Using Leach Telltales to Trim Mainsail

[Poozer]

I have leech telltales on my mainsail (no luff telltales) and I understand the objective when sailing upwind is to get the lower tells streaming back all the time and adjusting twist so the top leech tell streams "most" of the time.

The question I have is, how do I know when I have the angle of attack correct on the lower section of the mainsail? Here's my confusion: when the boat is head to wind with the mainsheet eased, all the leech tells stream back, but clearly the sail is not driving. So how do I set the angle of attack for maximum drive? Do I sheet in until the lower leech tells curl around the back of the sail and then ease out a bit until they're streaming back? If I'm close hauled, I never achieve this, even with the boom on the center-line they stay streaming back without ever curling around the back of the sail.

To complicate things further, I have a cat with a dual mainsheet system and no traveller, so I spend a lot of time doing trial and error tweaking of both sheets to set the angle and twist. I just haven't found a good system that makes me feel confident that I have the main trimmed correctly for upwind points of sail.

Any advice is greatly appreciated!
Doug

[cal40john]

Leech telltales only tell you when the sail is stalled out. They stream forward on the leeward side when that happens. I only use a top leech telltale to tell me when I have taken enough twist out, so I know the top of the sail is working, not partially luffing.

John

[Poozer]

Originally Posted by cal40john

Leech telltales only tell you when the sail is stalled out. They stream forward on the leeward side when that happens. I only use a top leech telltale to tell me when I have taken enough twist out, so I know the top of the sail is working, not partially luffing.

John

OK, but how do you know when the bottom part of the sail is trimmed correctly?

[SaucySailoress]

Perhaps it would be worth sticking some telltales onto the body of your sail - top and middle... I find that mid sail telltales are much more useful than the leech ones.... they give a much more complete story.

[GordMay]

See ➥ Telling tales ...

And ➥ A Truer Tale of Telltales

And ➥ A Trim Primer for Main and Headsail Balance

And ➥ Telltales: One man's fact, other man's fiction

And ➥ RACING BASICS - Beginner's Racing Manual

[Bash]

"when in doubt, let it out." ease the main until the luff begins to luff, and then trim it back until the luffing stops.

[Strait Shooter]

Originally Posted by GordMay

See ➥ Telling tales ...

And ➥ A Truer Tale of Telltales

And ➥ A Trim Primer for Main and Headsail Balance

And ➥ Telltales: One man's fact, other man's fiction

And ➥ RACING BASICS - Beginner's Racing Manual

Thanks as always Gord!

[Strait Shooter]

Originally Posted by Bash

"when in doubt, let it out." ease the main until the luff begins to luff, and then trim it back until the luffing stops.

+1
and continue trimming from there.

[Poozer]

Thanks for the advice everyone!

I read the articles that Gord listed and attached tells to the middle of my mainsail today. It's a whole lot easier seeing what's going on now. I was over trimming way too much before!

[OldFrog75]

Originally Posted by cal40john

Leech telltales only tell you when the sail is stalled out. They stream forward on the leeward side when that happens.

John

And the solution is to tighten or loosen the main sheet?

[monte]

some good info here on catamaran sail trimming.
Twixter -* Sail Trim & Reefing

[sailr69]

Originally Posted by Bash

"when in doubt, let it out." ease the main until the luff begins to luff, and then trim it back until the luffing stops.

at last a good racing sailor who knows what he is talking about!


one would need to see sail interaction in a wind tunnel to understand this well. with a sloop (two sails) interacting. both sails are trimmed as though it was one. leach telltales are the most important ones to pay attention too. they show parasitic drag. (when sailing upwind). off the wind chord depth is more important. down wind? just sail area. like a leaf being blown across the pond. If you are racing, you learn how to manage all this to it's best advantage. mastheads, frac's are all different. this is why usually the same boats always do well in races.

[sailr69]

Originally Posted by OldFrog75

And the solution is to tighten or loosen the main sheet?

more then that. you got a boomvang? traveler? halyard tension? too much trim in on the jib? jib fairlead in wrong position? decent sails? masthead rig? frac? inboard track, outboard track(slot control) on the wind or off?

[Cheechako]

Originally Posted by OldFrog75

And the solution is to tighten or loosen the main sheet?

Yep, in theory they should be streaming back, not curling to either side. Also if the top one or two are not streaming properly, but the botom one or two are, you need to change your sail shape with the luff tension, traveler location, cunningham etc.

[foolishsailor]

1. Trim the main until the luffing just stops

2. Use further mainsheet tension or ease/take in your boomvang tension - until the top telltale is flying aprox. 50% of the time - the rest of the time it will be dropping or flying up behind the mainsail.

This will let you know you have optimal twist in your main.