Wingmast Sails


SPREADERS: I believe that I can get away with just 2 sets of fixed spreaders, each pair able to pass inside the side shrouds.
The measurement between both side shrouds chainplates on my RC yacht is 302mm.

        If the mast pivots at the leading edge, it is possible to affix the midway point to the mast by gudgeon/pintail in a
           vertical plane.
        The spreaders must be so shaped in order to allow the leeward side of the mast room to pivot without touching the 
          trailing edge of the leeward spreader.  If this is a desired mast support, it is my belief the spreaders have the  
          ability to pivot with the gudgeon/pintail being applied in a horizontal plane at their midway point.  But only if 
          the spreaders are affixed to the leading edge of mast.

        I believe the spreaders should be > 1.4m up mast from deck level and be 300mm (maybe 280mm)long in total
        I believe the spreaders should be > 1.4m down from top of mast   and be 110mm (maybe 100mm)long in total

        The outer form of the spreaders are able to freely rotate around their circular tubing, as though they are flags in 
          the wind.  As the mast rotates, the direction of breeze on spreaders changes and if yacht is heeling at any sort of 
          degree, the underside of the spreaders will create drag! Reduce the drag and get there sooner.

        There are sorts of ideas for spreaders - I will leave that to you to decide.

        The spreaders must be configured into a diamond set.

        Lower anchor point for lower spreader at heel of mast -> outer end of lower spreader arm -> directly under upper 
        spreader arm.
        Lower anchor point for upper spreader immediately above lower spreader at mast -> outer end of upper spreader arm
        -> mast head.

I was talking earlier about a weight swinging on an aft facing prodder to assist the mast rotation. This could also be used on any foresail system and a lightweight mast along the foresail luff affixed at it’s head could increase the foresail area by moving the heel of this so-called mast forward. The length of the weight on prodder could determine the rotation to enhance lift…!! ??



 Place both spreader arms end to end with the outer ends being on the outside.  Keeping the joined ends together, move the 
 outer ends apart until the angle between the arms are about 100-110 degrees apart.  Affix the spreader arms to the side 
 shrouds so that they are on a horizontal plane.  The centre of the spreaders (so to speak) are an unknown distance (let's 
 say for example 50mm) forward of the leading edge of the mast.  Take a straight short bar and attach one end to the inside
 corner of the spreaders and the other end to the mast by gudgeon/pintail, the mast can rotate without being impeded by the  
 spreader arms.

 The only problem with that idea is that although the mast will be supported (just) at that point, when the mast is in the
 rotated or over-rotated position, the mast would be allowed to flex/bend sideways, reducing the 'lift' efficiency.

 By attaching the spreader arm to the mast, so they are in a permanent position (as are diamonds), no matter how the mast is, 
 whether set in-line with the boom, or over-rotated, the sideways moment on the mast will be the same.  Because the mast
 is longer in the fore-aft measurements. it will not tend to flex/bend, so the soft sail will tend to keep it's shape far 
 more than if the top of the mast was allowed to bend aft.

 I have being examining a photograh of Bruce Ewing's "Wing Thing"  The photo shows that the mast has an aft facing 'prodder'
 at the heel of the mast and that the kicking strap/boom vang is attached to it.  It illustrates what I have said in one of 
 my previous screeds - in as much that if you attach one end of the KS/BV to the underside of the boom and the other end to 
 the trailing edge of the mast and then rotate the mast, because the boom is in-line with the KS/BV, the tension of the 
 KS/BV is constant.  If however, having attached KS/BV to boom and the other end to an aft facing bar/prodder as in  the 
 photographs of Bruce Ewing's mast and then rotate the mast, the distance between theboom and the bar/prodder will increase.
 This action will cause the boom to be forced downwards, increasing the mainsail leech tension.  I am not sure that that is 
 the desired result.  There are certain wind conditions that favour the leech tension being sightly reduced, not tightened!


 In my experience, an OVER over-rotated wing mast is just as inefficient if the leading edge of the mast is allowed to go 
 beyond a certain point as an UNDER over-rotated wing mast.  It has a disasterous result in efficiency.  It stalls the lift!
 I have been experimenting with tubular sections and aerofoil sections of masts on sailing dinghies over the past 10 so years.
 It would appear that if the centre-line (Leading-trailing edge) of the mast is allowed to over-rotate beyond 15 degrees 
 to windward, there is no gain.  You must restrict the over-rotation of the mast by fixing a fixed length line between the
 aft side of the boom and the leading edge of the mast.  You may if you wish add a line jammer on the boom, so you may 
 experiment with the length of line and rotation of mast.

Increasing the area of a wingmast :

It is possible with a fabricated wingmast to increase the total mast area by a sliding mechanism, pushing the leading edge of the mast forward. How’s that for different? One could almost double the fore-aft measurement. Using a gearing device, when the mast begins to tack the overall fore-aft measurement decreases to allow the leech of the foresail to easily pass the mast and then when the LE of mast has passed the centre line, the mast then starts to increase it’s fore-aft length and is restricted by a manual adjustment prior to sailing.


By the addition of a horizontal elongated cross section (onto which the fore & backstay/side shrouds attach) over the head of the rotating mast, It is very possible to increase the forward length of the cross section to incorporate a second forestay to run to a short (or however long you wish) bowsprit. This could be used for a flying jib!


If so desired, attaching the exsisting forestay to the elongated forward section, thus able to increase the foresail area, particularly at it’s head and down the leech.


NIMMS, you’ve certainly got alot of interesting ideas! What were you considering building this out of? An internal carbon spar, or a stressed skin over foam? The uniform taper on the width dimension leads me to think it must be the carbon spar. Have you built a prototype of the mast, or is it still in the design stage?

Regarding your idea about increasing the area of the wingmast, I would be concerned about 2 issues: weight & complexity. Will the aerodynamic gain outweigh the price you’ll pay for added weight? Are there other ways to equal or surpass the same gain? In any case, keep the juices flowing & let us know what you come up with.

HOUNDS @ 70% ??

What I would like to know is…Whilst I appreciate that the leech of the mainsail tapers towards the top of the mast and the jib/genoa also tapers, what is the percentage loss in drive/lift between a jib/genoa head at the mast head to hounds being 70% ??



My view is that although it may make sense to attach the side strouds to the position for the hounds, I belive it also makes sense to attach them to the head of the mast [more leverage].

Having said that, if they were attached at the hounds, the angle of attack to mast would be different [like pulling a door open either by the door handle (100%) or by a handle some 70% out from the hinges…?

The other concern is that if the side shrouds were to affix at the hounds, the spreader lengths would have to be altered to fit!


<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Originally posted by NIMSS

HOUNDS @ 70% ??

What I would like to know is…Whilst I appreciate that the leech of the mainsail tapers towards the top of the mast and the jib/genoa also tapers, what is the percentage loss in drive/lift between a jib/genoa head at the mast head to hounds being 70% ??

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

Good point. You obviously will lose some area & power from your jib & will have to consider whether the design trade off justifies the potential gains. I should start by noting that I’m coming from the perspective of iceboats & land yachts, where a jib is rarely used except in older stern steering designs. Since these craft significantly exceed wind speed, it has been found that the jib produces more drag than benefit from added power. In fact, I’m not at all sure that softwater displacement hull boats will derive much benefit from a wingmast rig in the first place, although I understand a 10-Rater had some success in Britain a few years ago. The exception to this comment would be for multihulls where potential speeds may be greater.

The benefit that I see coming from a 70% fractional rig is mainly structural. Since the mast is supported by the stays at a lower point, the effective length of the unsupported span is less. Also, the 30% of the rig above the hound will act in cantilever, which reduces bending moment on the lower 70%. This will allow the mast to either be built lighter, or eliminate the need for diamond stays, so reduced weight &/or windage aloft is a big plus. Besides, if you’re planning on a 3.5m mast,having the hound at 2.5m still allows you to have a darn large foresail. Hope this helps answer your question