3 generating sources (3 sail tips), and the constructive or destructive interference with those portions of the rig behind the leading elements. Induced drag can easily be as high as 75% of the total air drag of a sailboat. Shaping the sails for minimum induced drag is most important for good performance…..and many a sailmaker has anticipated great results from a shape developed in theory, only to find it didn’t pan out that way in real life. I’ve not seen a lot of theory that predicts with any certainty, or qualitatively, the induced drags of a sailing rig. My rig would be interesting to view in a wind tunnel smoke test.

Most of the mast-aft rig experiments I can find thus far, have all moved the mast to the very stern of the vessel. Thus they are unable to maintain adequate headstay tension. Without this tension our headstays sag with increasing winds, our sails become fuller rather than flatter, which is exactly what we do not want, and thus the poor performance of previous experiments. With sag they all had to continually re-adjust their sails, and thus they were all seen as problematic. I think I have solved this problem. The key to proper forestay tension is proper backstay tension! First look at my masthead. The single backstay at this location is actually pulling aft at a more favorable angle than on most all other sloop rigs. This might suggest that we could decrease the tension load of this stay, but wait, lets keep it tight in order to maintain the mizzen’s leading edge shape as well. Hard to see on the website drawings, but the bottom end of this backstay is attached to the frame member of the vessel that supports the mast…the backstay’s tension upward is countered by the mast’s compression load downward…….less strength required from the frame structure, and it cancels out the dependency of this backstay’s tension on the stiffness of the aft sections of the hull structure. (The frame structure itself is also a major bulkhead of the vessel). At the hounds is where we really load things up. We have the inner forestay tension we wish to maintain, and we have the significant forward push of the aft jumper as well. Lets employ two quasi-conventional pieces of rigging: 1) the two forward facing ‘baby’ jumper struts are rigged in such a manner that both jumper stays are always sharing the load rather than allowing one to go slack, 2) the lower backstay from this hound location is split into two legs in a geometry that promotes both legs are always sharing the load rather than the normal situation with a slack leeward stay. All the rigging is working full time, which imposes less load to any single member and less load to their attachment points. Note I have 3 backstays working full time. The x-wide staying base of a multihull allows for x-wide spreaders (note no overlapping genoa) thus lower compression loads from the shrouds…..and they in turn are anchored to this same cross frame member that supports the mast. Patent protection has been sought with respect to some of these rigging details in combination with the mast-aft configuration.

My mast will experience lots of compression loading, particularly in the lower sections, so the key is to keep the mast in column. Heavier wall sections are not necessarily the answer. Keep it in column. This is where subtle changes to the geometry of the sailplan could produce the most optimum form……it might predict factors such as the optimum overall height, spreader placement, jumper strut lengths, attachment points and methods, etc. This is where I believe the computer and a finite element analysis could be very helpful in analyzing all of the rigging loads as a result of modifying any single link and determining the load requirements for all the parts. I am seeking funds for this comprehensive study so we get it right the first time out….and I would love to have someone with Tom’s analytical capabilities involved, including Tom himself.

For a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.

How about the use of a bi-pod or A-frame mast as I have hinted at previously. The slickest example I can reference was onboard Olaf Harken’s innovative “Procyon” (photos avail). But I’ll save this discussion for another time, as I just received a whole packet of new info on this subject.

My apologies Tom for not ‘showing you the numbers’. My observations are still more qualitative than quantitative, but I think I’ve put together enough qualitative material to justify some serious wind tunnel testing time, finite element analysis and/or CFD. And even though I may not go racing with this rig, the cruising potential of this ketch style rig is a very viable option. Chris White certainly appreciates a ketch rig. Check out his Concept 63 ‘Sailplan’, ‘Sailing Report’, and ‘Whitbread Comparison’ on his website
<www.chriswhitedesigns.com/concept63/index.php>



*Note: I’ve just learned that Mr.Ollier has designed a new boat for the next ‘RACE’, and it is longer. No details have yet been released as to its details and in particular its rig.

[tspeer]

My appologies if I've sounded like I was running down your design, Brian. I didn't mean to do that.

I'm genuinely in the dark as to how this arrangement would improve efficiency of the rig. My comments were intended more to encourage you to come up with some quantitative trade studies, either through prediction or test. I think that if it does turn out to be superior to a conventional rig, it would be very interesting to see why.

It's certainly an innovative variation on mast aft rigs. Past efforts at mast aft and bipod rigs have been disappointing, and I've often suspected it was because the designers didn't treat the whole rig as a system - they tried to make gains in one place at the expense of huge losses elsewhere. I hope you'll be able to avoid this and come up with a balanced design that is a real step forward.

Cheers,

[Tord]

Seems there is a lot of merit in a rearward rig with a really big genua and small, double-sided, rigid main, in conjunction with an mostly unstayed mast, where the main essentially is a flap (to use an aircraft term) to the genua - double rear stays might be needed to keep the front stay rigid!

This way the drag of the mast will be very low, the rear stays can have an aerodynamic fairing, like double-decker aircraft used to have, or have an oval cross-section. If the mast can rotate with the "main" the design of the main sail can be simplified, and the mast be profiled, to further improve flow.

[gonzo]

Since the thread was about adding a sail to a motorsailor, upwind performance is not really important. An advantage to a tripod setup is that it can clear the side decks of rigging clutter. Also, it can be used for other amenities like hanging a tarp and a couple of hammocs under it. Another use could be to eliminate the radar arch an other supports that would be installed anyway. In a race boat it may not pay to have a tripod, but in a motorsailor I think the pros are predominant.

[CT249]

Re

"I also find it interesting that the latest ‘state-of-the-art’ Volvo 60’s appear to be evolving from their fractional rig plans to a masthead arrangement with their new flat cambered Code Zero sails (large genoas?) for close reaching work. I think this speaks to the superiority of the masthead verses fractional rig."

Not really, surely. It's just that the VO 60 rules allowed a Code Zero of much larger area than the VO 60's #1 genoa. Not mystery to the fact that a much bigger Code Zero powers a boat up much more than a smaller #1 (and I think only Dolphin & Youth went for large overalap on the #1, so they were small sails).

If the VO 60 "masthead" rigs are so great, why aren't Shockwave, Zana, Xena, Scandia Wild Thing, Pyewacket, Morning Glory, etc masdtheaders? Answer - 'cause the VO 60 "masthead" rig is created by the rule.


re "Just when we thought evolution was favoring a smaller jib/larger main, things re-adjust. Evolution doesn’t always follow mother nature’s preferred path, it can get skewed off- -course a bit following rules put in place by handicappers."

If the masthead rig is so great, and fractional rigs only survive because of handicapping, why are so many classes OUTSIDE of the handicapping rules fractional? Just about every high-performance "open" class from the cats for The Race, to 18's skiffs via sportsboats are fractionals (apart perhaps from some use of light-air Code 0s)?

[Aleksander B C]

I design afterrig 20- 25 years ago. I name It thie "polish rig" and disuss it with
John Letcher. Ask him to calululait mast. He cud'nt. (not convensional). I find very simple solution for it. Bay the way this baoat is ander costruction!, (also not cnvensional) . Are you interesting? Aleksander Bronislaw Ciechanski

[brian eiland]

(I reposted this posting as I had made it as a 'guest' rather than a registered member, and was having trouble finding it for use as a reference)


Contrary to what one might suppose, I actually enjoy receiving some of the criticisms I get on my mast-aft sailing rig concept……particularly when they come from a knowledgeable, intellectual source such as Mr. Tom Speer. He forces me to work harder at justifying the viability of this concept, as obviously his grasp of the theoretical and mathematical aspects of the aerodynamics exceeds my capabilities. I was never a professional in aerodynamics, but I’ve done some studying.

I think Tom Speer & I are both in agreement as to the superiority of the genoa sail from an aerodynamic viewpoint. And we are in agreement that much of its superiority is gained as a result of its interaction with the mainsail. (We had previous discussions of this interactivity under the subject headings, “The Slot Effect” and “How Sails Work”. Where we probably come to differ a bit is the extent of this superiority of the headsail. I give it greater creditability than he does……and particularly as I have it designed.

We know that the restriction presented by the ‘slot’ tends to divert more air around the two sides of the slot, i.e. the windward side of the main and the leeward side of the genoa. This higher flow rate on the lee side of the headsail increases its effectiveness. Now if we also overlap the mainsail with the trailing edge of the headsail, we further increase the effectiveness of the headsail, as it is able to carry this increased flow rate much further aft along its span than if it was to have to dump its flow at free stream velocities up at the leading edge of the mainsail. This overlap is important.

Now imagine looking down on the sailing rigs from directly overhead and evaluating the cross-sections at various vertical levels ( I probably should draw a diagram of this view and post it on my website). You would discover that my two parallel headstays present uniformity in both the slot between the two sails, as well as the overlap of these two sails. And this uniformity is consistent from the foot of the sails up to the hounds.

Significantly this is no-where near the case with the traditional Bermudan rig, either fractional or masthead configured. In both of these cases the throat of the slot is decreasing in size as we move vertically up the mast, while the wind velocity is increasing with this height……sort of a reverse of what we might desire. And the overlap of the necessarily hollow-leached headsail is at best really only effective at the bottom 1/3 of the sailplan. Seems there are many more questions of the compatible interactivity of the main and the headsail of the Bermudan configuration than with my twin headsail arrangement. In this comparison I think my rig configuration will prove significantly superior.

Note also that this nice uniform genoa overlap is attained while utilizing only what amounts to a 110-120% genoa rather than a radical 150-180% sail (Bermuda rig designations). And the foot areas are fully compatible, unlike the raised boom region of the Bermuda rig. Above the hounds the natural twist in apparent wind should help to make this upper portion of my genoa be a more productive sail area, certainly more productive than the thin strip of Bermudan mainsail hidden behind a mast structure on a fractional rig vessel. Just possibly the slot formed between my bare mast and the genoa sail in this upper region may create an upwash that could assist this productive task.

One might equate the twin headsail portion of my rig to the old ‘cutter’ arrangements. In fact the old cutter rigs many times demonstrated a superiority to the standard sloop when a reasonable open slot was designed between the two sails (too close a slot was an Achilles heel of the cutter arrangement). I also find it interesting that the latest ‘state-of-the-art’ Volvo 60’s appear to be evolving from their fractional rig plans to a masthead arrangement with their new flat cambered Code Zero sails (large genoas?) for close reaching work. I think this speaks to the superiority of the masthead verses fractional rig. Just when we thought evolution was favoring a smaller jib/larger main, things re-adjust. Evolution doesn’t always follow mother nature’s preferred path, it can get skewed off- -course a bit following rules put in place by handicappers.

While on this flow subject, I wish to bring up one other matter. Almost no one including the textbooks addresses the triangular nature of the slot (throat of the slot) in the traditional Bermudan rig, and how this might redirect (divert) some portions of the airflow up or down vertically (3 dimensions)? Everything is treated in a 2 dimensional manner, in a plane parallel to the water’s surface. Wouldn’t this more restrictive slot at the upper regions combined with an increased flow velocity, tend to deflect some airflow in a vertical manner? I’ve certainly seen it with my telltails…..and if my Bermudan mainsail is diverting wind upwards it must be pushing back downward on my mainsail (for every action there is an opposite and equal reaction). Or how about that ‘lift’ I seem to experience with some headsails. Where is the theoretical data to suggest and/or collaborate these observations? Things in nature don’t always follow our assumed calculated rules.

As Tom noted “then there’s the problem of the mast”. Believe me I have always been concerned about the drag of my ‘bare’ mast. I’m acutely aware of those dramatic statistics that implicate round cylindrical sections (mast or wire rigging) with creating a drag force that is somewhat larger than would even be suggested by just their cross-sectional areas. For this reason alone I would not even consider using a round-sectioned mast. Rather my mast is a foil-section for both drag purposes and strength purposes. The significant fore-to-aft forces imposed on my rig (particularly at the hounds), in combination with the necessity to keep the mast in column under significant compression loads, dictates an asymmetrical (elongated) mast section. The ideal sectional shape would be determined in the tests that I hope to conduct prior to building this rig, and may be different yet from that of a conventional rig. The aero configuration of this section will be of prime consideration, both its own drag and its affect on the mizzen sail. In any case I don’t feel it will have anything near to a ‘ten times’ affect hinted at in Tom’s posting. In fact if my sailing rig is really doing its job properly, that of smoothly redirecting the air flow so that my vessel benefits from the reactionary push, then my twin headsails will be directing that airflow over the mast located in their wakes…..and in this case my mast may actually experience smaller angles of apparent wind incidence than a mast sitting up front exposed to the much more variable incoming airflow. This coupled with the airfoil shape should help minimize some of the separation behind the mast. Then there is always the possibility of adding a small flexible piece to the rear of the mast to act as a flow stabilizer (splitter plate, per Tom’s reference).

Per Tom’s comments, “when you add up the frontal area of the mast plus any struts and all the rigging, you get a lot of windage”. How true! I once added up all the frontal area of a sailing rig on a traditional 50’ boat and came up with something like the equivalency of almost a 6’x 8’ sheet of plywood. Wow! Imagine sailing to windward holding up a sheet of drag producing board like this. Sure would be nice to have some wire covers of some sort, that could swivel around to the airflow and fair out these trailing edges. Actually some of the newer wire rigging substitutes (kevlar, zylon, PBO, etc) are of such a strength that their required diameters are much smaller.

Lets compare the frontal area drag of my rig with a traditional rigid-masted Bermuda rig and a modern 3 point stayed, rotating mast rig. In the case of a twin spreader, rigid mast, sloop rig, the required spreaders, diamonds, shrouds, forestays, backstays are just about the same rigging as required for my rig, except I have one extra rear jumper strut at the hounds, one wishbone boom on the mizzen, and a ‘bare’ mast…. However, I also have a rig that’s about 25% shorter in height for the same sail area. Net result, I probably have a slight bit more drag area, but I’m betting tests will show I have more drive per same sail area…..so my drive to drag ratio is similar or better. Close call.

I’ll concede that my rig has considerable more drag than a 3 point stayed, rotating mast rig…...and for that reason it very well may not be a candidate for a ‘RACE’ boat. Believe me, I’ve surely experienced the dramatic improvements in sail propulsion offered by rotating wing-mast rigs compared to rigid rigs. But wait a minute, what if the boat lengths increase for the next ‘RACE’…..and surely they will! I wrote of this subject in a letter/proposal to Paul Cayard (copy available). If the boat lengths increase (*note), then surely the sail driving areas must also, and yet, can it be done with a sloop rig?? Mr. Ollier has carried out EXTENSIVE tests and determined that the size of the mainsails carried on the boats of this past ‘RACE’ were the maximum size that could be handled by man-power alone (unassisted by power). If this is so, then what can be done to increase the sail areas….a multiple mast rig…..a ketch, schooner, etc?? Now, I just might be tempted to challenge a double-masted rig with my ‘single-masted ketch’. I think I might have less frontal area in this case.

Frontal area drag is not really as prime a concern, induced drag is far more critical. I expect much less off the bottom of my rig than the traditional low jib/high boom configuration of most Bermudan rigs. But at the top, I’m unsure as to all the factors, particularly with as many as 3 generating sources (3 sail tips), and the constructive or destructive interference with those portions of the rig behind the leading elements. Induced drag can easily be as high as 75% of the total air drag of a sailboat. Shaping the sails for minimum induced drag is most important for good performance…..and many a sailmaker has anticipated great results from a shape developed in theory, only to find it didn’t pan out that way in real life. I’ve not seen a lot of theory that predicts with any certainty, or qualitatively, the induced drags of a sailing rig. My rig would be interesting to view in a wind tunnel smoke test.

Most of the mast-aft rig experiments I can find thus far, have all moved the mast to the very stern of the vessel. Thus they are unable to maintain adequate headstay tension. Without this tension our headstays sag with increasing winds, our sails become fuller rather than flatter, which is exactly what we do not want, and thus the poor performance of previous experiments. With sag they all had to continually re-adjust their sails, and thus they were all seen as problematic. I think I have solved this problem. The key to proper forestay tension is proper backstay tension! First look at my masthead. The single backstay at this location is actually pulling aft at a more favorable angle than on most all other sloop rigs. This might suggest that we could decrease the tension load of this stay, but wait, lets keep it tight in order to maintain the mizzen’s leading edge shape as well. Hard to see on the website drawings, but the bottom end of this backstay is attached to the frame member of the vessel that supports the mast…the backstay’s tension upward is countered by the mast’s compression load downward…….less strength required from the frame structure, and it cancels out the dependency of this backstay’s tension on the stiffness of the aft sections of the hull structure. (The frame structure itself is also a major bulkhead of the vessel). At the hounds is where we really load things up. We have the inner forestay tension we wish to maintain, and we have the significant forward push of the aft jumper as well. Lets employ two quasi-conventional pieces of rigging: 1) the two forward facing ‘baby’ jumper struts are rigged in such a manner that both jumper stays are always sharing the load rather than allowing one to go slack, 2) the lower backstay from this hound location is split into two legs in a geometry that promotes both legs are always sharing the load rather than the normal situation with a slack leeward stay. All the rigging is working full time, which imposes less load to any single member and less load to their attachment points. Note I have 3 backstays working full time. The x-wide staying base of a multihull allows for x-wide spreaders (note no overlapping genoa) thus lower compression loads from the shrouds…..and they in turn are anchored to this same cross frame member that supports the mast. Patent protection has been sought with respect to some of these rigging details in combination with the mast-aft configuration.

My mast will experience lots of compression loading, particularly in the lower sections, so the key is to keep the mast in column. Heavier wall sections are not necessarily the answer. Keep it in column. This is where subtle changes to the geometry of the sailplan could produce the most optimum form……it might predict factors such as the optimum overall height, spreader placement, jumper strut lengths, attachment points and methods, etc. This is where I believe the computer and a finite element analysis could be very helpful in analyzing all of the rigging loads as a result of modifying any single link and determining the load requirements for all the parts. I am seeking funds for this comprehensive study so we get it right the first time out….and I would love to have someone with Tom’s analytical capabilities involved, including Tom himself.

For a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.

How about the use of a bi-pod or A-frame mast as I have hinted at previously. The slickest example I can reference was onboard Olaf Harken’s innovative “Procyon” (photos avail). But I’ll save this discussion for another time, as I just received a whole packet of new info on this subject.

My apologies Tom for not ‘showing you the numbers’. My observations are still more qualitative than quantitative, but I think I’ve put together enough qualitative material to justify some serious wind tunnel testing time, finite element analysis and/or CFD. And even though I may not go racing with this rig, the cruising potential of this ketch style rig is a very viable option. Chris White certainly appreciates a ketch rig. Check out his Concept 63 ‘Sailplan’, ‘Sailing Report’, and ‘Whitbread Comparison’ on his website
<www.chriswhitedesigns.com/concept63/index.php>



*Note: I’ve just learned that Mr.Ollier has designed a new boat for the next ‘RACE’, and it is longer. No details have yet been released as to its details and in particular its rig.

[brian eiland]

Brian wrote:
I found this discussion today on the web that I took the liberty to add to the forum discussion of cutter rigs, and to this aft mast discussion that features two raked headsails acting in a somewhat similar manner

Raked Cutter Rig by WindSpeedYachts.com (http://www.windspeedyachts.com.au/sailing_multihulls.htm)

History.
Ever since 1851 when the Schooner America with her 11.5 degree mast rake won the America's cup, mast rake has been used to improve the performance of sail power as a propulsion method. Every high speed craft including land yachts, ice boats, windsurfers and racing Multihulls use mast rake to improve performance.
Yachts that race to a handicap don't use mast rake because it is penalized by the handicap rules. In handicap racing the fastest yacht is not the winner, the yacht that sails closest to her handicap is the winner. Our yachts are not designed to any racing rules they are designed to be safe, efficient and comfortable.
The cutter rig has historically been the rig of choice for the monohull cruising sailor.

The Modern Raked Cutter Rig.
In 1991 we proudly redeveloped and introduced the modern, efficient raked cutter rig into cruising Multihulls.

The Raked Cutter Rigs features:
+A 7.5 degree mast rake, the key to the whole modern cutter rig working so well:
+Parallel fore stays for the greatest cutter effect.
+The distance between the forestays is spaced for maximum sail efficiency.
+The Jib easily tacks between the stays.
+Low aspect ratio rig to increase stability, reduce rig loads and reduce pitching.
+Low centre of gravity, low wind resistance cruising rig.
+The stay sail is close to the deck which improves efficiency and pressurizes +the windward nets and lifts the leeward nets reducing on board spray and increases stability.
+With the roller furling Jib on the composite bowsprit, which is wide enough to walk on and the fully battened stay sail on the fore beam, the fore triangle is broken into two easily handled sails.
+The large fully battened mainsail is reduced in area by the mast rake.
+This long low sail plan increases stability, reduces the sail handling effort required by the crew and off the wind increases the power to propel the yacht.

Notes
This rig is the complete opposite approach to the trend for high aspect ratio fractional rigs being installed on cruising yachts.
We have observed the trend by designers and builders to increase the height of masts to "improve performance" however we are informed by boat owners that increased speeds are achieved by reefing the mainsail. This is not surprising, tall masts raise the centre of effort of the sailplan, this increases the heeling force which pushes the leeward hull further into the water increasing hull drag. If you look into the hull shapes, for example a 12 m catamaran with fat hulls 1.2 to 1.4 m wide on the water line and fixed keels, the drag on these hulls when the leeward hull is depressed increases considerably. This type of hullshape is happy with both hulls evenly floating while motoring or sailing down wind not being pressed hard to windward or reaching.
The high aspect ratio racing rig works exceptionally well on racing yachts however it does not make slow hull shapes fast hull shapes.
How does mast rake increase yacht speed?

The more horizontal the fore stay angle the greater the vertical lift generated by the jib. Effectively lifting the bows which reduces the yachts displacement which reduces wave drag and increases the yachts speed. Raking the mast aft has a similar effect to fore stay angle.

With a vertical mast the forces generated by the mainsail are forward and downwards but by raking the mast aft these forces are rotated to become forward and upward resulting in increased speed due to decreased displacement.

The effect of mast rake is apparent sailing to windward but far more obvious when reaching and running.

Because the bows are not driven down by sail pressure we can use finer bows which further reduce drag and pitching.

Another advantage of mast rake is reduced pitching caused by the lack of the pendulum effect.
With a vertical mast in a sea way the masts mass and momentum forces the bows and sterns up and down alternately greatly increasing the pitching.
With a raked mast in a sea the masts mass and momentum forces are rotated to force the bows forward and the sterns up and down alternately greatly reducing the pitching.

The combined effect of the lift generated from the raked cutter rig, the lift generated from the under wing, the extra buoyancy and dynamic lift generated by the inboard flair and the stabilizing effect of the rudder mounted foil combine to reduce heeling, under wing wave impacts, yacht motion and increases average speeds.

The Raked Cutter Rig of the WindSpeed 40 has proved to achieve higher average speeds than any other rig aboard a liveaboard cruising Multihull yacht yet encountered.

Test results
Test have been undertaken on many yachts over many years but the most convincing test was aboard a 2000 kg 10 metre racing Multihull with a 15 metre rotating mast. This yacht started life with a vertical mast, and over two years the mast was raked progressively aft with consistently improving performance. The lift generated by the raked mast allowed us to carry more sail area in stronger winds off the wind and when sailing to windward, the crew of four would sit forward of the mast to keep the bows down.

On a 1.5m long radio controlled test model trimaran the mast was raked so far aft that the model capsized bow over stern from the lift generated from mast rake!

Note: We were testing the feasibility of using surface effect wings for racing trimaran beams at the time and these foils may have contributed in the capsizes [tested in 1981]

Conclusion
Our theoretical calculations and practical testing indicate that the raked cutter rig on the WindSpeed 40 generates 240 kg of vertical lift in 18 knots of apparent wind and sailing to windward at 8 knots this reduction in displacement equates to approximately 0.1 knots extra yacht speed! The lift generated by the raked cutter rig increases as the sheets are eased which increases the improvements in downwind yacht speeds

(opinions of www.windspeedyachts.com.au)

Brian added a note: It doesn't appear from their posted drawings that the mast rakes back 7.5 degrees?

[gggGuest]

Brian wrote:

Because the bows are not driven down by sail pressure we can use finer bows which further reduce drag and pitching.



Betcha the bows are always driven down by sail pressure. (well unless you are using a kite anyway) Draw the force triangles. However the stern can be effectively lifted, and if significant this "displacement reduction" will of course affect the way the hull goes though the water

[Dutch Peter]

Betcha the bows are always driven down by sail pressure.

No, they're not. That's the difference between a lee or luff helm. It's actually considered safer when a boat will luff up, otherwise the boat will run away when your down in the water.

[brian eiland]

Betcha the bows are always driven down by sail pressure. (well unless you are using a kite anyway) Draw the force triangles. However the stern can be effectively lifted, and if significant this "displacement reduction" will of course affect the way the hull goes though the water

First I would like to note to 'gggGuest' that that quote he attributed to me should really be attributed to the fellows at WindSpeedYachts whose website I got this discussion from.

Next I would comment that he is correct that there is a moment force created by the sail force centers (other than kites) above the hull resistance centers that does tend to drive our bows under. But the contributions by the headsails can be so much less than that of the Bermudian mainsail that it may appear as a bow lifting experience. Many sailors have expressed this sensation. Even Herreshoff comented on these bow burying forces aboard his catamaran, and the lifting of the bows by the headsail.: go to http://www.herreshoff.org/frames/Chronicles1.htm and click on the 1988 heading of Herrshoff's Catamaran (http://www.herreshoff.org/images/1985-1995/1988_p1.pdf) Be sure to scroll back to page 4.

You might also visit another tread on this forum at "Herreshoff's catamaran reasoning (http://boatdesign.net/forums/showthread.php?t=5843)"

[brian eiland]

....just an observation....
14 Jan 2005

Back at Cape Horn, MacArthur went round early yesterday morning in the
sort of epic conditions for which that feared headland is infamous. With
winds gusting to more than 60 knots, MacArthur's 75ft trimaran, B & Q, was
sailing under staysail only, yet was still hitting more than 30 knots of
boat speed as it surfed down huge waves squeezing their way between the
tip of South America and Antarctica.

These were some of the roughest and most dangerous conditions of
MacArthur's voyage and by the time B & Q got past the Horn, about 35 miles
south of the lighthouse, MacArthur had collapsed exhausted in her bunk.

[brian eiland]

...I think Tom Speer & I are both in agreement as to the superiority of the genoa sail from an aerodynamic viewpoint. And we are in agreement that much of its superiority is gained as a result of its interaction with the mainsail. (We had previous discussions of this interactivity under the subject headings, “The Slot Effect” and “How Sails Work”. Where we probably come to differ a bit is the extent of this superiority of the headsail. I give it greater creditability than he does……and particularly as I have it designed.

We know that the restriction presented by the ‘slot’ tends to divert more air around the two sides of the slot, i.e. the windward side of the main and the leeward side of the genoa. This higher flow rate on the lee side of the headsail increases its effectiveness.....

The gentleman who most deserves credit for finally getting the explainations of sail aerodynamics corrected, and upon which several excellent books by Tom Whidden and C.A. Marchaj are based has recently updated his website to include many of the technical papers and magazine articles he wrote on the subject originally. I had mentioned his name, Arvel Gentry, in these postings previously, but I could not make a direct reference to his many documents as they were not posted on his site at that time.

From his site, "I got involved in the technical aspect of sailing because I started racing. Reading the sailing books and magazines, I began to realize that most of what was written about the aerodynamics of sails was wrong, or certainly very misleading."

"The explanations for how lift is generated were based on popular myths. The description of the interactions between a jib and mainsail, the 'slot effect', did not make much aerodynamic sense."

"I was soon launched on a quest to discover how our sails really worked. Over the years this resulted in a number of technical sailing papers and magazine articles. The technical sailing papers are archived in this section of my web site. My magazine articles can be reached from my Home page."

"If you are interested in sailing aerodynamics and how your sails work, you have come to the right place. All of my sailing technical papers and magazine articles are archived on the Technical Papers and Magazine Articles pages."

Arvel Gentry's updated website http://www.arvelgentry.com/

[brian eiland]

Something different...a gentleman wrote to me recently;

I have been interested in the idea of a forward raked mast with an
unusual sail layout for quite some time now, originally seeing the
idea at a student design show. The boat looked like the sailboat
equivalent to a future speculating auto show "Concept Car", with wild
ideas that gave little concession to practicality.
Kyle


Have a look at this futuristic design (http://boatdesign.net/forums/showthread.php?p=72778#post72778)

[FAST FRED]

The best reason for an aft stepped mast is it will be used to mount the Flopper Stoppers in that location anyway, for comfort under power.

Most M/S dont strive for FANTASTICASTIC WINDWARD ability , they just try for a higher than adverage transit speed.

Modern roller furling gear would be a good gamble with large forestaysail & staysail

and a fully battened main , as they M/S so well.

FAST FRED

[scot]

I ran across the pro/con discussion by Brian and Tom quite some time ago, and recently the mast aft rig has popped back into my mind. I have some ideas that I have not seen mentioned before, and I thought I'd bring them up and let Brian and Tom have at them.

To summarize, mast aft advantages:
Staysails have less turbulence than a mast, and so generate more lift.
Staysails on parallel stays will provide good slotted wing performance.
Staysails are easy to roller furl, allowing continuously variable reefing.

Mast aft disadvantages:
Bare mast has lots of drag, not practical to streamline for all points of sail.
Forward inclined mast generates huge backstay tension.

So first let me address the drag issue. Why not wrap the mast in a rigid wingsail with a short chord, maybe a NACA 0012. Allow the sail to rotate about the mast 360 degrees, and balance it so that it points into the wind. This will significantly reduce the drag of the mast on any point of sail, and the rigid wingsail won't flutter and thus shouldn't need to be reefed, as feathered it will produce less resistance than a typical mast with a reefed or stowed mainsail.

Next, on stay tension, what if you were to use an aft rake rather than a forward rake? This would put the base of the mast near amidships rather than near the stern, but it would equalize the forestay and backstay tension. It moves the COE significantly forward, but with Brian's "mizzen staysail" you could correct for that. The resulting rig is a hybrid of the cutter (which puts the mast pretty far aft to begin with) and Brian's mast aft rig, with it's mizzen staysail. Unlike a traditional cutter, the mainsail is a wingsail, and thus doesn't have the "shadow" of the mast to contend with. Since rigid windsails need to be super-high aspect ratio to be light, the mizzen staysail takes up the slack behind the mast, providing sail area lost by the high aspect wingsail.

The disadvantage of this setup is that the mast, rather than being out of the way at the aft of the cockpit, is back near the center, but by basing it on a structural arch that formed part of the cabin roof, then it could be worked around. The advantages seem to be pretty good:

1. The three primary sails (jib, fore staysail, and mizzen staysail) are all fairly high aspect ratio sails that can be quickly roller furled
2. The foresails can interact with each other, and when close hauled with the rigid wingsail as well
3. The rig tensions shouldn't be significantly greater than a standard sloop or cutter rig
4. The rig can be sailed with one sail (fore staysail, fethered wingsail), two (jib and mizzen staysail), three (all staysails), or all four sails, if the wingsail is sheeted in.

Despite the apparently complexity of the 4-sail rig, it should be fairly easy to handle. The wingsail can always be left unsheeted during tacking and jibing, and the mizzen and fore staysails can be provided with booms to make them self taking; the jib can overlap, and be furled partially or fully during the tack to keep it out of the way. For jibing, all sails can be quickly furled, the wingsail can rotate forward of the mast, and the sails can be quickly redeployed after the jibe.

Any comments? It seems like this hybrid addresses Tom's issues about aerodynamics and preserves most of the advantages of Brian's mast aft rig. If anyone sees any holes in the idea, please point them out, and I'll see if I can address them. I'll also work on a sketch of the concept; I think the wingsail might have to be split at the level of the spreaders/inner forestay, and it might be the case that the upper portion is independent of the lower, but so far that's the only part of the rig that's not fairly straightforward.

--scot

[tspeer]

You're almost describing a cutter rig with a wingmast.

It's not clear to me that there's any advantage to having a rotating wingmast by itself instead of having a sail attached to its trailing edge. A wingmast/sail combination provides more leading edge thrust than a staysail because of the greater thickness of the leading edge.

Nobody yet in this thread has offered up any quantitative estimate as to the performance advantages of their design over a conventional sloop or cutter rig designed to the same requirements, or shown how there's any weight savings in the structure. I can understand the desire to simplify sail handling with roller furling staysails. But any improvement in performance is by definition a quantitative issue, not a qualitative one.

[brian eiland]

Nobody yet in this thread has offered up any quantitative estimate as to the performance advantages of their design over a conventional sloop or cutter rig designed to the same requirements, or shown how there's any weight savings in the structure. I can understand the desire to simplify sail handling with roller furling staysails. But any improvement in performance is by definition a quantitative issue, not a qualitative one.
Hello again Tom. Once again I must beg off on a ‘quantitative’ reply to the advantages of the headsail arrangement on my mast aft rig concept. I believe just as with the rigging load questions (http://boatdesign.net/forums/showthread.php?t=2293), a straight-forward quantitative calculation as to the superiority of the efficiency of the headsail over the mainsail may well be an incalculable quantity from a purely mathematical standpoint. So I have to rely on a variety of observations gathered from history, from pass designer’s applications, from current theorist, from real time sailor’s experiences, etc.

So I will present a few of those observations:
1) Lets begin with a ‘pictorial’ example. Rick Loheed recently posted these images here (http://boatdesign.net/forums/showpost.php?p=89766&postcount=148), “I found a post that had a reference to JavaFoil, Martin Hepperle's 'relatively simple' inviscid foil analysis program that will do multi-element airfoils. It is great for illustration purposes here. Clearly it shows the affect of the whole system- actually, as a cascade of foils. Further Aft foils must have more incidence- but when incidence is added, they help increase circulation around the whole system, increasing the forward foils effectiveness by inducing more incidence and accelerating more mass about the whole mess".
Which sail looks most effective at driving you forward.

2) Another JavaFoil analysis by Rick here (http://boatdesign.net/forums/showpost.php?p=89921&postcount=151), “Here is a comparison using Javafoil of a simple 15% camber (pretty high lift) 40% max camber location Jib/main combination arbitrarily loaded to near Max CL, and a 20% Clark 'Y' wingmast shape based on methods from Tom Speer's wingmast paper. For an input Aspect ratio of 10 for each case, this simulation shows a Max Cl of 2.11 for the main jib combo readily achieved for the combination, whereas the wingmast gets to a fairly typical Cl of 1.2 max”

2) Excerpted from aerodynamicist and North Sails consultant Paul Bogataj’s paper, “How Sails Work” http://www.northsailsod.com/articles/article6-1.html (http://www.northsailsod.com/articles/article6-1.html)
‘Sails in Combination’, “Each sail by itself is much simpler than the combination of a foresail and mainsail as in the sloop rig. The sails are operating so close to each other that they both have significant interaction with the other. The most interesting feature of this is that the two sails together produce more force to pull the boat than the sum of their forces if they were each alone.
The foresail of a sloop rig operates in the upwash of the mainsail. The wind as far upstream as the luff of a genoa is influenced by the upwash created by the mainsail. Hence, a jib or genoa in front of a mainsail has a higher flow angle than it otherwise would have by itself, causing an increase in the amount of force that the forward sail produces. So, while the mainsail is experiencing detrimental interference from the foresail, the foresail benefits from the interference of the mainsail. Notice that more air is directed around the curved leeward side of the foresail. This causes higher velocity (lower pressure) and more force. The net result is that the total force of the two-sail system is increased, with the foresail gaining more than the mainsail loses”

3) Its been some 40 years ago that I did extensive study of some of the classic sailing boat design books, but I can distinctly remember how there was applied a ‘performance factor’ to the headsail of 1,3 to 1.5 more effective than its actual sail area when computing the CE of the sail plan. So even though the theory was not thoroughly understood at the time, real time observations came into the equation.

4) Redcooprs was talking of the subject under the ‘Fraction Rig’ discussion (www), “However, the design of sailforms is very much a practical nature. In terms of sailing, the feel is that our jib supplies the driving power - and wind tunnel tests also show that it has a very large Cl compared to the main. The main on the other hand, is very responsible for the righting moment and general tuning of the boat.”

5) etc

[yokebutt]

I'm realizing from reading this thread and the masthead vs. fractional one that this type of rig would have the same type of "backwards" dynamic response in puffs, where the forestays sag and powers up the sails, just when you don't want it.

Yoke.

[brian eiland]

I ran into an old friend at this year's Annapolis Sailboat Show, Rob Underwood who for years was managing director of Prout Catamarans.

We had a few discussions, including one about the 'Prout' name brand being sold to an Asian boatyard I visited recently.

Rob is now heavily involved at BroadBlue catamarans. As I was looking over their literature I noted that one of their models (the 385) was being offered with a standard sloop rig, and also with a mast-aft rig similar to the older Prout vessels.

That prompted a question from me, what is the acceptance quotient of the aftmast rig compared with the std rig? Rob’s response almost surprised even me, "10 to 1 the folks choose the aft rig over the conventional one"

I went on to ask why this might be? Taming the handling of the conventional mainsail seemed to be a primary motivation.

There might be a marketing message here?

[Richard Hillsid]

I found this beuty in Brian Eiland's gallery

http://www.boatdesign.net/gallery/showphoto.php?photo=1075&password=&sort=2&thecat=995

Actually im quite interested on this subject and happy it popped up.

I bought a old 100’ 100 ton small cargo ship with a old but nice ship engine. and have been toying with the idea of a sail for it, something that would give 4-5 knots and able to point 40-44 degrees to the wind and help keep out of harms way if something goes wrong with the engine.

Also it should be able to save some fuel with favourable wind.

No keel so plenty of leeway without the help of motor, but might give a nice ride.

[brian eiland]

Hello Richard,
Just wondered if you also saw this subject thread, "Wishbone sailing Rig"
http://boatdesign.net/forums/showthread.php?t=1999 (http://boatdesign.net/forums/showthread.php?t=1999)


...and particularly this posting, "Variations on the Mast Aft Rig Concept"
http://boatdesign.net/forums/showpost.php?p=109336&postcount=34 (http://boatdesign.net/forums/showpost.php?p=109336&postcount=34)


...and here's some photos of the shorter version of that rig under sail
http://boatdesign.net/forums/showpost.php?p=110510&postcount=39 (http://boatdesign.net/forums/showpost.php?p=110510&postcount=39)

[Richard Hillsid]

Brian no i wasn’t familiar with these posts, they lead me to more info thanks.

Bear in mind im not trying to make a sailboat out of the cargo boat, its just that I have sailed my life and always trust a sail over motor. Now with this new toy im trying to be self reliant as I know I will be doing some adventures on this one too.

The alternatives I have are a Latin rig or an aft mast, cant have anything to high or overpovered.
The Latin rig gives me a mast forward for nav lights but requires a long boom, no problem but gives no manner of hoisting stuff.
The aft wishbone gives nav light, radar and vhf stand, a hoisting platform and long luff I can hang some sails to give me the in this case 20 + hp. I need to keep out of harms way, with a wl of 92’ its not asking for 2 much.

[brian eiland]

Bear in mind im not trying to make a sailboat out of the cargo boat, its just that I have sailed my life and always trust a sail over motor. Now with this new toy im trying to be self reliant as I know I will be doing some adventures on this one too.

The Latin rig gives me a mast forward for nav lights but requires a long boom, no problem but gives no manner of hoisting stuff.
Maybe you should consider a 'junk rig' or a modern square rig like Maltese Falcon. Both of these rigs could give you multiple vertical mast for hoisting stuff, and a low overturning moment.
http://boatdesign.net/forums/showthread.php?t=12459
http://boatdesign.net/forums/showthread.php?t=12172

[yokebutt]

Brian, while the mast-aft concept has one factor that theoretically is better than a regular bermuda rig, it still seems to me as having most other aspects working against it. Has there been any real-world testing done?

Yoke.

[brian eiland]

Brian, while the mast-aft concept has one factor that theoretically is better than a regular bermuda rig, it still seems to me as having most other aspects working against it. Has there been any real-world testing done? Yoke.
1) I might suggest you go back and reread posting #13 (http://boatdesign.net/forums/showpost.php?p=23390&postcount=13) above. I think you will find I am suggesting more than 'one factor' improvement.

2) To the 'real world testing' issue, I'll copy a letter I've taken to sending out to inquiries as a sort of 'form letter' for now:

John J Ward wrote:
I am John Ward and I have an interest in your mast aft system. I have read your entire web site and can not find a reference to an existing boat that I could look at. For all of the advantages of the system, I do not understand the lack of interest in building this system, unless there is a fault that has not been discussed or written about. Any information would be appreciated and the status currently of the system.

Brian responded:
Thanks for your patience. I have received quite a lot of interest from my website posting of this design, and even to the degree that I am experiencing some trouble keeping up with it all.

There has not yet been a vessel built utilizing my specific mast-aft design. There have been in the past a number of experiments with various mast-aft concepts, most of which were unsuccessful due to their placing the mast at the extreme aft end of the vessel, and thus were unable to provide adequate forestay tensions for the larger headsails. I have studied a number of these attempts and collected what info I could find on them. I have chosen at this time not to publish all of this info on my website as I felt it would be a distraction to my design.

I don't know how long you've been associated with sailing, but I would wish you to know the EXTREME difficulties of promoting new and different ideas in this very conservative market....and even more so in the very conservative USA segment. I've been associated with multihull craft for almost 30 years now, and they are just now gaining some considerable respect. Want to see some exciting innovation in sailing craft, go to France or to some lesser degree New Zealand.

I originally put this project on total 'backburner' until several years ago when I revitalized it for my gamefishing design....boy, will it work great in this application! It will also work great in a cruising application, particularily onboard a motor/sailer. It may not work in the racing application I sight in the letter to Paul Cayard, but then these ultimate racing rigs are not what we want to emulate on a cruising boat where stability questions (particularly multihulls) and short handed crew list are important factors

This rig possesses a number of aerodynamic advantages over those conventional rigs of today. It also possesses some disadvantages. The extra drag of a bare mast is a primary concern, but wait a minute, I don't have the extra mast & rigging required of a conventional ketch rig (mine is a single-masted ketch). The forward raked mast will experience much additional compression loading in order to maintain racing equivalent tight forestays.....but modern materials and their creative placement (mast, rigging, and bulkheads) will not present a formidable obstacle to this goal. With tight forestays and the overlapping genoa, I will put this rig design up against the best of the windward boats and give them a good run for it.

Current status? I'm working on a client who can appreciate the potential offered by this design, and with hopefully the funds to do at least a minimal FEA (finite element) analysis prior to construction. The FEA is not a necessity to get an operational rig out there, but it sure would be nice to optimize it as much as possible at the beginning.

Still looking for that bold, adventuresome sailor

Regards, Brian


P.S. There are some alternative variations of this rig concept I would like to investigate concurrently. One such variation involves the ‘bi-pod rig’ development onboard Olaf Harken’s “Procyon” project. Another considers a ‘wishbone’ arrangement onboard two custom 48 footers

[brian eiland]

This posting came up on the 'wishbone mast thread' and probably is more applicable here


Brian,
Did you know this?:
http://www.barefootsworld.net/windwa...ilingcalc.html
What's your opinion?
I've just found it.
Cheers

Yes Guillermo, this was brought to my attention a couple of years ago. Reference posting #20 & #21 of this thread:
http://www.boatdesign.net/forums/sho...2&postcount=20
http://www.boatdesign.net/forums/sho...3&postcount=21

..photo at:
http://www.boatdesign.net/gallery/showphoto.php/photo/6863/cat/500/ppuser/399

[Guillermo]

The guy wrecked close to Malaga:

Nov 26, 2005
"0800, force 3, northerly, clear, high 40s. It is cold. Drew the last €500 to pay the repair, then returned to boat, and prepared for the trip to Sotogrande and Gibraltar. Left Malaga harbor at 1100, sailing at 4 kts in force 4 wind. Pleasant day until 1500 when the wind jumped to force 7 gusting 9 by 1600. I got the sails off, and motored, first into the wind then off the wind after dark as I could not hold it into the wind. I set the sea anchor at 2200 to ride it out and was setting well, until a wave skewed the boat and one side of the bridle was cut on the bow anchor, forcing the boat to lie at a quarter to the waves. A large wave broke on the stbd breaking a hole where the patch had been made, starting the flooding of the stbd ama. About 2330 the ama was swamped and water was sloshing into the cockpit not long until the main hull swamped so I sent a Mayday while I still had battery and lights and engine. A tanker about a mile away answered. From then on for about a half hour I was able to flash the mast work lights. The wind was force 9 gusting 11 and the seas were approaching 20 feet and breaking. A breaker swamped the main hull and the engine died, the batteries shorted and the lights were gone. I showed a waterproof hand lantern as the tanker passed me the first time a 100 ft upwind at 5 kts. They made another turn to slow and came alongside downwind letting me drift down on them. I was in the water up to my chest for about an hour and a half battling the waves and flotsam in the cockpit, getting beat around a bit.
In the process of getting from the swamped Windwalker to the tanker Aescepulis I received a line with ring buoy which I placed around my chest and the crew pulled me in the dinghy to the boarding ladder. Just as I was coming in the wave dropped the dinghy below the ladder foot and I slammed into it bruising my lower ribs and twisting my back.

On the next wave I was cleared and the crewmen lifted me to the ladder, virtually carrying me to the ship’s deck, and to the infirmary. There I was stripped and dried, clothed in a coverall and warm socks, given a good cup of hot coffee and a couple of Snicker bars for some quick energy. As I warmed up, having been in 65° water for an hour and a half, I was examined by “Jim” and “John”, Medical Officer and the First Mat, then photographed and interviewed by John and the Captain. The Captain mentioned that I did not seem to be greatly distressed, and that apparently I had been in life threatening situations before (more than once for sure) was just damn grateful to be alive, sucking air, vertical, not badly injured and sober. I was then taken to a cabin and put to bed."

And previously he dismasted close to Bermuda:

May 20, 2006
"0600, wind E - 4-6 kts, seas 3 ft, mostly clear, high 60s. Wind veered dead E right on my nose. On stbd tack heading 045° making 5 kts northing. Swell making for a rough ride. Motored for 1/2 hour getting sails set and on heading after being hove to. Big ketch on port tack crossed my bow at 0700, distant 1/2 nm. I went on a port tack, set the heading, went below to fix another cup of coffee when WHAM ------

DISASTER - 0800 - DISMASTED - A Norseman backstay fitting failed, crystalized in the threads. 116 miles from Bermuda - vicinity of 32° 05'N, 67° 16'W - drifting and securing what I can. All wreckage, mast and sails on board and secured by noon. I still need to get antenna from end of mast so I can put out a MAYDAY.. I got the antenna and mounted it above the cabin. On the first Mayday call I got an answer from a boat just behind me over the horizon, the BABSAN from Wisconsin. They came alongside, went through a real hassle siphoning 4.5 gal of fuel for me from their tank. I calculate it will give me just almost enough if the wind will let up. The BABSAN went on ahead as they are faster. They notified Bermuda who notified the folks back home. There is another boat behind me about 5 miles, the WEED."

He rerigged later with a conventional bermudan rig.
Cheers

[brian eiland]

He rerigged later with a conventional bermudan rig.
Did you find that in his logs? I've not read them as there appears to be almost no mention of the sailing capabilities of the vessel.

[brian eiland]

...a recent inquiry I received making reference to the genoa sail and sail handling..

"Are there any new developments on aft mast multihulls? I keep an eye on various internet sources and don't see much happening.

My personal experience is that my Gemini cat is about as fast with just a big genoa alone as it is with main and jib. Maybe not as weatherly, but certainly easier to handle, it's not exactly race material anyway.

As we look to upgrade to a bigger cat and I get older and less able your words are hard to forget.

If there are updates on the scene I sure would be interested as we are considering having a Hughes cat custom built." Anonymous

[Guillermo]

Did you find that in his logs?
Yes, he says that somewhere, but it's difficult to find among the very long logs. The general feeling I got is that the boat as a whole was a complete disaster (And I have my doubts about the mental sanity of the man....)

[Richard Hillsid]

Here are 2 images of the boat 81' wl she has a keel 7'' and 2 whatsamacal them stabiliser full length.
I just put in 22 tons of concrete and she still floats bow high at 1.2 meters stern at 1.7 meters so plenty of room for more ballast or cargo.

Square rig sounds interesting.

Comments?

Maybe you should consider a 'junk rig' or a modern square rig like Maltese Falcon. Both of these rigs could give you multiple vertical mast for hoisting stuff, and a low overturning moment.
http://boatdesign.net/forums/showthread.php?t=12459
http://boatdesign.net/forums/showthread.php?t=12172

[brian eiland]

Did you find that in his logs? I've not read them as there appears to be almost no mention of the sailing capabilities of the vessel.

Yes, he says that somewhere, but it's difficult to find among the very long logs. The general feeling I got is that the boat as a whole was a complete disaster (And I have my doubts about the mental sanity of the man....)

As I wrote you in a private email, I also questioned the sanity of this gentleman, but that’s all another subject.

When I was first made aware of his original website and his rig calculator, I was very surprised at the exact wording on his site that copied the wording right out of my website verbatim. Here is a gentleman who never once had contacted me about this subject he had such a great interest in, nor ask any permission of me, nor given any references on his site back to mine. I wrote him a letter about these matters, which he chose to ignore answering, and instead took down some of his web pages from his site.

In that letter I also expressed some concerns about his interpretation of my design. I was particularly concerned about his lack of a resistance element to the forward force that will be generated by the upper aft facing jumper strut over which the masthead backstay passes. In contrast I have provided a triangulated (diamond) jumper strut arrangement to help counter this forward pressing force. I have also provided two additional backstays at this point to counter forestay loads.

…photo of vessel under discussion: http://www.boatdesign.net/gallery/showphoto.php/photo/6863/cat/500/ppuser/399 (http://www.boatdesign.net/gallery/showphoto.php/photo/6863/cat/500/ppuser/399)

In other words I was concerned about his variation of my design. But since he had chose not to communicate with me about my concerns, and since he had already built it, there was not much left to do but wish him the best. Maybe his mast section would stand up to the loads, but I seriously doubted it. I was also concerned about his disproportionably long, lower mast panel.

Another of my concerns was his use of three headsails. To my way of thinking this placed the headsails too close together to be practical. We know from past cutter arrangements that should we have the headsail and the staysail too close to one another it became difficult to maintain the trim on both such that they were always fully engaged. Plus, it became more problematic in a tacking situation. And he obviously had not sailed enough to recognize the balance that can be had with a jib-mizzen combination.

Your reference to the rig being replaced with a conventional one was rather brief, leaving the impression that this mast aft experiment was a total failure.
quotes: The guy wrecked close to Malaga…..He rerigged later with a conventional bermudan rig……Be careful about the trust ability of that calculator. The guy dismasted….The general feeling I got is that the boat as a whole was a complete disaster
I don’t think we can assume this just yet with the VERY limited information we have. All I see so far is a failure of a piece of ordinary rigging, “a Norseman backstay fitting failed, crystallized in the threads. That could happen with any rig. Certainly it appears to be a backstay component, and if he had only a single backstay with this 3-headsail arrangement that would be a real problem. But lets not condemn the mast aft concept in general based upon this flawed design experiment.

And finally I might even have to give some credit to this fellow. At least he went out there AND DID IT, more than can be said for many dreamers.

[brian eiland]

As reported in the new 'online' english edition of the popular French sailing magazine "Course au Large" , the new publication linked here "Ocean Racing" (http://www.ocean-racing.net/home.html).

This new edition has an announcement/article on the a new 'maxi-trimaran' to be sponsored by Banque Populaire. Interestingly there are hints of 'aftmast-ism' ;

"The fact that we are talking about the world's largest multihull is not totally untrue, but at the same time, that does not tell us everything.... A length of forty meters is obviously impressive, but let there be no mistake; we are talking about the measurements concerning the central hull, since as you can see, the floats are around 3 meters shorter.

The height of the mast in relation to the boat's length gives the impression of a rather cautious sail plan (although this adjective seems out of place, if we are talking about 50-knot winds!). With an eye on safety, the designer continued, we tried to achieve a relatively low center of sail force. As for the geometry, the mast is situated 2 meters behind the center of the floats, so the boat has a natural tenency to sail stern down, once again limiting her crashing into waves.

It can be noted that the idea of pushing back the sail plan was the result of a long series of studies carried out before the construction of the 60-foot Groupama 2.

As for her sails, the boat has at her disposal 5 different types of foresails (Brian's note: That one headsail is almost mast-headed, and obviously there are plans to fly two headsails at one time.)

Here's a 3D imaging:
http://www.voile.banquepopulaire.fr/3d_maxi.asp (http://www.voile.banquepopulaire.fr/3d_maxi.asp)

[yipster]

a racer, but what a boat :eek:
makes me wanna check how much is won compared to say 10 or 20 years back
"ocean racing" has some great articles, fine magazine, thanks

[miloman]

I have a friend who built a 20 foot sharpie with a fixed fin keel which he rigged with an aft mast. According to him it was a pretty good rig, but wasn't as fast as he expected. Apparently it required a lot of attention to keep it pulling to it's best advantage. He said that it didn't seem to be noticably faster than the marconi sloop rig he has on it now. He changed the rig because It required a little less attention to sail. He said that at times the rig would pull very well and he could get burst of speed which he never gets with the sloop rig. He claims that the sloop is overall a faster rig though.

I suspect that there were some other issues to be looked at here. I highly doubt that the forestay was tight enough for real performance. I suspect that for anything other than an all out racer this rig makes little sense. A sloop or cutter will be a little easier to handle, with less stress on the rig. The mast would have to be a pretty strong mast with a large cross section to stand up to the compression loads of a tight forstay. A bi-mast would give you the strength, but also a lot of air-resistance. Another consideration is the stress loads that your boat was designed for. This compression will tend to push dwn the middle and pull up on the bow. In a boat not designed for those kind of stresses saftey and hull-life may be compormised. I believe that a bendy-mast sloop will probably outpreform the aft mast rig all other things being equal. Up wind she'll just sail away, and with a large spinaker to set downwind, she'll out run her too.

One other though is that the aft mast would be nice at anchor. With all that windage aft she'd just come right up into the wind. Also all the rigging weight is aft instead of on the fordeck holding the bow down.

Phil Bolger designed a small sharpie "stailsail cat" similar to the one my friend built. He writes about her in his book Boats with an Open Mind. He has several interesting comments. Interestingly he uses a wishbone, which would be nice down-wind keeping her sail from twisting.

I suspect that overall the rig just isn't all that practical.

I hope this is helpful.

[brian eiland]

I have a friend who built a 20 foot sharpie with a fixed fin keel which he rigged with an aft mast. According to him it was a pretty good rig, but wasn't as fast as he expected. Apparently it required a lot of attention to keep it pulling to it's best advantage. He said that it didn't seem to be noticably faster than the marconi sloop rig he has on it now. He changed the rig because It required a little less attention to sail. He said that at times the rig would pull very well and he could get burst of speed which he never gets with the sloop rig. He claims that the sloop is overall a faster rig though.
Who was that friend, and does he have some pictures to post here. I would think he might find this discussion interested and possible be interested in posting a few comments?

Another consideration is the stress loads that your boat was designed for. This compression will tend to push dwn the middle and pull up on the bow. In a boat not designed for those kind of stresses saftey and hull-life may be compormised.
You might have a look at these discussions
Vessel Substructure to Support the Rigging Loads (http://boatdesign.net/forums/showpost.php?p=114487&postcount=59)
Alinghi Cat (http://www.boatdesign.net/forums/showpost.php?p=98787&postcount=39)

Phil Bolger designed a small sharpie "stailsail cat" similar to the one my friend built. He writes about her in his book Boats with an Open Mind. He has several interesting comments. Interestingly he uses a wishbone, which would be nice down-wind keeping her sail from twisting.
I will eventually post some of Boger's work in this regards after I get a little more info

In the meantime have a look at this aftmast design:
http://www.boatdesign.net/gallery/showphoto.php/photo/7043/cat/500/ppuser/399 (http://www.boatdesign.net/gallery/showphoto.php/photo/7043/cat/500/ppuser/399)
I'm waiting for the english translation of the article that went with this magazine photo

[brian eiland]

I guess as a long time proponent of this subject of aft placed mast or mast aft, I've become somewhat of a clearing house for info related to the subject; either that info I found when I was looking around, or info from other persons that was sent to me.

I usually try to get the person sending me the info to place a posting on this forum, but sometimes they either do not wish to do so or have some other reason. I usually ask if they mind if I post it, and I usually omit their name unless they decide to join the discussion

Here is something I recently received that is quite 'stylish' in its rendering. And there is a website referenced:

"For years now I have been toying with the idea of a stern mounted mast on a sailboat. I believe it is time to present my thoughts,
for criticism, both positive and otherwise. I may learn that the theories are wrong, or that the idea is unworkable for some reason. I might receive some reinforcement for my idea as well. Either way, I am bound to learn something...and that is the benefit behind any outlay of thought."

http://snow.prohosting.com/trollrg/experimentsail.html#topposition

[brian eiland]

The July issue of Cruising World had this Tayanna 55 listed in the classified section.
http://www.tayana55.com/index.html

It caught my eye as a prime example of something I mentioned long ago in reference to removing the conventional mainsail of a ketch and replacing it with a staysail;
"Conventional booms excessively flatten the foot of the mainsail, and are often oversheeted, contributing significantly to the leeway forces. I once had a copy of a test on a Morgan 41' Out Island ketch , where upon removing the mainsail, the boat lost only 1/2 knot of speed, but cut its leeway in half (from 11 to 6 degrees). A staysail was then rigged between the masts in place of the mainsail, and the boat regained 1 knot of speed while retaining its decreased leeway"

In fact I brought this subject up recently here:
http://boatdesign.net/forums/showthread.php?p=151921#post151921 item #202

Now if you could accomplish this all with one mast rather than two....;)

[brian eiland]

....interesting letter I received last summer, '07


Hi Brian, my name is alan smith...I am looking at an Ian Farrier Design 39 foot trimaran....I have enough sailing experience both in chartering and racing to know that what you have postulated in your article on aftmast propulsion to be exactly what I have been looking for....I am 56 years old and with that comes loss of muscle mass and flexability.

I want to world cruise and my biggest seagoing dilema is the mainsail. As you mentioned the full batten mainsail is a beast. i had considered putting a power wench near the mainsail for aid in lifting it....but when you are at sea and singlehanding...it can be so frightening ...when in the middle of the night
some weather blows up quickly...your thoughts are muddled and you are trying to figure out your best course of survival...ha ha ...even on a rotating mast getting the slides to cooperate, the battens not to get hung up on the jiffy sail lines is no laughing matter.

Recently while on a 41 foot Lagoon cat in Greece we went from 15 knot breeze to over 40 knots in a channel between islands. Now mind you, there were 8 of us board this monster of a boat. It took one steering into the wind, one on the mainsheet traveller, one on the mainsheet rope clutch and wench, two handling the mainsail...clawing like hell to pull the slides down, and one lookout watching the battens didn't get hung up in the jiffy lines...which happened several times...up a little...no, down a little,,,,no damnit...up a little you idiots...and so it went.

With your idea we would have just furled the jenny half way and struck the mizzen and we would have been fine...It is a brilliant idea. Just fricking marvelous brilliant....

Now I have a few questions for you....Sailing downwind....dead downwind....of course a spinnaker is completely out of the question for a singlhander...too bloody much work and nervous work at that..Ian Farrier has a good set up with the screecher on a bow pole...you can wing and wing the main and screecher if you get lucky with course desired and wind direction...but I am interested in what you would recommend for a 3/4 wind or full aft wind?

Is the narrow hull of a trimaran going to present in back stay problems for the forward leaning mast? Does the mizzen need some sort of boom? What percentage decrease in mast height will effect the same capacity of sail area with the 3 sails versus two sails of a bermuda rig....

Thank you Brian....I am hoping that you will take a few minutes to answer my questions...it is so refreshing for me to have found this article....your idea hit home like the truth of god...ha ha ...well, fair winds to you...alan smith

[brian eiland]

I post this as a cross reference of discussions for some future time.

Here is another forum discussion initiated by a gentleman interested in a Main-Less Rig combined with a bi-pod mast for easy lowering:
http://www.boatdesign.net/forums/showthread.php?t=21274

[Fanie]

Well Brian, it seems your aft mast setup is finally beginning to enjoy some more attention. And rightly so. There are numerous advantages compared to the conventional bermudan boomed sail setup.

I have a few experiments to do on the little trimaran I've built for testing and gaining a little experience using it before I am going to apply it to my boxy fisher cat currently under design.

I have a friend who also has a small trimaran but with a bermudan sail setup. I must admit that it's much easier and quicker to furl my main sail than it is for him to rotate his mast to control the sailing area.

Also the down force of the bermuda sail rig pushes his leeward hull under the water while the aft mast sail provides so much lift I hardly notice it. Maybe I've got too much boyancy ;) but I get the feeling if the windspeed picks up enough one could well see a planing displacement hull (or three).

Currently the sails are in for modification - I'm adding another 30% sailing area combined to the leech and the foot of the sail. Could make for a slight increase in performance :D and better control since the centre of sail force is moved more amidship.

Anyway, so far I'm glad or rather relieved that I did came across your article on this sailing setup. Liked it right away and it makes more sense. I'm sure once the nitty gritty is sorted out it's going to be a winner.

[Pericles]

Brian,

With reference to the letter you received last summer from Alan Smith, did you suggest a traction kite as part of your reply? Hope you don't mind me asking. :)

Regards,

Perry

[brian eiland]

Brian,

With reference to the letter you received last summer from Alan Smith, did you suggest a traction kite as part of your reply? Hope you don't mind me asking. :)

Regards,

Perry
Actually Perry, I did not. I was not so convinced of their viability at the time.

[MAINSTAY]

Tom Speer,

I admire you greatly for your "show me the numbers" approach.

But you torpedo that approach when you say, "The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer."

Yes, there are NACA airfoil tests in a wind tunnel that numerically support that statement. But you discourage new rigging designers with it.

Do you really believe that in the sailing environment a 50-ft x 1-ft diameter mast has the same drag as a 10-ft wide x 100-ft long x 50-ft high NACA shape on the same hull? If you do, even within the "20-30 degrees either way", then "show us the numbers" or please withdral from this forum. If not, please retract the statement and never use it again to criticise another design.

Larry Modes

[MikeJohns]

.........

Then there's the problem of the mast. It's almost impossible to fair an isolated mast because of the range in apparent wind angles. The apparent wind will meet the mast from 20 - 30 degrees either direction. No section shape for the mast will avoid massive separation under these conditions, causing a lot of drag. The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer - with drag coefficients based greater than one. In other words, the drag of an isolated mast can be almost as much per square foot as the sail produces in lift per square foot! When you add up the frontal area of the mast plus any struts and rigging, you get a lot of windage.....................


.........."show us the numbers" or please withdral from this forum. If not, please retract the statement and never use it again to criticise another design.

Larry Modes

Larry
I think the message is that with the wind off the foil axis the drag can be considerable, for example consider a cylinder........... (at least that is how I read it).

Tom has been very forthcoming and helpful in this forum, occasionally all of us manage to misrepresent what we are trying to say particularly when trying to popularize a subject for a layman.

I don’t think there are any grounds for your rather brusque demand of a retraction and I very much hope that Tom does not withdraw from our forum since he is a knowledgeable, educated and willing contributor.

A more genial approach would be better in the future even if you are (?) an expert in this field.

Cheers

[MAINSTAY]

Mike,
I appologize for the brusque tone of my post. I don't want Tom Speer to withdraw. That would be a targic loss. There should always be someone in this forum who demands to see the numbers. It spurs us to go beyond the qualitative hopes, to the quantative modeling of our claims. And Tom is that person for us.

I'm asking of Tom no more than he has asked of others, to "show me the numbers" for his claim of the 10x100x example, or stop using it.

I fear that he believes the 10x100x numbers are applicable in the world of sailing and because he believes the 10x100x example somehow helps new designers in mathematically modeling their inventions.

I dread the possibility that he is knowingly or inadvertantly discouraging amateur designers by using wind tunnel numbers that are irrelevant and counterintuitive in the real world.

None of the newbies are going to challenge his example. Tom is a giant in our field, and they are not Davids.

However, "show me the numbers" is a valid request, perhaps THE valid request, from any member or guest of this forum. I am requesting it.

Larry Modes

[Richard Atkin]

Fanie, I like the way you take a big bite into a new project, and work with enthusiasm, and 'gut instinct'. But man...don't work with too much gut instinct!! You should do some maths or listen to those who have already done it.
Tom Speer raises some important issues regarding the aft mast setup....and your boat is going to be dealing with very large forces. Also, with all the windage from your huge cabin, you will need all the aerodynamic efficiency you can get.
I would hate to see you jump in with all that passion, and work all those hours, and then end up with disappointment.
I know you have the boatbuilding skills and you can't wait to see the thing growing in front of you....but geeez....slow down dude!! :D
The aft mast might be a good idea for your project, but you don't know that yet.

[Fanie]

Hi Richard,

but geeez....slow down dude!!

He-he-he... Yeah !! By the time you guys are done talking I'm fishing from it already !! :D:D

I feel flattered that you can see the enthusiasm :rolleyes: I'd hate to do this size a project without it :D

I haven't done anything wrt the cat, all I have is the little tri and I'm doing some experiments with it to try and figure out how and if what will do when and where. If it doesn't work well on the tri it won't work on the cat either.
If it works well on the tri, there could be a very good above avarage chance it's going to work on the cat as well. As a comparason I sail the bermuda and compare that with my aft mast.

I'm not going to run blind into this project. (The cabin is not really the windy problem - the hull's are ! but does contribute.)

Nothing is carved in stone as yet - remember I was looking for an excuse to go 12m instead of 10m and couldn't rely on you guys for the motivation ? :D Well. it's still haunting me.

The following has to be set up here before I can commence -

Another looong (for10m) or loooooooong(for12m) double garage (plans already approved)
I have to finish my laser cutter - measuring and working by hand... Yuk, no way hosay !!
Accessories - the list seems endless :mad: I guess this would be where the most work would be in, not the hulls or the cabin...


So, relax, take a load off. I'm reading all I get on the subject, and I'm watching Brian Eiland's every move ( just pretend so it's not that obvious). I'm sure he's hiding some secretive tricks on the matter, but sooner or later he's going to slip up and I'll get something from it. :D

[Richard Atkin]

Okay Fanie. I feel better now :D During your experiments, see if you can compare your aft mast rig results with a bermudian WING mast rig. That would be very interesting.

[Fanie]

As I've said in my 'sailing experience' thread, the downward force of the bermuda defenately pushes down quite a bit (my friend's tri). Then with a jib fitted as well there is an improvement due to some lifting force from the jib. Makes almost say 10km/hr difference before the hulls goes under water again and drag limits speed.

My little tri has only the mainsail that is a jib on streroids :D, there is no sign of the downward pushing into the water, so with the angle my forestay sits I can almost assume the foreward thrust and the upward lift is close to one another. If it could happen the wind would lift the little tri up ( like in planing) it can easily be adjusted by making water :rolleyes: or simply by letting the sail out :D

I cannot compare sailing to windward yet as my forestay is too limp due to mast bending and no keel or daggerboard so I have a lot of side drift.

[masalai]

Here I go again... Me pontificating, I mean... I like part aft mast idea well just stepped back a bit so NO MAIN and 2 roll-up genoas on each side and a blade-jib/storm sail between the hulls a-la hitch-hiker - look up "X-it" on this forum...

I reckon the genoas could be positioned so that all 4 sails are the same size... the foot being around the distance between the fore-stays to the respective hull bows... Use the leeward sails... Lazy sailing and comfortable setup... Not so much "downward force" as position of sails will apply lift - as in less heeling moment...

[Richard Atkin]

Having lots of smaller sails with sharp leading edges is good for versatility, and each sail should perform well in it's own right....but when reaching or running, small sails lose more wind around the edges than a big sail. Also, the best foil shape is achieved when the rig consists of only one sail (no gaps between sails).

So...in theory, the most ideal rig would be just one big self-supporting sail with no mast or stays. The sail would magically stretch to become tall and narrow when beating to windward, and round when sailing downwind.

I try to keep this image in mind when I am looking at various rig possibilities.

[masalai]

Richard, in my case I am talking of a 12m LWL cat with 6m separation on the centreline of the hulls, so I figure on a foot of around 6m on all 4 sails plus the blade jib/storm set mid beam forad of the mast. No main as it is next to useless... Search for "John Hitch" & "X-IT" on this forum to see one version...

For your purposes look at a foil-kite sail as used by performance "hang gliders"

[Pericles]

Yeah, I say unto you thrice.

Traction kite.

Traction kite.

Traction kite.

Pericles

[masalai]

Pericles, does that mean you prefer "Traction Kites"?

Something similar to the attached image is what I mean. I think that is slightly different & suited to smaller applications... It will point higher into the wind...

[Pericles]

Masalai,

Traction kites make great sense on downwind legs and as an emergency sail in the event of being dismasted. Brian Eiland has been promoting the idea for some while. You posted there.

http://boatdesign.net/forums/showthread.php?t=20319&highlight=brian+eiland

http://www.skysails.info/index.php?L=1

http://www.youtube.com/watch?v=q4A0B_-aQK4

http://www.kiteship.com/

http://www.kit-cats.com/kite/kite_sail.htm

http://www.dcss.org/speedsl/index.html

http://www.voilecerfvolant.com/Test/Gb/home.asp

Regards,

Pericles

[masalai]

Do you want to log in to my head as the mental de-fibrilator - can't think of another word to get my memory to find what I am thinking I would like to recall...:D - Thanks

[brian eiland]

Having lots of smaller sails with sharp leading edges is good for versatility, and each sail should perform well in it's own right....but when reaching or running, small sails lose more wind around the edges than a big sail. Also, the best foil shape is achieved when the rig consists of only one sail (no gaps between sails).

So...in theory, the most ideal rig would be just one big self-supporting sail with no mast or stays. The sail would magically stretch to become tall and narrow when beating to windward, and round when sailing downwind.

I try to keep this image in mind when I am looking at various rig possibilities.
.....humm...no mast, no stays....sounds like the kite sail :cool:
(kite-assisted powercat (http://www.boatdesign.net/gallery/showphoto.php?photo=10642&cat=500))

.....or a single sail that would stretch to be tall and narrow, and round for downwind...sounds like the modern Dynarig (http://www.runningtideyachts.com/dynarig/) :cool:
Interestingly the overall profile of this sail plan almost perfectly matches that of the idealized semi-ellipital/parabolic planform shape. The lift/drag factors for this optimized shape are so much superior to those for the triangular sail-shapes of the Bermuda rig.

[masalai]

Aaaah He stole my device, a skyhook attached to the boat:D

[Fanie]

I was considering the mast setup for ie a 10m cat... if one uses two masts side by side, each close to a hull, could one end up with lighter masts, but more sailing area yet more controllable ?

Ok, how about if the one mast is more foreward and the other more aftward ?

[masalai]

Not a real good thought there Fanie, two masts do not make for "redundancy" as one would pull the other over:D.... Better to stick to a single stick unless one is looking at 100m? (lost a "0" somewhere?)... Remember, bigger is better and 12 is such a nice rounded number - with overhangs makes 13 - a bakers dozen:D

[Fanie]

Hi Masalai, have a look at this.

http://www.youtube.com/watch?v=A7vD7wALP5M

Ok, it's a hydrofoil, but look at the sails. What would a single sail look like to replace those two ?

[Fanie]

Here's another one
http://www.youtube.com/watch?v=0y91vkBUvHw&feature=related

I was lying in the soap box thinking (my most productive place :rolleyes:) two masts that have the same sailing area as the one big sail, ok, but your combined forestay would be longer thus better speed to windward, same speed when running, smaller and lighter masts, aft mast sail lift ie on a cat should be better distributed - less heeling ?, much less down force on the beams (no beam centre down force), lighter construction, easier to handle.

One thing no one seems to mention.
On the bermuda rig the mast is the device pushing the boat foreward, the boom supported aft on the boat
On the aft mast setup the forestay is pulling the boat foreward. Ok on the mast too, but better balance.

As I have it,
a boat being pushed is more difficult to steer
a boat being pulled is easier to steer

[masalai]

It is a matter of "horses for courses", do you put a thoroughbred horse in front of a plow? when you really should be using a reliable draft horse? or do you put a jet turbine on the top of an outboard leg? and expect fuel economy and performance reliability as opposed to 1000mph speed? if you get my drift?
See post 21 and imagine a slightly shorter mast set a bit further back so the stays near midships went forward a bit so a furler could be used... http://www.boatdesign.net/forums/showthread.php?t=21274&page=2 There would be reduced downforce to push the leeward hull deeper, easier to control, and no boom, (or attendant sheets & wenches etc), to decapitate or kneecap (ouch), you whilst reeling in those fish:D

Remember those earlier thoughts of yours to keep it simple, several smaller sails for ease of handling...:D That rig on the foil is strictly for performance and demands constant attention... You will note that "Crash Helmets" were worn!!! So, make 2 boats, one 12m as "mother-ship" and small toys for the speed thing, carried on the aft bridgedeck roof, as there will be no "main" there to cause other problems...

Re post 70, "as I have it," - sometimes...:D

Look at the angle from the central mast and the forestays/furled sails and think of the reduction of bad down-forces... It helps to make a simple model to see where it is at... Look carefully and be pleased... not necessarily a "sailing model" but a convenient post, mark the boat with whitewash (tennis court marker from your tennis court) or even driveway and tent pegs to mark the bows then a bit of bedsheet (whilst wife is away shopping) and see how it sits...

[Richard Atkin]

Brian Eiland
The Dynarig is very interesting. The curve of the sail is symmetrical, unlike an optimised foil shape. Does this affect performance much?

[Richard Atkin]

Fanie, regarding pushing and pulling... I've heard that cats don't like the centre of sail area to be too far forward. This can cause steering problems. This is why cats generally have their mast further aft than monohulls. But I'm talking about bermudian rigs. I have no idea if this principle applies to the aftmast rig, which should have more upward lift

[ironmatar]

a question iv not seen posted here why not leave the mast<s> vertical and instead maby use a forward rigged arm or gaff in order to move the top point<S> forward the desired amount of rake?

[Fanie]

Good idea, Ironmatar. It would be a way to decrease lift and increase foreward pull.

[brian eiland]

Brian Eiland
The Dynarig is very interesting. The curve of the sail is symmetrical, unlike an optimised foil shape. Does this affect performance much?

For years I've always understood that an ellipitical or parobolic shape to the head of the sail was best for limiting 'induced drag', which can represent a considerable amount of the total drag of the sailing rig. I found this forum discussion, and this referenced paper that gives the subject more detailed response:

Square-Top Mains
http://www.boatdesign.net/forums/showthread.php?t=9668

Minimum Induced Drag of Sail Rigs and Hydrofoils
http://www.tspeer.com/Planforms/Planar.htm


I've even ask Tom to reply to my possible mis-quote;
"Very interestingly the overall profile of this sail plan almost perfectly matches that of the idealized semi-ellipital/parabolic planform shape. The lift/drag factors for this optimized shape are so much superior to those for the triangular sail-shapes of the Bermuda rig."

[Richard Atkin]

Sorry Brian, my description was not good. I was referring to the camber and twist of the sail. I am wondering how important these factors are, relative to the Dynarig sail plan. How much control do you intend to have over sail shape?

[Richard Atkin]

I am a laymen...please excuse me if I am using bad terminology

[brian eiland]

Sorry Brian, my description was not good. I was referring to the camber and twist of the sail. I am wondering how important these factors are, relative to the Dynarig sail plan. How much control do you intend to have over sail shape?
The camber on the DynaRig can not be controlled, but was rather optimized at a 12 degree arc.

And the twist one might wish to incorporate as the impending wind varies up the height of the rig was also disregared in favor of KISS.

You could read more about the Dynarig on there site, thru google, and on these two forum discussions:

http://boatdesign.net/forums/showthread.php?t=12459

http://www.yachtforums.com/forums/perini-navi-yacht/2487-perini-navi-maltese-falcon-sailing-yacht.html

[yipster]

square rigged clippers delivered 6000 sail hp now burning half a million liter fuell for an atlantic crossing
here some more background and links http://www.windschiffe.de/theorie.html

[MAINSTAY]

Aft-mast and kite rigs seem to get more drive by giving the sail luffs clean air. Even rotating masts and wing masts do it, but with complexity. I can see kite rigs in open water, but I can't see sailing it into a slip or thru a draw bridge. I've seen aft mast designs with a bipod mast and 1 or 2 backstays, and Brian Eiland's with a single mast and 2 backstays. The simplest I've seen had a single mast, one shroud and no backstays.

Richard Atkin's comment about no mast and no stays brough it to mind. Imagine a jib and main on stays with no mast. Both would have clean air and could be roller furled easily. This was done on a multihull without a backstay by canting and raking the mast. The mast was stepped at the third point of a line at about the two-thirds of the way from stem to mainluff. The single shroud is outboard on this same line. The forestay strain is balanced by the vertical mainsail stay, which acted as the backstay. Since there is no actual backstay, the mainsail could have a broad head and a generous roach.

I'm modifying my Hobie 16 to place the mainsail on a vertical stay bridled from the shroud chainplates and the mast stepped in the same place on the cross arm. The aft shift in the center of effort may require a larger rudder, or just a shift in crew placement, or not. I'm also trying to use as many standard class parts and as few custom parts as possible. I'm still working out the numbers to see if it is even possible. If so, I hope to get the NA association to let me race against other 16's, even if my time is not eligible for trophies.
Larry Modes

[Fanie]

Hi Larry, any chance one can have a peek at your new setup ?

It seems the only problem one have with the aft mast is the mast bending hence aft stays. I was actually thinking in the lines of having the forestay connect to the aft stays via a mechanical lever that would pull the aft stays as the forestay pulls, but so the aft stays have the advantage of the movement to put more pull on the forestay. Just an idea though, haven't thought it through yet.

[MAINSTAY]

Here are beam and headon views of the half A-frame I mentioned.
There is no backstay to limit mainsail size of shape.
In a gust or as wind increases, forestay and mainstay tension automatically increase and balance each other.
The is only one shroud. Forestay and mainluff stay provide lateral support.
Sails may be roller furled.
The mainluff stay may rise vertically from or near transom.
Additional stays may be added in plane of stays for smaller sail areas. Usefull on large boats and cruisers.

On my Hobie modifications, the mast head is moved aft, so I may need to add a skeg or enlarge the rudder, or something else to move the CLR.
Larry Modes

[yipster]

now i see what you mean but how to tack with a one side shrouded lateral canted mast, downwind forges on the main sail stay may be another concern

[MAINSTAY]

The attached file BtFm3.xls shows 3 lateral views of the half-A-frame with mainluff stay.
1) as an aft-mast rig with a mizzen-like main,
2) with a mid-boom mainsheet to the transom, and
3) similar to a sloop rig.

It should tack like a rig with a staysail and swept-back shrouds. But, with less chaffing during tacking, no running backstay, and little possibility that sail will chaffe or boom will rest against a shroud while running.

One of the criteria for the strength of the mainluff stay is the forces while running.

Larry Modes

[RHough]

Tom Speer,

I admire you greatly for your "show me the numbers" approach.

But you torpedo that approach when you say, "The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer."

Yes, there are NACA airfoil tests in a wind tunnel that numerically support that statement. But you discourage new rigging designers with it.

Do you really believe that in the sailing environment a 50-ft x 1-ft diameter mast has the same drag as a 10-ft wide x 100-ft long x 50-ft high NACA shape on the same hull? If you do, even within the "20-30 degrees either way", then "show us the numbers" or please withdral from this forum. If not, please retract the statement and never use it again to criticise another design.

Larry Modes

WoW

I doubt that Tom has discouraged any well researched and documented rig design, even from a newbie.

New rig designers get discouraged and sometimes surly when their pet idea or claim cannot pass the reality test.

This forum is full of such ideas. Some of them get repeated fairly regularly (golf ball dimples for hulls comes up at least twice a year). :D

When I see a claim that seems obviously wrong, I question it. I do the math to try to prove it one way or the other. Sometimes I learn, other times I point out the flaws. Sometimes I get into heated debates with zealots ... :(

Anyone that is going to design a rig, would do well to read Brion and Skene before they post their latest greatest rig idea.

I was not going to respond to this post until I noticed a post from 2006 (IIRC) that your MainStay rig was described. It is now 2008 and you are still talking about it. You mention using a Hobie as a test bed, have you built and sailed the rig yet?

If you pay yourself minimum wage for all the time that has been put into the idea, you could afford a working example.

Hobie 16's are cheap, rigging wire and polytarp are cheap too ... I would guess that you could have an answer for $500-1000. That is pocket change to R&D the basic concept.

Spending the time to read a couple of rigging texts to get a grasp of the loads involved might lend some credence to the idea too ... if you can show the numbers.

If you are not comfortable with the math, think about the standard rig on your Hobie. Does the leeward shroud go slack when sailing upwind? Can you put enough tension into the rig so the leeward shroud does not go slack?

In your MainStay rig, the mainstay is the windward shroud on one tack and the leeward shroud on the other tack. Just how much tension will the rig have to be under to keep the mainstay under tension when it is on the leeward side?

Headstay tension is the least of your concerns with the rig as you have drawn it.

What you are doing is trying to set a sail on a shroud that is not under equal tension on each tack. That does not sound like such a great idea to me.

Cheers,

Randy

[RHough]

I'm modifying my Hobie 16 to place the mainsail on a vertical stay bridled from the shroud chainplates and the mast stepped in the same place on the cross arm. The aft shift in the center of effort may require a larger rudder, or just a shift in crew placement, or not. I'm also trying to use as many standard class parts and as few custom parts as possible. I'm still working out the numbers to see if it is even possible. If so, I hope to get the NA association to let me race against other 16's, even if my time is not eligible for trophies.
Larry Modes

I have to smile. In a post dated March 2008, you say you are modifying your Hobie to a Mainstay rig ...

Would you be:

Title:Mainstay rig
Document Type and Number:United States Patent 6250242
Link to this page:http://www.freepatentsonline.com/6250242.html

Abstract:The mainstay rig is an improved standing rig system for wind-powered vehicles that travel on water, snow, ice, land, or rail. Mainstay rig uses a mast at a rake and uses a vertical mainstay to support mainsail luff, which gives less disturbance of airflow at mainsail luff and greater driving force. Mainstay rig can use jib-furling mechanisms for mainsail furling. Mainstay rig eliminates backstay and gives a greater choice of mainsail shape which allows more efficient energy extraction from wind because sails can be shaped with larger roach or be shaped closer to an ideal elliptical shape. Additionally, mainstay rig can use one shroud, which reduces windage.

Inventors:Modes, Larry (Houston, TX, 77062)

Application Number:09/547410
Filing Date:04/11/2000
Publication Date:06/26/2001

Patent filed for in April 2000?

And in March 2008 you are going to see if it works?

Amazing, and to think some people think that patented ideas have to work.

I notice in another thread where someone is trying to get a patent on the bumps on whale flippers. Is it time to find the absurd patent thread and start adding to it?

I have to give Mr. Modes credit. He did not come in and brag about the patent, he made it sound like a new amateur rig design. People offered comments and provided feedback ... all the time the rig is patented. Is Mr. Modes trolling for customers/investors? Nice try.

[MAINSTAY]

RHough
Your condescending attitude is inappropriate in this forum.

The name of my patent is my screen name. Perhaps its other meaning was lost. But having a patent does not mean it is a viable idea, only that is it's new and original, and not previously patented.

So don’t do the vector diagrams. Here is a 2D trigonometric comparison of the Bermuda, mainluff stay and aft-mast rigs.

It is set up to have the same forestay sag, the same jib halyard tension, the same main halyard tension (it can be different than the jib) on all three rigs. It compares the 3 rigs with the same sailplan, on one boat, on your boat, or on any boat you choose. Enter data in the 6 boxes: I, J, L, forestay tension, and halyard tensions. The SS does the rest. The cells are not protected, so you can mess it up quick if you do anything else. The formulas are in the cell, for anyone to check their accuracy.

There are numerous aft-mast rigs each with a different mast step. For this comparison, the step is located so the mast bisects the main triangle. Likewise, the mast of the mainluff bisects the foretriangle.

The numbers I entered show an increase of less than 10% in compressive mast loads in the mainluff stay rig. It is the aft-mast (with the same sailplan) that has a 2x increase. With your help I would like to use loads that have some semblance of reality to them, and to expand the analysis to include shroud and sail loads.

Are you are willing to continue to dialog with a sailor who thinks outside the box, but who holds a patent?
Larry Modes

[Andrew_Davis]

I am so pleased to have stumbled across this thread. While it may look like I'm a first time poster, I believe (but I can't say for certain because my Alzheimer's disease is so bad!) that I have posted previously as AndrewDavis or AndyDavis or ADavis...I'm the same guy, I just keep forgetting my user name and password.

I am a naval architect in Richmond, California, and I have started to keep a blog:
http://www.tallshipdesigner.blogspot.com/

Essentially, I just rant about what I had for breakfast or what they're doing in the yard, and what does any of this have to do with this thread? Well, my last entry was about just this subject...one of these aft mast things is next door to my office and, in my ignorance, I thought it just had to be unique. But lo, I see there has been a whole world of energy devoted to this rig.

In the blog I pleaded for information about the vessel. Does anyone know it? Could one of you knowledgeable (and honorable) persons look at the pfotos and post anything you may know about the boat. Or you can post to the blog (even if you don't know the boat, feel free to post just to say what a waste of electrons the blog is!).

Hey, keep up the good work. I'm going to stayed tuned to this forum (and try to remember my user name).

[masalai]

Hi andrew, and do what I do, have the browser remember the password & username stuff and also set up the site in your favourites, then it is just a couple of clicks & the first letter of the user name (for you "A") and click away. All my regular sites have the same username and password... :D:D:D

[brian eiland]

... Well, my last entry was about just this subject...one of these aft mast things is next door to my office and, in my ignorance, I thought it just had to be unique. But lo, I see there has been a whole world of energy devoted to this rig.

In the blog I pleaded for information about the vessel. Does anyone know it?
I think if you look back thru this subject thread you will find a number of references to this vessel outside your door. Look at posting number #28 in particular for some cross reference subject threads.

I've even managed to contact both the new owners of the tall and short versions of this rig design and encouraged their communication with one another, as well as this forum

[brian eiland]

It is set up to have the same forestay sag, the same jib halyard tension, the same main halyard tension (it can be different than the jib) on all three rigs. It compares the 3 rigs with the same sailplan, on one boat, on your boat, or on any boat you choose. Enter data in the 6 boxes: I, J, L, forestay tension, and halyard tensions. The SS does the rest. The cells are not protected, so you can mess it up quick if you do anything else. The formulas are in the cell, for anyone to check their accuracy.
I guess I'm not enough of a computer person to find 'the formulas' you used. Can you send these to me?

I believe you have been a little less than fair with some of your comparisions on 'an equal basis'.
1) What would your formulas tell you about the backstay tension in the aft-mast rig if you did not include a second luff tension equal to the forstay tension?
2) Or what mast compression might be expected in the sloop rig if it were a cutter?
3) How does you main halyard tension affect the backstay tension in the slooop rig?

[Andrew_Davis]

Brian,
Thanks for the tip...I had no idea that there could be more than one of these! I understand now that I exist in virtual isolation here...dwelling in Plato's Cave. This thread is amazing. It really sustains the central thesis (if I ever had one) of my blog:
http://tallshipdesigner.blogspot.com/

[MAINSTAY]

Hi Brian,
It's good to hear from you.

To see the formulas, download the SS and in the Excel main task bar, click on View, then within that dropdown menu click on Formula Bar. That sets up a line (fx) where the formula in a cell appears when you click on a cell.

This SS was a special case study. It shows that mast compression is NOT double, as some thought obvious. To prove this I used identical sailplans. This was for two purposes: to eliminate any differences and complications that might have been said to prejudice the results in my favor; and to simplify the task to a 2D analysis so I could get it done quickly. I have left it open for a 3d analysis, but I need someone with real rigging expertise for that.

As set up the SS does not analyze anything but masthead rigs, and then only considers the longitudinal forces. But considering this limitation, try entering 0 for the mainluff stay and 0 for the main halyard. J still has to be measured to a point directly below the masthead, the angle of the mast is controlled by L which will have to be measured to the point where the upper backstay line intersects the deck line, well aft of the hull. Anyway, use it first on the jib and upper backstay for the compression due to the stays in the upper mast. Then repeat using the innerstay and lower backstay for compression in the lower mast due to the inner stays. Then add them.

DO NOT DESIGN to this compression. It does not include compression caused by the backstay spreader, or that caused by the shrouds and sails.
Larry Modes

[brian eiland]

Larry,
Thanks, I'll get back on this subject when I have a bit more time.

Meantime here is a note & photo I recieved recently from a gentleman at SAIL mag;

Hello Brian
Found you via Boatdesign.org, which I troll from time to time just for the
hell of it. On your site I found the answer to a puzzle that's been bugging
me since January, when I first saw this boat at Culebra, of Puerto Rico.
Unfortunately we headed out early next morning before I could track the
owner down to find out more about his boat.

Cheers
Peter Nielsen

Editor
SAIL Magazine
98 North Washington Street
Boston, MA 02114, USA

[masalai]

Brian, re your post #95, I see no great advantage there as 14 stays?, including one attached to a "bridle" at the stern... I cannot see any advantage there...

[brian eiland]

Brian, re your post #95, I see no great advantage there as 14 stays?, including one attached to a "bridle" at the stern... I cannot see any advantage there...
I believe you are also seeing a number of hayard lines or whatever, not all stays. Haven't taken time to inventory them.

[brian eiland]

Over the past number of years I have attempted to make a positive case for my aft-mast {mast-aft} sailing rig configuration, both within, and aside of the technical discussions of sail aerodynamics. I now see some renewed technical discussions of the headsail/mainsail interaction, and lift/drag factors of cruising boat rigs under the Sail Aerodynamics (http://boatdesign.net/forums/showthread.php?t=457&page=18) subject thread; and some interesting new participants with respectable technical backgrounds.
http://boatdesign.net/forums/showthread.php?t=457&page=18

I’m going to refrain from re-entering these technical micro-flow discussions at this time, and watch where they go. Rather I will choose to do a review of why I pursued my alternative rig configuration for cruising vessels based upon the real-time, observable phenomena that we experience as sailors.

So here are a few other observations I based my thought processes on:


POINTING CAPABILITIES
If properly set up with reasonably good sail shapes and a tight forestay, the jib-headed sailing rig will outpoint the uni-rig vessel. Overwhelmingly I believe the majority of sailors would agree that the jib and/or genoa headed vessel will go to windward better than under mainsail alone….just good old practical observations from multiple sources. Hopefully we’ve come to the understanding that this phenomena is a result of the interaction of the leading sail and its following sail….the two sail combination producing a more favorable wind flow to the headsail that allows it to point slightly higher….again supported by multiple sources of which I will only sight two at this time.

I’ve referenced this experimental work by Hall Spars before, but I will again for a re-emphasis of their findings: Eric responds, “ first, of course, the boat would be improved upwind with a No.1 jib. Generally, we could not point as high as the others here (Block Island) and therefore had difficulty holding lanes.”
http://boatdesign.net/forums/showpost.php?p=5685&postcount=3
…again, good solid real-life experimental results from a respectable source

2) In racing situations we’ve often seen, or made use of, this ‘extra lift’ phenomena when we sought to make use of the ‘safe leeward position’ and force our windward opponent into a pinching situation. Even while we are just leeward of him in the race, the flow disturbance off his rig gives us a slightly better lift to weather.

3) Numerous other examples are available that I just didn’t have time to reference.

So, like any respectable sailor, I wanted at least the ‘capability’ of good weatherly performance to come to my rescue when I really might need it. I believe this aftmast design is capable of good windward performance, perhaps even exceptional in some cases.



SIZE OF THE HEADSAIL
Here is where a real argument will arise….mastheaded vs. fractional, big genoa vs. jib, how much overlap, etc.

From practical experiences I would be willing to bet that most all of us would prefer a fairly good size genoa sail in light-airs, for either pointing, reaching, or even running (particularly if we have no dedicated downwind sails). A Bermuda rigged cruising boat without a good size headsail or furling reacher is destined to be a motorboat in anything other than substantial breezes.

So I wanted my new design cruising rig to have a good size headsail, a genoa. And since I was not intending to utilize a rotating mast, why not make it a mastheaded sail where I could get the max sail area in the lowest CE form. On a multihull vessel I’ve got a good wide sheeting base to make better use of this genoa on a reach or a run.

Again, from practical experiences and theory both, I recognized the effectiveness of a good leading edge sail. I wanted one, even at the expense of a self-tacking headsail. This was to be a cruising design, not a racing vessel requiring multiple tacking capabilities. Fractional rigged designs are a requirement if you intend to have a rotating spar, or a self-tacking jib. I did not want to limit my effectively good headsail size in difference to the smaller self-tacking jib nor rotating mast. Besides, since I was looking to eliminate the mainsail, I saw no need for a rotating mast.

Please note I utilized the word “headsail” to speak of the most forward of the sails on my rig, even thought some would say I have a second ‘headsail’…a staysail.



STAYSAIL or MAINSTAYSAIL
Some sailors might term my second sail a ‘second headsail’, or an inner ‘staysail’ as one would find on a cutter rig. I’ve chosen to call it the ‘main-staysail’ because I have no traditional mainsail to perform the functions of the ‘following sail’ subject I addressed above (the interaction of the leading sail and its following sail....the two sail combination producing a more favorable wind flow to the headsail ). In recognition of this need for a good helper sail, I chose a cutter type configuration with a good parallel slot arrangement. Regardless of what you believe about the ‘slot theory’, etc, eventually you will have to come to the conclusion that with a multiple-sail vessel, the leading sail is helped more by the trailing sail than vice-versa.

So I wanted my second trailing sail to 1) help my leading edge genoa, 2) be self-tacking, and 3) be of a size and disposition that it be easy to handle. I had had experiences with a standard staysail on my personal ketch/cutter-rigged vessel, and I knew I needed to improve upon the staysail’s self-worth. I knew it needed to be separated some greater distance from the headsail to be more usable in a greater number of conditions, so it needed to be moved back. Could it be made a bit bigger and substitute for the combination of staysail and mainsail of the traditional cutter rig?? Why not, particularly since I desired to get rid of the traditional mainsail. And lets make it a bit bigger, locate it over the center of the vessel such that it could be utilized alone in higher wind conditions, make it self-tacking, and make it roller furl.

At this stage I realized I had a net overall lost of sail area compared to the traditional sloop or cutter. But wait a minute; I always had a deep appreciation for the ketch rig for a cruising vessel design…..lets add a mizzen.

KETCH RIG ATTRIBUTES
To those cruising sailors that have had the pleasure of utilizing a ketch rig, I do not think I need to sell them on the concept. In fact I think most of them would join me in the praise of this rig configuration. Besides the full sail configuration, they are happy to be sailed under genoa/mizzen, with the mainsail stowed or reefed, and under mainsail alone, or with a combo of genoa, mizzen staysail and mizzen sail. This is a balanced and very versatile cruising rig.

Of course they do require two masts and correspondingly some extra amount of rigging.

Could I add a mizzen sail onto my double-headsail configuration and come up with a ketch style rig?? Wow, I believe so!! I could even term it a ‘single-masted ketch’ !. The idea was born.:idea:

There is another big plus for a ketch rig on a multihull. The overall center of effort, CE, is lowered by a considerable amount compared to the sloop rig, and particularly the fractional sloop rig. Have a look at the illustrations below, and the illustration I will be providing for a big tri project I was consulting on. The rig heights can be a good 25% lower, and the overturning moments considerably reduced.

The overall sail area could even be increased on this lower aspect ratio rig. Besides, too much emphasis has been placed on hi-aspect ratio sailplans that are really only good for windward work. Marchaj, et al, have shown the virtues of low-aspect ratio sails for off-wind sailing….often two times more efficient!! Lets design cruising rigs for cruising sailors that….

…rarely want to go out bashing to windward. Here is an interesting first hand ‘cruiser’s analysis’. A Liveaboard Cruiser for the Real World
http://www.boatdesign.net/forums/showpost.php?p=35945&postcount=27
Having voyaged over 30,000 miles I have come to the conclusion that idyllic trade wind sailing with steady winds of 15 to 25 knots for 24 hours is a dream, or a myth made up by writers of cruising stories.
. And here a Capt’s experience with multiple head sails (cutter rig) http://www.boatdesign.net/forums/showpost.php?p=39964&postcount=80

Chris White has very high praises for a ketch rig onboard a multihull. Have a look at this separate posting below (http://www.boatdesign.net/forums/showpost.php?p=198607&postcount=99). I excerpted a few observations by Chris White during one of his voyages onboard his client’s 63’ foot ketch rigged catamaran, Concept 63. :cool:

My own experience; I have been the owner of a few sailboats, and one of them was a ketch-rigged vessel…more specifically a staysail-cutter ketch. For a cruising boat I really liked this ketch rig. It broke my total sail area down into more manageable size sails, it lowered my overall rig height, it allowed for helm balance by ‘tweaking’ the mizzen sail, it allowed for ‘mainless’ sailing under headsail/mizzen combo, and, had it been roller furling, it would have been even easier to sail single-hand. I went thru a particularly nasty offshore storm by initially running off downwind with just the small staysail, then upon full fatigue, lying slightly upwind under a backed staysail and reefed mizzen. Here’s a subject thread on going ‘mainless’ http://www.boatdesign.net/forums/showthread.php?t=21274

What did I dislike? I always thought the cutter staysail jib was too small, and it was marginalized by its too-close proximity to the headsail. And I was disappointed in the strip-area of the mainsail behind the spar that appeared to do nothing for forward drive. Now remember this was back in 1973, 35 years ago. I searched out as much info as I could find on cutter-rigged vessels, and I had heard of some aft-mast experiments in AYRS. My webpage “Sail Propulsion (http://www.runningtideyachts.com/sail/)” describes a few other items/processes that influenced my selection of this aft-mast configuration.

So now I’d come up with a single-masted ketch that I thought even looked very presentable….not too radical. But it had a mast canting forward!! That would prove to be a VERY tough sell to the conservative sailor. Sailors are a very conservative bunch that cling to tradition.

Just by happenstance a sailing friend/professional captain came across a magazine clipping of a vessel named Diomedea Exulans (http://www.boatdesign.net/forums/showpost.php?p=198608&postcount=100). That clipping is in the archive section of my website, and I’ve posted it below. Here was a vessel with almost the same mast inclination as mine. This vessel’s rig design reinforced my thoughts about the possibilities of a forward raked mast

I had chosen a 10-degree forward cant to keep things in proportion, and allow for fairly good size twin headsails that would not overlap the spreaders. This cant could be reduced. In fact there was a problem with adapting this style rig to an existing in-build trimaran where I decided to reduce this cant to 6-degrees, and increase the size of the mizzen sail. The point is, the 10-degree cant is not set in stone, nor is the placement of the mizzen sail on the vertical backstay, nor do the spreaders need to be straight athwartships verses possibly raked back, etc, etc. There may be extra-light weight synthetic runners added to the tip of the aft jumper strut to counter the mizzen’s head from adding a torque force thru the aft strut to the mast at the hounds. And there could be other rigging additions as well.

What is needed is a ‘mapping of the rigging forces’ in this rig design, which might lead to subtle modifications that would optimize this rig. Personally I do not have the computer skills to set this program up. I had hoped that an adventurous client would come along with the funds to do this stress mapping and FEA as required to optimize this rig concept.

Is it worth the effort?? I would argue that it is a form of the ketch rig with lots of virtues for the cruising vessel, and particularly the multihull vessels. All three sails can be roller furled for great ease of handling. It should go the weather, and reach very well. It may well have more rigging members added to it than I have shown in the preliminary drawings, but it should still have less rigging than a conventional two-masted ketch.


BACKSTAY TENSIONS
The single biggest concern voiced about this mast-aft rig configuration is the large amount of backstay(s) tension it will experience as a result of the geometry and the need to maintain tight forestays, and then the extra compression loading this will impart to the mast.

This subject alone will consume more time and space than I care to give it with this individual posting here…so I will delay it for awhile till I post some other material I have collected on the aft mast subject.

But let me leave you with the analogy that came to my mind when I considered this aft-staying subject. When I looked at the profile view of the upper portion of my mast aft rig I saw what appeared to be an analogous situation to the athwartship staying of a mast by conventional spreaders and shrouds. My aft ‘jumper strut’ was acting as a spreader, and my masthead backstay was the upper shroud wire….and like a conventional rig, my lower backstay was a ‘diagonal’. The genoa’s headstay pull was analogous to the aft/sideways force of a twisted-off mainsail headboard, and the cutter sail headstay loading could be considered analogous to the headboard pull of a conventional reefed mainsail. These forces can be accounted for in a conventional rig, so why not with my aftmast arrangement??

In fact I can utilize a larger ‘cap shroud angle’ for my upper backstay than might be considered prudent with a conventional rig as I don’t experience the same degree of torsional instability that a conventional rig might experience. A larger ‘backstay angle’ could possible represent a smaller backstay load.

Oh well….more later. (sure would be nice to do a three dimensional space frame computer modeling of the rig where lots of the variables could be changed around to arrive at the most ideal form of this rig).

[brian eiland]

…excerpts from Chris White’s sailing report aboard his client’s Concept 63, ketch rigged catamaran design HERON
_________________________________________________________________
Sunday, October 25, 1998, I joined Bill Shuman owner/builder of the new Concept 63 catamaran HERON and crew Joan Welsh for a sail down the east coast of the USA.

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Immediately, I was struck by the way Heron slides along at 10 knots in relatively light conditions. Our speed varied from 9 to 11 knots sailing close hauled in 12 to 14 knots of true wind speed with a rolling swell. During the first night the wind shifted to NE and fell away to near calm so we motorsailed into the next morning. Our first days run was about 230 n.miles.
As we neared Cape Hatteras the wind built stronger out of the northeast. For a while early on day two we had 25 knots of wind astern with waves of 6' to 8'. These waves were large enough to surf and we had a number of nice rides producing 16 to 18 knots of boat speed under full working sail. The Alpha autopilot did a fine job of steering but was not quite as good at catching waves as an attentive helmsman. In a ketch rig it pays to sail a very broad reach rather than a dead run since this prevents the mainsail from being blanketed from the mizzen. This we did and the sails were drawing well with only an occasional backwinding of the jib. The jib was snatch blocked to the rail giving a nice wide lead while main and mizzen each used a combination vang/preventer led to the leeward rail which provides the sail control of a 28' long traveler without the weight and expense.

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However, we had to jibe back to fetch Diamond Shoals 30 miles to our south but did so a little too early. After dark, with dinner in the oven, we strayed back into the Gulf Stream. The water temperature immediately shot up to 83 degrees! Over a period of 15 to 20 minutes the waves grew to 10' or so and steepened such that tops were falling over and the wind built to near gale force. Wow, that was quick! It was fun to let Heron strut her stuff for a little while, and strut she did with prolonged surfing rides generating 20 knots or more of speed. But it was also getting a little raucous below decks and with a full mizzen Heron was developing a lot of weather helm. We decided to get some sail off (double reef in the mizzen and rolled up about 20% of the jib) and jibe back to the SW to get out of the worst of the current

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Now that we were around the corner we were able to head more toward the west which brought the apparent wind up closer to the starboard beam. Heron loved this! With the wind direction NNE at 20 gusting to 25 we took off on a beam reach at a steady 14 knots occasionally reaching 17 in the puffs. The moon was bright, the wind now cold since it was coming off the land rather than the warm Gulf Stream and we were streaking along dry and comfortable with Cape Lookout 70 miles ahead but getting rapidly closer. But in the wee hours the wind once again fell away. Near Cape Lookout we finally gave up pure sailing for motorsailing at nearly 10 knots by running a single engine at 2300 rpm with light wind on the beam.

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Late in the day the breeze came around toward the SW and gradually built in strength. This was a great opportunity to see Heron sail upwind. We strapped the sheets in tight put both daggerboards down, set the autopilot and watched in awe as she powered up past 10 knots to 11.5 hard on the wind with full sail in about 18 knots of breeze. We had a wonderful fresh yellowfin tuna dinner in the main saloon watching the sun set while Bill's beautiful new machine devoured the miles toward Georgia. Under autopilot we were barreling along upwind enjoying our meal and spectacular view at the same time Joan's nearly full wine glass rested peacefully on the smooth table top without a ripple inside. Before dark I had a good chance to look at the masts for movement. With about 25+ knots apparent and full sail the rig was very stable. The masts were very straight and the leeward rigging still reasonably snug. A small amount of movement was seen in the mizzen masthead but this is to be expected with a long cantilever masthead. Most cats suffer from too much headstay sag which makes windward sailing less productive or requires a running backstay to remove. Heron has no running backstays but her rig is so efficient and stable due to the wide chainplate spacing and resulting large shroud angles that headstay sag is very minimal

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The NOAA forecasters had changed the predicted wind direction 4 times in the last 12 hours so the next wind was anybody's guess. My guess was that because the only wind direction that they had forgotten to predict was southeast, the wind was surely to arrive from that quadrant. Well, by mid afternoon we were having a beautiful sail with 12 knots of SE wind, beam reaching along toward the Sea Islands of Georgia where Bill and Joan planned to cruise a few days and I planned to depart.
As evening rolled into night we saw some of the nicest sailing that I have ever had the pleasure to enjoy. The moon was nearly full, the wind a gentle breeze from the port bow and the ocean absolutely flat. By now we were far enough south so that it was warm. I spent hours of my watch sitting in the trampoline near the windward bow watching the slender hulls slice cleanly through the water at a steady 8 to 9 knots
The wind, while very steady in direction became progressively lighter. By 3 am it was 7 knots by my best estimate (no wind speed instruments on board). It is always hard to evaluate performance of a new design without having a boat of known ability sailing alongside but these were ideal conditions to see how Heron sails to windward in light wind. By recording GPS and knotmeter speeds and headings over several minutes and averaging the readings I was able to get consistent results with little data scatter. We also tried several daggerboard settings and found that in this light wind it seems that Heron's best windward performance was obtained by having only one daggerboard fully down. Our best upwind VMG seemed to be at 5.93 knots boatspeed at an angle of about 53 degrees to the true wind. Pretty respectable for a conservative ketch rigged cruising cat in 7 knots of wind

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It was a great sail and very instructive for me. We saw a variety of conditions although the weather was generally light for the trip. Heron, with her long fine hulls, covers ground very well. I really like her rig, which although modest in size, is efficient and easy to handle. Going upwind in stronger conditions I had complete confidence in the spars which are extremely well supported by the long swept spreaders and efficient shroud angles. Light air performance was the big surprise. I knew that she'd be fast in a breeze but I did not fully appreciate how well she would sail in light air. This feature I ascribe to her more slender-than-normal hulls which are just so easy to move through the water.
Heron demonstrated that the catamaran Achilles' heel, underwing clearance and related pounding, could be dealt with successfully. We saw (actually felt) a few kicks to the belly in the sloppy conditions rounding Cape Hatteras but they were less frequent and less severe than most cruising cats that I've sailed. Sailing upwind in waves there would be a rumble of water noise every now and then as a wave top was mashed between the hull and wing intersection but it was easy to ignore. For her weight and overall beam the C-63 design has fairly generous underwing clearance. But it seems that the larger advantage is in her slender hulls which create much smaller (almost non-existent) bow waves. It seems to me that that hull waves are often responsible for a lot of the underwing slamming as they cause existing seas to peak upward at exactly the wrong time as the lowest part of the wing passes over them. (BE noted: my observations as well)
Another issue of importance in a cruising cat is no wind, or very light wind. Racing boats are disqualified if they use the engine. Consequently boats designed to race (and the cruising boats that emulate the racing designs) have sail plans optimized for light air, which are often too large and too fragile for offshore cruising. Cruising boats, on the other hand, use the engine when the wind quits. And the time spent motoring, or motorsailing, is often quite significant. The term motorsailer has had negative connotations for decades. Normally motorsailers neither SAIL nor MOTOR very well. So they've been viewed with some disdain as neither fish nor fowl. But I view the Concept 63 design as a motorsailer that works. Her power performance with twin 50 HP diesels is quite good with 10 knots average speed at an easy 2750 rpm. Fuel consumption is very moderate and she achieves about 5 miles per gallon at 10 knots (typical for catamaran power boats is 3 mpg or less). But the real benefits happen when there is some wind too. Running one engine often is all that is needed to bring the apparent wind forward to make the sails work harder and the combination provides much better results than either motoring or sailing alone. And of course when there is wind you can shut off the noise makers and enjoy superb sailing at faster speeds than any reasonable engine could provide. I know that there is now considerable interest in power catamarans, with all the builders coming out with updated models. But honestly, there is nothing in the world quite as nice as shutting off the damn engines and SAILING.
In terms of weight or cost Heron is no more boat than the typical 50' cruising cat, nor does she require any more effort to sail. But by drawing out the hulls to 63' in length substantial benefits are gained in performance and comfort. This combined with her 3' draft, the ability to pass under 65' bridges and excellent performance under power make her an incredibly versatile and pleasing cruising boat.
Chris White
Chris White Designs

Brian added: I agree wholeheartedly with all of the above !!!

[brian eiland]

Unusual but practical…much original thinking on the part of both her owner and her designers.

Designer’s Comments:

Diomedea Exulans is the result of a joint effort on the part of a yacht owner and a firm of yacht designers to venture beyond conventional concepts in order to achieve results not attainable by conventional means. Both believed that the features incorporated in the dsesign were dictated by sound reasoning, and several seasons’ experience with the boat appears to confirm this belief. This is a point that requires emphasis at a time when a great deal that is unconventional around us is intended largely to surprise or amaze…yachts as well as yippies.

McCURDY & RHODES

__________________________________________________________


Owner’s Comments:


THE GREAT WANDERING ALBATROSS, Diomedea Exulans according to Linnaeus, long puzzled scientists by sustaining flight without movement of the wings. In the light of modern analysis the bird is seen to accomplish a wonderously elegant maneuver based on his extraordinary aerodynamic efficiency—which only “appears” to be perpetual motion (But it surely does look like it until a vector analysis is made of the wind velocity gradient). Modem sailors are much more puzzled by the vessel which bears this name. She is, perhaps, best described as a “staysail ketch.”

Her arrangement was devised to reduce—or eliminate work on the physical limitations, and to take advantage of the aerodynamic efficiency of sails with wire leading edges (having no spar at the leading edge)—this efficiency to compensate the penalties for high freeboard and great beam. At the same time it permitted all sail management, including hoisting, lowering and reefing to be accomplished from the cockpit leaves the cockpit except to “unreef” or to get a gasket on the mainstaysail after lowering.

The whole rig lays down on the pulpit and slides aft to stow. One man can do this jo two are better. Two men are required to raise the rig; shipyard facilities are not necessary.

In answer to the inevitable question as to the positions and attitudes of the masts: The main mast is stepped far aft to eliminate overlap and permit the sail to ‘be self The arrangement of the mizzen puts the sail on vertical “jackstay” and eliminates any sail over the cockpit.

There are a number of collateral features which tend to reduce manpower requirements, hut equipment and finish are very simple: contrary to rumors, there are no power winches or auto-pilots. The result is a very roomy and easily managed cruiser only requiring help in picking up the mooring in a breeze. Otherwise the owner considers her a singlehander—for a slightly younger man.

FREDERICK M. TRAPNELL,
Vice-Admiral USN (retired)
Seawanhaka Corinthian Yacht Club,
Oyster Bay, N.Y.

[Alexluk]

Hello Brian,

I'm new in this forum, but I do search a lot about catamaran. After reading and comparing lot of different designs, I perfer to have a catamaran which can be easy handle.
According to your idea and concept of ‘single-masted ketch’ , I try to build by first catamaran, and I should to express respect to you; in the below is the blog of my builder.
http://***************.blogspot.com/2008/04/ive-been-commissioned-by-couple-from.html

I may become a genie pig, but I think besides the theory, a real experiment can provide more improvement in sail boat.

I hope I can share it with you and give my input to the ‘single-masted ketch’ design.

Alex

[yipster]

"Houses are but badly built boats so firmly aground that you cannot think of moving them. They are definitely inferior things, belonging to the vegetable not the animal world, rooted and stationary, incapable of gay transition... The desire to build a house is the tired wish of a man content thenceforward with a single anchorage. The desire to build a boat is the desire of youth, unwilling yet to accept the idea of a final resting-place."

– Arthur Ransome, Racundra's First Cruise, 1923

a great essay and i do like that motorcat sailing design
for some more rig ideas look in my gallery

[brian eiland]

Hello Brian,
According to your idea and concept of ‘single-masted ketch’ , I try to build by first catamaran, and I should to express respect to you; in the below is the blog of my builder.
http://***************.blogspot.com/2008/04/ive-been-commissioned-by-couple-from.html

I may become a genie pig, but I think besides the theory, a real experiment can provide more improvement in sail boat.

I hope I can share it with you and give my input to the ‘single-masted ketch’ design.

Alex
Hello Alex,
I tried to send you a private message but you left no email address on your 'profile'.
I'm going to wish you the best of luck with your project, but let you know I'm not pleased that ***** has chosen to act as though this idea of a aft-mast is his own with no reference to any other sites discussing this idea.

I will also make you aware that I've done some research on Thai building, particularly since I recently married a Thai lady and intend to retire to Thailand. and I will make you aware of some concerns in a private email.
Regards, Brian
info@runningtideyachts.com

[brian eiland]

...I thought it might be interesting to revisit this portion of Paul Bogataj's paper

SAILS IN COMBINATION
Each sail by itself is much simpler than the combination of a foresail and mainsail as in the sloop rig. The sails are operating so close to each other that they both have significant interaction with the other. The most interesting feature of this is that the two sails together produce more force to pull the boat than the sum of their forces if they were each alone.

Earlier, upwash was identified as the increase in flow angle immediately upstream of a wing. There is also a corresponding change in angle, called downwash, just behind a wing, where the flow leaving the wing has been turned to an angle lower than the original flow. This is the cause of the well known “bad-air” that a boat just to windward and behind another boat experiences.

The mainsail of a sloop rig operates in the downwash of the forward sail, causing the flow angle approaching the mainsail to be significantly reduced from what it would be otherwise. This decreases the amount of force that the mainsail produces. The observed affect commonly referred to as “backwinding” is partially a result of downwash from the foresail, but is also due to the higher pressure on the windward side of the genoa being very close to the forward, leeward side of the mainsail, causing the flexible material of the mainsail to move away from that higher pressure.

The foresail of a sloop rig operates in the upwash of the mainsail. The wind as far upstream as the luff of a genoa is influenced by the upwash created by the mainsail. Hence, a jib or genoa in front of a mainsail has a higher flow angle than it otherwise would have by itself, causing an increase in the amount of force that the forward sail produces. So, while the mainsail is experiencing detrimental interference from the foresail, the foresail benefits from the interference of the mainsail. Notice that more air is directed around the curved leeward side of the foresail. This causes higher velocity (lower pressure) and more force. The net result is that the total force of the two-sail system is increased, with the foresail gaining more than the mainsail loses.

There is a converse affect to a windward boat receiving “bad air” (downwash) from a boat ahead and to leeward. A leeward boat gains additional upwash (“good-air”?) from a boat just to windward and slightly behind that acts like a lifting windshift until it moves ahead of the windward boat. This is the same phenomenon from which a foresail of a sloop rig benefits.

Another consequence of the difference in flow angles that the two sails experience in each others’ presence is that the mainsail must be trimmed to a much closer angle with the boat’s centerline than the foresail, which is able to be trimmed to a lead position well outboard. This angle represents the difference in upwash on the foresail and downwash on the mainsail due to each other.

MASTHEAD RIG.
On a masthead rig, where the forestay is attached to the top of the mast and both sails taper to basically zero chord length at their heads in a similar fashion, the interference effects of the sails on each other are similar along the entire height of the mast. The mainsail ends up being rather tightly trimmed all the way up becauseof the genoa’s downwash, and the genoa gains from favorable upwash all the way up.

FRACTIONAL RIG.
A fractional rig has the more complicated characteristic that the top of foresail is not as high as the top of the mainsail. This means that the top of the foresail is very close to the front of the mainsail at a height where there is still an ample amount of chord length in the mainsail. As the foresail luff approaches the mainsail luff, the upwash on the foresail due to the mainsail increases, because the low pressure behind the mainsail has more affect the closer the flow gets to it. This causes the top of the foresail to experience even more upwash and contributes to a fractional rig’s foresail being trimmed more twisted than a masthead rig’s foresail.

The top of the main on a fractional rig extends well above the foresail, leaving the upper portion of the mainsail free to experience the apparent wind without the downwash interference of the foresail. Apparent wind toward the top of the mast comes from a much higher angle, so the mainsail above the foresail experiences much higher wind angles than the lower portion of the mainsail where the genoa is causing substantial downwash. This change in flow angle with height on a mainsail is quite dramatic with a fractional rig and leads to trimming a fractional rig’s mainsail with more twist than a masthead rig’s mainsail

...and a couple of flow sketches (please excuse their older rough nature)

[brian eiland]

….wandering thru a library the other day I happened on a few books from which I extracted some interesting passages. This one is from Brion Toss’s book, “The Complete Rigger’s Apprentice"

A Portfolio of Rigs

If there’s one thing that characterizes rig design, it is endless variation. Riggers and designers take the apparently simple task of holding a mast up and render it in more, and weirder ways than you'd ever think possible. With such a profusion of structures it can get confusing out there when you're trying to make decisions for your boat.

The good news is that sensible variations are responses to sensible considerations; hull type, climate, sailor's temperament, and other factors inform how a finished rig looks. So if you understand those factors you'll be well along in understanding design. The following portfolio is intended to illuminate design decisions, and to show some (mostly) appropriate results. Soak it up, and then turn new eyes on your rig.


MIZZENS
In this sloop-happy world, mizzenmasts don’t get a lot of respect. Ketches and yawls generally don’t go to weather as well as their single-masted cousins, and so are viewed by many sailors as inefficient—that is, by those whose sole definition of “efficient” is “able to tack through 70 degrees.”

“The elaborations of elegance are at least as fascinating, and more various, more democratic, more healthy, more practical….though less glamorous….than the elaborations of power.” Wendell Berry

But a mizzen can be more than just an extra mast. It can be evidence that designer and owner have decided that versatility and comforting redundancy offset a loss of absolute weatherliness. That the expense and complexity of an added mast is off-set by reduced size, expense, and labor-intensiveness of the mainmast. That any inconvenience and clutter,…the mizzen of a ketch does sit right in the boat's busiest work area…can be more than offset by a center of effort lower than that of a comparable sloop, by less sharply focused hull stresses, by a more versatile sail plan, and by increased power on a reach. This last reason is why so many of the vessels in the most recent Whitbread Round-the-World Race were ketch-rigged.

Because a small (under 33 feet or 11 meters) sloops and cutters already have relatively easily handled sails, mizzens are most appropriate on larger vessels. Crew laziness or non-agility, or a particularly large sail plan might justify a mizzen on smaller vessels.

Regardless of vessel size, a mizzen always presents a challenge in rig design. How do you stay it adequately without interfering with the main? With few exceptions (see Sundeer below), there isn’t room between the mizzen-mast and the main boom for a forestay. There often isn’t even room for much of an angle on the forward-leading mizzen shrouds. And because the mizzen is so far aft, there’s also rarely room for a backstay. Designers have risen to these and other mizzen challenges with varying degrees of success. What follows is a spectrum of configurations analyzed for interrelationship.

[...text on other designs from original book omitted here ]

SunDeer
Yacht designer and world cruiser Steve Dashew brings mizzens into the New Age. There’s a high-aspect, double-spreader, intentionally bendy rig on his evolutionary ketch Sundeer. And there’s even a forestay and backstay, details more commonly associated with mainmasts.

Modern details aside, this mizzen has a lot in common with the ones mentioned previously. Like them it’s a place to hang a staysail for reaching power, makes for a lower center of effort than a sloop of comparable sail area, and is part of a versatile easily-handled sail plan.

But there are two other important mizzen virtues that Sundeer in particular exemplifies. One, mentioned briefly at the beginning of this essay is the mizzens helpmate-relationship with the main. Sloop proponents talk about a split rig’s ‘inefficiency’, then usually go on to how having a mizzen means you have to buy a whole extra mast, sails, and rigging. They admit only grudgingly that a ketch or a yawl might be easier to handle or more versatile. And they never mention that the main on a ketch can be much smaller and cheaper than it would he if it had to absorb the mizzen’s sail area. Nor do they take into account that the mizzen prolongs the main’s life by reducing the intensity of the cyclic loading that contributes to metal fatigue. On Sundeer the mizzen is over half the size of the mainsail. This is a big mizzen (20 to 40 percent of main is more typical) for a ketch. But any appreciable mizzen is a lot more than an extra mast stuck in the back of the boat.

The other mizzen virtue has to do with the relationship of the mizzen to the hull. By distributing stress over a wider area, a split rig is kinder to its hull than a monomast. With many boats, this distribution advantage is qualified, since mizzens, at least on ketches, are often reefed or lowered first when the wind comes up, letting the main to deal with heavy weather. This is sometimes done because main and staysails provide more drive than mizzen and staysails, but most often it’s because, on most vessels, weather helm increases sharply with increased heel. Mizzens, being so far aft, only exacerbate weather helm, so down they come. But this is a design flaw in hull, not sail. A balanced hull like Sundeer’s does not suffer hull-induced weather helm as it heels.

And on Sundeer, Dashew has gone a step further, intentionally matching hull and sail plan so that there is always a great deal of weather helm, all of it mizzen-induced. On most vessels this would result in a hard-to-steer boat, but Sundeer has a large balanced spade rudder, so the helm always feels neutral. Why do this? Because a big, properly shaped balanced rudder can provide lift, just like a keel. If it can provide enough lift, you can make the keel smaller and still go to weather well. So Sundeer’s rudder is helping the keel, just as the mizzen is helping the main. The net result is that this 67-foot LOD ketch draws only 6 feet loaded, yet will outpoint many sloops, especially in a breeze, when speed gives the rudder more lift. Balanced spade rudders are generally frowned on by cruisers as fragile, vulnerable things, but Sundeer’s is built around an 8-inch diameter rudder shaft (!), and has a sacrificial “crushable” bottom; it’s extremely unlikely that even a violent grounding would cause significant damage. (Brian’s note: Hot idea, loading up the rudders like we did with asymmetric catamaran hulls to reduce leeway !).

It is unusual to have rig and hull so creatively interlinked, but it’s possible to optimize the performance of any split rig relative to the hull it sits in. On some boats this might involve flatter- or fuller-cut sails, adding a bowsprit, changing mast rake, etc. A qualified rigger or yacht designer can help you with particulars. Meanwhile, I hope this section has given you enough information to extrapolate from, whether it’s for a configuration that will allow you to disconnect a springstay, or to let you see force relationships more clearly, or just as an introduction to the next section.


MAINMAST
Mainmast are more than just great big mizzens. The loads they bear are a whole other order of intensity and complexity…. continued in book

[masalai]

Thanks Brian, That was a nice read... One question for me is relating to the stresses on the mast of a "hitch-hiker rig" - does the removal of the main reduce the loads?

[brian eiland]

The Prout catamaran rig had considerable influence on me when I first began to develop my aftmast concept.

So it was interesting to have just this evening run across a forum discussion group that includes a number of Prout owners who seem to be quite happy with their aftmast rigs for cruising, albeit not raked rigs.

http://www.cruisersforum.com/forums/f48/prout-rig-3362.html

[brian eiland]

...this subject came up here (http://www.boatdesign.net/forums/showpost.php?p=214891&postcount=26)...and I felt it better to add my response here, as it concerns this rig concept

Wonder how the authorities would view a saling yacht say 60 feet without a motor, in other words so you really needed skills to enter and leave a port, river, dock ♠
I imagined being able to do that as well with my 65 catamaran with a single masted ketch rig;
You know I can still imagine sailing a big 65-foot catamaran with this rig right off the mooring, and back to the mooring, without the engine, by myself, with so little effort that I might take it out having only a few spare hours to kill, or a day sail. I could simply unfurl my 'central mainstaysail' and back it over if neccesary to go backwards or fall off the wind...all very tame and controllable in and around a crowded harbor area.

And I would rig mine with tiller steering rather than a wheel and get a really good balanced helm. I would be less concerned with reefing by myself if the wind were to really come up. If I were short-handed at sea, I would have many of the benefits of a ketch rig, without the necessity of slab reefing the main and mizzen sails of the traditional ketch rig. And I wouldn't have to uncover any sails, nor recover them when I returned to port....I could be at the club's bar while everyone else was putting their boats to bed.

Interestingly the 290' Maltese Falcon with its modern square-rigged "Dynarig" has manage to sail off, and back to its mooring.

[Pericles]

Brian,

"Cornish fishermen are rigging their boats for sails, as we report today, is one of the few (but possibly the first of many) positive results to arise from the rocketing price of fuel."

http://www.telegraph.co.uk/opinion/main.jhtml?xml=/opinion/2008/07/20/dl2003.xml

Perry

[brian eiland]

...this comes from another forum, and I post it here to make reference to it in the near future

...I think general acceptance of something this new tends to go like this: The engineers trust the numbers, the daring try it out, and over time acceptance is gained from experience of those that went first. But the numbers are the lynch pin in my opinion. So I keep coming back to the question, but from three different approaches:

The Godfather – Have you floated this past C.A. Marchaj yet? I think he would lend a great deal of credence to the work.
I'm uncertain that he is still with us? Certainly he has not made any recent contributions to the subjects he so adamantly contributed to. Besides his contribution would likely be primarily aerodynamic in nature. I think I've shown that the aerodynamics of the situation conform with his findings and will be just fine. It's the stress loading that will be tricky.


Loads - The occasionally voiced concern of those that have read everything they can find on aft-masts is the crystallized thread of a Norseman backstay and the later switch to a conventional sloop rig from by Barefoot who, as pointed out above, didn’t follow what you were saying in the first place.
I don't know exactly where his Norseman fitting was located in his rigging plan. If he had only one single backstay on his rig that was clearly not enough. And I am unsure as to what size rigging wire and fitting were utilized. I have a feeling that his fitting was faulty, and/or his installation of it. The reason I say this is in reading his log I can find nothing really heavy or extreme weather-wise that should have brought the rig down unless it was greatly underdesigned by his own design calculations.



By extension, the concern is that the rigging might be sized to take the loads but the hulls couldn’t or would at least need some reinforcement. And yet, this is contrary to your position that the rig would have less stress because of a lower Center of Effort.
I suppose the answer is running a finite element analysis of the whole deal but I am not a Naval Architect. So I’m asking you, the chief proponent – Brian, what are the loads involved and have they been rigorously calculated or has this been done with an applied engineering approach?
First let me clear up this point about 'less stress'. I'm sorry if I've given the impression that my rig would be less stressful. Rather in fact it will be more stressful, both within itself, and in transmitting its forces to the hull structure. I only meant to say that because it has a lower CE, it will have less overturning moment on the vessel than the corresponding sail area of the taller sloop rig. So the side shroud loading could be less from a geometric point of view. BUT, on multihull vessels, this shroud loading can be SIGNIFICANTLY higher than on a monohull due to the huge stability factor** of the beamy hull form...yin and yang.

Here is the gentleman & firm I want involved in the final stress analysis of this rig concept, Chris Mitchell of AES (http://www.aes.net.nz/). I'm currently in discussions with him about this consultation work, and hoping to have a definitive client willing to pick up part of that expense.
**(have a look at this paper, Design Notes (http://www.aes.net.nz/Rig%20Design%20Commentary.html), and particularly under "Cruising Catamaran Rigs", )
(while you are in this paper have a look at "Geometry:Cap Shroud/Chainplate". I will reference that in a minute)

Please understand that there are many designers and naval architects that could not do adequate justice to rigging analysis that falls outside the 'norms'. Free-standing mast systems are another of these 'outside-the-norm' design projects that need a specialist involved. Eric Sponberg (http://www.sponbergyachtdesign.com/Masts.htm) is another choice of mine to evaluate unusual rig designs as he has had to do on many free-standing projects before. I'm the concept guy, no longer an engineering specialist.

Having said that let me point out a couple of critical items I see in my aftmast rig design:
1) Masthead Loading: Some folks have noted that I would not be able to maintain a reasonable tight forestay as a result of the mast leaning forward. But look closely at my masthead. The single backstay at that point is making a greater angle with the mast than many traditional sloop rigs....more reward pulling advantage...about 27 degree 'back-capstay' angle...pretty good.

2) Hounds Loading: Here is were I will experience some problems. As drawn at present There is only a 10 degree angle between the lower backstay and the mast....thus significantly higher compression loads to the mast. But if I attach this backstay to the front of the mast and run it to the very sterns of the vessel I get a 15 degree angle...much better. And if I chose a 6 degree rake for the mast rather than the 10 degrees shown, things change again...likely for the better. This is a portion of the 'stress mapping' I am seeking, and this is Chris' forte.

3) Capshroud Loading: As Chris points out in his paper you neither want too small a capshroud angle (big compression loads), nor too big a capshroud angle. But why not bigger....because on a traditional rig with a mainsail the head of the mainsail bends off to leeward and tries to twist the top of the mast excessively. I don't have this 'head-of-mainsail' load as I have no mainsail...so I might well make use of very wide spreaders and big capshroud angles to lessen the significant compression loads to the mast imparted by the stability loading

[brian eiland]

Interesting multihull site just brought to my attention by Sailing Anarchy.

As I paged thru the site, this feature jumped out at me,
"Several features give the M61 the most powerful and versatile rig possible for this sized yacht: a racing standard all-carbon rig, with an aft-of-amidships raked wing mast"

Moxie Yachts http://www.moxieyachts.com/
Click on their 'M61' model and then under 'Innovations', have a look at the 'Rig'

...(BTW it's not raked fwd, and it's not a mastheaded rig)

[Pericles]

Brian,

Here is a site with a great explanation of the development of eastern coastal sailing vessels from log canoes to skipjacks with their aft raked masts.
http://www.mariner.org/chesapeakebay/waterman/wat002.html

Best regards,

Perry

[brian eiland]

Here's an interesting variation of a aftmast rigged sailing craft that was bought to my attention some months ago, but I only recently found it in a stack of papers I've ignored for quite awhile.

http://www.wiebel-sailing.com/index.html

..and here some other forum discussions of that craft
http://www.boatdesign.net/forums/multihulls/new-speed-sailing-contender-25856.html

[Spiv]

Well, it has taken a long time, but my new boat design is nearly complete.
I engaged Richard Woods as my consultant in the design of the hull.
He has patiently guided me while I designed the sailing rig and the accommodation and he has been exceptionally professional in his approach to the hull design.

Brian, you can see a lot of your thinking in this rig with a mixture of other ideas of mine and from pictures. I hope you will give me your blessing, but please feel free to comment on any aspect of it.

Here are the drawing of the rig.
While I know that they will not suit every taste, they are just what I want: a mainless rig that is easy to handle single handed and that I can safely lower in a minute to go under bridges.

The two fore sails will be on 'Stay Furlers', since the forestay are Dianeema rope, they can be bent over the trampoline when I lower the mast. They do not reef, so they will be either in or out according to the wind.
The mizzen is on a conventional Furler that can be reefed.
Lastly there is a storm sail that can be hanked in the unfortunate case I get caught in a gale.

There you go, I reopen the subject for all to participate in the discussion...

[Fanie]

Eh Spif,

It looks very nice. I like the width, although some think it just takes you longer to get to the head. You can't go too wide either else you won't fit in any harbour :D

I like your sail setup as well. For your purpose I can certainly see why you have it as it is. That 128m^2 main sail is going to be a nice and powerfull bugger, better add a proper grab rail and some gloves... or get a decent winch. You may want to add a detachable boom on it's foot, especially for when you run.

[Spiv]

Thanks Fanie,
The actual size of the sails might still change a little, but the foremost sail will be a Yankee of ~120mq, the Genoa is ~60, while the Mizzen ~40.

I don't think i will keep all the 220mq up in more that ~10kn of true wind.
Then I will furl the Genoa or the Yankee depending of what the wind is doing.

At 25kn, perhaps just the Genoa and furl the mizzen, then swap and just sail with the mizzen.
With furlers it is going to be easy to reduce sail even going downwind!

[Alik]

I see Spiv's version of aft mast rather practical. Mast is close to vertical, frame stucture for transverse stiffness. It will be good to test it, but I do not expect excellent windward performance.

Actually I do not belive in aft mast rig so much advertised by Brian - it has never been built and never proved working. Unfortunately some people are mislead by this nice but unproven concept.

I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Aslo there are serious concerns about windward performance. Anyway soon we will have chance to test it on one of our designed cats.

[Spiv]

.....Actually I do not belive in aft mast rig so much advertised by Brian - it has never been built and never proved working. Unfortunately some people are mislead by this nice but unproven concept.

I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Also there are serious concerns about windward performance. Anyway soon we will have chance to test it on one of our designed cats.Hi Alik,
you are right that Brian's mast has not been tested yet, however the concept is aerodynamically excellent.
You are mistaken if you say that aft masts have not been built as we already know of several, I repost their pics here.
I have spoken to the owner of boat No3 and he very happy with his rig and assures me that the she goes to windward exceptionally well.

My personal experience is that i could tack my 42' cat without problem when sailing with jib only.
Anyway, who wants to beat to windward when cruising???

[Fanie]

On a smaller scale, haven't you guys seen what I did with the little trimaran I built ? Aft mast...

I've slowly started on the 10m cat and have decided to do a 8m to 9m one as well, both with double masts and sails.

[Alik]

I never said 'aft mast has never been built'. There are few boats built most known is 'Prout rig'.

I just stated that Brian's aft mast rig has never been built and tested. It is aerodynamicaly excellent (if we neglect slack of forestay :) ) but structurally weak, and mainsail does not seem practical.

[Spiv]

Fanie,
you're right, I remember, you had great result with your rig.
One more proof that it does work.

I agree with Alik thet forestay tension is important, but good sail performance could also be achieved with designing the sails for 'not so tight' a forestay as they have in the racing rigs.
In any case, I believe I can achieve good forestay tension as I have two backstays on winches.

My challenge is with engineering the CF mast. Any FE designers out there??

[masalai]

Bob Oram is suggesting I go aft (well further than standard design) mast for my "hitch-hiker rig" - but at present I am happy with where it is - as it looks like I am just too lazy/broke to buy/put a standard "mainsail" - but actually I want to use the space for PV solar panels (up to 10kW) - Bob is apparently considering an aft-mast rigged design somewhere down the track...

I will probably cant the mast aft a bit to get more sail area from the twin genoas and put the centre of effort a bit further aft - just ideas at the moment...

[Manie B]

my 2 cents

I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Aslo there are serious concerns about windward performance. Anyway soon we will have chance to test it on one of our designed cats.

most of my sailing experience is on 35 to 39 foot bermudan sloop mono hulls with full keel and "barn door" style rudders
then also PLENTY dinghies and lasers and hoby cats

i can assure all of you that after i sailed on Fanie's little tri i was completely blown away by it's excelent performance to windward and its ability to tack. Admitted this was on inland waters but it was a gusty blow.

the system that Mas intends to use with twin head sails is a very good choice for cruising and Fanie's experiment clearly shows that the aftmast concept works exceptionally well - absolutely nothing to worry about :D

[Alik]

Manie, it is common knowledge that cats with 'Prout rig' are more difficult to tack compared with conventional rigged cats. This is because of big genoa that blows out and creates yawing momentum that prevents the tacking motion. Small mainsail is not capable to balance the genoa. Of course, it could be different on different boats depending on many other factors.

Anyway, this is just talks. Brian's rig should be built and tested before we can make conculsions and actually before it is marketed. He needs at least a 20-30' cat built with this rig... instead of hundreds of pages written on the subject during many years. I mean that prototyping and engineering are important before someone start investing real money in 50-60' boats with this unproven rig.

[Fanie]

I'm building two boats where the aft mast rig goes on. One is a 8m cat the other is a 10m cat. Both will have double aft mast rigs similar to what I had before. Needless to say there are changes, but not much.

I don't like referring to this sail as a genoa, a genoa seems to be clumsy and less controllable.

We should find a proper name for this.

[Alik]

Fanie, but You built a prototype before start building bigger boats. This is right way to go, really appriciated!

[Fanie]

Yes well the way things are going here financial wise it seems I'll only get one finished in about 250 or so years :(

[brian eiland]

....I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution. Aslo there are serious concerns about windward performance.
Almost makes you wonder how this vessel ever manages to tack or go up wind :rolleyes:

[brian eiland]

..I just stated that Brian's aft mast rig has never been built and tested. It is aerodynamicaly excellent (if we neglect slack of forestay :) ) but structurally weak, and mainsail does not seem practical.
I agree Alik, my rig is not to be put on many boats as it needs a good foundation to accept the high loading. Creating this good foundation may add considerable to the engineering and the price of the vessel. So its not for all.

I wrote a few discussions with reference to a few situations where 'unusually' high loading is involved:
http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-6.html#post223385

Vessel Substructure to Support Rigging Loads (http://www.boatdesign.net/forums/sailboats/sail-loading-rig-rig-loading-vessel-2293-4.html#post114487)

[Alik]

Brian, You have to put big disclaimer on Your website saying that these concepts have never been built.

For years, You are talking about these 'aft mast rigs' instread of building and testing a prototype. Sorry to say, but without engineering, prototyping and testing Your ideas have zero value.

As to the photos You post above - completely different situation, pls note the position of mainsail to CLR of boat.

[brian eiland]

I never said 'aft mast has never been built'. There are few boats built most known is 'Prout rig'.

Reference Posting #7 above
...for a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.

[masalai]

It is not, it is sailing downwind faster than the wind :D:D:D:D:D

[Alik]

Reference Posting #7 above
...for a moment look at the profile drawing of my rig and picture it as though the mast was standing straight up vertically with its masthead in the same location as mine now is. Contrary to Tom’s statement, my forestays are really no longer than a conventional sloop rig, in fact they are likely shorter. And his comments about the angles between the backstay & the mast and the forestay & the mast are not quite correct. In reality it’s the horizontal (not vertical) component of the tension forces in these two stays that determines the ability of the rig to resist sag in the forestay……my masthead backstay has a more advantageous (rearward pulling) angle than does my forestay pulling forward. Interestingly, this phenomenon was probably most detrimental to the Prout mast-aft rig. Their short vertical mast at the aft position resulted in a highly sloped forestay that was both too long for the rig’s overall height, and it could over-exert a forward pulling force on the masthead that was indefensible by the shallow-angled backstays…..result, big time sag, sails too full. This rig had other problems as well….not an example of a successful mast-aft rig, but a case study in some things to avoid.


Talking again... Show us the boat!!! :D

[brian eiland]

..As to the photos You post above - completely different situation, pls note the position of mainsail to CLR of boat.
I'm unsure as to what you are insinuating here...the balance of the CE over the CLR, I assume??

Are you claiming the main on the tri is of a larger area than my mizzen, and located more rearward, and that is more balanced?

If you look at my original design I think you will find that me CE for my full rig (all 3 sails), and the CE for the combo genoa/mizzen (2 sails) are both very close to one another fore-to-aft. and both are almost directly over the CLR of my centerboard

..and you might also refer to the illustrations in posting #98 above

[Alik]

I'm unsure as to what you are insinuating here...the balance of the CE over the CLR I assume??

Are you claiming the main on the tri is of a larger area than my mizzen, and located more rearward?

If you look at my original design I think you will find that me CE for the full rig (all 3 sails), and the CE for the combo genoa/mizzen (2 sails) are both very close to one another. and both are almost directly over my centerboard CLR.

The geometric CLR/CE relation is basic thing and it seems correct from Your sketch. To be accurate, this is simplified repersentation that works only for proven rigs. I mean that CE of sails will move during tacking motion of boat, and this will seriousely effect tacking performance.

I say again: reference to posts, guesswork and basic geometry are not sufficient to prove feasibility of this rig. Show us working boat, at least a dinghy, with Your rig!

[brian eiland]

It is not, it is sailing downwind faster than the wind :D:D:D:D:D
Not sure of what you speak?

This tri in the photo is most likely not sailing downwind judging from most indicators, particularly the closeness of that headsail sheeting and the small amount of twist in that fat-headed main

[brian eiland]

The geometric CLR/CE relation is basic thing and it seems correct from Your sketch. To be accurate, this is simplified repersentation that works only for proven rigs. I mean that CE of sails will move during tacking motion of boat, and this will seriousely effect tacking performance.
Yes, and I stuck to the conventional method of centers of the areas just as a conventional rig. I don't claim my individual sails to 'different' from ordinary 'proven' sails.

[Alik]

The aerodynamic CE of sail is not at its geometric center.

[brian eiland]

..I have serious doubts if aft mast rigged boat is capable to tack due to sail area distribution.
I will have similar problems tacking that an ordinary cutter rigged vessel will have....getting that genoa around the 'babystay'.

Note that both my mizzen and staysail (mainstaysail) are both self-tacking. The genoa is probably best left alone (allowed to backwind against the staysail) until the tack is completed, and then hauled around....somewhat std operating procedure in cruising vessels with a big headsail.

[brian eiland]

The aerodynamic CE of sail is not at its geometric center.
I think we all realize that...it is usually forward of the geometric center. But MOST designers for YEARS have continued to use this geometric center rule to happy results.

[Alik]

The CE of sails is moving during tacking motion and resulting aerodynamic force will try to push the boat back on original track once genoa is luffed.

On conventional rig, this force is balanced by mainsail, but in Your rig mainsail is rudimentary.

Forget about geometric CE - this does not work in Your case.

[Alik]

I think we all realize that...it is usually forward of the geometric center. But MOST designers for YEARS have continued to use this geometric center rule to happy results.

... with conventional rigs where they have plenty of statistical data for this empirical method.

[brian eiland]

Manie, it is common knowledge that cats with 'Prout rig' are more difficult to tack compared with conventional rigged cats. This is because of big genoa that blows out and creates yawing momentum that prevents the tacking motion. Small mainsail is not capable to balance the genoa. Of course, it could be different on different boats depending on many other factors.
And I agree with you here.

[brian eiland]

The CE of sails is moving during tacking motion and resulting aerodynamic force will try to push the boat back on original track once genoa is luffed.

On conventional rig, this force is balanced by mainsail, but in Your rig mainsail is rudimentary.

Forget about geometric CE - this does not work in Your case.
On a multihull vessel there are times when guys have had to unsheet the tight mainsail to prevent the vessel from going into irons. The mainsail does not help the tacking situation, but rather may hinder it!!.

Most important in tacking a multhull is to 'turn' the boat into the tack, and not stall it by throwing the rudders over to quickly. Second it pays to have a nice 'pivot point'. For that reason I MUCH PREFER daggerboards or centerboards to long shallow keels.

Get the bow just thru the wind, and that genoa will immediately backwind and push the vessel thru the tack.

[brian eiland]

Brian, You have to put big disclaimer on Your website saying that these concepts have never been built.
That is the first thing I say to a person who is inquiring to my rig....and it is likely the reason it has been so hard to attract clients for this rig. And when I tell them it needs some good engineering work on the final staying arrangement(s) most sailors aren't willing to spend for that extra analysis.

I don't have any doubts as to the performance of this rig. I do have serious concerns about rigging it properly and substantially. And I have not tried to hide this from potential clients. See "Backstay Tensions" in posting #98 above.

[Alik]

On a multihull vessel there are times when guys have had to unsheet the tight mainsail to prevent the vessel from going into irons. The mainsail does not help the tacking situation, but rather may hinder it!!.

Most important in tacking a multhull is to 'turn' the boat into the tack, and not stall it by throwing the rudders over to quickly. Second it pays to have a nice 'pivot point'. For that reason I MUCH PREFER daggerboards or centerboards to long shallow keels.

Get the bow just thru the wind, and that genoa will immediately backwind and push the vessel thru the tack.

This is guesswork form Your side unless supported by sea trials.

[brian eiland]

...Here are the drawing of the rig.
While I know that they will not suit every taste, they are just what I want: a mainless rig that is easy to handle single handed and that I can safely lower in a minute to go under bridges.

The two fore sails will be on 'Stay Furlers', since the forestay are Dianeema rope, they can be bent over the trampoline when I lower the mast. They do not reef, so they will be either in or out according to the wind.
The mizzen is on a conventional Furler that can be reefed.
Lastly there is a storm sail that can be hanked in the unfortunate case I get caught in a gale.

There you go, I reopen the subject for all to participate in the discussion...
Did you see this website Stefano...lots of photos and a write up on an A-frame masted vessel:
http://www.sail-works.com/KOLIKA/index.html

[brian eiland]

This is guesswork form Your side unless supported by sea trials.
This is NOT guesswork, it comes from multiple years of sailing multihull vessels, both small and big.

Have you ever tried tacking a Hobie 14 catamaran??....mainsail only design, and no 'board' to pivot about.

[Alik]

This is NOT guesswork, it comes from multiple years of sailing multihull vessels, both small and big.

Have you ever tried tacking a Hobie 14 catamaran??....mainsail only design, and no 'board' to pivot about.

Brian, I sailed/raced B-class cat for many years, plus other bigger cats. Besides, I did a Ph.D. on subject of sailing craft manueverability where did computer simulations of tacking motion as part of research, including tank tests and GPS measurements of trajectories.

The things You're taking about is Your guesswork, because they are not supported by engineering calculations and/or sea trials. So we want to see prototype boat with Your rig built and tested before can contunue this discussion.

[Fanie]

Alik,

The recent trip the Vaal dam with the little trimarang with it's aft mast sail had similar responses from some hardened sailors there.

This one guy told me he saw those aft mast sail setups before... on Kenya lake (the philamons in Africa are years ahead of us) and they can only sail downwind.

So there you go. Aft mast setups come from Kenya, the philamons have been using it for YEARS there and they have trade winds they sail downwind in only.

The dumb f idiot at the Vaal never saw me sail in and out of his marina the three days we were there. The wind blew us out and back in so our timing must have been good coming in and going out.

It was rather a matter of him being very PO because he was trying to catch us in his big mono, and he never even came close. Beat him to wind too. He must have been an inexperienced sailor.

If I was you I'd stick with what you was tought in the phd. This sailing setup will not work for you. It requires a bit different thinking and as I said before there is a few tricks to it you miss.

Now you know why nobody sails them ;)

[Alik]

Fanie, I do noy say that aft mast will not work, I just say that there some problems involved. For sure those can be solved but prototype needs to be built and tested. Your experience is really valuable because is based on building and testing real boat.

[Fanie]

The 'problems' involved are only there because nobody ever took the time to figure them out. Common sail types have had more than their share of attention, if the same is done with aft masts there would be even less problems.

Personally I favour them for their ease of operation and simplicity to use.

I'm going to try and find someone who will be interested in this to sponsor a decent cat with such a sail setup. I'm too friggin poor to get this done in an acceptable time span.

Will post if I have somehing more on these sails.

[gonzo]

Brian:
Than trimaran windsurfer picture is a really poor photo montage. If you are going to post fake shit, please take the time to make it more credible.

[brian eiland]

Gonzo, what trimaran windsurfer are you taking about??

Ohhhh, now I remember, you are talking about that posting I did back a few pages ago:
http://www.wiebel-sailing.com/index.html

I don't believe I represented it as anything other than what it was, a group of Dutch fellows, technical types, looking to break some speed records with a craft that happens to have an aft mast concept:
http://www.wiebel-sailing.com/Theteam.html

Sorry if you get offended by futuristic concepts...keep an OPEN MIND

[Spiv]

Did you see this website Stefano...lots of photos and a write up on an A-frame masted vessel:
http://www.sail-works.com/KOLIKA/index.htmlVery interesting Brian, like all those pictures, they show how he approaced and solved some problems.
I think the airfoil masts are not the best shape because they would only be effective at anchor; anytime sailing they would increase windage comparing with a round mast.
I have been thinking about it for a while: the bent whishbone mast with its internal bracing, is going to be very strong and will not bend or buckle from side to side, but is not so strong fore-aft, so an elongated section fore-aft would make it stonger, I am thinking a slightly elliptical shape could be the best.
I am getting the help of an engineering group to give me the best shape and will report back on their finding.

[brian eiland]

I think the airfoil masts are not the best shape because they would only be effective at anchor; anytime sailing they would increase windage comparing with a round mast.

I am thinking a slightly elliptical shape could be the best.
You definitely do not want to use round mast...just too much drag. I'm unsure as to you definition of 'airfoil mast' as apposed to 'elliptical mast'??

Peter Wormwood came up with an interesting mast section for the Stiletto 23 catamaran (rotating mast) that emphasized the leading edge of the section to be most optimal for a variety of wind incident angles. It consisted of several different radius's on the front of a modified elliptical section. I chose this same mast section for my Firefly trimaran. Don't know if I can find a sample now or not.


I have been thinking about it for a while: the bent wishbone mast with its internal bracing, is going to be very strong and will not bend or buckle from side to side, but is not so strong fore-aft, so an elongated section fore-aft would make it stronger, I am thinking a slightly elliptical shape could be the best.
I am getting the help of an engineering group to give me the best shape and will report back on their finding.
What I'm getting at is I feel that elongated section would be best aerodynamically and strength wise. In many cases your headsail(s) are going to be redirecting the airflow to a somewhat fore-to-aft direction by the time the flow reaches the mast.

Pay close attention to the joint where the two legs come together. There are some unusual twisting forces here that can be detrimental. Procyon experienced this as well. And if you build in carbon fiber remember it doesn't like some of these 'off-center' twisting loads.

As a secondary thought, maybe you could construct the A-rig with round sections and add fairings. But this might only make sense if you were using alum, not hand building carbon fiber.??

Did you get that private message I sent you about another gentleman there in Aus looking for a similar size vessel with the same requirements to get under a bridge??

What did they do 'Downunder', bridge all your inlets. :rolleyes:

[Fanie]

So that's where the 'down under' part comes from... down under the bridge :D

[brian eiland]

On a multihull vessel there are times when guys have had to unsheet the tight mainsail to prevent the vessel from going into irons. The mainsail does not help the tacking situation, but rather may hinder it!!.

Most important in tacking a multhull is to 'turn' the boat into the tack, and not stall it by throwing the rudders over to quickly. Second it pays to have a nice 'pivot point'. For that reason I MUCH PREFER daggerboards or centerboards to long shallow keels.

Get the bow just thru the wind, and that genoa will immediately backwind and push the vessel thru the tack.

This is guesswork form Your side unless supported by sea trials.
____________________________________________________________________________

Interesting 'sea trial' that has just today been reported on another forum...excerpts:

"I spent the weekend test sailing the Dolphin 46 my sister purchased. It was her first sail on the boat (her second on a Dolphin). This was my first sail on a Dolphin, but I have chartered a half dozen slightly smaller cats over the years. The boat is docked in Ft. Lauderdale way up river.

The winds were from the east at 12-18 both Saturday and Sunday which made for some rough waters (6 - 7 ft confused) , but a good test for the boat(and our stomachs).

There was a slightly off axis swell mixed with the wind driven swell that keep all but a handful of boaters in their slips. On Saturday we counted 3 other sailboats boats within 12 miles of the Ft. Lauderdale entrance and Sunday there were 8 (3 of them cats). Obviously, the ocean state wasn't what South Florida sailors consider a "fun weekend", but we were happy to have the adverse conditions to test the boat.

With a single reef in the main and full jib the GPS averaged 8.8 knots hard on the wind. We ran on NE and SE tacks to take the current out of the equation. On a beam reach the boat averaged 11.5 knots going north and south with a wind speed of 15-16 mph. Not too bad for the sea state. The tell tales were laying down only about 30% of the time and it wasn't because the sails weren't trimmed correctly.

One of the ways we tested the Dolphin's sailing ability was by going close hauled with a single reefed main and no jib. I told my sister if the boat could tack with the main only in this sea state and wind I would be impressed.** With only the single reefed main, boat the speed dropped to 4 knots, but we completed a tack! Sure we had to ease the main and fall off to 90 degrees on the new tack to get the rudders working, but the boat did it. The same maneuver with jib alone was much easier of course."

** Note by BE: The Dolphin cat is a daggerboard vessel, and that surely contributed to this ability to tack under mainsail alone.

[Alik]

Brian keep posting his guesses, weblinks and other 'valuable proofs' from forums. Really tired to read this multi-page rubbish... :D

Brian, SHOW REAL BOAT WITH YOUR RIG TO PUBLIC!

[Gary Baigent]

Brian, I'm all for new ideas and experiments but your mast aft rig is ....... a no exit street IMO. This talk of round masts too, is also no way; if there would be anything that you really need, it would an airfoil mast section that rotates so as to reduce drag behind your large (and sagging luff) headsail. Presumably you are having a furling arrangement up front - because dragging differing sized sails up there on a pitching deck is awkward and dangerous. This is one of the main reasons that NZ racing designs went against the accepted grain of large headsail/small mainsail and pioneered the opposite, almost going to una rig proportions - plus of course the bendy mast and feathering rig; this almost four decades ago. Your theory on tacking a large headsail is also suspect: unless you have your keel, dagger, centreboard well forward, that rig wants to bare away - you would be more comfortable grannying around than tacking, an oxymoron (so to speak) when beating to windward.
There is a headsail rig that functions reasonably well and that is the Pacific lateen .... but that is on a proa and they end for end the assembly when they shunt, and to do so they at first bare away. And to sail to windward on those craft, they sail letting off the sheet, if sheeted in hard, they want to bare off - how frustrating must that be?
Once, on my light 32 foot catamaran, the clew ripped from the wing mast luff track which damaged it and so we had to sail with just a headsail, an unpleasant experience with huge amounts of lee helm and, being unable to tack while beating up a channel in fresh wind, (the boat would lock itself in irons, and we had the area of the wing mast to help us round too) so we had to gybe around - resulting in large and precious distances to windward lost. You can have it mate.

[masalai]

badly balanced boat?

[brian eiland]

This talk of round masts too, is also no way; if there would be anything that you really need, it would an airfoil mast section that rotates so as to reduce drag behind your large (and sagging luff) headsail.
Do you realize that I was NOT talking of using round mast sections on my particular version of the aftmast concept?? But rather I was addressing the A-frame rig that Stefano is building in order to lower his mast to clear bridge obstructions. Two different situations, and in both cases I have suggested NOT using any round sections. I believe he plans to build the mast himself, and that was the only reason for suggesting the possibility of a round section with fairings added afterward.

Presumably you are having a furling arrangement up front - because dragging differing sized sails up there on a pitching deck is awkward and dangerous.
Of course I have furling on all three sails...no sail changes. Perhaps you should have looked here:
http://www.runningtideyachts.com/sail/
...and balance is obtained by the selection offered by a ketch rig layout.

Your theory on tacking a large headsail is also suspect: unless you have your keel, dagger, centreboard well forward, that rig wants to bare away - you would be more comfortable grannying around than tacking, an oxymoron (so to speak) when beating to windward.
Any sailboat seeks to have 'balance' whether its rig is located forward on the vessel or rearward. We taylor our CLR/CE relationship accordingly. One item less understood by monohull sailors about multihull boats is the lack of a need for the 'lead' of the CE over the CLR. Since the multihull does not heel over this lead distance is virtually zero

There is a headsail rig that functions reasonably well and that is the Pacific lateen .... but that is on a proa and they end for end the assembly when they shunt, and to do so they at first bare away. And to sail to windward on those craft, they sail letting off the sheet, if sheeted in hard, they want to bare off - how frustrating must that be?
I'm not familar with that craft, but my first question would be, 'does it have a board??'. I rather doubt it, in which case I could understand the lee helm.

Once, on my light 32 foot catamaran, the clew ripped from the wing mast luff track which damaged it and so we had to sail with just a headsail, an unpleasant experience with huge amounts of lee helm and, being unable to tack while beating up a channel in fresh wind, (the boat would lock itself in irons, and we had the area of the wing mast to help us round too) so we had to gybe around - resulting in large and precious distances to windward lost. You can have it mate.
Did your 32 footer have a board or a very shallow, long keel??
Did you consider purposefully backing the jib to push your bow thru the tack??


You seem to want to thrash big headsails as leeway inducers, or old style, or etc. Yet we see a lot of use of CODE Zeros (http://www.doylesails.com/sails-codealpha.htm) these days

[brian eiland]

You might look back at the illustrations in posting #98
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-7.html#post198605

That fractional rigged cat with a 90 foot wingmast carries about the same sail area of my mast aft rig with a 73 foot mast. And my forestay is just slightly longer than his fractional jib forestay. My sail area is balanced over the pivoting centerboard.

[Gary Baigent]

Brian, quite correct, it wasn't you advocating a round mast but others posting here. And thanks for the Running Tide link. And to be honest I have only briefly followed this thread, but realize your mizzen is very important for the cat's balance, and there is nothing wrong with having balancing boards forward to counter bare away effect once the mizzen is down - do you have them?. However, to be honest again, the rig looks very clumsy and holding those forestays tight with their furlers looks problematical.
My lightweight 32foot cat had deep daggerboards and when I say light, I mean a platform that doesn't carry weigh on once head to wind. That plus the lee helm (and admittedly the boat was not set up (CLR too far aft) to sail in that configuration) tacking was almost impossible in a fresh wind. There is a lot of nonsense spouted about backing headsails - that is guaranteed to stop a lightweight multihull dead in its tracks - maybe okay for a loaded down, plodding cruising version. Equally, tacking una rigs on light multis, as long as the traveller and main sheet are eased as you pass through the eye of the wind, then you can make it across, tricky, yes, requires timing, but way better than holding a headsail against the wind.
Yes, code zeroes are carried high to windward in light conditions - but if you're caught in a decent gust, lee helm goes way up (unless balancing foils forward are carried).
Oh, the Micronesian proa, of course the traditional ones did not carry boards, just a large, angled aft rudder steered by a skillful foot and strong arm by canting the foil- check out "East is a Big Bird" - Thomas Gladwin.

[brian eiland]

Gary, I developed this rig concept long ago (1973-4), and primarily because of those big sectioned mast we had in those days that just destroyed the drive from the first foot, foot and a half, of mainsail area. And I personally owned a 47 wood staysail ketch at that time. Those two factors drove this design. I laid it aside for many years. Procyon's development (http://www.boatdesign.net/forums/sailboats/procyon-project-bold-experiment-10771.html) rekindled the interest.

Granted the mast sections these days are much smaller and more aerodynamic, so my reasoning for eliminating the mainsail is less applicable. but I still defend the aerodynamics of this configuration, and the ease of use in the ketch configuration. Regrettably the forces involved in trying to maintain a 'tight rig' add considerably to the mast compression and loading on the hull structure. So these factors are the real limiting ones, not the aerodynamics.

I'm actually more interested in the Dynarig (http://www.runningtideyachts.com/dynarig/) and Kite-Assisted Multihull (http://www.boatdesign.net/forums/boat-design/new-age-trawler-motorsailer-kite-assisted-poweryacht-20319.html) at the moment

[Gary Baigent]

Yes, Dynarig and kites are VERY interesting.

[brian eiland]

Very quitely, shuu....Not many folks have brought this question up, but there could be real problems with tacking that dynarig on a catamaran.

Rob Denny has done some interesting model work with a dynarig application on a shunting proa...videos (http://www.boatdesign.net/forums/sailboats/maltese-falcon-hit-miss-12459-11.html#post219062)

(I might add that Rob is another major critic of the mast-aft concept...oh well, that's go with the forum's purpose ;)

[Manie B]

Not really an aftmast setup

but very much the single "foresail" setup, i dont really know what you call this

but it works :D

http://www.youtube.com/watch?v=8TtcZjAuF4A

nice sailing anyway:D

[Fanie]

Now that is what I call desperate. Besides, that is not an aft mast rig. That is something about mono's that put me off completely, where do you find so many people to weigh it down ? I also don't want to hang my butt in the water. Especially where we're going this month end they say you steer the boat between the bull sharks to get out the river mouth. Hang your butt out there.... yeah right :(

How do you fish from that boat ?

[brian eiland]

Interesting Manie, never seen that. Learn something new everyday :cool:

[Earl Boebert]

Not really an aftmast setup

but very much the single "foresail" setup, i dont really know what you call this

but it works :D

http://www.youtube.com/watch?v=8TtcZjAuF4A

nice sailing anyway:D

Looks like a lateen to me. "...uncompromisingly described as the most dangerous rig ever devised by the wit of man." (Phillips-Birt).

Cheers,

Earl

[masalai]

Looks a simple setup to make where fancy technical components are not available and lots of fun...- What is this "most dangerous" rubbish and think of "Fastnet" disaster of years ago, the danger is the foolishness of the skipper/crew....

[broggerp]

(Just happened upon this topic -- I know it's old -- and just registered.)

Something like ~25 years ago I saw an aft-mast boat docked in Westport, WA -- apparently being lived-aboard. IIRC, it was a monohull that had a yoke mast rising from well aft and leaning forward at a steeper angle than depicted in the images linked to this thread -- with a VERY hefty backstay attached at a not-too-different angle at the stern, and no provision for a "main". I remember two big roller-furled sails (jib & staysail) and overall rough condition of the boat. Seems to me it had some huge legend on the side, and was ~40 feet long. (But it's been a while . . . )

FWIW

[brian eiland]

....Something like ~25 years ago I saw an aft-mast boat docked in Westport, WA -- apparently being lived-aboard. IIRC, it was a monohull that had a yoke mast rising from well aft and leaning forward at a steeper angle than depicted in the images linked to this thread...
I suspect you are talking of the vessel(s) in this subject thread
http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999.html

[brian eiland]

This subject has come up more than a few times before on this tread, and often there are so many modern interpretors that seem to want to throw away those big overlapping headsails in favor of fractional jibs.

Well here is a nice shot of 'LeBlack', a superhot racing catamaran on Lake Geneva that is possibly a lot of the inspiration for the latest AmCup cat 'Alinghi (http://www.yachtforums.com/forums/general-sailing-discussion/11517-next-americas-cup-multihulls.html)'

Now LeBlack is a real fast boat...one that makes it's apparent wind likely go way forward in most conditions. I realize this is termed a 'screecher' she is flying, but I don't image its gets a lot of reaching work :rolleyes: . I venture to say it does a lot of windward work. So why an overlapping big headsail ;)

And then there is Alinghi using a double headsail arrangement...all too confusing :rolleyes:

[Fanie]

Brian, you started this aft mast thing. What the heck do I shout back at people when they shout at me 'what the hell is that thing you have there' ???

[brian eiland]

Brian, you started this aft mast thing. What the heck do I shout back at people when they shout at me 'what the hell is that thing you have there' ???
BOLD experimentation...something they're affraid of...too conservative

[ChiefOren]

Sirs, as I have been looking at the Aft-mast rigging, I would like your opinion on the idea of incorporating an A-frame mast configuration with the Aft-Mast configuration. I could then use 2 jibs as main, and a third permant station for a storm jib. I would also not be using a wishbone sail as you have planned in you site. As I am building a 50' sailboat here in Israel, I would be particularly intrested in any feedback about this idea.

[masalai]

There are lots of engineering considerations to be calculated - I am going through that process now as I will be using a John Hitch sail configuration on my Bob Oram designed 39C - have a look at the links in my signature area below....
The images 2372 & 2373 on post 437 of thread "My little piece of peace" for an early mock up of the layout... The mast is canted about 15 degrees aft... A genoa on reefing/furlers to each bow giving 39.5 sq metres (425 sq ft) each and a blade jib on reefing/furler of 9 sq metres for a total sail area of 97 sq metres (947 sq ft) - Objective is to keep everything as simple and elegant (engineering wise as possible) whilst being very easy to manage for an ageing owner :D:D

Here is John's current yacht "X-IT" - John is my senior and sails solo...

[RHP]

I wonder how well she points Mas?

[masalai]

35 degrees apparent... More info on my build thread don't seek to pirate this thread...

[Fanie]

After buggering around with my little tri and it's TRUE aft mast and jib like main sail, I can say that there is a lot more that has to be learnt from this setup. Although it works well and is easy to handle (with some help from a winch of course on bigger sails) I don't think I have it all figgured out yet.

For instance, I've added a boom to keep the foot of the sail more streight, and it does make the sail easier to control but then if I had a winch on an auto tacker it may have been just as easy. I'm not convinced the boom made enough of a difference to say you have to have one. I don't like booms, the wind always seem to change when you're not looking :D

The shape of the sail was also not experimented with enough, being of the poor workers class I cannot afford to make up different shapes to compare.

I would have loved to put the same but larger setup on a slightly bigger sailing cat - one on each hull and play with that. It would make for a very large sail combined and just may become competitive for speed ;) as well as ease of handling, which this sail offers for sure.


BOLD experimentation
I have people charging up to me or following me to see what the contraption is. Quite cute, you get to smile at the wives and the girlfriends and the guys think you are very friendly :D


I plan to do away with the little trimaran soon, so unless any of you can come up with something else that needs testing or experimenting with, I am going to retire her to the lounge.

Speak now or forever hold your piece.

[RHP]

Difficult to type and hold my piece.....:D

If you dont like a boom on what is mean to be a relaxed rig why not go for a wishbone setup? It'll maintain the sail's shape and add rigidity.

Typing quicker now as my assistant it holding my piece for me.... :P

[Fanie]

Hi RHP,

The standalone masts's sail works basically the same as the wishbone's.

Difficult to type and hold my piece.....
I see you get a couple of characters in in between swapping hands, fortunately you need only one hand with your's ;)

The little tri is gone. A guy came here and said he wanted it and he left with it.

[Chris249]

BOLD experimentation...something they're affraid of...too conservative

Brian, would you mind not being so arrogant and insulting?

Plenty of other people have tried 'bold experiments' without throwing around insults. Some have even done more with their 'bold experiments' than writing about them on the web, without throwing around insults.

Some people choose more conservative craft because it happens to suit the rest of their life. Some people with quite conservative craft are leading the way in other areas of their life (like the professions or sciences.

Others simply are not convinced by the supposed efficacy of the aft-mast rig (a viewpoint that can be backed by the years of experiments with such sails) or are fascinated by other developments that create faster or more refined rigs.

It may make you feel good to insult others for daring to have different tastes, but it doesn't necessarily make you look good.

[brian eiland]

Brian, would you mind not being so arrogant and insulting?

Plenty of other people have tried 'bold experiments' without throwing around insults. Some have even done more with their 'bold experiments' than writing about them on the web, without throwing around insults.
I don't think you've been on this forum long enough to understand where I am coming from...or lets say where I have been.

I was not trying to insult anyone. I grew up with the start of the whole multihull beginnings, and I was very much involved with the marketing of these vessels for many years. I experienced directly the many hurtles we had convincing the monohull sailors that multihull vessels were viable sailing craft. It took years for to happen.

Even something as simply as a fully-battened mainsail was criticized, let alone some of the other innovations that came from this 'renegade group of sailors'.

And guess which nationality of sailors were the most conservative in my findings...the Americans, of which I am one....but they would never believe that of themselves. :rolleyes:


BTW, that was a pretty bold experiment by Maltese Falcon. There were a lot of naysayers to that project.

[Manie B]

Chris249 you are an idiot

Brian, would you mind not being so arrogant and insulting?


READ THE FLIPPEN WHOLE THREAD PROPERLY

Brian was NEVER insulting - YOU ARE




idiot

[masalai]

Wow Manie, for you to boil he must really deserve the title or whatever:o::!:

[Chris249]

I apologise for the use of the word 'arrogance', Brian, but it certainly seemed that in using 'afraid' and 'too conservative' you were trying to insult someone. Accusing someone one being too conservative and cowardly is not exactly showering them with compliments.

I still can't see why in the world someone deserves to be abused (and saying that they are scared is certainly an insult) merely because they ask an innocent question about a rig.

My family was involved in early multis too, and in early windsurfers. Sure, some people criticised them - so what, many windsurfers and multi sailors criticised conventional craft and ignored the issues with the new breeds. Those who dish it out should also take it.

Much of the early pro-multi promotion was overblown and surely people had the legitimate right to become annoyed by such claims, which often cast existing craft in a bad light. If one is going to criticise the boats people own (as innovators often do) surely one cannot complain when one is criticised in return.

BTW as I'm sure you'd know, the fully-battened mainsail was not an innovation from a group of catamaran sailors but an old idea, regularly used in mono classes in some parts of the world for decades before multis became popular. It was, for example, used in the '20s on the German lake dinghies and in the 1930s in International Canoes. The cat pioneer Austin Farrar has written that his Little America's Cup winning full-batten mainsails were inspired by mono and canoe sails, which underlines the fact that cats did not introduce them.

The reason that many people rejected full battens was NOT simply blind conservatism, but because for many boats full battens did not (and do not) work as well in some situations. I've currently got 18 fully-battened mains around the house and shed and we've had full battened boats in the family for three generations so I'm not bigoted, but for many craft they are not the best way and surely people must be allowed to say that without being criticised.

I apologise if I over-reacted, but your comment made it appear that any one who asked about a mast-mast rig (and again, we've had them in the family) was a coward and a luddite, and that it simply not the case.

PS re "I don't think you've been on this forum long enough to understand where I am coming from...or lets say where I have been."

There's only 11 months difference in our joining dates (although I've had slight tag changes in that time).

[Earl Boebert]

A newly constructed model yacht with same is discussed at:

http://www.rcsailing.net/forum1/showthread.php?5471-Delta-rig

The boat is an RG65; class rules are (basically) 65cm LOA, 110 cm mast height, 2250 sq cm area. Typically run 1 kg with 500 gr bulb.

Cheers,

Earl

[brian eiland]

A newly constructed model yacht with same is discussed at:

http://www.rcsailing.net/forum1/showthread.php?5471-Delta-rig

The boat is an RG65; class rules are (basically) 65cm LOA, 110 cm mast height, 2250 sq cm area. Typically run 1 kg with 500 gr bulb.
Cheers,Earl
There has been a number of instances that my mast-aft rig design is compared directly with the 'Delta' rig....whatever that is exactly? I believe this 'delta rig' that is being discussed in this modeling effort could more ideally be compared with this mast-aft arrangement I saw in Holland a number of years ago:
http://www.boatdesign.net/gallery/showphoto.php/photo/7043/cat/500/ppuser/399

This fellow Kees Radius sent me some pics and a few emails quite awhile back and I posted a few of the pics in my gallery. I had meant to post more about this design, but it must have slipped by me. I did find this:
http://www.boatdesign.net/forums/sailboats/mast-aft-rig-11164-2.html

...and this:
http://www.boatdesign.net/gallery/showphoto.php/photo/7269/ppuser/399

Let me make this point briefly since I don't have much time at the moment. I don't believe I have ever expounded that this 'delta' style rig with its single headsail should be any more efficient that any normal vessel sailing with its big headsail up in a uni fashion. So whether the mast is raked aft, forward, or backward should not make a great deal of difference in the aerodynamics of the situation.

On the other had my mast-aft design was geared toward a larger cruising vessel that might seek to have a lower aspect rig of multiple sails for stability advantages and balance advantages. This mast-aft configuration sought to emphasis the efficiency of headsails, particularly the genoa benefiting from updraft created by the following sail.

I can really appreciate the efforts at modelling and testing these fellows are expending. But I would really appreciate them putting their efforts toward something more akin to the configuration I have suggested, and/or some more Dynarig experients

[Earl Boebert]

Oh, it's just a "try it and see what happens" kind of playing around -- easy to do with toy boats :-) I doubt that Claudio would argue that it was anything more than that.

Cheers,

Earl

[Dave Gudeman]

Brian, I've read a lot of the posts on the mast-aft rig. I think the idea is very interesting and I've got a couple of question I hope you can answer.

First, you have mentioned that one of the advantages is that the rig can be easily lowered to get under bridges and such. But you also say that the head sails are roller-furled. I'm having trouble visualizing how that is going to work. When you lower the mast (presumably forward) what do you do with the fore stays that the sails are rolled up on? Surely you can't just roll the lines up with the sails wrapped around them?

Second, one of the big criticisms of the rig is that the tension on the back stay is too high. Why not use an un-stayed mast?

[brian eiland]

I don't think I said it would be an easy rig to lower forward. I think you likely picked that notion up in someone else's discussion of my rig. That said it might be possible to furl the sails up around a forestay made of the newer hi-tech cordage rather than the alum foil style forestays. I don't really promote that lowering aspect as a feature of this rig.

Forestays are not really workable on unstayed mast even if the are standing straight up. The unstayed mast would likely never be strong enough to resist a hi-tension rigging of any sort (forestay or backstay).

[Dave Gudeman]

Thanks, Brian. You are probably right that I am confused about who said what. I thought that I had read it on your web site, but I read through all of this aft-mast rig stuff a month ago before I joined the forum so it may have gotten a little murky.

[boat fan]

I apologise for the use of the word 'arrogance', Brian, but it certainly seemed that in using 'afraid' and 'too conservative' you were trying to insult someone. Accusing someone one being too conservative and cowardly is not exactly showering them with compliments.

I still can't see why in the world someone deserves to be abused (and saying that they are scared is certainly an insult) merely because they ask an innocent question about a rig. ............



Oh Boy ,you really enjoy putting things "out of context" don`t you ?

The claim that yachting , on the whole , is 'too conservative' , is true.
The reasons often have much to do with cost.
Rating rules are also a major culprit.( bermudan rig ring a bell ?)

Scared ? certainly ...much money at risk.

Not insulting , but a reflection of the costs involved in yachting these days.
Also factual.
Brian told it as it is.
No malice intended.

[CT 249]

It's possibly not out of context to object to yet another use of a rather old accusation about our fellow sailors. This criticism has been aired many, many times, but surely something that is so subjective and so much a matter of personal taste and circumstances as the type of sailboat one owns should not be a source of insult.

What is so bad about objecting to the use of derogatory terms about the mainstream of our sport and what they happen to like?

Who is the judge of whether their fellow sailors are too conservative, or not?

In what other sport do so many people spend such vast sums on toys that become obsolete so quickly? If there aren't many other sports where so many people lose so much cash, by what yardstick are you judging sailors?

Who can can claim to stand in a position of perfect objective truth and work out how conservative people should be with their very expensive toys?

People like Larry Ellison, the co-founder of Skype, and many other leaders in other areas are quite happy sailing comparatively conventional boats - are they are scared of innovation too?

Basically, what is so hard about respecting the sailors who actually get out there and go sailing, and the choices that they make? Exactly how does it hurt the sport if everyone gives respect? It certainly seems to hurt the sport when sailors start insulting their fellow sailors simply because they dare to have different tastes.

Surely it would HELP with innovation if we took pains to understand why other sailors choose what they choose to sail, rather than simply throwing derogatory labels at them?

PS - I'm not sure of the meaning of your reference to bermudan rigs and rating rules - rating rigs normally give a large benefit to gaff rigs, schooner rigs, ketches and yawls, rating them as much slower than bermudan sloops of similar area. And there's little evidence that the few boats that are not bermudan sloops are disadvantaged under IRC, for example.

[brian eiland]

A long time ago I was watching a morning show interview with the CEO of Rubbermaid Corp (http://www.rubbermaid.com/Pages/Home.aspx). On a table in front of the two gentleman there was a whole display of ALL sorts of kitchen items that Rubbermaid producted....and there were many different colors to these plastic items.

The interviewer ask, 'why so many colors' and 'what are the most popular colors'??
The CEO responded that 'in America that would be white, black, and beige'.

Interviewer: Then who buys all the other colors?
CEO: The rest of the world, particularly Europe.

My deduction and that of the two gentleman, 'America is a more conservative market than many believe'. Thats not a bad thing, it just a fact.
________________________________________________________
Another incident I might relay. I was exhibiting our new 37' Louisiane catamaran at the Annapolis boat show. It was a very crowded weekend day, when I spotted a gentleman in the crowd that I knew owned a hi-tech motorcycle shop in a town nearby. I was almost surprised to see him at an ALL SAILBOAT show as opposed to the up coming powerboat show. I pulled him aside an ask what he thought of this BIG crowd of people out to see a sailboat show??

His response was quite interesting from a retailer's perspective. He said, "I think what you have here is a bunch of Volvo buyers. They probably take forever to pick out a product, and they research it to death."

That fit so well with what a boat salesman once told me, "it is so much easier to sell the powerboat guy...generally they want to know how much HP it has and what colors does it come in" :rolleyes:
_________________________________________________________

American sailors are a conservative market in my opinion. I learned it the hard way...trying to sell them multihull sailboats for years