Square rig variation

[brian eiland]

I am planning to build a variation on a square rig where yards are fixed to the mast for rotation, but raise and lower in tracks on the mast.

I'm currently putting a 15' cat together to act as a prototyping platform and I'll have to play around with that in strong wind.....

Interesting project there Goeorge. Hope you don’t mind my entering your discussion as I’ve had quite an interest in that Dynarig style square rig myself. I’m actually surprised more folks haven’t taken the same interest as yourself.

I’ve been playing around with a few ideas myself ever since I drew up my dynarig motorsailing catamaran. But I’ve not put any great deal of work into those idle thoughts, hoping that would come as a result of a qualified client who would really want to go forward with such a project.

I would divide my ‘concepts’ into two groups; 1) as simple as possible non-automated version, 2) automation and furling of the sail sections by mechanical or electrical means. In both cases I’ve sought to eliminate the need for ‘in-mast’ furling of the sails (MF). That requires a more hi-tech mast and practically dictates a carbon fiber mast.

For your project and this discussion lets just think about the most simple version of my thoughts,

.... but be aware that I'm not aiming to produce the worlds most efficient sail here, just an effective rig thats fun to play with and cheap to build (but with less damn strings than a junk rig...

I would choose to utilize an elliptical mast section, in fact likely an exaggerated one that might be fairly long for its width. You might find this type in an old ‘mast junk yard’, as a number of early alum-masted vessels tended towards this shape to minimize the aero disturbance to their attached mainsail. As a bonus this style tended to be rather heavy-walled, an advantage for the free-standing nature of the ‘variation on the square rig’ and/or the dynarig.

My yards would differ from yours in that they would be relatively flat plate ‘sickle looking shapes’ built to the idealized 12 degree arc curve. They would be one piece across the entire span and taper at the outer ends. They would be wide enough at the mast such that an elliptical whole cut into the yard would slide down over the mast,

My yards slide up and down the mast like yours. To facilitate this sliding I would utilize several possible materials. The least expensive one would be UHMW polyethylene. In a thin sheet form it could be wrapped several inches wide around the two ‘proud sides’ of the elliptical mast section and attached with countersunk screws. Sliding against this ‘mast surface’ would be ‘blocks’ of UHMW cut and fit to the adjoining hole in the yard(arm). This UHMW material is cheap, workable with std wood working tools, tough, slick, and sea-environment friendly. Alternatively, there is a more expensive sheet and block Teflon material that could be similarly fashioned.

NOTE: The alum (or whatever) mast with thin sheets of UHMW attached at the ‘pointy ends’ would be a relatively clean structure to the wind and to other rigging lines, etc, as opposed to ‘channels’ or a ‘rail’ projecting from the mast surface.

Each sail would reach across the entire span of the yard’s forward edge and attach to the yard via a bolt rope arrangement in a track/groove on the surface of the yard. The sail material could be extremely light-weight cloth as it is supported along the full two longest edges. Aerodynamically this gives a very clean outer surface to the aerofoil…the most important of the two sides. The inner surface of the ‘sailfoil’ is interrupted by the slim side of the mast at its center, but likely the airflow will re-attach to the inner curve of the sail’s inward arc…. (and helped by the end plate effect of the flat yards top and bottom).

The ‘flat plate’ yards need to be constructed of a very stiff material that will resist bending from their ‘arched shape’, and from their tips bending up or down. Their ‘sickle shape’ (top view) should help significantly with maintaining their arch shape. There will need to be a cross wiring of their tips to attachment points at their center reinforced ‘holes’ that surround the mast. This likely could be accomplished with small tough, pre-stretched spectra line. Not only does this keep the tips from bending, but also it contributes to the yard itself riding a straighter line up the mast and resisting cocking and binding.

NOTE: There would be the temptation to build too much vertical depth into the bearing/sliding material to prevent jamming of the yards as they slide up and down the mast. This should be avoided as too much depth could actually increase the binding when the mast itself bends slightly under sail loading. It would be better to have proper cross-wiring (bracing) of the yards themselves, then a two part halyard pulling on the top yard, and a proper two part restraint on the bottom yard in a reefed configuration. Too much depth in the slide bearing would cause additional problems with stacking the stored sail rig.

I’m not near my scanner at the moment so I can’t post sketches (rough ones)

....Torque will be produced by sail drag and lift forces in varying proportions as sail angle of attack changes. I can find some data for lift and drag coefficients, but very little for the location of the centre of lift and centre of drag...

Have a look at this posting and referenced PDF. Surprisingly the CE is very near the geometric center of the sail:

"The rig geometry illustration shows the effect of the wind gradient on the angle of attack. Fortunately, with the sails trimmed for optimum performance the CE of the sails sits just forward of - and near the centreline of the mast. Hence twist of the mast is low and has no great negative influence on the angle of attack. The aerodynamic forces on the rig cause the rig to twist the wrong way, closing the “leech” instead of opening it. However, the complication of making the yards hinged was not thought worthwhile for the performance gain expected."
http://www.hiswasymposium.com/pdf/2004/Gerard%20Dijkstra.pdf

...might have a look here as well
http://syr.stanford.edu/HISWA_Tyler_2002.pdf

On a more serious matter however, having all the yard braced to the same angle will be very inefficient due to the wind velocity gradient from the surface to the masthead. The lower yards will need to be braced further around than the upper yards to maintain a consistant AOA across the sail.

I raised this question as well over on the Maltese Falcon thread. As Someone said it just complicates things to much to try and account for this twist,,,so forget it.

Hope I’ve added some new points for discussion. I’d like to see a small model built and tested.

 

[ancient kayaker]

Brian: I agree this is an interesting and thought-provoking thread, and it's nice to see it getting more attention. I have had an interest in wing sails for some time but the practical difficulties have stopped me going ahead so far. George has shown the way ahead here. I definitely want to try something along these lines. George: per your analysis the wind shear does not seem to be enough to worry about but in my case it will be an order of magnitude greater due to the much lower mast (~4m); not sure how to deal with it at present but I have some ideas.

 

[Autodafe]

Hi Brian,

Thanks for your thoughts and for the links.
I had the Tyler paper but the Dijkstra is new to me; Its good to see that they feel centre of effort will lie close to centre of area. I think I'll stick to my conservative estimate to work out the worst case effort required to "sheet" the mast - I'm using that to calculate size and reduction for mast drive systems.

Since I started researching a few years ago I've been surprised at the total lack of any reference to square rigs with "dipping" yards, as it appears to me to solve most of the problems with making a useable square rig:
-Reduces weight and windage aloft in heavy weather and at anchor and
-Avoids the requirement to have a reliable furling system on each yard.
It's good to know I'm not alone in seeing some possibility here, thanks to Terry and yourself.

Like you, I've been thinking elliptical mast section.
I don't consider the reduced sail turbulence would be highly significant for my application, but the reduced windage when reefed and at anchor I consider an important consideration, particularly as I plan to use a very large (hence stiff) mast section: 300mmx600mm hollow plywood.

The reason I have gone for slides in tracks rather than bearing the yard on the mast is that I feel this will make reducing free play of the the yards easier. Any movement of the yards around the mast is likely to be sail twist in the wrong direction. Machining mast-shaped slide bearings for each yard with adequately small tolerance sounds beyond my level of expertise. It would also restrict my somewhat carefree approach to mast construction to have to ensure a uniform section shape - easier if extruded section is used

The "deep" slides I'm talking about are not all that deep, only around 70mm on my current plan, precisely to avoid the issues you mention.
I'll see how it goes on the model.

My thinking on the straight yard sections is twofold, both simplifying construction and reducing the chance of sail chafe on the yards. As with all aspects of the rig it's going to be a suck-it-and-see design process.

I love the notion of free standing rigs, but as my plans involve a pod-cat and biplane rig I have elected to go with a stayed design (ref. my sail plan sketch). It would be possible to engineer mast and bearings for a bury of 800mm, but not easy. The cross beam at the mastheads gives me a good place for nav lights and wind instruments anyway

George

 

[Autodafe]

Hi Terry,

Those bottom few metres are the real killer for wind gradient!
I'm glad I'm not worrying about them, but I look forward to hearing how you progress

George

 

[ancient kayaker]

George: from your first post I gather you are still in the early stages of building the boat so the rig is some way off yet. I recently completed a small (10 ft/3 m) sailboat that I can try this idea out on, but it will still have to wait for warmer weather unless I want to try it on an iceboat

For me the rig poses a problem, when changing tack there is no way to feather the rig, it must be hauled round on the other tack and be backwinded, stopping my lightweight boat in its tracks, unless I wear ship. I still want to try it out, but I am also thinking of having a double skin forming a full aerofoil profile which would symmetrical on either tack and self-tacking - i.e., the wing-sail that I wanted for Christmas!

In my earlier adaptation of your concept I planned a one-piece sail with pockets for each yard instead of separate sail panels. I don’t know if that is a usable idea for you; it cuts down on rigging but may only be suited for light duty use, and the yards must be threaded through the pockets. Alternatively, I see no reason why you can’t use sail tracks on the yards which would make for easy maintenance and replacement, and even provide the opportunity to have a heavy weather suit with less height per sail to reduce the strain on the yards. For light winds, the square riggers of old extended the width of the yards to increase sail area, although a spinnaker is probably simpler. I’ll just throw those ideas into the melting pot!

In a strong wind a square rigger would sail under topsails alone; it always seemed counter intuitive to me but it kept the sails high where they were less disrupted by surface effects. With separate sails you have the option to remove or brail the lower sails and send the upper sails back aloft. It's a thought in case you plan on blue water sailing. *

I think your concept of reefing from the bottom is more practical than the in-mast system used by MF, although it may have been the best solution for MF since that is a push-button operation. For the design shown in your first post, you need to consider how you will access the full width of the yard in a storm to brail the sail. I think lazy jacks were mentioned earier but they will disrupt the flow of air slightly.

Addressing the design of the uphaul; I think that your design will need more tension than a typical fore-and-aft sail of similar size, as you want to force it into a given profile whereas a fore-and-aft sail can take a natural shape between the mast and clew, and much of the tension is at the clew. I don’t remember if you addressed it before but using the downhaul to apply full tension might be easiest.

Having read both your comments and thought a lot more I agree with you and Brian on the depth of the slides. The upper sails and their yards will be hauled down by the lower sails and the whole thing will tend to resist any tendency to cock except at the bottom, where the yard is withing reach. Providing the uphaul is carefully designed or the top yard has extra slider depth I see no problems with this. However, if you plan to sail under topsails per * above additional slider depth may be wise unless the yards are wired to each other at their ends.

 

[brian eiland]

Cross Reference of Subject Threads

Thought I might make a cross reference link to this other discussion as it may get even more folks and opinions involved:
http://www.boatdesign.net/forums/motorsailers/dynarig-motorsailer-ala-maltese-falcon-16276.html

I may not participant in these discussions for about a week as I will be out of town. I posted this message over there, "But this other subject thread has me thinking about a 'bare bones' version....buildable in back yard. Started writing and sketching a bit yesterday, but now headed to Florida to visit an old friend for a week. So probably won't finish that until I return."

 

[Autodafe]

Just think how much an iceboat would extend your sailing season

My boat is still a good way off, but the rig testing dinghy is just about ready to go in the water.

A enclosed wing sail is an interesting possibility. Speeding up tacking is a strong attraction, but I prefer the aesthetics of simple sails, where yard and slide can be inspected easily.
I may try out both on my test dinghy and see how I feel about it then. Thanks for that idea Terry

I have been considering electric or pneumatic assistance for mast rotation to speed up tacking, but I would prefer to avoid the extra complexity of mechanical assistance. An enclosed wing could help here.
I am proposing to use a pulley drive system to control mast rotation rather than sheeting to the yard, and my early calculations suggest a reduction ratio of 40 or 50:1 may be required if I get caught out with full sail in a gale, which would mean perhaps 30 seconds to tack each mast manually through 160 degrees. Faster would definitely be nice.

I am hoping that with a large number of yards to hold sail camber and reduce sail span the halyard tension will not need to be high for good sail shape, that is the yards will act in the same way that battens keep junk sails under control.

I'm planning to use lazyjacks for sail control, and hopefully will not have to access the entire boom to reef.
Interesting point about using tops'l only in heavy weather. Perhaps I should put dual tracks in the mast and hoist a small storm sail on the opposite side of the mast to the main sail when required. It could have a downhaul to hold it at any desired height up the mast and I wouldn't have to go to the trouble of removing the main sail from its yards in strong winds.

I agree with your assessment that the top yard will require extra care in slider and uphaul design to avoid being jammed.

Bluewater (high latitude) cruising is part of the long term aim, but I expect to spend a couple of years working the bugs out in coastal cruising before that, as there are many aspects in addition to the rig that are rather experimental.

 

[ancient kayaker]

I am wondering how the power of the wind can be used to turn the mast. May be too violent in a storm, but it would have more power when you needed more power. I have no idea how it could be done at this point, just the seed of an idea.

 

[Autodafe]

The idea certainly has potential.
I've occasionally wondered on the same lines, either an adjustable trim tab arrangement on the top yard to move the CoE or a mechanical wind turbine drive where clutches can be used to drive the mast either way.
Due to the potential complexity I think I'll try the manual control first then add external power if required

 

[sharpii2]

I am planning to build a variation on a square rig where yards are fixed to the mast for rotation, but raise and lower in tracks on the mast.
Mast rotation is used to control sail angle on all yards simultaneously. Reefing and furling is achieved by lowering some or all of the sail and yards. The bottom of each sail is connected to the yard below, forming in effect a single sail rig, allowing a single halyard to raise and lower all sail and yards on the mast. Refer to attached (Crayon?) sketches (not to scale).

This is to be installed as a biplane rig on a cruising cat, each sail approx 40 square metres (eventually - I've only just started building the boat...).

I am currently considering options for controlling the mast angle, so would like to be able to estimate typical and maximum torque produced by the sail about the mast.
This parameter is similar to “pitching moment” used in aircraft design, but finding a value for given windspeed and angle is taking me out of my aerodynamic depth.

Assume for the purposes of calculation all sails rectangular and identical up the mast with a foot of 3 metres. Yards are symmetrical about the mast, and sail is simple single layer fabric.

Torque will be produced by sail drag and lift forces in varying proportions as sail angle of attack changes. I can find some data for lift and drag coefficients, but very little for the location of the centre of lift and centre of drag.


My question is then, can the torque force on the mast be simply approximated and if so how? Any info most welcome.


Feel free to post comments on other design aspects as well, but be aware that I'm not aiming to produce the worlds most efficient sail here, just an effective rig thats fun to play with and cheap to build (but with less damn strings than a junk rig ).

For anyone interested, I've attached a short pdf I wrote on the reasoning behind the rig.

Thanks in advance,
George

Why the biplane rig.

Why not just make a single, larger rig that could be controlled from a more central location.

Really, the big advantage of a square rigger, and the main reason they were used for large ships, was that the sails always stayed on the same side of the spars.

This enabled crew to get behind the sails to furl or set them.

I don't see any reason why a rig like you want to set up cannot work. The mast could be allowed to twist somewhat for the sails to set at a slight wind variant.

The real problem with this set up is weight and co$t.

It would certainly be cheaper, simpler, and probably more reliable to set up a fore and aft rig. Especially on a multi hull, where the inital stability is quite awe inspiring.

If I were to go with a square rig on such a boat, I would use sheet lines to control the yards, even if I went with an unstayed mast.

This way, I would put less strain on the yards, allowing me to make them of smaller and lighter sections.

An unstayed mast, however, offers too much benifit to a square rigger to pass up, as there is a lot more freedom of movement for the yards, allowing them to be sheeted tighter to the wind.

But the mast section would certainly have to be large, even if it is made of carbon fiber. And TWO masts would each have to be the same section as ONE mast, so one of the masts could be bare to shorten sail.

The truss rigging you show between the two masts would certainly be a proplem, as it would restrict the freedom of movement for the yards.

 

[Autodafe]

Why the biplane rig.
Why not just make a single, larger rig that could be controlled from a more central location.

Mainly, why not? It is slightly less efficient than a single rig, true, but the difference is smaller than many other refinements that cruising boats don't bother with. It will be slightly heavier than a single rig, but not much, and the weight is lower offsetting the loss of stability.
The main reason for me is that I am starting from the premise of a pod cat, and I have no desire to have to climb on the roof every time I want to inspect or adjust sail. Solution: put the masts down at deck level. There are quite a few other benefits to biplane rigs, discussed in depth in some other threads.
With a square rigger biplane also means that I could sail one hull forward and the other backward. This is pretty pointless in these days of motors, but could be highly amusing in tight spots with onlookers
If I didn't think it would be too difficult to control lots of masts simultaneously I would have four, one at each corner

Really, the big advantage of a square rigger, and the main reason they were used for large ships, was that the sails always stayed on the same side of the spars.

This enabled crew to get behind the sails to furl or set them.

It also means the mast and yards are nicely on the windward side of the sail where turbulence does the least damage.

I don't see any reason why a rig like you want to set up cannot work. The mast could be allowed to twist somewhat for the sails to set at a slight wind variant.

Sadly the twist is in the wrong direction for induced windshear assuming the mast is sheeted by the base.

The real problem with this set up is weight and co$t.
It would certainly be cheaper, simpler, and probably more reliable to set up a fore and aft rig. Especially on a multi hull, where the inital stability is quite awe inspiring.

If you're right on this one then the rig isn't getting built but I've done some fairly detailed materials breakdowns and I think I can get 80sqm of sail in the air for under 6kAUD and total weight (including sails and rigging) of just over 300kg. Not light, but not particularly heavy either, and definitely cheap.
Because the sails have almost no cut shape I can buy cloth and sew it myself. Mast and yards are to be out of epoxy timber with some glass, built at home. I may add some CF if it's too flexible at testing, which could add another 2kAUD and ~15kg.

If I were to go with a square rig on such a boat, I would use sheet lines to control the yards, even if I went with an unstayed mast.

This way, I would put less strain on the yards, allowing me to make them of smaller and lighter sections.

The load on each yard isn't very high, even in 60kts, as the supported area isn't large, so the yards are surprisingly light (at least on paper) to cope with the engineering loads. I suspect that sheeting every yard would add more weight in running rigging than it would save in yard weight.

The reason I am thinking pulley-cable system to drive the mast rotation rather than sheeting the boom is that I don't want to have to move the sheeting point of both sails every time I tack.
This would be less of a problem with a single mast rig, but it would still require changing sheet and sheeting point every tack.

An unstayed mast, however, offers too much benifit to a square rigger to pass up, as there is a lot more freedom of movement for the yards, allowing them to be sheeted tighter to the wind.

But the mast section would certainly have to be large, even if it is made of carbon fiber. And TWO masts would each have to be the same section as ONE mast, so one of the masts could be bare to shorten sail.

The truss rigging you show between the two masts would certainly be a proplem, as it would restrict the freedom of movement for the yards.

I agree that the ability to sheet the yards hard on the wind is vital, and the main reason traditional square riggers couldn't sail to windward.

It is not entirely clear from my sketches, but my rig does have this feature. The stays are connected to the mast top-strut (not the mast) and chainplates are on the bow and stern of each hull. This keeps the stays well clear of the yards, allowing them spin freely to any angle, while still giving me a staying base nearly the full width of the vessel and consequently small compression loads in the masts. This is another benefit of the biplane rig

 

[brian eiland]

Junk Rig

...might make an interesting cross reference of subjects

http://www.boatdesign.net/forums/sailboats/chinese-junk-rig-5703.html

...and another:
http://www.boatdesign.net/forums/sailboats/square-rig-pointing-questions-5991.html

http://www.yachtingdirect.com/white_papers/philip_goode/weatherly_square_riggers.htm

 

[Elmo]

Here's a sketch of what I had in mind: perhaps it can help you? It works out well for my car-topper sailboat as it folds compactly. Something I have also been looking for!

An interesting rig.

A question , if you don`t mind :

Have you devised some equation (or formula / ratio) to determine the
variations in radii to yard length ?


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

http://www.youtube.com/watch?v=qtJpm7DCxHA

http://www.youtube.com/watch?v=FUQvBOX566A&feature=related

 

[ancient kayaker]

Elmo: the numbers in my sketch are pure guesswork at this point, rounded off to suit available material. I can get Al tubing with 1.5 mm wall thickness in a series of sizes, intended for radio masts.

I prefer working in wood than in metal, so the yards will likely be laminated wood carried on a telescopic Al mast. I will finalize the yard and mast dimensions based on expected forces and material strengths.

For me the practical attraction is its ability to drop or shorten the entire rig rapidly to pass under a bridge then raise sail again. This is the only rig I can see being able to lower the rig literally in seconds without finding myself a horrble mess of lines and flapping sails. Honesty also requires me to admit that I just like experimenting.

p.s., I should mention the reason for estimating the yard dimensions was to project the approximate height of the collapsed bundle. For my small car-topper boat it is likely to fit nicely under one arm which suits me, as I sometimes have to launch a fair distance from my vehicle.

 

[brian eiland]

Bi-Rig Discussions

...This is to be installed as a biplane rig on a cruising cat, each sail approx 40 square metres (eventually - I've only just started building the boat...)

A little cross referencing of similar discussions here:

1) http://www.boatdesign.net/forums/multihulls/multi-masted-sailing-cats-25508.html
Amended: Perhaps this was not the most appropriate link...better one would be
http://www.boatdesign.net/forums/multihulls/bi-rig-performance-cruiser-22150.html
2) Bi-Rig performance Cruiser
http://www.cruisersforum.com/forums/f48/new-bi-rig-performance-cruiser-12688.html