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post #7 of Old 07-14-2009
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Thumbs down A little knowledge


I think you are referring to what is called the fairbody line and it - by itself - will tell you almost nothing about a boat...

Jeff H

I have no doubt that you have the best of intentions, as well as more experience sailing than I do. I also have no doubt that you are wrong on so many points it is scary.

In my mis-spent youth I designed a couple dozen boats - power boats. The market for sailboats having bottomed out in the early 1980's. But I do know how to design a sailboat. Yacht design is a fascinating subject. A lot of things in life are a blend of different aspects of science and art, are subject to differing opinions and subject to the uninformed jumping to the wrong conclusions about what makes something tick. But none more so than boat design.

Yes, the Cape Dory 28 is a full keel. I don't know where this "A keel whose length on it bottom is 50% or less of the LOA or length of sail plan which ever is longer" came from but it is nonsense. If you want to see a real full keel ship look a couple hundred years ago - and look at the clipper ships as an intermediate stage with more lateral plane at the bow and stern than was usual for hundreds of years before. Yes the Bristol Channel Cutter and Westsail 32 are full keel boats, but they too are modified full keel boats derived from the ships/boats that preceded them. And yes the Cape Dory (and even the Southern Cross) could be said to be another modification of full keels compared to them - but full keel boats they most certainly are.

A fin keel is by definition a keel separated from the rudder. The Contessa 32 with a skeg mounted rudder is still a fin keel design. Any and all proportions of fin keel with a separate rudder is still a fin keel.

A rudder on the end of the keel - however short - is still a full keel.

As far as stability and motion comfort calculators are concerned it is widely acknowledged that they are to be taken with a grain of salt. I do not know how you calculated your example with "...a 500 pound weight at the top of the mast" but stability is a far more complex subject than a layman can understand from just being in a boat. And indeed - simplistically - raising the centre of gravity could make a problem boat more seaworthy, more comfortable - as long as it did not lose too much range of stability so as to be dangerous.

Stability has two components - initial stability and the range of stability - both are important. Both need to be 'balanced' shall we say for the type of boat and what it is going to be used for. It is generally accepted that the more the boat is 'in' the water rather than 'on' it, the more it has a little less initial stability combined with a larger range of stability the better it is - the safer it is - for an ocean going sailboat.

The Contessa 32, Alberg 30 - among others - are perfect examples of this.

Why then are so many modern sailboats like a big flat dinghy with a lot of their beam extending all the way aft and large sail plans combined with a low centre of gravity? Because they sail fast and they have room to be floating cottages. They accomplish with brute force and a hull strong enough to take the punishment what used to be accomplished by subtler and slightly slower means and ways. The higher initial stability that lets these boats carry more sail and go faster is also what makes them less safe than something like the Contessa 32, Alberg 30 or even the Cape Dory 28. Higher initial stability is pretty much always combined with a smaller range of stability. On the ocean these boats want as much as possible to be 'upright' on the water, 'upright' on the face of a wave. Even if that means that they have to turn turtle to do it. Boats with a little less initial stability/higher range of stability just keep going...

As I said - you mean well - but you are spreading what amounts to gossip as if it were fact...

Sometimes a little knowledge is a dangerous thing.

Last edited by Ericb; 07-17-2009 at 04:13 PM.
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