one more...

and one more

You need a lighter retrieval line, that is for sure <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

The processed image is attached. I had to cheat a little as the seam lines dont go horizontal, and the image was not too good (collapse at the second retrieval patch).
As you can see the measurement show that your spi has a draft of ca. 27% at 46% and 49% from the luff. I would say that this is too deep with draft too far aft. Was your kite trimmed for light wind in the pictures?
Why dont you try lowering your spi pole a notch and see what happens to the luff and shape?

If you want to play with the software yourself, it's available at: http://www.ukhalsey.com/accumeasuredl.asp
It runs fine on all modern windows versions, and under Wine in Linux.

Rolf,
Thats neat stuff. Thanks for the info. The wind was just a shade off of DDW because that was the orientation on the beach already. I think I might take some pics with a little more realistic point of "sail." I have heard that this kite is a fuller kite meant to run "deaper" than others, but I don't know for sure. I would like a little better wind to really get a better pic. The retrieval line is 1/4 tapered warpspeed which could probably be a little lighter but there was little wind. The low wind was certainly allowing the patches to be pulled a little more than normal. As for luff tension, I was able to twist just under 90 deg with my fist. I might try to lower the pole a little but it already seems really low- esp when running through chop and although a longer pole would help, it would screw up the sheeting angle, etc.
As for the numbers you mentioned, what, in your opinion, should the numbers be?
I have a better pic (I think) that I will take a closer look at.
And while I am at it- what really happens to a spin that is "blown out?" Does the draft move further aft?
p.s. sorry that this isn't an F16, but the same principles apply. Next time maybe on the general forum.

Personally I don't think the retrieval line needs to be tighter at all. Am I missing something ?

Secondly you can also get a tighter luff at the top of the spi. Alot of crews run a bead in the halyard line there and you can move that closer to the top of the spi or remove it completely. Additionally I suspect your F18HT has a spi gat made of simple high tension line. You can pull this a little tighter and get a tighter luff as well. And if you really have to then you made yourself a higher spi gate very easily with a drill and a piece of high tension line. So I would try to get the spi luff more tight by modifying the gate setup at the top.

Do you have pics of this spi gate ?




Don't worry about it !

Just don't tell this to W.F. he'll go ballistic if somebody tells him that the F16 calls is now supporting the F18HT sailors. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Welcome to the club PTP.

Wouter

Wouter



read above again....

Ooops ! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Wouter

I just changed the "gate" as you call it to the spectra wrapped around the mast as opposed to the SS bale that was rather limiting in rotation and also high friction. I have a 29mm carbo block with the spectra "bale" running through the center of the block and the block itself is attached to a pig tail with the hound about 3-4 feet up from there (some people have modified their HTs to have a longer luff spin and I wanted to preserve that option). The knot is as tight as it can be both on the halyard and tack line- but I think I will get rid of the stopper ball. Don't see the point really. Thanks for the help... gotta go crew on a monoslug... sort of kills me that I am doing that instead of sailing my HT.

PTP: Compare the shape of your spi with this old blown out Tornado spi from Gran segel. This spi have had it's luff line tightened to bring it's draft forward a bit and the leech line is overtightened. In a picture of a new spi, there would be less draft, positioned further forward. Entry and exit would also be a bit flatter. These spis are the "class standard" in the Tornado class, and I dont think your boat is much slower than a Tornado. I have some other photos showing the setup of this spi I could send you by e-mail if you are interested. Just PM me your e-mail adress.

PS: The spi in the picture is really tired!!

Rolf

don't you think that the Tornado class rule (minimum SMG set at 3,45 m i.d. 81,2% of maximum foot set at 4,25 m) makes the Tornado's spi different from the others? i.d. more "fat"?
All the other catamaran class rules states a SMG which is 75% of foot. This could explain the reason why Gransegel spis are excellent for Tornados but fairly poor for other catamarans (for istance F18s)
Thanks in advance for yr opinion

Question is wether the 6.2% difference in mid girth (SMG) dicate a different shape to Tornado spis as compared to F-16 and F-18 spis.

I dont know, and if we could get some definitive answers at all from e.g. Gran, Landenberger, E.P (Harry Pattison), Glaser e.a. about what constitutes a fast spi I would be really thrilled. It seems like the big sailmakers dont go public with their knowlegde about fast catamaran spis, but perhaps they share some with good customers. For mainsails and jibs the 'fast' parameters are well known.
I can speculate tough, and I would think the 6.2% difference in girth not enough to dictate a radically different shape. I know Gran Segel have made some F-18 spis with success. But penetration into the F-18 class is harder than the open Tornado class as the best teams usually are bound to specific gear by sponsor agreements. In my opinion, the important part about the leech is that it should not backwind the mainsail. Getting the balance between a open leech and well setting luff is hard, especially if you want the spi to be easy to trim and fast in different windspeeds. I am looking quite hard into the topic right now (from an amateurs viewpoint), and it's quite hard to get right.

Rolf,
I usually keep my main centered and sheeted relatively hard on downwind running the spin. It seems like you owuld have to REALLY oversheet the spin to cause backwinding of the main. If the wind were a little more crazy and you travelered down the main (which could arguably power you up more I guess which is not what you would want in high wind) then you might get some backwinding but in those conditions you wouldn't be sheeted in really firm on the spin anyway. Just wondering... not sure I have enough experience running a spin to qualify my opinion.

PTP,

we are discussing design, and I just stated what properties I would look for in a leech, not what a sailmaker would deliver today. Get a really old spi, designed to go slow and deep and try sheeting it in hard. I bet you would see a closed slot and backwinding main, unless you get separation first. You can also get a closed off leech if your luff isn't set up right, in my experience.
I have had the pleasure of owning a spi which had a leech closing the slot and backwinding the main if we tried bringing the virtual wind too high, hence my comment on the leech.

We dont set the main traveler centered, but let it out 15-30cm, depending on windstrength. We also sheet the main quite loose but not too loose, which is slow. We trim the main to the leech telltales until crew is on trapeze downwind, first then we need to sheet the main quite hard (but again, not too hard, which is slow <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> ).