Re: mainsail trimming by telltale
Posted: Sun Jul 07, 2013 9:33 pm
Dave – (My response in black, your words in red).
I'm trying to hone my trimming skills.
Me too -never stop!
There are way more variables than I mention here, I recommend one of the googleplex of books on the subject, but in a few words...
Then I'm setting my mainsail so that it is essentially parallel to the genoa and its leading edge is head on into the wind, adjusting the vang to help it stay off the genoa.
While it might be an initial starting point, because the main functions in the backwash of the genoa,
it is not efficient to position your main and genoa parallel to each other because the genoa should (almost!) always be at a greater angle from the boat's centreline than the main.
When I look up at my mainsail leech telltales, they are often backwinding. i.e. they are pointing FORWARD on the LEEward side of the mainsail i.i.e.e. in the slot.
Telltales will flutter on the lee side when the angle of attack of the sail is too great relative to the wind, it indicates that the sail is stalled in that area, so sheeting out will correct that, if your heading is maintained.
If I'm lucky, I can get the lower telltale to stream straight back, but rarely do I get the upper telltale to stream back.
What you are describing is likely a lack of sufficient twist in the sail – that is some parts of the sail are set at the proper angle, but others aren't. The wind speed is higher the higher you go up the sail, so to maintain a constant ideal angle of attack the sail must be at a different angle to the airflow at different heights. Twisting the sail accomplishes this.
Other than using the mainsheets, the lack of a main traveler makes this more difficult to do in an X (without special modifications), but a boom vang can help twist the sail, more or less, depending on the point of sail. Tighter sheets= less twist, looser sheets= more twist.
Eyeball it upwards from below the boom - you want to get the upper part of the sail nearest to the leech (at the top batten, or where it would be if you don't have one) parallel to the boom. It's safer to err on the side of too much twist, than too little – it gives you some leeway for suddenly changing conditions.
For the genoa, the twist is controlled by the traveller car position, move it aft to increase twist. When you turn and head into the wind and all telltales flutter at the same time, your genoa twist is correct.
Note that getting all telltales on both sails to be perfect is really not practically attainable in the real world – sometimes you just have to judge some of them by the amount of time (like, say, 50%) they spend where you want them and be happy.
A sail is most efficient when it's just on the verge of collapse, but at that point there is little tolerance for sudden changes in conditions. That's part of the fun of sailing. Yer livin'on the edge!
ps. the dual mainsheet arrangement that mastreb suggests above also carries the advantage of performing as a preventer for better control (= potentailly less violent) of the boom when gibing.
Hope this helps - Brian.
I'm trying to hone my trimming skills.
Me too -never stop!
There are way more variables than I mention here, I recommend one of the googleplex of books on the subject, but in a few words...
Then I'm setting my mainsail so that it is essentially parallel to the genoa and its leading edge is head on into the wind, adjusting the vang to help it stay off the genoa.
While it might be an initial starting point, because the main functions in the backwash of the genoa,
it is not efficient to position your main and genoa parallel to each other because the genoa should (almost!) always be at a greater angle from the boat's centreline than the main.
When I look up at my mainsail leech telltales, they are often backwinding. i.e. they are pointing FORWARD on the LEEward side of the mainsail i.i.e.e. in the slot.
Telltales will flutter on the lee side when the angle of attack of the sail is too great relative to the wind, it indicates that the sail is stalled in that area, so sheeting out will correct that, if your heading is maintained.
If I'm lucky, I can get the lower telltale to stream straight back, but rarely do I get the upper telltale to stream back.
What you are describing is likely a lack of sufficient twist in the sail – that is some parts of the sail are set at the proper angle, but others aren't. The wind speed is higher the higher you go up the sail, so to maintain a constant ideal angle of attack the sail must be at a different angle to the airflow at different heights. Twisting the sail accomplishes this.
Other than using the mainsheets, the lack of a main traveler makes this more difficult to do in an X (without special modifications), but a boom vang can help twist the sail, more or less, depending on the point of sail. Tighter sheets= less twist, looser sheets= more twist.
Eyeball it upwards from below the boom - you want to get the upper part of the sail nearest to the leech (at the top batten, or where it would be if you don't have one) parallel to the boom. It's safer to err on the side of too much twist, than too little – it gives you some leeway for suddenly changing conditions.
For the genoa, the twist is controlled by the traveller car position, move it aft to increase twist. When you turn and head into the wind and all telltales flutter at the same time, your genoa twist is correct.
Note that getting all telltales on both sails to be perfect is really not practically attainable in the real world – sometimes you just have to judge some of them by the amount of time (like, say, 50%) they spend where you want them and be happy.
A sail is most efficient when it's just on the verge of collapse, but at that point there is little tolerance for sudden changes in conditions. That's part of the fun of sailing. Yer livin'on the edge!
ps. the dual mainsheet arrangement that mastreb suggests above also carries the advantage of performing as a preventer for better control (= potentailly less violent) of the boom when gibing.
Hope this helps - Brian.
mod very simple 