Centre of lift of a sail?

Just because it's variable that doesn't mean you cant measure it.
Whats more the COE for any model/size of sail falls within a definite range for its recommended rigging.

i don't agree notwal.

coe is a function of so much. and to be honest, measuring the coe of your rigged sail on the beach will only tell you where it is on your rigged sail on the beach. sails use dynamic shaping when under load and that will vary depending on amount of load etc.

the only way to understand how a sail performs is to sail it.

this is exactly why i don't agree with the concpet that static seam shaping locks the draft. all it does is reduces the range.

...nevertheless, one of the core aims and challenges of good race sail design is to enable the COE to remain stable (both horizontally and vertically) through the varying loads that the sail will experience, whether via changes in wind strength, angle of attack, or water state.

Ideally it should be very easy to position your harness lines and your hands so that when you are hit by a gust you experience acceleration without needing to change the position of your hands or your body. If you can remain relatively still, everything remains balanced, you trim better and you go faster.

Despite this, on many race sails, being hit with a gust produces instant back-hand pressure, and this leads to a chain reaction of problems as everything has to adapt. Ultimately loss of control, loss of confidence and loss of speed are the consequence.

On this basis it's perhaps less important to know exactly where the COE is, than it is to enure that it stays there!

That's a fair question. Having not tried enough different brands of race sail I can't give anything like a comprehensive answer but I can say that North and NP are examples of manufacturers who have got it right on this score.

It would be interesting to hear other opinions on this.

As for sails that don't, there is no need to name names. If you find it difficult to get your harness lines into what feel like the right position, there is a good chance that the COE of your sail is moving. If it's moving then by definition there is really no way to position your harness lines so that they are always in the right spot.

The importance of a stable COE (from a race / speed perspective) cannot be underestimated, as it is one of the few things that actually can move. Once you are a sailing, your fin doesn't move, and nor do your foostraps, your mast base, your boom height or harness lines. All of these things relate directly to the COE of your sail, and your ability to set / tune them correctly is heavily reliant on the COE being stable.

If the COE moves around, for example when you get air or there is change in wind speed, then your body has to move to compensate. If your body moves, then everything else is thrown out of balance to varying degrees. One of the most common consequences is overloading the fin, which is not only slow but increases the chances of spin out - particularly when you land.

It was that machine (according to Windsurf Mag) that Bruce Peterson was playing with when he discovered the virtue of a loose leach.

With respect to "feel", sure only hands on feeling can provide that (forgive the tautology) but the rule of thumb is that feel can not reliably tell you anything to closer than about 10% variability. Designing by feel alone is second rate design.

i htink you're taking things a little out of context there notwal. either that or i put it poorly in the first place.

i am not suggesting that sails be designed by feel alone. for sure they need to be computer designed. it is a definate advantage to work out the flex variables, panel layouts and so on on a computer. certainly the brain can't do it as fast, accurate or efficiently.

but, at the end of the day no matter how advanced the sail software is all manufacturers need to rig the sail and test it. the advantage with the pc is that that feedback can be plugged back into the computer so it is there forever.

look at audio gear, the product with the best spec sheet doesn't always sound the best.

yes, that's what i said, but i wasn't saying it should move around when you are sailing.

i have no evidence but my gut feel is that the software enables a computer model that loads the sail and measures exactly where the coe is under load as well as drag figures, mast curves, foil etc.....

it would then spit out a panel pattern that allows it to be laser cut and stitched and also gives batten specifiactions.

i guess the KA boys are the people to ask as most of the sail makers (including all the big guys) us McSail.

so why i said it is irelevant to measure it is

a. because to get a true understanding of where the coe is you need the sail to be under load. and a stationary sail on the beach is not under load.

b. because you can adjust the coe when you rig the sail, including how high or low it sits, so you will get multiple outcomes

lol, i didn't metion any brands.

i should say though, i'm not a ka sailor..... i'm a sailor that chooses to use KA sails.

i switched to KA after demoing a Kult and sold all of my Ezzy sails which i felt didn't suit me. i also sold all of my north race sails once i tried the KA formula sail.

but that was a long time ago an i know ALL brands have come a long way and make great products.

now while we're on the subject, i think the last thing that could be said about KA is a lack of draft stability. actually it's the one thing most people comment on when they try them. not to say that is only a ka thing. most of the sails these days have great draft stability. NP being another very good example.

could it be that notwal started this thread because of the sails he uses.

no offence taken. i saw your tongue in your cheek!

whole i got your here, you being a deputy and all.......

I've started pestering Laurie about a photography forum or specifically a surf photography forum...... do you have any special powers! looking through the state forums a lot of photography stuff gets talked about.

ok, now back on track!

dave likes photography,