OK by allowing twist... which is like feathering the top of a sail, and in effect stopping it working.
It is good to watch a video of sailboards sailing with a lot of twist in the sail... I once saw a sailboard speed week championship video, the tops of the sails were flapping like a flag... the battens and tension on them stopped a fair bit of it but they were flapping. Next time your on the water watch other sails for the top flapping about just a little. (you won't see it on your board as your looking almost straight up)
I normally don't take into account twist to much because its one thing that the sailor can control with sheet pressure and angle.
And yes if you allow lots of twist of sail top feathering it will lower the CE, but it will also cause air drag.
I have done a picture of what would occur if the tops of these sail were twisted or feathering, the twisting line would be about where the black line is.... and if we then do the same line drawings on the effective sail area we end up with a totaly different CE point.
Sorry I must disagree here. A twisted sail on a landyacht can still be producing drive. In fact more drive if you consider the direction that the wind is traveling over the surface. The sail shape becomes more like a turbine accelerating the wind in an upward direction.
It may look like the wind was coming from behind, but I can assure you the wind was from the side as I was standing next to the photographer. Yes the photo is an extreme example of sail twist, but my point was that a twisted sail can still hold camber and still be producing drive.
There was earlier mention of Sail Feathering and Air displacement over the top rear of the sail. I have mounted Long Woolen Telltales at the top of the new sail and it would seem that the tendency is for a fair bit of wind movement upwards and off the sail. This is where I was going to try a Truncation/Stall Packs to redirect the Air straight back over the sail. I am sure it would cure the p[roblem but whether it is worth the effort is the question?? How much efficiency it would gain?
Ron]
btw the formula for determining the spanwise position of the centre of effort for a wing with different lift at the root and the tip is as follows:
Position = Span * (A + 2B) / (3A + 3B)
Where A is the lift at the root, and B is the lift at the tip.
So for a triangular sail, the position is as follows:
Position = Span * (A + 0) / (3A + 0)
Position = Span * (1/3)
So the position of the centre of effort will be 1/3 of the way up the mast, measured from the boom.
If you know the theoretical position of the centre of effort (centre of pressure) for your particular foil, then you can draw a line between this point at the root, and the tip of the mast. The centre of effort will be 1/3 of the way up this line.
For a sail with a fat head and twist, you can assume that the lift at the top will be minimal, so the height of the centre of effort will still be 1/3 of the way up the mast.
Unfortunately theories are fine for solid objects ... soft sails are VERY variable things the CE and the position can be changed up / down and forward / back.
Sailboards use this principle to the maximum for steering etc.
Knowing about CE, CB, CG, CLR / CR etc it's more about knowing what your yacht is doing and why its doing it......
Ya missed one... CE One third up One quarter back
In verticle line or thereabouts with the other two
Go sailing 
I found the balance point for aus230 today using a board to find the point with the sail fully sheeted. Could someone mark the center of effort point on the attached pic. Thanks
Cheers
vic
As close as i can make out it would have to be a point directly on the top of the three
on the left hand third(RedSquare)
Where the diagonal red lines intersect is the center of area of the sail. Draw a horizontal line at that point. I would balance between 25 and 33% back on that chord line. Directly below where you had your ratchet pulley attached. Dont believe a word these lefroy guys tell you Vic. They're just messin with ya.
thanks guys. That helps me heaps up to now I have been adjusting my sail rake without actually knowing what it is all about
Cheers
Vic
OK I just measured two of my sails, and the results are as follows:
7m: centre of effort is 30% back from the luff, as measured
5.2m: centre of effort is 27% back from the luff
So around 28% would be a pretty close sort of figure. You could even use 25% (1 quarter) as it would be near enough.
Note that the centre of effort does move around in gusts and with different amounts of outhaul and downhaul, but experimentally it only moves around a percent or two.
This is what I got:
Note that this is assuming full twist under load -- if the sail is cut so that the head still provides lift then this point will move slightly up and backwards.
when I laid it right back the back wheels pushed sideways(on a loose surface). If I stood it right up there was no speed. Somewhere around 10 to 12% seems to work best
Not quite sure what to make of this but i9t all sounds very familiar. Could it be that we are getting the mast Balance and tension to the point that it is acting like a Mast and Sail on a Square rigger only sideways Most certainly feels that way, particularly through a turn as one is bringing the machine through stronger winds and the Apparent Wind increases the whole unit slides sideways
Ron
PS; Is that what you are feeling AUS?
keep in mind that vics yacht has tall skinny wheels
the tall wheels give better resisstance to lateral forces, so the CLR moves back, which allows you to move your CG back and sail with less weight on the front wheel
this allows you to rake the sail back even further than you could if you were running 4.00x8 wheels.
the cl5 sportif heavy pilots were all raked at12degrees in Argentina, the light pilotsback at 10 degrees, and the promos were all between 7-10 degrees.
I suppose i could have told you all that before , but it was kinda nice to sit on the measurements for a few years
Clarifying once again [sheeesh] the yacht I was referring to above was a class5
also with tall skinny wheels
The mini with 4,00x8 wheels doesnt seem to be so sensitive to the CE position
or is that due to the unsurpassed skill of the designer? 
[landy]
sorry , cant the credit there, original width,length and mast position were from a blokart , so credit to Paul Becket
raking the mast more, going back to a traditional rig, cutting the cost, getting the feet back to work,starting a Y frame race,
getting you all making your own sails,and generally having cheap fun.......
...... happy to take credit for those minor details
