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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Just to add that as the water is much denser than the air, it takes
just a little keele to compensate for all the sail surface.


On Wed, 23 Jul 2003 16:20:09 GMT, Terry Spragg
wrote:



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.

This is a document.

I've been involved in this discussion before. Yes, the keel does provide
Lift but it also produces DRAG. Ask any sailor with a swing keel and
they will tell you they can increase speed by retracting the keel.

The Keel is for the purpose of direction (to reduce leeway) It's
design is basically to reduce the drag that it creates as much as
possible.