That is, the distance between pulleys, when you're sailing along.
Should you:
a) Always shorten your extension if you can, and so usually show 3-5 cm?
b) Not worry about it unless there's more than 10 cm showing?
c) Always have more than 10cm showing?
Why?
you should always keep it as low as you can.
if you tune ur rig up to make the sail look like you want it and you could go down 1 hole on the extension then do it.
it lowers the centre of effort of the rig which will allow for more speed and better control. mainly coz you can raise your center of weight to match
i would guess the gap between my pulleys would never be more than 5cm apart, usually less than 3cm.
No gap at all, i spend about and hour on each new sail to get it rigged perfect so the the pulleys are touching each other on minimum downhaul, then if i need more i go up one hole in the extension and pull it all the way down again for high wind setting, this way my rig is always rigged the same and i can rig it perfect realy fast before the wind and wave bugger off, another good idea is too draw a line around my extension so i know how much i need for each sail, and no excuses for sailing crap that day apart from pilot error. the lower the rig is, the lower the centre of gravity and better control, also for slalom and race gear they will be faster with less gap between the board and sail.
i think 10cm is a tad too much really depends on the settings but then again the luff base is somewhat of a mystery with different sail brands..even with correct downwhaul there is too much luff pocket left
1-2cm max.
more than that your extensions too long or your adjustable heads too short.
All the rigging guides I've recomend minimum possible no more than 1-2
With the Maui Sails, they want 2-3 cm of floating pully on the tr4. They have a recessed pully so it sits low to the deck anyway.
If you pull this block to block, there is too much pressure on the cam against the mast and it wont rotate..
I'm too embarassed to show ANY down haul "rope". ( so I cover it up)...Damn purple spectra !!!
Always good to leave a couple of centimeters I reckon.
Those last centimeters puts that extra strain on the rope and pulleys oh and my back.
yep there is no need to go totally block to block.
but what is important is knowing where the different manufactures measure the downhaul settings from and to.
No one is making an extension with really low pulleys like the old Chinook any more. For some of us it is important to keep the rig as low and as close to the deck as we can so block to block is the preferred setting. If you do use that setup its important that the pulleys align AND that the hole where the rope starts, and the cleat, are in the best possible positions to suit the line wreathing. If they put the pulleys lower this wouldn't be so critical.
The plain old tack cringle defines the fundamental line wreathing that all extensions that pretend to be universal should accommodate. The basic wreathing for that is line starts on the same side as the cleat, goes through the cringle loops over (preferably) a "loop and go" pulley then back through the cringle and into the cleat. If you introduce another pulley you then have to move the start point for the line to the opposite side from the cleat. So at a bare minimum a universal extension should have a start point for the rope on each side of the pulley block.
I could go on....
i always set my extension so that the pulleys come all the way down to the bottom so the bottom of the luff is covering the bottom of the extension.
what i cant understand is WHY T.F. do they not have the pulley block on my old gaastra GTX oriented the same way as the extension pulleys? when you downhaul it the block twists around putting more stress on it and you cant get it all the way down cos the ropes jump off the pulley and makes it really hard to pull the last bit on.
another question is , what does everyone else do with the excess downhaul rope left over?
i used to just wrap it around and tie it off but now i stuff it up into one of the lower adjustment holes of the extension. 
i've seen rental shops do that alot but in time they get corroded and the teeth tend to get dull and suddenly the downhaul rope just unloosens..and it's a long day trying to get back to the beach
OH yeah, last to days I've downhauled till the pulleys touch, but that jams the rope into the cleat so it doesn't want to release. Have to twist the sail pulley, to unjam the rope in the cleat, then the downhaul detensions with a bang, not good for sail, so I'm going to leave a few mm in future.
[}:)]
