Mast aft wing sail

I’ve been testing a solid wing variation of the mast aft (or Delta) rig. I first tried it on a small trimaran, but it was really a bit too small to draw any conclusions. I’ve now tried it on an RG65 (albeit, a poor excuse for an RG65 - got soundly beaten by a fleet of MMs recently). Apart from the advantages related to the conventional mast aft rigs and wing sail, the main advantage is that it is a very simple arrangement.

To keep the wing light I built the main element from 3 layers of 2mm Depron foam (airfoil profile) and the flaps from single 2mm pieces. Because the wing hangs it simply rotates on swivels.

[LEFT]The camber is controlled by having the base of the trailing edge of the bottom flap able to slide up and down a boom, with the extent to which it can slide controlled by a cord with adjustable length attached to the end of the boom. I’ve tried to show this in the video below.

For a first attempt I’m quite impressed with this sail. The boat seems to tack better than it did with the previous sail, and down wind it doesn’t seem to nose dive as much, and seems quite fast. Like the delta rig, it also seems to perform well in light winds.



Pretty neat, Mij…I feel inspired to try the wing as a Una rig.


Hi Jim,
you adjust the lenght of the cord before the ride, is that right?

You could do that job on the fly with a full camber at the downwind and a flat camber at the upwind.
I supose you took an arm winch, you could use this servo for that cord too.
That cord should go near the pivot from the bow to the boom and from the boom to the rear of the front panel.
Sheeting in should give a flat camber, sheeting out a full camber.

Bill: sounds interesting, let us know how you go.

Wolfgang: excellent idea, but unfortunately there isn’t much room inside this boat, so the winch arrangement isn’t ideal and is already very tight. If I get an opportunity I might try this sail on a more conventional hull, and if so I’ll implement your suggestion.

Hi Mij,
Being the first having suggested this type of rig for RC models, I made various experiment back in 2005 after reading the Philip Bolger Books.
In principle, this type of set up, should not present the typical “nose down” effect when running because the orthogonal force applied to the jib surface is going “up” compared with the water surface. Similarly with all other Jibs if the Main would not destroy this force being pushing horizontally, and higher and under gusts, also down.

The radial boom is a solution to achieve what said above, my experimental work of 2005 was a failure anyhow since I could not control the boom lifting, see images.
The radial Jib require also a strong rotational axis and a strong hull to avoid canting a hull distortion.

During my experimental work on a chine Class M hull, the balanced boom composed by two segments of carbon tube retained by an aluminum tube, broken under the pulling force exerted by the Jib. The jib was using the same Class M Surface, in this case was 6850cm².
The pictures below illustrate my attempts of 2005.
As Bill says, me too I’m intending to use this rig on a Footy

Hello Claudio,

I’m pleased to hear that you will try the sail out. The design is based on your original posts. I didn’t realise that it solved the problem with the boom lifting, however, the resistance to nose diving is aparent on the water. I’m planning to test it on a more conventional RG65, as I don’t the hull I have tested it on does it justice

It will be interesting to see how it goes on your Footy. I think that the 2 mm foam will be ok. I use 5 mm sail making tape for the internal joins, and for the external seams luff tape seems to be ok. In the front panel I used an aluminium tube to run the cord through. I’m sure you will come up with a more elegant construction, but when I get a chance I will pat some more details on the method that I use.


Considering Claudio’s statement above I thought that it was worth trying this sail on a catamaran:


The boat is still a bit rough (excessive lee helm and doesn’t sail close to the wind), but it is certainly resistant to pitch poling. The sail is supported by two light weight masts, one resting on each hull and joined at the top. This arrangement seems quite stable, and is supported by a single stay. The whole assemble is very easy to dismantle and assemble.

Some footage of sailing in very strong and gusty winds:



Hello Jim,

  • barefoot at a winter day in victoria - I hope you didn’t catch a cold :wink:

Nice to see your improvements!
According to the feedback around the world :wink: - I suppose we have foiling days
(allthough the AC72 show reasonable rake at their wings, everyone is attracted by the foils).
And those small boats you build won’t step into the speed range of a mini40, but not everyone is aware of it.

I like your improvements, especially to use the resources (wind) effectively.
And when that is done, there still are add ons left, which produce drag and may lead to a foiling system :wink:

If I had three wishes I would like to see:

  • a catamaran in mini40 size
  • a depron wing with reasonable (lot of) rake and adjustable camber (I’m feeling comfortable as long as the mast isn’t straight upright or tilt forwards)
  • a mast-aft-wing-sail used as a jib with (self-) adjustable camber (your wing isn’t luffing like a soft sail while a tack and a jib with adjustable camber I havn’t see until now)

When I look at your results, I have to admit you are quite close to this.

(where is that thumbs-up button?) :wink:

Hello Wolfgang,

We have a similar vision for an rc multi hull, although I would like to achieve what you have described with a boat less than 1 m. I think that the self adjusting camber mast aft wing should be easily achievable using the method you described earlier in this thread. Now that I’m confident that this type of sail will produce a cat less prone to pitch poling I’m planning to build a better wing, and I will test your idea on it.

I’ve also been thinking about foiling, and even I tried a basic system on this boat with a conventional wing, but I haven’t yet had any success. I would like to come up with a simple approach. Hydroptere’s foiling cat with retractable foils is a bit too complex for me, and I would prefer not to use the fixed angled daggerboard approach. I’m thinking about starting with skimming rather than foiling, perhaps using very short acute L foils.

According to Aardvarkissues foiling won’t occur below 4 knots, I’m not sure that I can achieve this with a sub 1 m boat. I need to measure the speed the boat can currently do to see how close it is.

Something interesting I forgot to mention. The boat righted itself twice. Unfortunately I didn’t actually see what happened. It might just have been a consequence of the strong wind, but I wonder if the extreme rake and the buoyancy of the sail at the rear of the boat kept enough sail out of the water to catch the wind?


(Just in case people are wondering what you are referring to I should point out that I removed the long intro with me without shoes from the clip. I live in hope that one day I won’t have to resort to my kayak to recover the boat, and consequently never have appropriate footwear. Unfortunately I can’t simply wade to recover my boat.)

Considering the comments above regarding a simple retractable foiling system the following approach occurred to me:


Clearly it would need a very powerful servo. Any thoughts as to whether it is possible?

… standing torque, stall torque, self locking gears…
a drum winch with an endless sheet comes into my mind

but I don’t know how much travel is needed.

as an arm servo option: try a look at servos for the steering of rc-buggies (shockabsorber might be usefull)
but those are hungry big block servos with some overweight.

I’ve started with a small but reasonably strong arm servo (ca. 15kg):


I plan to test it without angled foils first to see if the servo is strong enough.

Some footage of on-water testing in a light breeze:


Both the self-adjusting camber on the wing, and the retractable dagger board system need minor adjustments but worked quite well. The boat drifted a bit and had too much weather helm, but both should be easily resolved by adjusting the size and position of the dagger boards, and the position and shape of the sail.

Now I need to make some foils.

To begin with I’ve made a simple foil from polycarbonate. This won’t be light or strong enough for the long term, but it is easy to shape and bend which makes it ideal for testing different shapes and profiles. The foil isn’t very long, so even if it works the boat will probably only skim the water rather than foil properly.

The clip below shows the new foil (only on one side to begin with), and how it can be rotated into and out of the water. It also shows the self adjusting camber on the wing sail, as suggested by Wolfgang.


Love the self adjusting Camber, maybe a little more L section and you will be off and foiling.

Jim: Wolfgang can take the credit for the self-adjusting camber idea. When you say more L-section, do you mean that it is currently too much of a U-shape? Which of the two bends would you suggest that I adjust?

Has anyone come across any information regarding the profiles of the foils being used on the AC72s? I’ve struggled to find any descriptions of what is being used.

What they use won’t matter to us, Reynolds Numbers. NACA 0009 air foil is what most foilers are recommending although I am going to start with an 0010 because I am going to use the Bradford height adjuster and tilt the foil instead a flap and it has a higher stall angle.

Air foils here[maxCamber]=0&m[sort]=5&MAirfoilSearchForm[textSearch]=0010&MAirfoilSearchForm[maxThickness]=&MAirfoilSearchForm[minThickness]=&MAirfoilSearchForm[maxCamber]=0&MAirfoilSearchForm[minCamber]=&MAirfoilSearchForm[grp]=&MAirfoilSearchForm[sort]=5&yt0=Search

Just type in the foil you want in the search text section, I get a virus warning when I click on the detail section to the right of a foil, so be careful.

Thanks Jim. What shape foil are you planning to use and will you vary the profile in different sections?

I will build T foils and will not vary the profile, at least to start.
Foam foils here

I will cover in F/G for a plug and make molds.