Sail Trim Question

[jackdale]

Originally Posted by rockDAWG

Most knot meters do not work. I have never had a boat that works.

The knotmeter needs to be pulled occasionally to clean it.

[RichH]

Originally Posted by jackdale

+1 - a little luffing is OK. I trim by easing the main until I get a little luffing.

In light air you want a full sail shape - both foresail and main.

errrrrrrrrrr ...... In light air you want a FLAT sail shape - both foresail(s) and main.
Light winds do not have the 'energy' to 'stay attached' to the leeside of a curved sail. So, the 'fuller the draft' (in light winds) the higher the risk of an 'invisible to the naked eye' SEPARATION stall - a stall where the low energy wind cannot stay 'attached' to the lee side of a sail.
How do you know you are having a SEPARATION? .... the tell tales on the LEEWARD side are not flowing 'aft' and are 'drooping down'.

[RichH]

Originally Posted by jackdale

+1 - a little luffing is OK. I trim by easing the main until I get a little luffing.

In light air you want a full sail shape - both foresail and main.

In light air you want a FLAT sail shape - both foresail(s) and main.
Light winds do not have the 'energy' to 'stay attached' to the leeside of a curved sail. So, the 'fuller the draft' (in light winds) the higher the risk of an 'invisible to the naked eye' SEPARATION stall - a stall where the low energy wind cannot stay 'attached' to the lee side of a sail.
How do you know you are having a SEPARATION? .... the tell tales on the LEEWARD side are not flowing 'aft' and are 'drooping down'.


Full draft for POWER (10-15+kts) ---- Punching through waves, or 'accelerating'; FLAT shape for speed (in 'flat water' and in 'light winds') 0-10 & 15+kts..

[overbored]

Originally Posted by rockDAWG

Most knot meters do not work. I have never had a boat that works.

Ever since I changed mine to the ultrasonic sensor my knot meter is dead on to the hundredth of a knot. no moving parts, flush with the hull and works even if it is dirty but mine gets cleaned with the bottom by the diver before each race. for sail trim watch the tell tales. if you have a row of three or four you can see whats happening much better . when it is so light that the tell tales don't work then you need to keep the sails flat

[BigNige]

I can recommend a good book: RYA Sail Trim Handbook

[Tempest]

Originally Posted by RichH

In light air you want a FLAT sail shape - both foresail(s) and main.
Light winds do not have the 'energy' to 'stay attached' to the leeside of a curved sail. So, the 'fuller the draft' (in light winds) the higher the risk of an 'invisible to the naked eye' SEPARATION stall - a stall where the low energy wind cannot stay 'attached' to the lee side of a sail.
How do you know you are having a SEPARATION? .... the tell tales on the LEEWARD side are not flowing 'aft' and are 'drooping down'.


Full draft for POWER (10-15+kts) ---- Punching through waves, or 'accelerating'; FLAT shape for speed (in 'flat water' and in 'light winds') 0-10 & 15+kts..

This has not been my experience...in very light air..I will ease the outhaul on my loose footed main to obtain a camber down low near the boom...and slightly ease the genoa to obtain a little curve at the foot. This has always given more power to my sails than..flattening them...

I want shape on my mainsail...the genoa may give me good flow...but the main has that big stick in front of the luff....

But, I'm open to discussion..

[emoney]

I don't know what the real answer is, but I tend to want to lean towards what rich said. At least around here, which is almost always "light winds-lol", flatter is better.

To the OP, and if I missed this, please forgive me, but where is your boom during this sail? Plus, like's already been said, if you were sailing "effeciently" and making good speed, what's a little bubble between friends.

[Sailormon6]

Originally Posted by Tempest

This has not been my experience...in very light air..I will ease the outhaul on my loose footed main to obtain a camber down low near the boom...and slightly ease the genoa to obtain a little curve at the foot. This has always given more power to my sails than..flattening them...

I want shape on my mainsail...the genoa may give me good flow...but the main has that big stick in front of the luff....

But, I'm open to discussion..

I know Rich's comment represents the most up-to-date theory, and I hate to disagree with both the current theory and with Rich, because both Rich and current theory are usually right, but this time I have to agree with Tempest. It has also been my experience that, in very light air, I'll get the best results by easing the outhaul, and easing both halliards. As the boat speed increases, beginning at around 2 1/2 - 3 kts, I'll start to gradually flatten the sails.

I don't know why there is a divergence between current theory and actual practice, in this instance. Sometimes the theory is overly generalized, when there ought to be exceptions to the rule. Perhaps current theory works with ultralite racers that are more easily driven, but not with somewhat heavier racer-cruisers. I can't explain the divergence, but, like Tempest, am convinced that current theory doesn't work on any of the more conventional boats that I race.

My suggestion is to try it both ways, and use the technique that works for your boat.

[blt2ski]

My post fastnet IOR 1/2ton also is a boat that likes slightly rounded sails when the wind is low. I usually pull the jib carr a bit forward, slack off the out haul, loosen the main sheet and put the traveler more to the wind side of the boat. loosen the halyards some. This gives me a bit more speed.

For a jib, a really light drifter may also help. I have a 3oz nylon spin cloth jib I use in under 5 knots of wind. This has kept me going many times when a heavier sail cloth does not pickup the zyphers. I also will remove the top full batten on the main, or put in the lighter of the two battens. Assuming the winds will stay light. If I know they will pickup from a forecast, I'll use the light batten.

Try many options, one will work.

Marty

[delite]

My experience has been the exact opposite of RichH. Flat sails in strong winds allow you to more easily "blade" the wind off your sails. Maybe its just my boat but flat sails in light wind means little boat speed.