Jib tracks
The problem you run into with any lead position is that the ideal spot for sailing upwind/close hauled in say, 5 knots of breeze is different from the spot for the same angle at 15 knots (it would need to be farther aft in higher winds). Alternatively, the ideal spot for upwind sailing in any breeze strength is not ideal once you ease sheets and begin reaching-this is because you lose relative load in the vertical plane as you ease the sheet, which unloads the top half of the sail-you will notice that when you are beam reaching for example (assuming the leads were correct for upwind-the "default position"-the top half of the sail is luffing... The answer is that the lead must go FORWARD (which increases the vertical loading on the sail) as the sheets are eased if you want to keep the entire sail working.
The way to properly locate the lead for any given sailing angle is to set the position at a point where the top and bottom telltales (the INSIDE ones) begin to "lift" or flutter at the same time as you either ease the sheet from a trimmed in condition, or head up towards the wind from a properly trimmed condition. If the top set breaks (another term for "lifts") before the lower set, this means the top of the sail is relatively less trimmed in than the lower part, and the lead must go forward (more vertical load trims the top of the sail). If the bottom set breaks first, then the bottom of the sail is relatively less trimmed than the top, and the lead must go AFT (more horizontal load trims the bottom of the sail).
My point at the top of this reply about the lead going aft as the wind builds is to illustrate that there are times when you DON'T want the WHOLE sail working at 100% efficiency-when you are overpowered, outside the range of the headsail being used, by reducing the vertical load, and "UNTRIMMING" the top half of the sail-you are basically easing only the top half of the sail-which will reduce heeling, mainsail backwind, and get the boat back on its' feet- a cheap form of "reefing". Conversely in very light air, when you cannot trim in as tight, if you ease the lead a bit forward from the 'default" setting, you allow the top of the sail to keep working even though it is slightly eased for the light air-and you keep the whole sail working for you.
How to adjust? A very good solution is of course to install some inboard tracks with a nice adjustment system-see Harken catalog for a good sketch of this-But you are not stuck if you want to stay with the snatch blocks on the rail-All you need is one more snatch block (easily opened) and a short piece of line-a "short sheet"-maybe about 15 feet long.
If you want to move the lead forward, place the extra block just aft of the hole where the "real" block is, and run the short sheet from the clew(you will briefly have 3 sheets attached) through the new block and to a spare winch. When it is tight, you can ease the "real" sheet, move the block forward, then reload the "real" sheet. You can now untie the short sheet and stow it (along with the extra block). To go aft, do the opposite, except in this case you may want to place the short sheet block just aft the the 'real" one as well, because if you are over powered you don't want the lead any farther forward. When the short sheet is tight, you can move the "real" lead back behind the short sheet block and reload..
Capiche?
I know this has been posted several times-but this will save you a search-however there is a lot of relevant material posted on this topic over the last few years-worth a look!
Fair Winds,
S
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