Alan, my response assumes that you are not sure of what a sea chest is or what it looks like. If you do, I apologize ahead of time, but may be of some benefit to others who are not.

All of the sea chests that I've seen are either offset enough to one side of the keel to clear it, or if the keel should swoop up before it reaches the end of the hull, the sea chest can be positioned far enough aft to clear the keel.

Perhaps you are thinking that the sea chest extends down below the hull? If so, you have the right concept, just invert it. The sea chest extends up into the boat and a plate, which is full of holes, is usually set flush with the hull, covering the opening. Any interference with water flow is minimal.

Kinda like an inverted cup set on a table top (the table substituting for the bottom of the hull), only the table top under the cup is full of holes.

Water take-offs (seacocks) are usually attached to the sides of the sea chest and since the sea chest is usually designed to extend above the waterline, the top is often removeable for maintanance. Many of the sea chests that I've seen also incorporate a strainer inside it.

Was that of any help?

Rudy
Briney Bug, Panama City, Fl

The sea chest is internal, in the bilge area. Most of the chest is below the
waterline. Some of it is above so that you can remove the top, while the
vessel is in the water, in order to access the "outside" of the thrucocks.
This of course should be done in still waters, otherwise the chest will
slosh about like a five year old in a full bathtub, and exercise your bilge
pump.

-- Jim