reefing a rigid wing sail

Wings on Moths need more development - particularly in figuring out how to make them fast off the wind where their "groove" is narrower.

Part of it is that ideally with a wing you would build a custom new hull - one that is lighter and configured potentially differently as to where the CoE and CLR are but that's not been an investment anyone's been willing to make yet given the continuing evolution of the in-water foils

 

I am not current on the rules for moths but I recall there was some controversy with early wing sails being ruled illegal. Are there rule conflicts with common 2 element wings?

About off wind and narrow groove, a well designed and controlled slot can make a 2 element wing that will not stall until a much greater angle of attack and camber. Aircraft make great use of this for landing but it is harder for a symmetric tacking wing. Can you tell me what a common range of apparent wind angles would be downwind?

About COE and CLR -My thought is that the mast step would be moved on an old boat until the wing performance is proven.

 

I was following Bora's wing effort closely at the time.

Even before they outlawed the gap, the wing surprised me in lack of any "moments of greatness". As something of a wingnut, I had high hopes and was somewhat disappointed.

I have come to be suspicious of a number of things:

• Wing trimming. The wing does not provide as much trim feedback as a soft rig and as a singlehander, the sailor has too many other demands to allow him to focus on the wing.

• Wing compromises between power and drag. In a wing, there is a tradeoff in the stuff needed to provide for power and the stuff you want for low drag.

• Wing compromises between simple and performance in all conditions. In bigger wings, complexity (twist) is valuable, but extra complexity in a moth wing is a no-go for now.

 

Well from the interviews that Charlie gave after Belmont the issues were in part the trim particularly offwind, and in part the lack of a gap, and in part the fact that the platform and the wing didn't quite mesh 100% together

By all accounts the drag/power tradeoffs worked just fine with same speed same height in lighter, but much better speed (less drag) when the breeze was up.

But I think your point about complexity in the boat - particularly a moth, is part of what is keeping folks from investing in this. Right now the foils are still a very fertile area for development and hence there is no need for the higher risk, lower reward design cycle of the wings

 

Low Performance

Not sure about lower performance. It's more about controllability. If you look at the wing of Saildrone and the wing of Greenbird they are very similar. Designed by the same guy. Check out Greenbirds speed record of 126mph on YouTube. Quite impressive and certainly not lower performance!

 

Harborwing have developed a two-element wingsail with tail that can rotate 360 deg. They also found it was necessary to split the wing into an upper and lower half that could rotate independently so as to alleviate the effects of wind shear. I haven't sailed on their X2 prototype (a modified Condor 50), but I have been onboard. Here are my pictures of it.

Being able to rotate 360 deg means you need to have a fixed mast stub that can take the heeling moment in bending. Upper and lower bearings allow the wingsail to rotate around the stub. Electrical power and signals can be transmitted between the stub and wingsail via slip rings. Mechanical control can be transmitted via pushrod at the center of rotation with bearings at each end of the pushrod that allow the wingsail to rotate relative to the pushrod, too. A rotary cam would also allow control to be phased with regard to the orientation of the hull.

Personally, I like the idea of a cantilevered wingsail with mechanical control of aerodynamic tails because I think the mechanical control is more reliable in a marine environment. Electromechanical or hydraulic control could be used to boost the mechanical control for better performance while still being fail-safe with regard to the powered boost and fail-operate with regard to the ability to still sail with just the mechanical controls.