[Rhodes22-list] sail trim and traveler adjustments

Slim salm at mn.rr.com
Sun Jun 12 15:10:38 EDT 2005


James, thank you.  Great explanation.

Slim

On 6/12/05 1:20 PM, "James Wilson" <jwilson22 at prodigy.net> wrote:

> 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.
> 
> __________________________________________________
> Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list



More information about the Rhodes22-list mailing list