Wing Masts, Rotating Rigs, and Solid Wing Sails

I agree with Claudio that we were moving off-topic in the AC120 Build thread, so with apologies to Ray for jumping too early, will start this one up witht he illustration I had from an article on sail evolution from soft to “hard wing”. While I thought there was more information accompanying the drawings, it appears these just supported the article. I will now have to search further, as I believe this came from an article on solid (hard) “wing” development for the 18 Square Meter, and the C Class catamaran. (And now, also for the A Class catamarans).

At one time, we were blessed with a poster who has gone on to be crew on the most currrent C Class cat champion from Toronto, Canada. On “Sailing Anarchy” he can be identifed by his handle of “Blunted” and the skipper posts under the name “Fredo” - but I will give “Blunted” a call to see if he would be willing to return to this forum and provide some technical insight into the Canadian championship boat. If you can’t wait, you can visit Sailing Anarchy and search for “C Class” for a lengthy discussion and some great photos.

Here is the illustration I was thinking about when I posted my reply to Gary a.k.a. “Dreamwakes”:

PS - before posting on this thread, lets agree to terminology?

  1. A foil shaped mast - is where the chord is only slightly longer than the width of the mast

  2. A wing mast - is a foil shaped mast with a much longer chord, and which still requires/uses a soft sail.

  3. A solid (hard) wing - is a complete structure which may be shaped similar to the wing of an aircraft, and while it may use a sof sail material, it is primarily of a lightweight structure covered by some form of covering, material or film.

  4. A rotating mast/rig is one that if there is no tension on the mainsheets (or lines) it will weathervane into the direction of the true/apparent wind.

  5. A swing rig - usually used on r/c boats, is a self supporting rig that controls the angle of attack of both the jib and main on a rotating structure. (not allowed in many classes)

By understanding these basic definitions, I hope to prevent two different visions of topic discussion by a reader.

Here are some interesting (and som very technical) article links - the first two being (in my estimation) the best discussion and theory.


[quote]Caludio -
one very popular (and International) monohull class is the International 10 Rater.

They are one of the few (maybe only) large monohull classes to use the rotating mast concept, and I would guess that if they are here in the U.S. and in the U.K. - they must also be sailed by a few in your country.

Boats are close to the same size as a Marblehead, so it may be worth looking into when you have time.

Regards, Dick [/unquote]

Hi Dick,
I tranfer here your message.

Yes I knows the 10R, very few in France. Time ago I was busy with special rudders equiped with adjustable foils and at that time I contacted Mark Gee aswell Mr. Grubisa of ISAF asking permission for the Class M. The answer was “no”.
10R are too large for easy transportation and they lost interest for that reason.

Some years ago , Mark wrote an article on the rotating mast on Model Yachting magazine n°138.

Unfortunately this article do not says very much about the forestay and its attachment to the mast if is a fractional sail plan. I’m not so certain how many ball bearings has been used to compensate the compression load, if any.

My actual design deal with these details. I’m expecting to receive soon the bearings, the idea is to use 2 bearing one on top of the other on both ends.


Hello Claudio -

on my beach catamaran (5.5 meter) with an approximate 10 meter rotating mast (18 feet long hulls, with 30 foot mast) was accomplished very easily, and lasted on my boat from 1982 until I sold it in 2006!

Basically it is a vertical stainless steel post with a nylon ball on top. It went through the front cross-beam, and there was a “cup” shape to fit the ball, located on the bottom of the mast base aluminum casting.

The multihulls and probably the 10 Raters do NOT use a backstay. Only a forestay, and two side shrouds were used, allowing rotation up to about 75 degrees each side from centerline to windward. Masts “usually” have side bend controlled by diamond wires. As the mast rotates, it is allowed to bend sideways, which pulls the luff in middle of sail forward and effectively does an automatic flattening of the mainsail. A set of loose diamond wires allowed mast bend, and a flat sail depowering in heavy winds and if diamond wires are tight to prevent mast bend, the mainsail stayed full and very powerful for sailing though waves.

The skipper only had to have diamonds adjusted to on-water wind conditions, and the mast was also fitted with a rotation limiter, to prevent mast from over rotating - and for keeping it at the proper attack angle for the sail shape.

The fullness of the sails were easily adjusted on the water and for different points of sail - mast bend to flatten sails, downhaul to move maximum camber forward, and outhaul to add camber for downwind reaching. The mainsheet tension on the rear of the boom controlled leech tension.

Very sophisticated, yet simple.

EDIT - ADDED Photo of Mast base “cup” and rotation limiter (color) and drawing of cross-beam with mast post and ball and how mast base fits on top of ball. Pin shown is a retained to keep base on ball as mast is raised or lowered.

Here’s L. Francis Herreshoff’s patent for the wing mast on his masterpiece “Live Yankee.” This was an R Class boat (same rule as the J’s, but smaller) and it killed the class in Marblehead, being the most expensive and fastest R ever made. It came out in 1927, but he was designing wing masts as early as 1924. It was the national champion as late as 1935, and of course the New York Yacht Club banned “rotating masts, double luff sails, and such contrivances” as soon as they got wind of what it would do.

The boat was full of innovations, including a hull built of formers and stringers like an airplane fuselage a rudder that bent like a fish fin rather than rotating on a pivot.



Earl -

he was sure the “innovator”. Wonder where we would be if the “stuffed shirts” would have left him to his design ideas and let him demo them in a practical manner - rather than just "killing’ them?

Do you have any links to his many patents? Would be great reading.


Ok, thankyou Dick for taking this thread up.

My main area of interest was in the fixed mast and the advantages/ disadvantages in choosing round or foil shaped sections…I am sure there is trade offs in either option and the aerodynamic variances would have alot to do with the method of actually attaching main sail to mast.

From the info presented thus far, I read that unless your foil section mast is rotating then you are better off with a round section. .

Which brings me to the conclusion that there are gains to be made with a foil section but because of the technical problems with building a rotating mast with fractional rig then the logical step would be a swing rig with foil section mast…the best of all worlds and simple.

Unless, you could develop an idea of a semi ( and free)rotating fractional rig with foil section mast.

I have owned beach cats with semi rotating masts and understand the simplicity as you described in your own beach cats but in the Rc world where ultra fine tuning does matter as well as weight and engineering complications , then I cannot for the life of me think up a easy method of building a effective semi rotating fractional rig.

Claudio, interesting that you are looking at the bearing idea, i had given this method some thought and considered it the only idea that could succeed, but I did feel bearings would create a set of problems…compression, environmental degradation, light wind effectiveness…etc…I look forward to seeing how you progress with this concept.



Ahh, the bearing idea.

Well, it was some time ago, I think around 2000 or so, I think the second Mystic Seaport RC regatta, there was this guy, I don’t remember his name, from Newport RI, at the time he was working there as a sail maker/boat builder (big boats) (he was making 10R/M keel from broken CF mast spreader pieces … something so stiff it was unbelievable), anyway, that year he brought an IOM and USOM he build, the USOM had a rotating rig, the mast was fixed per rules but he incorporated two bearing, one at the top of the mast and one at the bottom and made it so that the rig was rotating around the the fixed mast. If I remember correctly Jim Linville, the USOM secretary, found nothing illegal with it (the mast was in fact fixed). The rig was technically not fractional, it had a head stay jib, but the whole contraption was working fine, a little top heavy, but functional. We sailed the boat, but the hull had problems, it was a skiff design and when it was healing water was coming in, it had a really strange shape.
The next year he brought a wonderfully wooden build 10R with this incredibly stiff keel, no deflection at all, and he said that he did not do much more on the USOM… unfortunately he did not had internet (or a computer for that matter) and problems with the land line (apparently none), and the year after he did not show up…

This just to say that it has bee done before.

Hi All,
obviously what is done on real boat is no evident that can be done on models.
Here where I am :
Starting point = developping a rotating mast for the AC33

my problem is the forestay attachment !

the principle retained :

… 140g for 180x4x0.75 cm so far…

Last sketch

This is my contribution to the tread !

Any ideas ?


Another source for wing “mast” theory/use is the world of landsailing. While many are wing “masts” there are also a few that are solid wings.

It is truly unfortunate that my good friend Bill Korsgard has passed on, as he was an avid big boat sailor, ice boat sailor, and also a landyacht sailor.

One might do a search on this site for some of his mast/sail combinations for some of his land sailing creations.

In his absence, here is a link:

And heck - if it works on wheel or on runners - give it a try… although keep in mind that most are used on boats that “Create” their own apparent wind.

Hey Dick, is that Bill in the picture?

Well, been a bit occupied fixing a computer hardware issue but now that’s fixed I guess I should pitch in…

I’m working on plans for both wingmasts and wingsails as experiments but my thinking is further along on the former so I’ll stick with that for now.

I’m basing my wingmast on the paper by Thomas Speer:

The paper, at least to me, presents an understandable synopsis and suggests a practical approach to designing and building a wingmast.


To me the key to getting maximum benefit from a wingmast is to treat the mast/sail as an aerofoil, optimised for the air velocities that we operate in, i.e. low speed.

So if we treat the mast/sail assembly as a single aerofoil it follows that we should try to keep the flow on the ‘top’ of the aerofoil as smooth and continuous as possible in order to maximise the ‘lift’ and not introduce drag. The paper I mention previously has some good info on this.

Masts that are aero shaped and fixed fore and aft are, IMO, less effective than a round mast with a pocket luff or ring attachment, where the sail can rotate and to some degree approximate to a smooth aerofoil.

rotating aero masts are better but if used with a conventional luff chord will be compromised by the disconinuity at the boundary between the mast and the sail.

At the end of the day of course its still likley to be sailing skills that win races and installing a highly efficient wingmast rig will not make you a fleet leader overnight. My interest is simply to experiment and do something a little different.

I will be very glad to have anyone point out my misunderstandings or errors if it helps me to learn more.

I’ll post some thoughts on the rig I’m working on shortly.


Attached is a conceptual diagram of the wingmast I’m working on; apologies that its neither quite a 2D or a 3D diagram but hiopefully it will be understandable.

I’m planning to use a swing rig, the thick green line is the swing rig boom and the sheeting of that is what gives the rig the necessary angle of attack.

The blue teardrop shapes are the actual mast and this is allowed to rotate, within adjustable stops, seperately to the swing rig boom. This is to allow the mast to tack and also to allow some adjustment of the fullness of the rig.

The soft sail part will be fully battened and the red lihes represent the battens. You will see that these extend into the back two thirds of the mast, the idea is that they ‘flop’ over from one side to the other as the rig tacks, maintaining the aero section and by resting against the inside of the mast should provide a mechanism for the battens to take on the necessary curve.

The purple line is the jib.

As you can see, I’ve included two wing mast sections, one representing the bottom of the rig and the other the top. Both sections use exactly the same aeir section, just scaled to different sizes to allow the rig to taper further up the mast, however, you will also see that the actual mast section retains the same dimensional depth all the way up so at the top it constitutes a much greater percentage of the overall chord of the aerofoil at the top - the reason I’ve done this is that you will see that it produces a twist in the rig as you go up the mast, I think its around 15deg.

I have to get to work now but I’ll post some thoughts on the actual approach to construction later.


BTW, the black line is the pivot line of the mast

Hi Ray,
interesting, but if it is a fractioned rig (ex. at 80%) you have to solve the forestay attachment problem or not ?

Hi Claudio, the attached diagram will probably help to explain my thinking - essentially I would apply some rake to the mast. By keeping the pivot line vertical and raking the mast it can be arranged that the top of the forestay can be coincidental with the point at which the pivot line cuts the leading edge of the wing. With the addition of some extra local reinforcement it should be possible to use a simple wire hook through a small hole in the leading edge to attach the top of the forestay.

Remember that the mast only pivots around 20 or so degrees either side of the pivot line and because this is a swing rig I only need to accomodate a small degree of movement but the principle should hold for a conventional rig.


Nope - that is a co-worker, Pat Story, whom I have “drowned” in r/c sailing promotional discourse.

I thought I had photo of Bill from the ODOM Nationals held here in Minneapolis, but alas, none.

Just looking through the thread and picked up on the comment Dick made when referencing land yachts - he mentioned apparent wind.

I guess that if the forward movement of the rig creates apparent wind then that apparent wind doesn’t have the same velocity gradient as real wind (affected by drag as you get closer to the ground or water surface on which you’re operating) so perhaps the need for twist higher up the rig is reduced? Thoughts?


Claudio, I’ve been looking at your swivel arrangements, you appear to be putting a lot of load onto quite a small pivot?

I plan to pivot my wing mast on a short (say 20cm ) stub mast of a good diameter (say 15mm) made of a substantial CF tube that will slot into a tube embedded inside the wingmast. I’m planning to use PTFE tubing as bearings. I think using a longer and thicker pivot arrangement will spread the loads effectively.


Found some more of those “hidden computer photos” I had stored.

  1. Good example of mast on cross-beam with rotation control on leading edge of mast. Also note small white nylon ball at end of a “lever”. Pulling down on lever tightens diamond wires, which can be adjusted on the water for mast bend control. No turnbuckles, just diamonds and a lever.

  2. A photo (old) of friend’s 18 Square that shows mast on ball for rotation.

  3. An 18 Square “theory” design of a very large chord wing mast with trailing soft sail. Worked OK but had twist off problems assocated with the deep chord.

  4. Solid wing 18 Square (WILD TURKEY) and if you look close to top photo you can see how side shrouds and forestay connected. Under the “hood” on leading edge was a curved rod on which the shrouds could slide to allow wing rotation.

I’ll probably unearth even more hotos I didn’t realize I had in my “archives”

Cheers :zbeer: