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Old 02-02-2012
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Twin Keel is it an advantage?

Most of us think about twin keel as an advantage to moor in low tides scenarios. In the market there very interesting twin keel available, and my question is how these boats perform in severe weather, comparing with fin keels?

When the boat heels there is one of the keels that is further down than the other. Does the opposite one which is upwards helps to trim the boat to help the boat navigate more comfortable?
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Old 02-02-2012
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Quote:
Originally Posted by APP Mode View Post
Most of us think about twin keel as an advantage to moor in low tides scenarios. In the market there very interesting twin keel available, and my question is how these boats perform in severe weather, comparing with fin keels?

When the boat heels there is one of the keels that is further down than the other. Does the opposite one which is upwards helps to trim the boat to help the boat navigate more comfortable?
My first boat was a British bilge keeler called a Vivacity 20. It was far from fast but it was as stiff as a church. I had no basis for comparison until I went out on a Cal 20 - I couldn't believe how tender it felt compared to my twin fin.

I guess they act a little bit like the modern canting keels - as the boat heels, it is trying to lift the weather keel (and 1/2 the ballast) up and out of the water. Also, if the twin keels are canted somewhat, say 15 degrees, as the boat heels, the leeward keel becomes more vertical and theoretically should resist leeway better than a single centerline keel.

I've long wished a good designer like Mr. P would do his magic on this concept to see where it could go re: performance. There are a number of potential advantages but the increased wetted surface always seems to put people off the idea. They are popular in Europe because they can dry out without legs but the concept is usually seen on pretty tubby boats, not on anything with any performance illusions.
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Old 02-02-2012
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I have a Westerly Centaur bilge keel. Will lay over quick to a point and try to round up with some weather helm. If the wind stays constant she'll balance out and start humming but that 20+
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Old 02-02-2012
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Quote:
Originally Posted by SloopJonB View Post
...The concept is usually seen on pretty tubby boats, not on anything with any performance illusions...
Just answered your own question.
If you want to see what's fast and what works, look into race boats.
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Here's a link discussing twin/bilge keels..

Twin-Keeler Newsletter: The ultimate Twin-Keel advantage list

It seems there are some still being made in France - Wrighton Yachts | Builder of the Bi-loups, customizable twin-keel boats.

Agree with JSB.. it would be nice to see someone (designer) tackle this from a performance perspective. To some extent the twin daggerboard/canting keel designs in ocean racing are working on this principle as the canted keel has little leeway resistance on it's own - but the righting moment is not provided/nor required by the boards so it's not quite the same thing.
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Quote:
Originally Posted by zz4gta View Post
Just answered your own question.
If you want to see what's fast and what works, look into race boats.
Actually, it's more complicated than that. It has primarily been used for it's grounding ability which is why it's generally seen on tubby little cruisers. As far as I know, no-one has ever spent any time designing one from a performance perspective. There are some potential advantages that have never, to my knowledge, been investigated or experimented with.

I'm not talking about top level race winning performance here but I think their performance could very possibly be improved a bunch while retaining their existing virtues. For example, it might be possible to improve their performance along the lines of the twin bilge-board, canting keel boats, albeit to a lower level, but without the expense, incredible complexity and need for big, highly skilled crews. I think something better than the current crop of shoal, winged keels seems within the realm of possibility if a good designer pursued it.
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Old 02-03-2012
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Sloop, the reason top level race programs don't pursue a daul keel shape is b/c it's not fast. Programs don't spend millions of dollars trying to put lipstick on a pig.

There's nothing wrong with two keels, different way to skin a cat, but it's hardly the most efficient. It's a fine design if you're looking for something you can beach and let the tide run out, but there are better ways to do everything else. Like sail.
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Old 02-03-2012
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Quote:
Originally Posted by SloopJonB View Post
Actually, it's more complicated than that. It has primarily been used for it's grounding ability which is why it's generally seen on tubby little cruisers. As far as I know, no-one has ever spent any time designing one from a performance perspective. There are some potential advantages that have never, to my knowledge, been investigated or experimented with.
Actually they have RM YACHTS | Accueil
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Quote:
Originally Posted by zz4gta View Post
Sloop, the reason top level race programs don't pursue a daul keel shape is b/c it's not fast. Programs don't spend millions of dollars trying to put lipstick on a pig.

There's nothing wrong with two keels, different way to skin a cat, but it's hardly the most efficient. It's a fine design if you're looking for something you can beach and let the tide run out, but there are better ways to do everything else. Like sail.
I'm actually quite aware of that - I've owned both a twin fin and a world championship level 1/4 tonner. My point was as follows (condensed);

Quote:
I'm not talking about top level race winning performance here but I think their performance could very possibly be improved a bunch while retaining their existing virtues. I think something better than the current crop of shoal, winged keels seems within the realm of possibility if a good designer pursued it.
My thinking was more along the lines of improving boats like the current crop of Hunter's, Catalina's and the like with their short winged keels. Their windward performance is pretty compromised, their stability is only O/K and they can't dry out. The RM that Miti posted is more what I was thinking of.

Hey, it works for rudders on extreme race boats. (I know, I know. )
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A neighbor has a Bene 323 with twin keels-didnt even know they built them until I saw his. Never been sailing on her but he is an avid proponent of the design. However I think one of his primary reasons for his liking the boat is that he's able to put it on a lift at his dock-very little bottom maintenance.
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