Wing Keel - how does it work?

[Daveinet]

I've read many discussions on Wing Keel vs fin keel. Most of those discussions deal with how the boat acts, comparing one to the other, but no one talks about how a wing keel works.

I understand that with a wing keel, there is lift, that makes sense for down wind, as the boat should displace less water and should go faster - all well and logical. What I have difficulty understanding is what happens on a beam reach as the boat heels? You have a keel which by its shear weight is supposed to reduce how far the boat heels, but then you have a wing that is lifting on the keel. It seems to me that lift when heeled over would be counter productive. That's the part I don't quite get.

In context, I was thinking about what would happen if one added a pivoting wing to a boat with a center board. When the centerboard was down, the wing would function normal. As the centerboard is cranked up, the wing would pivot - staying horizontal and pretty much be neutral in its function - or atleast would not drag, so you could motor in to shore with the centerboard up.

Just trying to understand the advantage of the wing, and if it has value in other types of keel setups.

[deniseO30]

I'm no expert on this but I think the "wing" is just the way of getting enough mass to make up for the shortness of the keel and giving it less turbulence in the water. I don't think it has "lift" in the sense of wings on planes, but again.. I don't really know

[nickmerc]

I believe the wing portion of the keel "adds length" when heeled over. The wing that extends horizontally when not heeled. As you heel the wingtip actually goes deeper in the water.

Now, this may not work really well for the stubby wing keels, but this was the intent of the design.
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1LovelyKiss

[Faster]

I think there are a couple of things at play here.. hopefully Jeff H will weigh in with the definitive answer!

Center of gravity is lowered with a heavier mass deeper in the keel - this is nothing new, and a lot of keels in early years had a thicker section down low than at the root in a similar attempt to lower CG and hence addding righting moment. Another leading example of this idea was the Scheel Keel that was offered as a shoal draft option prior to the 'wing' trend. Our 1963 Shark had an "anvil shaped" keel that accomplished a similar goal. Stars and Cal 20s had bulb keels years ago too...

The 'wing' came into popularity after the Aussies took the AC from the US, when Ben Lexcan designed the 12 meter around a winged keel concept - in theory the wings add an 'end plate' that minimized keel tip vortex losses - blocking the high-to-low pressure path across the keel tip and increasing overall efficiency. The idea is similar in the winglets you see on airliners' wing tips today.

In practical terms, I think the wing keel has gained favour partly due to the initial 'trend', but mostly from the ability to offer shallow draft and a less compromised CG in the same package.

One of the knocks on the idea is that, once aground a conventional keel can be 'heeled off' whereas a wing keel actually gets deeper with heel as mentioned previously... in this case that's not a good thing... Of course the idea is not to run aground in the first place!

[seabreeze_97]

As I understand it, the wing is essentially producing lift, but in the opposite direction. It reduces lift-induced drag by acting as a winglet on the foil. This improves the aspect ratio. The inverted lift provides additional stability. When heeled, the same properties actually make the boat point better upwind. They usually suffer downwind due to greater surface area wetted surface drag. It does reduce draft.

[southshoreS24]

from a pro seaward site:Straight Talk about Seaward

The wings aft accomplish several things; 1.) They force laminar flow over the main keel section. 2.) They become miniature keels as the boat heels. 3.) They act as skegs (like feathers on an arrow) contributing to excellent directional stability They do not interfere with trailering at all.

while i do own a seaward, mine does not have the winged keel, and this sit is very skewed in opinion towards seawards. I love mine and find it a great boat for my uses.

[Omatako]

I don't know what winged keels do for boat specifically so this is just my uneducated take . . .

On race cars they have foils on the rear to produce down-force but this only becomes effective when the car reaches about 150 mph. On a passenger car at 70 mph, it's just additional weight.

On sailboats . . . . . I suspect it's pretty much the same.

[nickmerc]

The winged keel is not for adding downforce to a boat. No point in lowering the waterline as you go faster. I would buy the reduction in tip vortices but I am not sure how much of a return you would get at 5 kts.

On street cars the wing on the trunk is a spoiler to spoil the lift as cars go faster. It helps to keep the rear wheels on the ground. It is also for looks. Some of the street racing cars do have wings that produce downforce and at high enough speeds they do work. Those speeds are not legal in the US.
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Glass weed pipe

[Faster]

Originally Posted by nickmerc

The winged keel ...... I would buy the reduction in tip vortices but I am not sure how much of a return you would get at 5 kts.

That's probably true.. this was the touted theory at time of the 'breakthrough', but of course the entire Australian 12 was designed around it (the keel idea) and it had a lot of other advantageous features as a result.

In reality, I think it's a trendy way to get the ballast low.. if wings really worked I doubt we'd be seeing the proliferation of narrow corded deep bulb keels on the various new (non-canting) high performance boats out there now from Farr and others. In any event any "wing related" gain is probably only recognizable at a very high level of racing.

[deniseO30]

don't see how tons of lead or iron could do anything like hydrofoils do! and yes, some wing keels look like they were styled after hydrofoils

this is not in anyway to be confused with wing keels
HydroSail