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(Love a Sheep) wrote in message . com...
I am learning to sail and have a few questions. I understand that the
sails can act either as an airofoil (lile an aircraft wing) or like a
parachute where the wind simply blows the sail directly. My question
is this. If the wind is ahead of the beam ie we are sailing windward
then I expect that the airofoil principle must always hold there
otherwise we would be sailing backwards!

However, if the wind is aft of the beam on say the starboard side then
surely we have a choice where to set the sails ie they can be on the
starboard side (ie the boom is pointing to the starboard side) where
they act as an airofoil or on the port side where they act as a
'parachute' - is this right or am I missing something. If so which is
best?

Thanks

You can't really put both of your sails to what in your description
would be the windward side of the boat...well, not effectively at
least. here's why....

Unless you're sailing dead downwind (wing and wing, or by the lee, as
mentioned - boom toward the VERY slight widward side, also as
mentioned) you'll notice that no matter how far out you let your sails
when on an actual port or starboard tack, you're always going to have
the airfoil effect, not a parachute effect. Watch your telltails,
you'll see the wind moving across the sails, leading edge to trailng
edge. In your case, if the wind was from starboard, even fairly
significantly abaft the beam, you would still sail on starboard tack,
sails trimmed out to port. Once this becomes impossibly, it's either
time to jibe, or go wing and wing.

To relate this to a plane, think about the apparent wind when they
slow down to land and they 'set' the flaps to create much more 'belly'
in the wing to maintain that lift as the wind direction changes
(remember, apparent wind...of course, they're still going forward,
but the plane wants to fall, so the wind direction is now coming from
further under the wing, less in front of it, so they have to adjust,
just like you do) But there's no way a wing will act as a parachute on
a plane, it's still an airfoil. Same thing you're doing with your
sails. The difference is in the fact that a plane can also adjust it's
apparent wind direction by adjusting its speed. But the adjustments
are based on the same principle. If the plane went too slow, it would
fall of course, luckily, we don't have to worry about that, and when
the wind is directly behind us (i.e. the minimal amount of apparent
wind) - we CAN use the parachute effect. but it's only in that
scenario.

how's that for a long drawn out explanation! Sorry for the verbose
detail...hope it made even a bit of sense!

P.S. And yes, be careful sailing downwind wing and wing...accidental
jibes are not your friend. if you're going to do it for long, pole
out, and rig preventers, especially in rolly seas.

Good luck!

Capt. Rob Welling
Sarasota, FL

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