I was looking at different F-16 spi shapes in photos and measuring their basic geometry last night. It seems like there is a noted difference between sailmakers. The Ullman spis look like they are cut with a straight or even hollow leech (which I like, makes the spi easier to fly properly in weak winds), whereas others look like they have a quite rounded leech. What is surprising is the amount of round in the luff, and how slack they are when sailed.

I made a list of photos from the F-16 galleries, which show how different spis are set up:
http://www.formula16.org/gallery2/main.p...alNumber=1&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=1&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=2&
http://www.formula16.org/gallery2/main.p...alNumber=1&
http://www.glasersails.com/F16Spin.htm

Some small comments to the different spis. Looking at the last two links above, a Glaser spi and a Taipan spi (dont know the brand), the leech round is easy to see.
Having a rounded luff like in the pictures makes the luff longer, which is good. But it also means that you can not go as high (build as much apparent wind) as you could with a straighter luff. However, becouse the 75%mid girth rule is in effect for F-16 spis, there is a minimum permitted chord.


Have anybody measured the geometry of their spis, luff, leech, foot length and mid girth?
Some of those spis look like they are down to minimum mid girth (I measured some photos to have less than 75% mid girth, but photo analyzis is never correct!).
Are the newer spis buildt to their max size, 17.5m2?
Have anybody bothered to measure their spi luff length and compared it to the distance from the turning block on the spi-pole and the halyard block?

I am working on my own design, and feedback on the above would help a lot. If anybody want to download Sailcut and comment directly on the design, I'll post the design file.

My Landenberger spi has been measured on Texel, these are the measurements:

SF 3,40 (foot)
SL1 8,06 (luff)
SL2 6,7 (leech)
SMG 2,6 (mid girth)
area spinnaker 16,97
SMG as % of SF 76,47 (mid girth)

A picture: http://www.catamaranparts.nl/BladeF16b.htm
I think the spi is fairly easy to handle, doesn't collapse too easy. Needs a fairly high luff tension otherwise it will become very hard to prevent collapsing.

Maybe a little better spi than my last Goodall (2004) but way better than my first Gooddall (1999)

Geert

Thanks Geert, that was just the values I needed to confirm what I had found, that the F-16 spis are not up to max size. (Nothing wrong in that, better with an efficient shape than max. sailarea)

The shape of your spi looks just like the latest Landenberger Tornado spis. I like them, but will look a bit on draft distribution and the luff. I still think Gran Segels Tornado spis are a bit better.

Rolf,

I'll try and measure my new kite next weekend if I have time and let you know.

Pick the boat up Next Saturday / Sunday <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Looking forward to that Simon, and I would like lots and lots of photos of your new love even more!
If you (or others) have the opportunity to hoist the spi, lie down on the ground under it and try to capture as much as the spi as possible in the photo, it is possible to say something about the difference in shapes. This is something you should do with every new sail btw. document it's shape. Then it is easy to detect any changes in the sail, and determine wether it should be replace.

I'll try.

It will be a fairly long luffed kite as the new boat has a low bridal as per the Capricorn. We've not even designed the Jib yet as we need to work out exactly what shape the "space" will be.

Hey, that sounds interesting! I have wondered about how far down it is prudent to lower the spi-pole before you get into trouble in waves.

All this talk about Kites - What is the sail material <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

My spinnaker is pretty much uncomparable to todays shape, so no use giving you the specs on that. I have had no money to replace it.

Goodall 2002 shape. Geerts 2004 shape is better then mine and my spi was better then his Goodall 1999. Goodall did improve his designd significantly over these year apparently.

Wouter

Dermot,

what are you asking about? What materials the different spis are buildt from?

Yes Rolf, What spinnaker material is being used by the modern sailmakers.

Mostly nylon treated with different resins. Contenders SuperKote (SK) 90 is common in Tornado spis. The different cloth manufacturers have their own products.

Ref: http://www.contendersailcloth.com/SPICLOTH.asp?ProdItemkey=SL

Have you any thought on Dynalite ?

I have no experience with Dynalite. Only thing I heard was that some sailmakers charged a premium for working with that cloth <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

(You should know, I am no pro sailmaker, just trying to learn as much as possible about how to make cats go fast. Sailmaking is part of that. Normally I work with computers and system administration)

My Piggott spin is Dynalite. It looks good and snuffs incredibly easily, but the jury is still out on the shape/speed.

It's such a different shape to everyone else's Landys that I'm having to start from scratch on a sheeting position that works.....

It is very slippery and does snuff so well. Because of it's slipperyness it may be difficult to work with and sailmakers may avoid it.
It also stretches <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" /> especially along the luff, and I have had problems with this.

Do you have a luff line installed inside the luff tape (2mm spectra or similar, no cover/hose), or is it the cloth itself that stretches behind the luffline?

There is no luff line, only a leach line. The luff tape and sail material seem to stretch along the luff.

Interesting. Linsay Irwin only puts a luff line in his spinnakers and no leech line. Different thinking!

Here are some pictures of a professionals attempt at a spi for a fast beachcat.
I know what I think about it, but would like to hear opinions. Pictures are not the best, but it gives you an idea of how it would look when flying.