Wingmast Sails


Has anyone experience with sails for wingmasts?

Obviously they need to be flatter than the usual sail. The wider the wingmast the flatter.
But are there any rules of thumb? I.e.: If the wingmast is 20% of the cord line, the draft should be in a range of…?

Any info highly appreciated,



The only real experience I have had with this is on iceboats (E skeeters to be specific). As you say, the sail acts more like a flap than a full airfoil. The mast makes up a much larger portion of the total airfoil. The main thing you want the sail for is to control is the twist. The camber comes from the amount of rotation that you put into the mast.

Bill Korsgard probably has the most experience with wing masts. He is a member here but i’m not sure how often he checks in. He would probably not mind if you sent him an email off line. Dick Lemke also has some wingmast experience.

Other than that, the best thing I can suggest is to look at airfoil shapes. Super-impose your wingmast configuration and see where the mast ends and the sail begins. If you are using a 20% chord wingmast then there will still be some camber in the portion of the airfgoil comprised of the sail (normally the max camber is at the 40-50% position). If you have a 50% chord wingmast, then the sail would basically be flat as a board.

  • Will

Will Gorgen


My wingmast is close to 30% chord length in the middle. I had a nearly completly flat sail set up, that I actually got from superimposing it over a Naca profile. I think it was a clark Y foil.

The reason why I posted this topic, is that it looks wrong.
Since the Joe average sailor like me is used to narrow A-Cat wingmasts or similar, which have nearly the camber that sails on non-wing masts have, looking at a completly flat sail just looks so odd. [:-crazy]

I guess ideally you have to add twist into the sail not by the cut, but rather through a certain amount of flexibility in the masttop, like some C-Class Cats do. But that is hard to control compared to a soft sail. The masts that I am using right now seem to be to rigid for this.

How else would you control twist? If the mast is not flexing and the sail is more or less flat, you either get a sharp bend at the foot of the sail or a completly symmetrical profile at the top - depending how you sheet it.
If you want to avoid that, you would make a flat sail at the top - that you sheet following the line of the outer side of the wingmast - and maybe 6-8% Camber at the foot, close to the luff.

Sorry, if I am asking dumb questions.

Thanks for the tip thou, I will mail Bill.

The way to add twist for a rigid mast like your is with luff curve. By adding in a small amount of negative luff curve near the top, you will induce slack in the leach through the bias of the cloth (or shear of the film if you are using mylar film based sails). You can to a certain degree control this through the vang. As you pull down on the clew of the sail, you will induce a small amount of shear into the sail material which will reduce the slack in the leach and reduce the twist. Easing the vang will increase the twist.

It seems to me (and Bill may know better than I) that you can induce the camber you want in the foot through outhaul tension. The outhaul controls the draft in the lower 1/2 of the sail so be easing the outhaul you will get the camber you want there. for the mid sections of the sail (given your high aspect ratio) you can probably induce all the camber you need with positive luff curve. Then up top you induce the twist you want with negative luff curve. So I think it would be possible to get all the shape you want with clever use of luff curve. I think if you sketch it out you will end up with a slight belly to the luff curve between the 1/3 and 2/3 span and then it will go straight or slightly negative from the 2/3 to the top. You probably don’t need much. There are some good articles available on the web about how to calculate the luff curve you want to add for a given amount of camber for a given chord length sail. Finding rules of thumb for adding twist may be a bit harder.

As far as getting the draft forward on your sail, I think you will want to try cunningham tension for this. This works well for soft sails where the material can be easily deformed along the bias of the cloth. But for film sails it gets a bit trickier. But a nice thumbscrew cunningham should allow you to play with that tension and try to pull it forward without puckering the luff.

If all this fails, then you will want to cut some panneled sails. If you use the sail block method that Don has beendiscussing, you will want to set the peak of the block fairly fr forward on your sail so that the aft portion of your broadseams are purely straight cuts but the forward portion has all the curve. This will be tricky as you are really looking for a very small amount of camber to the sail itself. But if you cannot get what you need from the luff curve and cunningham, this is what you will need to do.

By the way, bill has done a lot of iceboating as well and may be able to put you in touch with some of the true artists in the wingmast field.

  • Will

Will Gorgen

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”> There are some good articles available on the web about how to calculate the luff curve you want to add for a given amount of camber for a given chord length sail. Finding rules of thumb for adding twist may be a bit harder.

<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

If you have any of these bookmarked can you post a link. I haven’t been able to find any.

Don Case
 Vancouver Island

Here are two nice sites that discuss areodynamics of wing masts. A third site/source is Tom Speer - but I would use caution with his theories - since many (most) are really just that - theory - and are still unproven. While he provides a lot of theory - I take stock in having actually proven design and ideas on the water as a bit more realistic and useful. We all can speculate/postulate what will happen, but the proof is to see the convergence of ideas, theory and practical results that <u>together</u> result in a product that can be demonstrated.

Hey Don,

I had them bookmarked but the bookmarks do not work any longer. most of the articles were from Larry Robinson in his old online technical newsletter. I think Lester may have inherited some if not all of that stuff. They were posted on the Seattle Model YC site, but they are not there any more.

The rest were from the Mesa Model YC but those are disappeared as well.

What ever happened to all those great techical articles???

Bummed. If anyone finds them, let me know…

  • Will

Will Gorgen Then go to “LIBRARY”

Now called Model Yachting Resource Center, a monthly (usually) e-newlette is published and sent by editor Dave Acree. Usually good general stuff as well as some local Southwest flavor info/articles.

I can’t count the number of times I have read Dave’s articles. Very good stuff, with one exception. The last article"Sail Making Cont." ends with him sewing the broadseams and saying," Next month, more on putting sails together". Unfortunately there is no next month and these articles were written in 2003. Now I realize that these articles were written out of the goodness of Dave’s heart but this is like writing a novel and leaving out the climax. Anyone know what happened to the last chapter or two? You know, the ones that tell me what I need to know.[:D]

Don Case
 Vancouver Island

Edited to add smilie.Is there another way to add smilies from the quickie comeback form?

Well, I can’t profess to be an expert in wingmast design by any means, but have some hands-on experience building them for my ice/land sailing craft. One of the beauties of the wingmast concept is that it offers the potential for a wide range of cambers (draft) to accomodate for the wider range of apparant wind velocities experienced when boat speed exceeds true windspeed (multihulls & hard surface sailers). The “soft” sail panel can be cut flat, as the amount of mast rotation will determine the amount of draft. Mast rotation is best controlled thru outhaul tension & can be reduced by a secondary sheeting arrangement as the boat gains speed. Thus the draft can be left full (~20% of chord)for power as the boat begins to accelerate & then reduced as max speed is approached & a flatter airfoil profile (say, 5-10%)is desired for less drag & higher top end.

I’ve found twist to be best controlled thru leach tension. This can be done solely with sheeting, but uses too much servo power & is not consistent thru variations in sheeting power. The best way is to use some sort of vang arrangement so the rig is tensioned internally. This allows twist to be controlled independently of sheeting, which now only has to effect angle of attack (AoA) of the rig. The problem with conventional vangs (either tension or reversed compression)is that they will impede proper rotation of the wingmast if attached to the trailing edge of the hard foil. The solution is to pivot the vang in line with the same axis of rotation of the wingmast.

BTW Dick, the wingmast link from the NZ site is straight from Tom Speer.I was surprised there was no attribution given. Also, more discussion of wingmasts can be found at:

AMYA 11052

I actually did a test with a paneled sail yesterday.
I made them flat in the upper third and added a a little camber to an additional seam 2 inches below the top. This turned out to be necessary since it is a square top rigg and would otherwise have too little stability up there. The lowest seam has also a little camber, even thou - as Will said - this gets totally lost in the outhaul setting.
The sail uses a cunningham made of a turnbuckle at the masttop (the bottom is already pretty crowded with the compression strut for opening and closing the leach).
I figured out a luff curve by hanging the sail into the desired shape horizontly fixed at 5 points . That way the luff curve automatically bends the right way (or at least I hope so…).
The bend of the luff curve is matter of 2 mm maximum thou since the sail is so flat.
Its a windy day here, so i’ll give it a test setup on the porch today and see how it turned out.

Perhaps you should cut the other sail flat without luff curve or broadseams. Then you could do a side by side comparison to see which method appears to produce a better looking airfoil. Tufts could be put on each rig to observe airflow patterns. The unique configuration of your twin rigs gives an ideal test platform.


I actually did this kind of parallel test with the first two sails already. Its working quite well.
When you sail the ship you can actually feel the difference. Depending on which sail pulls more, the boat will turn in either direction. The effect is subtle and in reality maybe more in the observers mind than on the boat, but its fun to do some testing anyway.

I will give the single panel sail a try, even thou I wonder how you keep the top from flipping on a sqare top rigg when the sail is completly flat. I always assumed that you need a little bit more tension on the leach to stabilize the top, that you achieve through at least one broadseam near the top.


That may be true about the square top rig which I’d forgotten you were using. A couple things may help, however: a diagonal batten to support the corner, or a small swivelling “gaff” mounted on the top of the mast. If a gaff is used it’s possible to pivot it slightly out of alignment with the axis of rotation of the wingmast so that it will increase tension on the leach as mast rotation increases. This will allow it to loosen tension as the mast rotates thru the eye of the wind so that rotation is not impeded.

I’ve tried the square top sail, but have gone back to using a fairly full roach which maintains camber to weather under normal conditions and twists off to spill air in a gust. I also have a diagonal batten & am using a stiff (4 mil mylar) sail fabric to help maintain sail shape.

Your comment about the sails steering the boat caught my interest. If you had separately controlled sail sheeting servos, would it be possible to use them to assist in your problem tacking? You could luff the sail on the inside of the turn & use the powered up outer rig to help swing the boat thru the tack. Just a thought…

Madison, Wi


interesting thought about the sail steering. I wonder thou if the advantage that the boat gets through the different driving force vector might be (over-)compensated through the disadvantage of loosing a lot of momentum with the loss of nearly half the sailpower when it enters the tack.

I’ll be at the lake this weekend, so we’ll see if my tacking problem still persists after adjusting the ackerman.


Finally, whare can I find Wing-Mast plan, please ?


Sailman [:-goldfish]

I’m not aware of plans available only for wingmasts. There’s a written description of the method I use for my composite masts on the F-48 Multihull forum:

Also, Robert Weber ( ) has come up with a beautifully simple way to build a nice unit we’ve named the “Weber Mast”. It involves pieces of balsa aileron stock glued up to form the trailing edge portion of the wing. Glue only the wider portions of the wedges, leaving at least 1/2" unglued area on the narrow side which will form a slot for your luff groove Then take some half-round pine molding & glue it onto the aileron stock to form the leading edge.Or you can hand shape the leading edge out of spruce, fir or basswood stock. Some pictures of this method can be seen at (scroll down, starting at Sept 6). This was done by Simone Chiaretta of Milan, Italy. He evidently couldn’t find aileron stock & used rectangular balsa which involves alot more shaping

Hi Bill,

I live in the UK.

Within the last year I purchased a ‘Passive’ designed “A” Class RC yacht.

I am in the middle of designing a 3.5m wingmast.

The diamentions are: 70mm leading > trailing edge at deck level and 35mm at head. 1.4m up from deck level the fore-aft measurement is 120mm. Width at deck = 22mm Width at head = 15mm and @ 1.4m = 20mm.

The straight luff groove is 25mm aft of the leading edge.

I have beed deliberating whether the mast pivot should be at the leading or trailing dege of the mast.

Forward or rear mast pivot?

Forward: When the trailing edge of the mast is allowed to leeward, I believe the whole mainsail area reduces the slot!

Aft: With the leading edge of the mast moving up to windward, the mainsail area will be virtually in the same area as a conventional rigged mainsail on a static mast, which will not reduce the slot.

[I am open to correction] !

It really depends on where the kicking strap is attached - at the foot of mast or onto the rear of an aft facing prodder swinging (in line with mast) at the foot of mast.

Without prodder : If the kicking strap is attached to the heel and trailing edge of the mast, the mast is allowed to rotate or over-rotate without too much loss of mainsail leech tension.

With aft facing prodder : The loss of leech tension appears to be connected with the length of the prodder. If the prodder is too long and the mast is allowed to over-rotate, the distance between the mainsail clue and tack is shortened and it would appear that the leech tension is reduced.

I believe the over-rotating wingmast can be controlled to stop it over over-rotating by securing a fixed length line from the leeward side of the boom to the leading edge of the mast, so when the leading edge is…then being applied to windward, the line will become tight and thus prevent over over-rotation.

It is also interesting to note that a wingmast with a prodder will always try to over over-rotate because of the tension on the kicking strap want to push the boom into the mast!

OK, so how do I help the mast to tack?

Attach an elongated cross at the top of the mast(long fore-aft & shorter arms across at right angles) on a horizontal plane with a pivot located in the centre of the cross. Forestay attaches at forward facing prong of cross and the backstay on the aft facing tang. The side shrouds attach to their respective side facing tangs on the cross. The mast should be allowed to rotate freely under the cross.

Attached at the aft of a prodder at heel of mast is a suitable weight that moves to leeward as the yacht tacks. It follows the leading edge of the mast will swing to windward in line with the prodder.


Attach a line to a forward facing prodder and control the rotation by RC.

It is also possible to attach a short forward facing prodder at the head of the mast and attch the side shrouds to it. The shrouds should not be tight. So when the yacht heels to leeward, the windward shroud come under tension which causes the leading edge of the mast to rotate onto it’s new tack.

A full length batten is positioned on the mainsail so that when fully rigged, the batten will be 1.4m from deck. The luff groove on the mast will be 100mm forward of the trailing edge of the mast at this point, so when the mast is pivoting onto it’s new tack, there is 100mm of trailing edge force being applied onto the batten to bend the batten the other way. This action will also assist the other battens to flip onto the new tack.

It is also possible to elongate the forward prong of the mast head cross forward and attach the forestay of the jib/Genoa to it, thus able to increase the foresail area…? !!!

It is also possible therefore to assist the fore-aft rake of the mast using the cross somehow…

The questions are endless…!

Hours of fun 2 U all.



ps I am also working on a conventional spinnaker system by RC. It is fun isn’t it?

Wow, that must be quite a boat to be able to handle a 3.5m mast. I was a bit confused by some of the dimensions you listed. From your numbers, it appears that the thickness profile goes from 31% (base) to 16% (1.4m ) to 42% (head). Is this correct? Something that thin at the 1.4 m midpoint will need to be made very stiff, or need diamond spreaders in order to not buckle over that length. Also, I wasn’t sure how the luff groove could be 25mm aft of the LE, considering your other dimensions.

As far as pivot location goes, I would vote for a forward position in order to assure controllable positive mast rotation. An aft pivot point could cause underrotation, flutter, or even counterrotation, but perhaps you should set different pivot points & see what happens. Amount of rotation can be easily controlled by outhaul tension on the boom with a forward pivot point. Your mention of the slot opening leads me to believe you’re using a jib, which can have it’s sheeting & twist adjusted for different amounts of slot.

I’m not clear what a “prodder” is, perhaps some sort of lever arm on the mast? In any case, the kicking strap (boom vang?) needs to be attached in the same axis as the mast pivot, or rotation will be impeded. If the vang/kicker pivots independently of the mast, mast rotation should happen easily from sail pressure & lateral force exerted by the windward sidestay on the leading edge of the mast. As you mentioned, a forward facing “prodder” will enhance the amount of leverage exerted by the side stay. You may want to consider attaching your stays lower on the mast than at the head. My masts have the “hound” at about the 70% point. One thing to keep in mind with any design is to “keep it simple”, as the more complicated the device becomes, more liklihood of problems develop. Please don’t take my comments as being too critical, as it sounds like you’ve got alot of ideas & are onto a good thing. I look forward to seeing what you come up with.

ps; here’s some pix of Bruce Ewing’s (NZ) “Wing Thing” (scroll down). Your fellow Brit Mike Howell has been involved with this as well.


Thanks for your imput - really appreciated!

Sorry that my measurements are confusing…I will try to rectify, so herewith

Mast head fore-aft measurement = 35mm
Mast 1.4m fore-aft measurement = 120mm
Mast heel fore-aft measurement = 75mm

Mast head width measurement = 15mm
Mast 1.4m width measurement = 20mm
Mast heel width measurement = 22mm

Luff groove being 25mm aft of LE shows that the luff of the mainsail is actually inside the mast.

Having posted my previous screed, perhaps if the aft 40% of the mast is of softer material than mainsail cloth to enable mainsail to integrate with mast - therefore better leeward airflow - better lift.

Spreraders soon.

Will complete this reply following 5 -6 hour gap.