Aftmast rigs???

Conservative,...or whatever we want to term it?


You probably need to consider the era that I went off on this aftmast tangent. It was an era when multihull sailboats were just starting to really come into mainstream market,...the late 1960's, early 1970's. I was one of those converts. Much of the conventional market was ignoring them or poo-poo them. You had to maintain a stiff upper lip to stay converted.

I took some notable quotes from better known names in sailboat design and put them on my webpage,..
Multihull Concept http://www.runningtideyachts.com/multihull/
BTW, I did not 'publish this website' until 2001 as I was not computer knowledgeable at the time. If you look at this archived article you will see that I started with this idea back in 1973-1974
RunningTideYachts, Ltd. - Archives http://www.runningtideyachts.com/archives/OrgMagArt.php

In addition to those quotes I included in that opening page of my website, I revised a portion of my 'Sail Propulsion' section with this experience during the introduction of Tom Perkin's BOLD experiment to build his DyneRig Maltese Falcon.

I might suggest that one have another look at this section of my website. The goals are still viable today.
Sail Propulsion - Revisiting a Mast-Aft Sailing Rig http://www.runningtideyachts.com/sail/

1) A cruising rig that is more aerodynamically efficient, which should enable you to get the same speed with less sail area, or more speed with the same sail area.

2) A rig that delivers a clean leading edge for all the sails

3) A rig that allows the whole sail plan to be roller-furled away or deployed.

4) A rig that allows the reefing of the sails without turning into the weather.

5) A rig that divides up the total sail area into smaller manageable sizes.

6) A rig that maintains its balance center (CE) with different sail combinations.

7) A rig that produces less overturning moments.

8) A rig that can be operated without leaving the cockpit. One single person could sail this fairly large rig from anchor up to anchor down. All the sails roller-furl, and the mainstaysail & the mizzen both can self-tack. Only the genoa needs to be tacked over, and this could be delayed until the boat has come about. Even motorsailer folks should appreciate this rig.

BTW: I was also the owner of a 47 wood ketch rigged vessel at this time, and that further inspired my desire for a ketch rig. And please remember I was seeking an improvement of a CRUISING RIG, not a competition rig.

 

Phil Bolger once experimented with an aft-rigged sharpie. He made the sides massively strong, and had larger than normal chine logs and shear clamps. This thing was trussed up like an electric guitar to have the straightest luff possible.

Did it perform?

Yes and no.

If the sailor gave his undivided attention to get the sheet angle exactly right, it did perform better.

But, with more casual sailing, he said it was about the same as a more conventionally rigged version.

Phil did not advocate this rig for performance reasons. He advocated it for safety ones. With the mast in the back, with its spreaders, shrouds and back stays, the boat could be made to heave to quite easily, much more so than one with the mast in the front.

But a catamaran is going to be much harder to make rigid enough to even have a chance of getting the stay tensions needed to get a performance premium, under any conditions.

Add to this its massive initial stability, and now you need even more thicker rigging and even greater tension, to make it competitive with a more conventional mast forward rig, even a really dumbed down one, with a triangular head and no battens.

And this is not even mentioning the co$t. The more conventional rig will be far cheaper, using far less rigging wire, rigging screws and other fittings. And the hull and deck structure will be under far more humane loads, so will probably be less expen$ive as well.

What you may get, if you ever get this to work, is likely to be a mediocre performer, but one which won't have a boom and will heave to better. If that's enough for you, carry on.

I wish you the best of luck.

PS. There is no reason you can't have a roller furling main without a boom. You'll probably have to take a performance penalty. But speed isn't everything.

 

I've documented with photos some of that Bolger work elsewhere in this long subject thread. One of the really good things about the the software that runs this site, is that you can do an individual search for the subject WITHIN this subject thread,...really neat.

Sharpii, I am going thru a painful time of acknowledging the difficulties of rigging this aftmast design that I have touted for so long. With the change brought about with my backstay loading, I think my rig configuration is in serious trouble. Yes I might figure out ways to make it work, but they just might add too much complication,...and high loads as you pointed out.

Yesterday I spent a good bit of time looking at this duel mast, biplane rig technology that has been developing up till this latest Chris White vessel 'Saphira', and that 'Ozone' vessel. Sure seems to have a LOT of possibilities to simplify things. In fact I think it might make a very good rig for my 'gamefishing under sail' vessel.




Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-77#post-880303
Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/page-77#post-880519

 

I stayed away for a few days to ensure that I was not derailing the thread. However, to get back into it....

In the late 1960s/early 1970s the sailing market accepted the world's most popular dinghy, the Laser; the world's most popular and innovative type, the Windsurfer; and the most popular cat, the Hobie 16. So how does that indicate a conservative market? In the '60s the most popular racing boat in the only state in Australia that recorded these things was the Quickcat, a ply cat. Exactly how is a new type rising quickly to #1 evidence of conservatism?

If we are going to claim that people in an activity have any particular attitude, surely we MUST have some yardstick. So as a yardstick, what leisure activity featured such a high percentage of users buying gear to new designs and costing that much in that era? I'm not making the allegation that sailors were conservative per se - others are. So let's see them actually provide some evidence.

With respect, quoting some designers is not evidence. For a start, designers and other people in the industry are biased because if more people buy new craft, the industry gets the cash. People in the industry therefore have an economic reason to feel bias. There are also other factors that bias people inside the industry towards demanding new kit - for example it's easier for a sailing journo to write an article about a new boat than to write a good article about an old one. So while there may be conservatism on one side, it also has to be balanced by the fact that the other side includes economic incentives, marketing, fashion, short term novelty and many other reasons that bias many people towards NEW designs.

Recently, the subject of "technological overshoot" and other factors involved in the social construction of technology have become the subjet of discussion. These discussions indicate that the drive towards further (and often "excessive" or "incorrect" development are strong and identifiable. Calling people "conservative" ignores all these factors. It is not logical to include subjective/societal/economic factors on one side, but to ignore the fact that the same factors affect the other side in the discussion.

To claim that other people are overly conservative basically includes the claim that the narrator knows better than the people under discussion. But the interesting point is that, with respect, many (and IMHO the vast majority) of those who call other sailors "conservative" are not in the same situation as those they insult, and therefore do not understand them. For example, I don't think that Hoyt, Perry or you are active, regular, long term boat owners. To those on your side, things like losing tens of thousands of dollars because your craft has become obsolete are largely irrelevant because they represent OTHER people losing their hard earned money and some of it may be coming your way. You also ignore the fact that people are are "conservative" may be protecting the boat they own because they love it; because they have sunk a lot of emotion into it; and because they don't give a flying **** about the factors that make newer boats allegedly better. For example, my wife and I don't give two rats about the fact that a newer 36' racer/cruiser may be "better" because it will get us around the course three minutes faster - we have very good reasons not to give a stuff (including the fact that if we want speed we drag out our boards or F18) and therefore to want to protect our current boat's position. It is illogical to ignore the fact that those promoting "excessive" change tend to not be in a position to understand the problems of those they are insulting.

Sure, some people have insulted multis and that's bad. But some of the multi sailors of the day were slinging lots of **** at mono sailors from a very early date, as can be shown by their writings of the time. If you sling abuse, you can't expect love in return. And the fact was that in some places, multis of the '60s WERE killing sailors are a horrifically high rate - almost certainly higher than any other leisure sailing craft in history. Only the callous could fail to understand that such a death rate was causing major concern amongst sailors and others. It damn well should have been, from my perspective.

Finally, using the oft-quoted example of Cascade proves just how wrong it is to claim that good advances were messed up by "conservatism" unduly. The simple fact is that the 37 foot Cascade was very slow for a 37 footer - the only reason she won anything was because she went through a loophole in the rule and rated like a 30 footer. A good contemporary mainstream 37 footer could kick Cascade's *** in most conditions, even when neither of them were using more than two sails. She was a slow boat - why on earth would you want to protect her and not boats like Farr's Tituscanby, the Listang or the Scampi which went much the same speed for much less money? Why claim that favouring fast little lightweights like Farrs is "conservative" and favouring a slow boat like Cascade is "progressive"?

Whenever I have spoken to the top guys at successful sailing brands, I've been struck by the fact that they listen to and respect the sailors of the world. They don't sit in an ivory chair, tell the sailors what they should choose, and then whine when they don't. Respecting others, rather than insulting them, seems to be pretty reasonable.

A few years ago, I took over running a class that had entered into major and (many thought) terminal decline. The previous year it had a worldwide championship attendance of about 6 individual entries, and was out of production. Now, I think it's the #1 selling sailing class in the world and outselling the Laser, Opti, Aero and dinghy and cat foilers combined. The major motif that has taken the class from the bottom to the top has been respect for sailors, not insults.

 

I think you are backing a much better horse now.

Sure, the biplane rig has its own problems.

Main among them is the need for free-standing masts. The masts must be kept as far apart as possible. This makes them almost impossible to support with stays. The only way I can think about doing it is with a ginormous spreader between the masts. Hardly seems practical. This means the masts must be very thick at their bases. And this means a lot of windage. The way to get around this problem is to streemline them by turning them into wing-sails. These un-stayed masts also impose great torsion loads on the hulls. But these hulls already have to deal with substantial torsion loads due to sailing loads. So you just have to make them that much stronger.

The second main problem is the lateral distance between the sails. Biplane airplains are said to increase their lift by only about 20 % by adding the second wing. But the wings of a biplane are much closer together, in comparison to mean chord length, than the sails on a biplane catamaran.

With a cat-schooner, with equal size sails, the aft sail is said to produce half as much lift as the forward one. As I see it, if the leeward sail produces more than half the lift of the windward one, you are winning the game. Also, since there are no downward rigging loads on the bridge deck, you can probably afford to make it somewhat wider.

It may not be able to compete with a fractional sloop rigged cat with the same sail area, but if being fastest is not your main concern, this hardly matters.

Finally, I'd like to say I admire you for pulling the plug on the aft-mast idea. You had put so much energy into it, I can understand why you were so stubborn in giving it up.

I don't hink stubbornness is a bad trait for design engineers and inventors, as long as they are willing to concede an idea when given substantial evidence of its likely fatal flaws.

And that you did.

 

Thanks Sharpii

And yes we need to look more carefully at that biplane rig and how it might be most easily attained. There are a lot of pluses that might be had,...even while I am not a great fan of its looks.

 

Brian,

It's kinda weird for me seeing finding the latest exchange. Rather than finding it because it is an active thread, I found it in a search to understand what happened to these mast-aft concepts.

I am an inexperienced sailor trying to understand the art by learning the science, coming up with questions and trying to find the answers to them. One of those questions was (is?) that, if the foresail provides so much of the power, why bother with the mainsail? That brought me to your rig.

That opened another question: if these aerodynamics were reconsidered in the 80s with free-standing mast rigs then, and your proposed rig (which promised some of the proported advantages of the freestanding rigs without the price) following it, why didn't these newer rigs take off? Both you and Sponberg's articles are written as a look back at research and work done and the state of it at the point the articles were written, but they were still written a while ago. I was looking to see if you still held the same views as when you wrote your article, and it seems like you're asking the same question. I'd love to hear your thoughts.

As for your design, I would like to state my inexperienced opinion of a better way to describe it: Instead of a "All furling one-masted ketch", perhaps it is simply a "Mast-aft cutter with a diminished wishbone-boomed main"? With the mast far aft, it's difficult to gain the leverage with the backstays to keep the forestays in tension like a normal cutter, but the hope would be that it would gain more room for the larger foresails. Please comment on how accurate you'd say this summary is.

In my mind, "ketch" is defined by number of masts. If I understood properly from my recreational reading, the mainsail often is used for balance and the foresail for power, so that job isn't unique to the mizzen sail on a ketch.

Also, if I can add another question, one of Sponberg's freestanding ketch's proported strengths is the ability (with a rotating wingmast) to position the sails backwards such that they still generate lift even while running. Does yours or any other rig have this ability (especially on staysails)?

Sincerely,
SPC

 

Its all in the thread somewhere, but you could lose the will to live finding it.
There are two issues.
The first is that our understanding of rig aerodynamics in the 70s and even 80s was a lot worse than we thought it was. We could never understand we things that seemed so good in theory didn't work that well in practice. Reason: our theory was wrong. So you have to be very very careful about any rig theory that isn't based on 21stC CFD work. Most especially anything to do with the effect of the mast. I still have trouble believing what the boffins now tell us, but it matches up with what happens on the water, and what seemed logical back then doesn't.
The second is that the rig works as a whole. When you have a properly set up jib and mainsail the jib does indeed produce a disproportionate percentage of the power - but only because the mainsail is there. Take the mainsail away and a jib alone is less effective than a mainsail alone.

 

In thinking about the commonly raised issue of mast interference with air flow on an aft mast rig, it seems to make sense to step the mast farther forward and tilt it back with extreme rake. My reasoning is that for a single genoa sail plan, that would put the mast in line with the verticle center line of the sail. This would mean it is in the middle of the windward concave, high pressure, slower air flow. Instead of interfering with smooth entry or exit flow where the air stream is joined and moving at near undisturbed airspeed, the mat is now part of the slower inside stream. It might even be shaped to contribute to slowing that windward stream further and help increase the pressure. This would increase the pressure variance across the windward and leeward line. More driving force.

Maybe not, but less effect on drag.

-Will (Dragonfly)

 

Will,

That's a good reminder that, unless it is perfectly round, we should consider the mast as an airfoil itself. If you have a rotating wingmast, you can even trim it, otherwise it's always close-hauled.

With that in mind, I think you have drawn a cutter rig with a jib, a "staysail" (the mast), and no main.

SPC

 

GggGuest,

Is the above effect, that masts work as airfoils, perhaps one of the effects you are suggesting was missed by the first exciting uses of CFD in the 80s? I could imagine it not being captured without high resolution FEA.

SPC

 

It seems that a perfectly round mast *with a sail behind it* produces power. Strange but apparently true. And it explains why folk like me who experimented with wing masts could never find the performance advantage that the theory we had back then predicted.

 

SPC, one of the things about sailing is that there are quite a few people who have only been exposed to a certain fairly narrow part of the sport, who then believe that (1) everyone else is locked into the same fairly small part of the sport; and (2) they are smarter than most people. They tend to see most things through those distorted lenses and (3) they don't do their homework because they'd rather prefer to believe (2) than the truth.

The Sponberg article, for example, carries lots of things that are just codswallop. It says early on "If we keep the triangular shape, we would have to twist the head of the mainsail to windward in order to reduce the vortex and induced drag. But this is nearly impossible to do".

Now, that is pretty much wrong. Twisting much of a mainsail head to windward is dead easy in many conditions. The most popular classes in the world have mainsails that are often TOO far twisted to windward, because of their rig geometry. The Laser is a classic example - the head of its sail is twisted TOO FAR to windward in light winds. Just about any other boat can twist the mainsail to windward just by having the mainsheet pulled on. It's very hard to see why the author ignored something that you will be referred to in just about any decent book on sail trim or class tuning.

The Marchaj pic that Sponberg shows is an example of old theory and experiment gone wrong. The sail in Marchaj's rig twists open too much for optimum performance in most conditions, but a sailmaker can easily cure that. Similarly, Marchaj's experiments that "showed" the harmful effects of masts on airflow were utterly unrealistic because they used ridiculously over-sized masts.

Similarly, Sponberg claims that " the only reason we have wires in the rigs is because we are afflicted in modern sailboat design with arbitrary sailboat design rating rules that, for no good aerodynamic reasons, require the wires in the rigs." That is completely and utterly untrue, and on this forum that was demonstrated to Sponberg himself. You can look at the text of many rating rules and see almost NO mention of wires being required. The only time a wire is normally "required" is because the position of the forestay is a logical place to measure headsail size.

Sponberg's claim that "the convenient measuring points for measuring the rig were where the standing rigging attached to the hull, deck, and mast" inthe first rules to measure sail area is just rubbish. Any reasonable professional who is going to write something like that in a piece that is promoting their services should have known it was rubbish, or would have checked it and found out it was rubbish. Classic old works like Dixon Kemp's show such rules and the measurement diagrams and not a SINGLE such point is mentioned.

People may write such stuff because it allows them to belittle others. Sponberg, for example, insults thousands of people with his claim that "Wires in the rig, and, therefore, triangularly shaped sails, are so inbred into our industry and our thinking that we blindly accept them without question" which is utter bollocks. It just never happened. For scores of decades people used lug, gaff and other sails that were not triangular. Most of the designs went to triangular sails because triangular sails were faster - there's many dozens of old accounts that show that. It wasn't all people being blind or unquestioning, and Sponberg is being insulting and arrogant when he says that.

Sponberg and others like him also show a very insular viewpoint because they manage to largely ignore the high-performance dinghy classes where no restrictive rules apply, and yet where unstayed masts are almost never used and where wingmasts have very rarely been proven to be worth the effort despite many decades of experiments from top sailors. The person who is being blind in this case is Sponberg and others who are too blinkered to consider that many top designers, sailors and sailmakers come from classes that do NOT use triangular sails, including Optis, the Australian, NZ, German and British development dinghies and skiffs, the cats, the windsurfers, the Open classes, the International 14, many Dutch racers, Moths, etc. It's sad that someone would slag off so many people with an insult that is so utterly untrue.

The sneering attitude of some people is also shown by Sponberg's utterly incorrect claim that "sailors and designers are insanely conservative people. There is no other explanation. The idea of a mast without wires is so foreign to most people that they just cannot fathom how a sailboat mast can stand up all by itself without something to hold it up." What a dumb thing to say (hey, Sponberg called sailors "insanely conservative" etc so he can't complain about insults). The world's most popular dinghy classes - the Laser and Optimist - have unstayed rigs. The most popular sailing class ever, the original Windsurfer, has an unstayed rig. The Sunfish, Topper, Finn, OK and many of the other most popular classes in the world have unstayed rigs. An enormous amount of sailors are completely and utterly aware of, and experienced with, unstayed rigs and probably the vast majority of sailors actually owned them and sailed them, especially in their formative years. That also means that many of us are very aware of their pros and their cons - I'm fairly willing to bet that I'd have spent more time sailing unstayed rigs (and wingmast type devices) than Sponberg has, and that would be very common.

The moral of this is that many of these tales where sailors effectively say "other people's boats and rigs are dumb because they are conservative fools" are actually based on ignorance. Similar things are said about the claim that bermudan sloops are unfairly advantaged by rating rules, the mono/multi issue, etc.

So when we're reading stuff about rigs or design, we've got to be really careful and look out for BS. If someone is going to make a claim, we should first look at proper evidence, and as Ggguest says in the real world many theories have been proven to be untrue. The old idea that a mast destroys flow over a mainsail is one of them.


PS - I've ranted for too long, but I may also mention that Sponberg's claims about rotating masts being banned are bizarrely insular and very largely wrong. It's strange how some people who seem to believe they are far sighted apparently can't even look outside their own part of their own country and one part of its sailing scene.

 

CT.

No harm in ranting about behavior you see as dumb or even stupid. Especially when you are able to offer evidence to back your claims.

Of the eight designs I have completed (none have been built yet), all have unstayed masts.

This is not because I believe such are inherently better than stayed ones. I never believed that. I designed them that way because unstayed masts better fit my design goals. One of which was to move the mast away from the centerline of the boat. This was to incure operational advantages, not performance ones.

The disadvantages of doing this are:
1.) the mast is heavier than it would otherwise have to be*, and
2.) the starboard tack is going to have greater heeling moment than the port one.

All eight of my designs have yards. These are meant to put more sail area on a short mast. They also facilitate getting the sail down quickly.

I would never have taken any of these choices if windward performance was my top priority. If that were the case, I would have gone with a fractional sloop rig with a tri stay system. This way, I could make the mast taller and lighter and still keep the vertical CG within bounds.

This simple formula is probably what has kept the fractional sloop rig dominant in the racing community.

It seems that if I use the same materials for both masts, the stayed one is always going to be lighter. And being lighter means it can be taller. And if taller, it can have a higher aspect ratio sail, and so on.

I hope the one of my eight designs I have picked to build gives a good account of itself going to windward. But I have no illusions about it even matching the windward performance of a fractional sloop. But hopefully it will come reasonably close.

 

Sorry for my ignorance, but why will you have different heeling angles on each tack.