Winged Keels

[CptCrunchie]

My next question is one I have been mulling over for the past 2 months. The boat we are looking at has a HUGE winged keel. This would be my first experience with one.





I spent last night reading the winged keel thread on SailingAnarchy.com. Oh my! Those guys cremated a number of my very best grey-matter cells. Wow! But while there were a few who sail with one, most were steeped in a highly technical debate. I read about the pressure dynamics, and about how those dynamics differ from the convention. I've seen all the various designs of them, and read opinions galore about which one would do better ...as compared to others of similar design.

I understand the comments about the issues of grounding a winged keel, that it could be major undertaking if stuck a mud bottom. And while I understand that could happen, I'm of the viewpoint that sailing or motoring into a mud bottom has more to do with seamanship than 'it's eventually going to happen'.

I also read all about Australia II, and how the Morgan, Catalina and other boat manufacturers jumped on that band wagon.

But in all my reading, I still have one question: What does it do when underway in various sea states?

Please understanding that I am not a yacht designer, nor do I have any experience with winged keels beyond reading about them. Please keep that in mind.

Here's my thoughts:

The old line that 'Waterline Rules', as in, the longer your waterline, the longer the wave you can sit in, the faster you can go. To me, a winged keel would hold - and possibly lower - the boat into the water, thereby increasing/maintaining a longer waterline. That would mean the boat would actually become slightly faster. Thoughts?

Then there's what happens heading into big seas. My thinking is that the wing would hold the bow up over the crest, and only once the keel neared the crest would the bow come down. Then, once that happened, the wing would hold the bow down to push it through the next crest .....versus the bow riding over it.

Anyone have experience with winged keels?

[sandy stone]

Wing keels were essentially an advertising gimmick, to make buyers think they could get upwind performance equivalent to a deep keel, with a shoal draft keel. After all, wasn't there one on an America's Cup boat? Well, the wing keel on Australia 2 was an entirely different animal (look at the angle on the wings). You might ask yourself why essentially no boats are built with them any more, if they were such a great development.
About the only benefit of a wing keel is getting more of the weight lower down, adding some stability. However, you can accomplish the same thing with a bulb, without adding all that extra wetted surface. You still have the unfavorable low aspect-ratio keel shape, unfortunately, meaning that upwind performance is still lacking compared to a deep keel.
As a part-time racer, my experience is that in general wing keels leave a lot to be desired for upwind sailing, due to the combination of low aspect ratio and high wetted surface. This may or may not be important to you. Actually, I'm a little surprised you found a shoal keel boat in the PNW, because I don't think there is any need for one. Shoal keels are usually what you find on the East and Gulf coasts where there is plenty of shallow water. Personally I think you would be a lot better served with a normal deep keel where the water is deeper, but at least you shouldn't have to worry as much about burying a wing keel in a mud bank.
And as far as dynamics in waves, I don't think most of us would ever notice the difference.

[billknny]

A "wing" on the bottom of a keel does nothing for the waterline. What it does do is make the boat "think" it has a deeper keel than it actually does.

Here is the simple (simplistic?) explaination:

You have seen airplanes with the vertical "winglets" out at the end of the wing? If you think about how a wing works in very simple terms, there is low pressure on top of the wing sucking the plane up, and high pressure on the bottom, pushing up. If the wing just stops at the end, the high pressure "leaks" around the end and raises the pressure on the top. Enough so the last few feet of wing really generate little or no lift, but still creatte drag, slowing the plane down and using more fuel. Put a vertical barrier there, and presto! You stop the "leaking" and the plane flies as if the wings were longer, but with very little extra drag.

Same with a keel. On the windward side the pressure is lower, sucking the boat up wind, and higher pressure on the leeward side pushes the boat upwind. Adding a wing reduces the "leakage" around the bottom of the keel. In the case of a keel, the extra weight down low also helps stabiity. The wings increase the efficiency of the bottom third of the keel, and the boat sails as if the keel was longer, all other things being equal (which they never are!)

Wings are not a perfect addition to a keel. They help in some ways, and hurt in others. They are mechanically more fragile. The idea of them "anchoring" the boat in mud is a fanciful and not very realistic meme, but they certainly can cause problems if you go to ground on a rough and rocky bottom by getting wedged in between rocks.

Of course you COULD have a keel 2 or 3 feet deeper and get the same performance back, and be more likely to run aground...

As for their usefulness or not on a cruising boat, I'd not make a selection based on that one feature. I can not imagine that being the ONE thing that drives the final purchase decision.

[B23iL23]

Another advantage is that they get the most weight down as low as possible. It allows you to have (on a cruising boat) a shorter keel, but still have a stiff boat.

[Compass790]

About 20 years ago I built a winged keel for our 30ft yacht or sailboat in American. The reason for this was to reduce the draft from 6ft to 4'6". It practically steered itself after the change & was a rocketship downwind as it would get a lift from the keels when surfing largeish waves. It was slower upwind but it was a crude design with the original bulb halves bolted on top of steel plates.
I did briefly consult a Team New Zealand keel designer about it & he said it would be slower but if my main aim was a cheap draft reduction it was ok to do.
The drawback was when you ran aground which we occasionally do by anchoring too shallow you couldnt heel the boat to get it off the bottom as that would increase draft.
I wouldn't hesitate to buy another winged keel boat.

[thomm225]

Today at the boatyard I actually saw a guy cutting the wings off his keel. I'm not sure what his plans are. Maybe he plans to lengthen it.

[a64pilot]

At the speeds most cruising boats are able to maintain, its likely that a wing keel doesn’t do a whole lot.
I was under the impression that the advantage lay in shoal draft.
I’m also under the impression that nothing can truly replace a deep keel for upwind work, but I for one am not willing to live with the draft.

[sandy stone]

Originally Posted by billknny

You have seen airplanes with the vertical "winglets" out at the end of the wing? If you think about how a wing works in very simple terms, there is low pressure on top of the wing sucking the plane up, and high pressure on the bottom, pushing up. If the wing just stops at the end, the high pressure "leaks" around the end and raises the pressure on the top. Enough so the last few feet of wing really generate little or no lift, but still creatte drag, slowing the plane down and using more fuel. Put a vertical barrier there, and presto! You stop the "leaking" and the plane flies as if the wings were longer, but with very little extra drag.

Same with a keel. On the windward side the pressure is lower, sucking the boat up wind, and higher pressure on the leeward side pushes the boat upwind. Adding a wing reduces the "leakage" around the bottom of the keel. In the case of a keel, the extra weight down low also helps stabiity. The wings increase the efficiency of the bottom third of the keel, and the boat sails as if the keel was longer, all other things being equal (which they never are!)

I'm not an aeronautical engineer, but I think the purpose of winglets on airplanes is to reduce the vortex created at the wingtip that increases parasitic drag. I don't think they actually increase lift.

I still maintain that given two otherwise identical boats, one with a deep keel and one with a wing keel, the wing keel boat will be left behind going upwind. To some people (such as myself) this may indeed be an important part of the purchase decision.

[Adelie]

Winged keels started out as a means of improving racing boat performance on the order of 1-2%.

There was then a flurry of consumer boats for about a decade that had them then they went back to being a racing feature.

The wing above probably it symmetrical with no angle of incidence so no lift. The intent of the wing is to control vortices creation at the end of the keel which reduces drag. It also lowers the center of mass of the ballast so the boat can be stiffer for the same draft and mass or if can be the same stiffness for the same mass but decreased draft.

Any lift that the wing generates will be at the expense of drag.

For general sailing the functional problems with winged keels have outweighed the speed benefits.

The effects are pretty minor and wouldn’t dissuade me from getting a particular boat if I liked it for other reasons.

[CptCrunchie]

Thanks all. Good info.

The winged keel isn't a deal breaker, nor was I looking for one. Since I have no experience with them, I just wanted to know how the wings effect performance in bigger seas. Since I am in no hurry, and from what you have posted, this particular boat with its winged keel should do what we want it to do.

Billknny, interestingly, I had a friend over last night who flies a sailplane. He made reference to the winglets on all the newer commercial liners, and how they remove the vortex off the ends the wings, removing a considerable amount of drag. Then he suggested I read upon dihedral, polyhedral and anhedral wings. This really helped me understand a little more of what the guys on SailingAnarchy were on about.

All that said, I will say, the framework under the salon sole is .....extensive, so much so that the battery banks are crammed in around the bracing. And someone appears to have coated the top of the keel (where the keel bolts enter the keel) with what looks like auto-undercoat. It doesn't look like it was done to cover something up, but more to protect the integrity of where the bolts enter the keel.

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[a64pilot]

Winglets on an aircraft only really have an effect at very high angles of attack, approaching a stall condition.
Believe it or not but an airliner at cruise altitude and speed is at a high angle of attack and they aren’t all that far away from a stall.

However I find it hard to believe that a sailboat keel is ever anywhere near a stall angle of attack, so therefore I’d be surprised if the purpose of a winged keel is to decrease drag by reducing keel tip vortices.

I was under the impression that they produced lift in a racing boat, and that they were more of an affectation of style on a cruising boat, sort of like the fins on 1960’s US autos.

[billknny]

Originally Posted by a64pilot

However I find it hard to believe that a sailboat keel is ever anywhere near a stall angle of attack, so therefore I’d be surprised if the purpose of a winged keel is to decrease drag by reducing keel tip vortices.

Don't forget, the tip vortex is the RESULT of the "leakage" of pressure gradient around the end of the foil. Eliminating the vortex most certainly can improve lift, even when not close to stall.

You might not believe it, but sailboat keels DO stall. How close to stall a keel runs depends a lot on the keel shape, no surprise there! Shorter, wider keels most certainly DO stall when the boat points too high--sometimes long before the sails luff.

And shorter, wider keels are most often found on... cruising boats which is why keel wings haven't yet faded away like so many other bad racing design ideas.

On very narrow, very high aspect keels like modern ocean racers, you do not see wings, because they do not help much. You just have the torpedo bulb, an even less practical design!

The reason wings on keels were such a dramatic success on the AC boat when first used was the keel length was limited by the rules. Adding the wings made a dramatic difference in the lift generated with the same length keel. We can argue all day about if the drag was reduced or the lift was increased, but certainly the lift/drag ratio was improved!

[Kenomac]

OP,

Our Hunter 450 had a winged keel that looked just like your photo. The boat was terrible sailing upwind.

[daletournier]

The wing keeled version of my boat needs 300kg more lead to obtain the same stability as the deeper fin keeled version which I have.

[a64pilot]

Originally Posted by billknny

Don't forget, the tip vortex is the RESULT of the "leakage" of pressure gradient around the end of the foil. Eliminating the vortex most certainly can improve lift, even when not close to stall.

They really do not, they are a fashion statement on most GA aircraft and boost sales because they look cool, but they serve no function. Their don’t increase lift, that isn’t their function, their function is to reduce drag, which at lower angles of attack they due to skin friction, actually slightly actually increase drag, it’s only at high angles that they function.
https://en.m.wikipedia.org/wiki/Wingtip_device

I suspect a winged keel on a cruising boat falls into the same category, looks cool and was put there by marketing.

I’m not saying it hurts, my bet is you couldn’t measure any difference whether they are there or not