[Rhodes22-list] sail trim and traveler adjustments

[James Wilson]

Not meaning to lecture the sailors who already know this,  but in every
group I find there are some who have not learned about apparent wind and the
need for twist in the sail.

Offered in the interest of sharing for those who might not know.  Hope I
don't step on the toes of those who do.

The easiest way to understand how to optimize sail shape with a traveler and
when is with telltales on the sail.

Three sets of telltales about 1 1/2 foot aft of the mast evenly spaced up
the sail,  one on either side of the sail is about right.  Alternatively
some people prefer three single telltales evenly spaced on the trailing edge
of the sail.

The goal of using either a vang, or a traveler or a sprit boom along with
the topping lift in lighter airs  to shape the mainsail is to allow the
proper amount of twist in the sail so airflow is attached to both windward
and leeward sides of the sail for current conditions to not have any stalled
airflow areas.  Or to put it simply,  make sure ALL TELLTALES STREAM AFT!

Why is twist important to accomplish this the novice sailor may ask?
Because the speed of the wind at masthead is usually faster than at cockpit
level.

Why?  Because, the closer you get to the water the more the layers of air
slow down due to frictional losses with the surface of the water.  The
molecules of air closer to the water move and hence present less frictional
losses to the air layers directly above and so forth up the air column.

Why is this important if the air is still all going in the same direction?
Why don't you just trim for angle of attack and keep the same angle of
attack all the way up the sail?  Because your boat is moving forward and is
creating some "Wind of it's own"  The combuination of boat speed wind and
the true wind creates an apparent wind that moves aft as you go up the wind
column as the true winds strength plays a proportionallyu greater part as it
is faster as you go up?

So,  you need the angle of attack of the sail closer to the midline of the
boat down near the cockpit and further out as you go up the mast.

Adjusting the twist of the mainsail so all telltales streeam aft gives you
the most efficiency.

Now,  really off the wind, a Boom Vang works best for this,  but when using
a traveler, the most advantageous position for a traveler is closet to the
mast in order to have the largest range of motion where the traveler can do
it's work.  Boat design however is a series of compromises so in the case of
the Rhodes, with the traveler aft,  you sacrifice some in terms of range of
motion where the traveler can work,  but it is the best compromise for the
boat.

Now,  how do you use the traveler to induce more twist?  The closer the
traveler car is to the sail, the less twist will be in the sail.

Moving the car all the way to the windward edge will induce the most twist.
Also,  in lighter airs where ther is not enough air pressure to cause the
boom to raie up with the traveler car to windward,  you can use the topping
lift to raise the boom and induce more twist.

As a general rule,  the lighter the airs, the more twist you need as the
greater effect boat speed has on the equation.  Hopwever allways trust the
telltales and make them stream aft.

When properly trimmed for close hauled sailing, or even further off the
wind,  iif a gust of wind hits, the apparent wind will always shift aft to
be more from the beam.  If tightly pinched to weather this gives you an
opportunity to pinch even closer to the wind to make your velocity made good
better,

If on the other hand you want to maintain course,  then easing the travelor
to the leeward rail will give you a better angle of attack and gain some
boat speed and then hauling the traveler back to windward as the puff eases.
This is more desireable than easing the mainsheet as it maintains the proper
amount of twist in the sail for the prevailing conditions and alters the
angle of attack for the entire sail at the same time.