My thought is this: the spin designer assumes the luff will be relatively tight (the "90 degree, likely less rule) when the spin is up and tight and "at rest." I guess the spin luff in the pics might actually be tight but then it seems an error in measurement ( <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" /> ) or a change in the pole height or simply thinking the spin is up when it isn't. I wouldn't think the spin is supposed to be set like that. But then again, maybe I didn't read the previous posts that closely or something else is going on (which I assume it is). I guess if he thinks his spin is not cut right to have that twist then he is trying to induce some.... but a well cut spin shouldn't be set like that.

going back and rereading- said he set it like that on purpose. That suggests to me that his spin is cut wrong IMO

I've heard of spinnakers being designed to be used with a tight luff but I've never seen any like that used here in Aus.

This is my new Irwin spinnaker with the designed amount of luff "tension" (or lack of it). The halyard is up all the way.

PTP - Assuming the kite is cut wrong could be used. But in this case i can tell you (because I made this spinnaker)that the kite was cut for a specific luff length & the photo does not reflect the original design.

Gill - letting out luff actually flattens the kite as you are effectively allowing the luff to "lay off" & therefore flatten the sail similar to bending the mast for the mainsail.

FYI - The photo of gary's boat shows luff let out as he is attempting to depower the kite (flatten the shape) for his 75kg weight, myself on the otherhand prefer the fuller kite for my heavier weight & setting the luff where the kite was designed for. There are many people these days setting their luff loose, but the forget the flow on effect - ie twist. The line of the leech should never fall inside the line of the luff & the more luff that get let out the closer the two become effectively choking the sail.

At the end of the day its a balancing act & utlimately the skippers chooses where to set the kite for the conditions, not particularly a designers fault.

Tim Sheppard has confirmed what his kite was designed for & he is utilizing that design to the max. Obviously a happy fellow who knew what to ask for. <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />

I suggest when ever anybody buys a kite, some simple questions up front will save a lot of tuning time on the water.

Gill,

I think Marcus said what can be said on what to look for. I am no professional sailmaker or racer, but I have my theories and experiences. Based on that, I think a spi needs a long luff and an open leech.
If there is too much draft in it, it will have too much drag and not be fast. It will feel powerful, and it really will be powerful, but not fast. Power is not always fast..
A long luff generates more power for not much more drag (Klaus, rein me in if I am wrong). If the luff is designed overlong for the distance from pole to mast, the sail will be hard to trim right and you can not generate enough apparant wind with it and will have to go deeper than optimal. The pet peeve I referred to earlier is that I think current spis are designed and set with a luff not tight enough. The Tornado is getting there, but I still think it should be a bit tighter.
An open leech will not backwind your mainsail but help airflow over it. Twist is designed into the sail to help the leech open.

Measurement rules and what shapes you actually can make and fly while sailing are all constraints you will have to work within. If you want to study shapes a bit, look closely on the luff tape from different angles on a 49er, Tornado and Vx40. Try to find pictures from 90deg to the side and from straight ahead.

In reality, running a slacker luff tension (by easing the halyard or tack line) causes the sail to flatten more at the luff. A tigher luff induces more curve in the luff section, to the point where the luff will roll frequently.

Now can we discuss leach flutter? The last several times I've been out I've noticed my leach is fluttering when I'm trying to point up with the spinny. I have eased the halyard a good 6" or so to try to see if that made any difference, it didn't.

Am I trying to point too high or is the block too far back or is the mast raked too far back or is the spinny blown out? As I go deeper it stops, but when trying heat it up to fly a hull, it flapps.

Does your sail have a leech tension line in it? These allow you to flatten (easing) or curve/hook (tightening) the leech. It's a bit of a black art to get the right setting...but it is possible to minimize the flutter. You should not have it "helicoptering" audibly but some flutter is fine. Charlie Ogletree told me having it hooked slightly along the last inch or two is fine.

If you do not have a leech tension line, can you move the sheeting point forward/aft on your boat? This can change the force on the leech or foot...more aft sheeting point eases leech/tensions foot & vise versa.