DSK wrote:

Nav wrote:

You really think that boat (?668) is beating to windward?


It looks like they are attempting to. Do you think they are heeled too
much for best VMG?



Please tell us about your sailing ideas where a spinnaker is carried as
a beating sail.


... Is 45 close to 30 when discussing trim and heeling?


IIRC at one point you said "30 to 40 degrees of heel" in relation to
being 'powered up' which you never could define.

No, I never said 30 to 40 degrees. It's your exaggeration coming in
again. I said IACC are powered up at 30.



In any event, 45 is a lot closer to 30 than it is to 20


Now you've gone from 30 to 40 to 45! Anyway you are wrong again. Wind
pressure (and therefore potential power extractionon) on the sail must
proprotional to the sine of the heel while leeway will rise roughly with
the cosine. OK?

The consequence of this is that keel boat speed will rise as wind
pressure on the sail rises but VMG will not continue to rise so fast and
will eventually fall due to leeway taking away from the windward
progress. Due to the shape of sines and cosines (I hope you know this)
the sine initailly rises more quickly than the cosine falls. Thus VMG
goes up monotonically with heel until sine and cosine functions have
opposite effects on VMG. At this point, the boat is sailing fast and
fastest to windward and to use my parlance it is fully powered up. A bit
more heel may well give more speed but VMG falls -and falls
progressively faster with more heel. That's why we have accurate VMG
instruments on board (but dinghy sailors have to guess their VMG which
is hard). From that design angle, VMG falls more and more quickly. The
designer picks a point to work on (typically 30 degrees as I said) to
decide freeboard. Thus at 45 dgrees heel VMG is probably well down and
the rails are going under (drag). This is not the same as when going
from 20 to 30 degrees heel. At ~30 the VMG for an IACC is highest, as I
said and this was also true for the classic 6m type Gimcrack whose very
accurate figures I gave you. Perhaps you should try to read Dr. Curry's
book 'Yacht Racing' (if you can find a copy) for qualitative discourse
on the effects of heel on real yachts? Now, It is possible to shape a
hull to have even more power at 30 degrees heel but the reason why this
is not done is that 30 degrees is also considered to be a human limit
for working comfort. If you had sailed offshore you would know that
heeling beyond 30 for any period is very hard on the body. I suggest the
current Beneteaus were designed to have lower human design angles for
the market they are aimed at -the charter/fun boat market. Mure purist
cruiser/racers (like Ella) take higher heel to reach peak VMG and also
carry full sail to higher windspeeds. Don't forget Ella was designed for
the roaring 40's -not the Med.

OK?

Cheers