full keel vs fin keel

[wingssail]

Originally Posted by Ken Fry

...A fin keel boat sailed with a lot of heel may develop a large amount of weather helm, indicating that it is being poorly sailed, rather than an inferiority in keel design...

I think the reason that many fin keel boats develop a lot of weather helm when heeled is that many of them are kinda fat.

When heeled over the fat side of the hull is imersed while the other side is out of the water. This presents an assymetrical hull shape which natually wants to turn.

A skinnier boat has less tendancy to do this.

[Ken Fry]

Originally Posted by wingssail

... When heeled over the fat side of the hull is imersed while the other side is out of the water. This presents an assymetrical hull shape which natually wants to turn. ...

Depending upon hull shape, this effect may not act in the direction that you would expect. Heeling increases wetted surface (and therefore drag) on the leeward side, so should cause the boat to turn to leeward, instead of to windward.

For most boats, the effect of displacing the center of effort of the sails far (several feet) to leeward creates a large moment about the underwater center of drag, in the direction that causes weather helm. The effect of changing the waterplane shape is less significant, in general, and does not always cause a moment to windward.

A windsurfer hull can be heeled by foot action, and the boat steers to starboard when heeled to starboard. Kayaks may turn one way or the other with heel, depending upon hull shape.

But, yes, fat boats tend to develop more weather helm when significantly heeled.... so they should be sailed relatively flat. My J24 was pretty fat compared to my Columbia Contender. They had essentially identical sail area/displacement ratios. Sailed well (flat) the J 24 was much faster than the Columbia sailed at its best (steeper) heel angle. In both, if I carried a lot of weather helm, it meant I was doing something wrong: it was not that one keel or the other had some particular bad trait -- it was that the skipper had some bad trait.

[Cynara]

Full keels are generally encapsulated. Many fin keels are bolted on.

[Jim Cate]

Originally Posted by Cynara

Full keels are generally encapsulated. Many fin keels are bolted on.

Well, fancy that!

Jim

[carstenb]

gosh, I guess we're a minority. WE have a Sun Fast 40.3, which is a racer cruiser. Deep fin keel, deep spade rudder, lots of sail. We don't have problems with weather helm (we simply reef down). Nor do we get exhausted at the helm (well in all fairness, when we were hand steering through a gale between Marquesas and Hawaii, we were tired) but otherwise not.

My advice is learn to trim our sails and your problems will be minor.

[Sherpa17]

My experience has been that setting proper mast rake has a significant effect on the helm, as was stated earlier. It's controlled primarily by the fore stay length and in the age of headsail furling systems, is often not optimal or plain wrong.