Fin vs bulb vs wing keels - Page 2 - SailNet Community
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post #11 of 31 Old 10-12-2012
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Re: Fin vs bulb vs wing keels

We may be on thin ice here lumping all wing keels into one category. There is no question that when you are up gainst a hard draft restrcition a wing can work quite well.
The Aussie winged keel worked well in conjunction with the upside down profile of that keel and the extra long tip chord with it's vortex problems.

When I designed the Islander 34 we did a 5.5' draft wing keel and a 7' draft straight fin. Islander built one of each as hulls 1 and 2. They were launched the same day with sails from the same sailmaker. I flew down with one of my helpers, a very good sailor, and for two days we raced these two boats against each other. The difference in speed was minimal if present at all. And, I was a skeptic to begin with. But after trading boats and sailing them upwind and down. I came away a believer. The wing keel boat was a bit slower off the wind, not much. Up wind the two boats were pretty much identical in VMG. This is not theory. This is first hand sailing experience with two identical boats.

But wings to be effective have to have aspect ratio just like fins. Short, thick stubby wings, like we have seen on many production models, are not efficient. They may do a nice job at lowering the VCG but they can be a lot of drag and be wonderful Bruce type anchors if you get stuck in the mud.

All I'm saying is to treat wings on keels on an individual basis.

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Last edited by bobperry; 10-12-2012 at 05:40 PM.
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post #12 of 31 Old 10-12-2012
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Re: Fin vs bulb vs wing keels

Every foil section is different. Some of the production wings just look wrong.
CS called the wing on my boat a hydrofoil. It is larger than any other wing I have ever seen. W/o measuring it's about 6' wide and 5' deep.
I have yet to meet another cruising boat that can out point w/ me and there has yet to be another similar boat I can't catch off the wind.
But that's my foil section. I think Tony Castro did some research.
Jim

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post #13 of 31 Old 10-13-2012
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Re: Fin vs bulb vs wing keels

As to shoal keels, fin is best for performance, and the deeper the better. You will point higher and track better. And if you race, whatever handicap you are given for another form of draft will not be enough. Don't have any experience with bulbs.
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post #14 of 31 Old 10-13-2012
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Re: Fin vs bulb vs wing keels

After I decided what boat I way buying, I chose a wing keel over the deeper fin keel model because of draft restrictions.

Does that make me a draft dodger?
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post #15 of 31 Old 10-13-2012
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Re: Fin vs bulb vs wing keels

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Originally Posted by RobGallagher View Post

Does that make me a draft dodger?
... or it just means you're a bit shallow.....
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post #16 of 31 Old 10-20-2012
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Re: Fin vs bulb vs wing keels

I view the differences between these keel designs from a number of angles:

First is the performance issue to to change in resistance. Rather than calculate actual resistance, I can look at wetted surface. It is interesting to compare the wetted surface between the wing keel version of my boat (Catalina 400) to the fin keel version.

When I crunch the numbers, I find that the wetted surface of the wing keel version is less than 4% higher than the fin keel. Granted, the resistance is probably less; however this shows how little effect the wing keel has on the overall resistance.

A rough calculation of the difference between a bulb at the same draft, with the same righting moment, I would find the difference between the bulb and the wing to be a similar 4%.

One has to wonder if the 4% difference is significant. It might be interesting to look at some of the advantages of the wing keel versus the others. A quick look at Wikipedia gives a bit of insite:


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post #17 of 31 Old 10-20-2012
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Re: Fin vs bulb vs wing keels

Now comes the interesting possibilities of a wing keel.

One aspect I find intriguing is the possibility that a wing keel is capable of increasing its leway resistance as the boat heels because its effective vertical surface area increases as it heels (as long as the wing is large enough). Neither the bulb nor the fin keel provide this benefit. Rather both the fin and bulb keels reduce their vertical surface as the boat heels. This increase in leway resistance can be quite dramatic for a wing keel designed to optimize this effect. The wing must be a resonable size. Also, as stated, the dynamic effects of water at the root of the keel.

The next aspect I find intriguing is that the wing keel is the only keel of the three that actually creates damping in the vertical direction. Furthermore, it can damp in the rising motion of the boat! This damping could be advantageous in reducing the dynamic motions of sailboats. Obviously, the hull creates damping as the hull falls, but the wing (unlike the hull) additionally provides damping as the hull rises.

The third aspect of the keels is damping to rolling. The wing keel also provides damping benefit to rolling due to its overall surface area and flow resistance at the root. The bulb keel provides no damping benefit from the bulb design, only due to the vertical area. The fin keel provides more damping benefit to rolling than the wing keel only if it is deeper.

I have a wing keel as I want shallow water capability. In the numerous times I have grounded, I have not ever needed to be pulled off, nor have I required a kedge. One interesting advantage, is that my wing keel increases draft as the boat heels (to a point). The result is that I suspect I am less likely to sail onto a shallow without my keel hitting. And when it hits, the large frontal area does not allow the wing to travel much into the shallow. These two effects, I suspect may make it less likely to get heavily grounded.

However, I appeciate the viewpoint of the wing acting as a disadvantage on a heavy grounding.

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post #18 of 31 Old 10-20-2012
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Re: Fin vs bulb vs wing keels

GTX:
Amazing, How scientific.
I do it the Neantherthal way:
I build two identical boats.
I give one a deep draft fin
I give one a shoal draft wing keel.
It's kind of hands on.
I give them identical suits of sails.
I give each boat a very competant crew.
I sail the two boats against each other for a couple of days.
I report on my findings.

Somewhere along the way I forgot to "crunch the numbers".
I was too busy sailing the boats.

But I am lucky. I have the benefit of testing these things in the real word.

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post #19 of 31 Old 10-21-2012
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Re: Fin vs bulb vs wing keels

My last post was made after a long and hard and succesful day of racing in lots of wind. I was tired and re-reading my post it now seems a bit snotty. My excuse is, I was feeling snotty. I'll work on being nicer next time.

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post #20 of 31 Old 10-21-2012
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Re: Fin vs bulb vs wing keels

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Originally Posted by bobperry View Post
My excuse is, I was feeling snotty.
Its a result of putting up with Idots all your life Bob.. In my 60s, I've delt with
many of the same.. and just the other day, I had someone at the Yacht Club Bar compairing his Full keel, Hans from the 70s to my First 42, in "race" criteria..
After about 10 minutes of his ramble, Instead of a rebutle, I just told him he was full of crap and I got up and left..
At one time, it was the chalange of the argument, Now days, dont have time for it..

sorry for the drift, now back to the origional channel..............

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