Mike wrote:

In books about sailing, I have read that the keel, going through water,
produces lift in a similar way to a sail. Given that water is a
non-compressible medium, I wonder how this can be so. Has it ever been
documented?


Incompressible, but not immobile.

The same as with a sail inthe air,the water is free to move away
from the keel. The equal reaction to that motion is what makes
the keel work, and planing boats plane, and wakes, which may push
the after quarters foreward on a boat with a pretty bum in
displacement mode, or get left behind by a boat approaching the
plane.

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