On Wed, 05 May 2004 17:16:13 GMT, Brian Whatcott
wrote:

On 05 May 2004 12:33:50 GMT, ospam (Stephen Baker)
wrote:

Parallax asks:

Why not underwater sails?

Because the size of the "keel" would be about the size of a normal sail, and
would have much the same effect. You already have one, in other words... ;-)

Steve

Another way of looking at this:

A sailboat glides on the boundary between two fluids. There must be
shear between the fluids for sailing to work. If there is no shear,
you are becalmed.

The foils must be of a size commensurate with the density of the
fluids. Hence, the keel is smaller than the sail.

The foils can be of suboptimal shapes and still sort of work. This is
the normal situation. Many successful centerboard boats have flat
plate centerboards (Snipe, Finn, Lightning). Many keelboats have keels
that would hardly be recognized as foils.


Rodney Myrvaagnes J36 Gjo/a


Ask not where the buck stops . . .