3 pages and I still don't think anyone has answered the original question 
..Is the 1/3rd measured along the boom or straight line between mast & clew..? ( I think that was the question..? ) I'd like to know too as I'm not sure..
If you are going upwind move the lines back.
if you want to go fast off the wind move the lines forward so you don't oversheet in the lulls.
but if there is a lull the apparent wind increases so wouldn't u need to sheet in for the LULZ?
ohh yeah the original question--
1/3 down a straight line down the sail.
(-its not down the boom because all booms are different shape and a completely arbitrary length.)
u can use an elastic cord with a mark at 1/3 and stretch it from the mast to the clew.
but why bother, my tip would be not to velcro the harness lines to tight so they can be adjusted while sailing, adjusted further and further back..
Its measured from the clew to the front of the mast, directly. I use a elastic rope with a loop that I put on around the end of the boom, and I store it in my harness.
Really helpful when you using rented equipment, or were on water adjustments are not easy to make. I just use it as a reference.
What size starboard code is that spotty? You must like ya codes dudeIs that the same one you use for wave sailing or is a different board? Are all your sails black dude?
elmo says hi by the way.. How is the trolling going in iwindsurf?? all the boys know you to well over there dont they?
I pulled out a measuring tape and set my lines at 1/3 today. Not enough wind to get int eh water, but I tried hooking in on the beach, and it felt seriously WRONG to me.
I'll give it a go on the water, but it's a long way back from where I had them. I had to move them nearly a foot back.
I used cribbs 1/3 rule on an "old" X3 160-210 boom and it worked a treat. Then tried it on a "new" x3 140-190 boom and it doesn't work by a long way.
All the 1/3 distances are at least 5cm too long going to the 140-190 boom.
In the end I just worked out where the lines sat best for each of my sails (on the water, not holding the rig on dry land) and marked the boom with a paint pen.
Minor adjustments then made on the water, based on the days conditions.
How can that be ?
Did the clew length change by 15cm because you used a different boom ?
FWIW, it was an X3 160-210 boom I used today.
I'd be interested to try this out with someone who uses the 1/3 rule.
Do people really move their harness lines inches when they change sails ?
I use the 1/3 rule on my RS Slaloms. Its definately biased towards the backhand. My front arm quite often gets a workout, however when max powered to overpowered its great. I end up sheeting out with my harness, ie bend back leg in, then when powered, straightening again. The rig tends to be more upright and sheeted in more often. This setup is faster on a reach, however needs to be tweaked when going upwind, downwind or in marginal conditions.
That's what I felt. I could balance the sail, but only with mucho front arm effort.
The height of your booms makes a difference. The 1/3 rule works best with high booms.
If you use seat harness and short lines the lines have to be closer to the mast.
For a neutral setting the centre of the harness lines has to fall on a line drawn from the mast foot through the coe of the sail.
"1/3 rule" is not a bad starting point when you have new gear and have no idea where the COP is going to be. But it doesnt make any sense to adapt to that as "the setting it has to be at".
Variables for harness line placement:
1) sail design- thats a huge variable.
2) body weight and height - lighter riders on the same rig need their lines forward. So dont copy the settings of the pros unless you are as strong and heavy as them.
3) wind character and sailing angles
Set them so you are comfortable most of the time.
The only time a less comfy setting is better is if you are chasing top speed, and your sail has the COP wandering back a lot in the gusts (mine dont but there are a lot of race sails out there that do). Then having the lines set back can be faster in the gusts, but in the lulls you will burn the front arm quickly.
aaahh - at last some common sense on this thread from some sailors (Spotty and Chris) that have their gear tweaked and tuned to 99.9999 % perfection.
Grrlpower!
further aft than where i would have them set(not to mention there prob 8 inches longer as well!)..i am guessing i am 15odd kgs shy of the slow one as well.. food for thought!
Boom, sail and mast flex less. Less flex= draft and center of effort stays in place.
