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

Very perceptive. However, when off the wind on most boats, the
rigging disallows the positioning of the sails to act as an airfoil.

CN

"Love a Sheep" wrote in message om...
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

On 21 Nov 2004 12:18:14 -0800, (Love a
Sheep) wrote:

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

Using the aerofoil analogy, the mast edge of the main sail and the
forward stay edge of the jib would be the leading edges, so I don't
follow that if the wind is from abaft starboard, why you would want
the boom out to starboard.

Brian W

Love a Sheep ) writes:

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?

When a boom gets much forward of 90 degrees to the centreline it's hard
to pull back in from behind, reducing your ability to control the sail.

I have small boomless sails on my tiny boats which I can let forward all
the way and rotate them right around the mast. I often let the sail go
forward of the mast on a run in the manner you suggest so it's partially
acting as an airfoil. The sail is much more stable in that position. Sails
are least stable when running downwind. Spinnaker sails work much the same
as my rotating sails when let out forward.

Even in the standard upwind airfoil position only 2/3 of the power of a
sail is the airfoil vacuum on the front of the sail. There is still 1/3 of
the power from the "parachute" pressure on the back of the sail. It's
never one or the other but always a combination of both. Even on a dead
run air is pushing around the edges of the sail making a vacuum on the
front side. (Actually I imagine a true parachute has a vacuum on the upper
surface caused by the air from below passing over the curved surface.
Modern parachutists use an airfoil parachute which glides.)

There are some sails like the crab claw sail that aren't an airfoil. The
crab claw works like a kite. The air passing the edges of the sail makes
powerful vortecies which create the vacuum on the front side of the sail.
Crab claw sails produce the most power per squate foot of any type of sail
I'm aware of. Unfortunately they're not as easy to handle as a sail with
its front edge attached to a vertical mast.

On my website you can see photos of my rotating sails and my of crab
claw sail which lifts over the top of a short mast for easier handling.

--
------------------------------------------------------------------------------
William R Watt National Capital FreeNet Ottawa's free community network
homepage: www.ncf.ca/~ag384/top.htm
warning: non-FreeNet email must have "notspam" in subject or it's returned

On 21 Nov 2004 12:18:14 -0800, (Love a
Sheep) wrote:

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?

You are right. But it depends on the particular boat where exactly the
optimum switchover from drawing to stalled takes place.

If you have shrouds, the decision may be made by how much chafe you
are willing to tolerate between spreaders and main. With an unstayed
mast you have more freedom to experiment.



Rodney Myrvaagnes NYC

Let's Put the XXX back in Xmas

On 21 Nov 2004 12:18:14 -0800, (Love a
Sheep) wrote:

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!

True

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?

No. If the wind is from starboard, and abaft the beam, the sails will
not normally stay out to starboard, as the sheets are rigged to pull
the boom (and jib) into the boat.

It is possible with the wind very nearly dead astern to have the main
and jib on opposite sides - this usually works best with the wind
slightly to the same side as the boom. This is called "sailing by the
lee", and will lead to an accidental jibe if you let the wind get too
far to the same side as the boom (then you will find out why it is
called a boom :-( )


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

"Peter Bennett" wrote in message
news.com...
On 21 Nov 2004 12:18:14 -0800, (Love a
Sheep) wrote:

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!

True

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?

No. If the wind is from starboard, and abaft the beam, the sails will
not normally stay out to starboard, as the sheets are rigged to pull
the boom (and jib) into the boat.

It is possible with the wind very nearly dead astern to have the main
and jib on opposite sides - this usually works best with the wind
slightly to the same side as the boom. This is called "sailing by the
lee", and will lead to an accidental jibe if you let the wind get too
far to the same side as the boom (then you will find out why it is
called a boom :-( )

For either the slow, stupid, or stunned, it's called the boom boom.

Using the sail's trailing edge as a leading edge is problematic.
They will not be efficient this way - tantamount to running an
airplane wing backwards.

Letting them out on the port side however would work provided
you could let them out that far without fouling the rigging.

CN


"Love a Sheep" wrote in message om...
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

On Sun, 21 Nov 2004 12:18:14 -0800, Love a Sheep wrote:

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've already got a lot of good answers. I'll just point out one more
thing which is that the two sails on a boat interact. That is, even when
the wind is aft of abeam, the wind flowing over the main may be dead abeam
or so, because the jib or spinnaker changes the direction of flow.

--Mac

(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
Once the wind if aft of the beam the generally accepted rule if to
have the boom at right angles to the wind. Likewise when you pole out
the headsail.