"Wally" wrote in message
...
"Donal" wrote in message news:bed29j$spv$1

There is an absolutely negligible difference in length between the
windward
and leeward paths.

I just drew a 3000mm long polyline in a CAD package and bent it into an
approximation of a section through filled sail viewed in plan. I then
offset
a new polyline from this by 1mm, simulating the thickness of the cloth.
The
lengths of the inner and outer surfaces on my model are...

Inner: 3016.6077mm
Outer: 3016.9590mm
Delta: 0.3513mm

(For reference, after manipulation, the chord is 2999.6548mm, and the
depth
of the 'belly' is 114.2920mm, 715.08mm from the leading edge.)

Doesn't seem like that could have much effect. Perhaps the Cappy's sails
are 2mm thick??



The wind pushes the windward side of the sail. The keel stops the boat
from
moving sidways, and the pressure is relieved by the forward movement of
the
boat.


Are you saying that the *only* force moving the boat forward is the push
on
the windward side of the sail? If so...

Ahhhh! What is the difference between "push" and "pull". The sail only
notices a "difference".



If your theory were correct, then a boat would go *faster* upwind.

...does it go fastest downwind?

Yes! I've done 15 kts downwind. (using a spinaker).

Me best hourly average (8.2kts) was done on a beam reach......... hmmm!
That might not be true. I've done Portsmouth entrance to St. Vaast lock in
9:45 under spinaker. WE must have had a few hours of 8.5 kts in that
trip. I suspect that we weren't writing up the log on that one. Otherwise
I'd remember it. I'll have a look tonight.


Regards


Donal
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