keel winglets

[Red Horse]

Hi folks,
I have recently purchased a Cross 38. I was talking to Jeff Turner about his fathers boat Thesis and he mentioned she had winglets on her minikeel and rudder. Does any one have knowledge of this type of mod? Jeff mentioned it added about 10 points to her pointing ability.
Thanks
Red Horse

[Alan Wheeler]

What do you mean by "points"? do you mean degrees??
I am not sure how it would add that much if it is degrees. The reason winglets are used on some racing keels is for reducing or stopping the vortex that spirals off the bottom of the keel. The vortex creates drag and reduces lift. So if the reduction of both of those adds to the ability to point higher, then yes you can. Pointing a further 10deg is a massive gain that I really doubt a winglet would provide. But then, I am no boat designer, so.....

[svquest2]

I don't believe it. Pointing ability refers to the angle of the relative wind on the sails when sailing to windward, and any modification to the keel or rudder would be to reduce the angle of leeway and that's not the same thing. There have been many mods to the keel that actually do that like having articulating rudders at the fwd and aft edges of the keel, the triangular athwart-ship cross section keel such that the windward side of the keel when heeled produces a greater airfoil curve in the horizontal plane than the leeward side, and the winglets which increase your draft when heeled and because of a greater airfoil shape on the bottom of the wings, they are supposed to give the boat a little lift to windward which in actuality reduces slip or leeway.

Any of these modifications to the keel would reduce leeway by there design but because of their increased frontal area resistance,and increased wetted surface resistance would slow the boat slightly which would cause a corresponding increase in the leeway. So I don't think there is any gain, and if I am wrong it would be measured in fractions of a degree and certainly not 10 points.

If the winglets in question were added as aftermarket add ons, then the increase in draft and ballast would make the boat stand straighter, and that would have a definite affect on pointing ability, but 10 points is still excessive.

[catty]

Originally Posted by Red Horse

Hi folks,
I have recently purchased a Cross 38. I was talking to Jeff Turner about his fathers boat Thesis and he mentioned she had wing-lets on her minikeel and rudder. Does any one have knowledge of this type of mod? Jeff mentioned it added about 10 points to her pointing ability.
Thanks
Red Horse

Because the mini keel is such a low aspect foil some add an end-plate to increase its efficiency. I would suspect that wing-lets would not be as effective plus possibly more prone to damage.

[Red Horse]

Sorry, I meant degrees. I will query Jeff and see if its possible to elicit some more info about the winglets. Maybe I can find out who designed them. I have a friend with a stretched Crowther 33 who couldn't out point Thesis when following him into the harbor once. The owner of the Crowther is very race oriented. Of course we may be comparing apples to oranges.
Red Horse

[Alan Wheeler]

I guess the question of pointing would depend on what degree does the boat pint now. If was say 60 and now can point to 50, then yes quite possible. Even say 40 to 30 is a do'er. But 30 to 20 is asking a bit much.

some add an end-plate to increase its efficiency.

I imagine the winglets are some form of an end plate. Either would do the same thing for making the keel more efficient.
I remember one (or was it more) Americas cup year, some teams used winged keels. The idea was two fold. To stop the vortex and to also add vertical lift to the boat. The idea was that as the boat tacked, the wings lifted the boat up out of the water slightly and made a point of effort that the boat wanted to turn on. But I don't think that part worked so well. I think I can remember they had issues in one of the legs. Either upwind or down wind, can't remember which. But it upset the balance of the boat to the point of not being an advantage.

[Red Horse]

I think what Jeff meant was a 10 degree total in increased pointing ability. As for the other issues mentioned as we say in aerospace every thing is a trade off. Jeff took a few pictures when Thesis was out for survey I'll ask him to post them to me and put them on the forum if I can ever figure out how to post photos.
Red Horse

[sandy daugherty]

A PDQ 34 I knew had inward turning plates on its minikeels. With the trade-off to wetted surface drag, it didn't seem to make a lot of difference. I read somewhere that a sharp 90 degree edge at the bottom of the keel had some stop-plate effect in tank testing, but I have no authority to cite.

[David M]

If it was a wonderful idea then more modern custom built racers would have it, and they don't. What you do see in modern racers are a lot of very deep, high aspect ratio bulb keels which adds to the boats righting moment and provide more efficient lift.

[fastcat435]

We have investigated the idea of adding small winglets to the bottom of the keels and in upwind conditions the performance would increase slightly and the pointing would improve with 1 to 2 degrees but in all other conditions the extra drag created lowered the speed , the vortices or whirlwinds are small , so small that the possible advantage is just not worth it.
My 2 cents worth
Greetings
Gideon

[David M]

I agree Gideon, it is probably best just to keep it simple. Otherwise it is yet one more thing to break or to start worrying about.

[fastcat435]

Originally Posted by David M

I agree Gideon, it is probably best just to keep it simple. Otherwise it is yet one more thing to break or to start worrying about.

Hallo David That is always our principle unless we get very good speed or weight gains from it , there has to be a real advantage to go a complicated route otherwise KISS.
It is hard enough to keep a yacht going without any extra burdens , the od thing is ( I have found out the hard way ) things always break when far away from civilization you are the one that has to fix it nobody else can do that for you.
Greetings

Gideon

[David M]

Yes, thats kind of the thing about it. If you are out in the middle of nowhere and something breaks, regardless of how much money you have to pay someone else to do it, if you are the only one available, then guess who gets to fix it?

[fastcat435]

Let me guess You or in my case Me

Greetings and have a good day

Gideon