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Old 04-23-2013
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Re: Bob Perry's take on Wolfenzee's dream boat

Quote:
Originally Posted by Brent Swain View Post
Most of these twin keelers would be a nightmare to cruise in. An anchor rode wrapped around the trailing edges of these keels would be impossible to unfoul, especially on a lee shore in the night. I originaly had that problem until I made some modifications. With such a tiny attachement to the hull, getting it structurally adequate would be almost impossible. A hull speed imact on one would drive the trailing edge of it up into the hull.
An angle of 15 degrees only helps a lot at angles less than 15 degrees. A 25 degree angle gives you much more leeway reduction, and reduces the interaction between the two keels, of water being forced between them.
Any keel breaking the surface is extremely noisy; slams and pounds, and as soon as it starts to break the surface, it's drag increases drastically. Excessive beam drastically reduces ones untlimate stability. Boats capsizing and staying capsized was never a problem, until beam was drastically increased.
Brent, I don't pretend to know that much but some of those boats are designed by some of the best NA around. They utilize CFD to study the hulls keels and rudders and I am sure that they are like that because it is the way they work better.

Regarding the canting of the keel what is the point to have a 25º angle on a boat that sails with 15/17º of heel? it seems to me that the better efficiency would be obtained with a vertical foil in what regards sailing heel.

Regarding the keels having a small attachment you are probably imagining that each one is fixed to the hull. In the RM case (and in many other boats with skinny keels) they are both connected to the same steel structure inside the boat that distributes the efforts by the hull.

Regarding beamy hulls reducing ultimate stability I don't know what you mean. That depends basically to how lower is the CG and normally those boats have considerable drafts a god B/D and bulbed keels. That gives them a good AVS and a very good reserve stability at 90º.

Yes, when inverted they have a big inverted stability but again how easily they return to its feet depends on the CG. It is convenient not to forgot that to the big inverted stability corresponds a much bigger positive stability, much bigger than in a narrow boat. In the end, besides a good AVS and a good reserve stability what is important is the proportion between the positive and inverted stability (a much bigger positive stability).

Regarding that thing about the anchor being wrapped about the keel, those boats are popular in France, there are hundreds of them and I never heard complaints about that neither anybody referring that as a problem with that kind of keels.

Regards

Paulo
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