Hook

[lewisboats]

Went to a Messabout this weekend and I was talking to the designer of Skiff America 20. One very interesting thing that popped up was the fact that his boat has what he termed a "hook" in the bottom. This is actually a concave section between the start of max beam and the transom. It is only about 3/4", with the apex about 1/3 of the total distance of the concavity from the transom. The boat is a planning design and he said that it is almost impossible to feel the transition between hull speed, semi-planning and full planning. Seeing it on the water, I can readily believe it. The bow of the boat never really did the usual "climb over the hump", yet the bottom is flat. Max speed is 20-25 mph with a 25 hp motor, yet fuel mileage is about 1 gal/hr or better at cruising speed. These are statements not only from the designer, but from 2 others who had their SA20s there too.

Anybody know anything more about this hook feature?

Steve

[cyclops]

Does the function of the hook sound a awfull lot like a step in a stepped hull?

[lewisboats]

No....I actually think it works more like a fixed, full width trim tab, forcing the nose down at an increasing rate as the speed increases, until the bowwave reaches a point well back of the bow....ie planning. At least this is my thought process. What ever it is...it really seems to function as advertised, go figure!

Steve

[Eric Sponberg]

Hook is quite common. You and your designer have not discovered anything new.

Eric

[CGN]

Professional boatbuilder has an article about different configurations for hull bottoms of planing hulls

[stevel]

WARNING: What you are about to read is not coming from an expert, and is offered up so that the experts can correct whatever is wrong with it and tach all of us something about the topic.

I've always thought of a hook as a defect, or a bandaid. The purpose of deliberately adding hook would be to get the bow down, but it causes drag at the same time. I think this is a compromise that gets used when the static bouyancy of a hull and the running angle can't both be engineered to the desired result otherwise.

Sometimes you get hook accidentally because a hull is pulled from a mold before it is cured, or sits on a trailer with improper support. This is the same thing that is being discussed in another string as a problem.

What say the experts?

[Skippy]

As Eric said, there are designs that are concave aft. The shape makes perfect sense as the underside of a foil generating lift at speed. It releases the water in a downward direction.

OK, now the experts can start.

[lewisboats]

Sometimes you get hook accidentally because a hull is pulled from a mold before it is cured, or sits on a trailer with improper support. This is the same thing that is being discussed in another string as a problem.


This is a Plywood boat and the "hook" was engineered into the design from the beginning.

Steve

[lewisboats]

Hook is quite common. You and your designer have not discovered anything new.

I suspected as much but I had never heard about it. Thanks