Is there some simple way to pin-point the centre of lift of a sail?
Obviously it lies on the line from the mast foot through the centre of the harness lines if the harness lines are positioned correctly, but how do you find the height?
Put a 3-way bridle on the sail, from the mast tip, the mast foot, and the clew, all meeting at the one spot.
Attach a line to this spot. Fly the sail like a kite.
When the sail reaches steady state (which will require some tweaking of bridle lengths, and will probably require someone holding it to stop it crashing) then look along the single line, and extend that line to the sail, past the bridle. It will hit your sail right where the COE is.
Edit: You may need to make up some form of support frame for the top bridle connection, which will make the mast tip bend away from the wind instead of towards the wind. I leave this as an excercise for the reader 
That doesn't take weight distribution into account. When the sail flies horizontally the mast booms and extension are all supported by the sail. The apparent centre of lift would appear biased towards the bottom of the sail where the weight bias is. It would be nice to be able to isolate the aerodynamic centre of lift from the weight of the gubbins.
I just had a thought. You could add weight to the mast tip to compensate for bottom weight bias. You could, just for the sake of repeatability and standardisation, add enough weight to put the centre of gravity half way up the luff. Maybe a third of the way up would be more practical from the point of view of flying the rig.
You wouldn't need to fly it from a bridle either. You could just stand in the wind and hold onto the mast at the balance point. You have the line through the mast foot and harness lines as one datum. You only need one other datum line and that would be perpendicular from the mast at the balance point presuming the sail was held perp to the wind.
So you would need some scales and weights and a felt tip pen and a string line and a calculator.
As a roughy hook into your sail on the beach. Then get someone to measure the horizontal distance from the lower part of your chest / upper waist (your COG) to what would be the board centreline. Make sure you measure perpendicular to the centreline.
Then measure the average windspeed, then get the calculator out. Sail COG = Your weight in kg x 9.81 x distance measured / (0.5 x 1.184 x (windspeed in knots / 0.51444)^2 x sail area in m2)
Notwal this is so easy.
Get planing and perfectly balanced. The COE lines up with the centre of lateral resistance and then is just up a bit.
Hmm OK a slightly easier method:
Make a two way bridle from the clew to a clamp that can be clamped at different positions up the mast.
Move the clamp up the mast until the windward deflection of your boge* is zero. At this point look along your single support line.
* When sailing along, my boge joint has a fair bit of visible shear deflection to windward. You might find an easier way to figure out the windward force on this point.
Its all about moments guys, lateral force at the uni doesn't affect the moment about the uni.
Depending on leach twist the COLR is at the centre of area
Scott COLR has nothing to do with the sail. It is the lateral resistance of the board. ......the combined effect of fin and rail length stopping the board going sideways.
So if the sail doesn't have any lateral resistance why is the board providing lateral resistance in the first place! 
If there is wind the sail has a centre of lateral resistance.
The sail has a Centre Of Effort (where the power comes from) dependent on draft position and sail shape.
The board has a Centre of Lateral Resistance which is the combined effect of fin and waterline.
On old longboards it was shown in diagrams when learnign as the board turned when the COE and COLR did not line up.... move the sail forward and the nose was pushed downwind (bear away) and if the sail moved back the tail was pushed downwind (rounded upwind)
You are talking about the sail's resistance to the wind - which is not the COE. You are talking about the sail as a 2D shape being exposed to the wind - like a piece of paper has it centre in the middle obviously. That si irrelevant as the centre of EFFORT (power) is affected by draft. It is not in the middle it is forward of the middle
I'm going to get myself a clamp and try this test. If it works I'll check all my sails and the effect of downhaul on the height of the coe.
It would be nice to know this dimension for other sails. The height of the coe is a significant performance indicator. This is one of the key differences between the S1 and the Blade. It is an indicator of the suitability of a sail for high jumping. It is important for speed and racing to keep the coe as low as possible. I have long been curious about Boxers. They reputedly have a high coe but who really knows?
Surf mag would probably do measurements like that. They are anal thorough and precise Germans. I wonder if they have done it in the past.
Not meaning to sound like I'm having a go at anyone but why do you need to know? What use is it?
The centre of lift in a flexible sail structure must surely wander a little (or a lot) in different wind forces and directions of air flow.
Even on finding its average position, what would it tell us that sailing won't?
All right kids, this time pay attention.
So you want to spend a loooong time ascertaining that your S1 will jump 1.8% higher then your Blade?
I'd rather know I had a stable COE (no draft shift) than know where it is.
Yeah, JP actually chop-hopped UP to the helicopter and landed there, 'cause it was too scary for him to jump down.
I'd be interested to see your results Notwal
Might even be interested enough to do some experiments myself... Mmmmmm science 
it's impossible to measure as every time you rig the sail you can vary the position of the COE
the COE is where you rig it to be.
if you want a high coe then use less downhaul,
if you want a low coe then use more downhaul,
want it forward use less outhaul, want it back further use more outhaul.
and so on.
a wise man once said, he who drinks the most coronas ends up with a lime helmet!
And the mast bend and flex response also affects it the COE on a wave sail it will be higher going out and jumping and lower while riding as the angle of attack and apparent wind will change as you are moved along by the sail. Going upwind and locked in it might be higher while going off the breeze it will be lower.
even the batten tensions might change height of COE.
I like to think of the COE as a beam of light shining on the sail depending on the angle of attack makes different shapes on the sail and can move depending on setting. I would say for a given sail/ mast and windstrength their is an eliptical area withing where the COE will lie depending on trim angle, sails setting, apparent wind angle and apparent wind speed.
