Winged rudders

Home Design Build Race Links Reports Other Topics


I photographed Ken Coles' winged rudder on an IOM some time ago, a simple delta shape at the base of the rudder.  It didn't seem to do very much, but Ken said it helped prevent nose-diving on the run when over-pressed.

The idea has taken off in full-size sailing, in the International Moth and the International 14 classes in particular.  Apparently the winged rudder does indeed help prevent nose-diving.  Thing is, in these classes the crew are all over the boat keeping it pretty level, so the wings can work exactly as required.  For the IOM or RM, the usefulness of the wings is reduced on the beat, and it is likely they add considerable drag.  Ken is more optimistic:

Winglets may reduce Induced drag, and make the keel more efficient - perhaps allowing a smaller rudder and hence reducing the drag from that source.  Some relevant Web sites include hanleyinnovations.com/sailaero, vacantisw.com/foildesign, and simarnet.com/yacht-keels.

The ideal angle of incidence of the wings is a question that isn't easy to answer.  My first guess is that something around -1 or -2 degrees is needed, and that this would be a problem for a wide-beamed boat, because the drag would be too serious as it trimmed bows-down, adding to the angle of attack.  So it would be a narrow-beamed hull that would have most chance to benefit.  Then, you'd really want to be able to adjust the incidence with a third servo, so the RM or 10R class would be the best bet.

These two shots are of the rudders on an RC "40" class catamaran.  Top surface of the wing is flat, while the bottom surface has a curved, aerofoil section.

The other effect on the beat is that the boat would most likely not be able to point so well.  That is, it would have lee helm.  This would be a bad idea, until the wind got up so much that you were developing serious weather helm -- and then the wings would help, counteracting that.  So if you insisted on sailing with your "A" rig when you really should be in "B", a winged rudder might be just the ticket.

Here is Eric Arndt's winged rudder on his Marblehead.  Looks really neat.  E-mail him at "Ericarndt@aol.com" if you'd like to know more.  He tells me the results are "sensational".

Brett McCormack has sent me some comments on winged rudders:

I've tried winged rudders on IOM, on a Highlander hull and also on a Bantock Rythym which was notorious for diving,  It completely transformed the Rythym, so it was able to carry top suit much longer than before. The foil used was 40mm across, 20mm wide and 4mm thick, a symetrical section set at 0 degrees.

I have used rudder foils on International moths for some years (it is common practice in the class) hence the reason to try them on models. The reason they are not used more in full size is that most yachts carry spinakers which you can use to keep the bow up, but this is not so on a model or Moth.  I believe that narrow hulls will benefit more than wider ones.  But, like I said, I have done no formal research.

Gordon Price has sent me some comments on winged rudders as well:

I noted the bit on winged rudders. International 14s use them when going up wind to lift the stern significantly up out the water and cant the boat forward much like a TS2 does when it heels. I believe the 14 boys are trying to reduce wetted area and keep the rig upright rather than suffer the rake back you get due to the windage drag when going up wind. They may also be using it to control weather helm like the TS2 - as you move the rig forward and fin back by lifting the stern. The international 14 implementation is variable by the crew and they no doubt use it the other way when going downwind. For a IOM a deep light rudder with a small heavy wing at the bottom (75 gm all up!) would be an interesting experiment. A removable one would be the way to go to evaluate the concept.

2008-12-08


2011 Lester Gilbert