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.
Rolf,
Did they give any idea of the "slack" in the luff when sailing.
While looking at my new kite I was very surprised at the amount of slack John was planning to put into the luff. Landy said 10% and after some faffing around waiting for some breeze (only about an hour) we finally proved that this was about right. AND, it looks very much like those pictures - we did not have time to take any as the wind was all over the place (direction and strength) and so we had to be carefull putting sails up in the yard. One un-intensional hull fly on land was more than enough to get the sails down !!!
Pulling the Luff tight gave a very full front 15% and looked V slow....
no indication from the sailmaker about how much 'slack' there would be when sailing. I always tought about this 'slack' in spis as negative luff round, but perhaps there is some other terminology that should be used.
Do you mean John, as in John Pierce?
10% 'slack' on a 8000mm long luff.. That is a lot of 'slack', if that is how it's calculated <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" /> 1% is more like what I would expect. If you pulled the luff tight and the spi was not designed for it, I would expect draft to move forward. With some real pressure in the sail, draft should move somewhat aft, but how much.. There is much fun to be had with saildesign, and especially with relatively free flying sails like spis.
Take care with your new boat, wich is much to beautiful to damage so early!
no indication from the sailmaker about how much 'slack' there would be when sailing. I always tought about this 'slack' in spis as negative luff round, but perhaps there is some other terminology that should be used.
Do you mean John, as in John Pierce?
10% 'slack' on a 8000mm long luff.. That is a lot of 'slack', if that is how it's calculated <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" /> 1% is more like what I would expect. If you pulled the luff tight and the spi was not designed for it, I would expect draft to move forward. With some real pressure in the sail, draft should move somewhat aft, but how much.. There is much fun to be had with saildesign, and especially with relatively free flying sails like spis.
Take care with your new boat, wich is much to beautiful to damage so early!
Opps, maybe not 10% <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />
2-300mm is still more than what I have seen on faster boats (F-18 and Tornado. But the F-16 two up should be as fast and this have similar apparent wind <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> ). Rule of thumb there is that you grab the luff with your fist, and rotate it between 45 and 90 deg, at least it used to be. I guess this lead to the following question: If you grab your spi-luff with a fist and rotate, how far can you rotate your fist before the luff becomes tight?
If 2-300mm is the norm, you need really big hands to stop at 90deg <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />
2-300mm is still more than what I have seen on faster boats (F-18 and Tornado. But the F-16 two up should be as fast and this have similar apparent wind <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> ). Rule of thumb there is that you grab the luff with your fist, and rotate it between 45 and 90 deg, at least it used to be. I guess this lead to the following question: If you grab your spi-luff with a fist and rotate, how far can you rotate your fist before the luff becomes tight?
If 2-300mm is the norm, you need really big hands to stop at 90deg <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />
Yes much more than the 35 - 90 deg rule. Kite just looked horrid when we set it up "how I thought it should be". Set it up with 300mm. I'll try and take pictures weekend after next.
We were out measuring and studying an old Gran Segel spi today. Measuring luff curve was fun. Pretty much straight, but not at the bottom. Otherwise the spi was cut more or less like a genoa on a 35foot monohull.
Picture show spi luff folded twice (luff folded and then folded back again), so the luff curve can be compared to the relatively straight edge of the fold. No wind today, so we spent our alotted time measuring og tinkering on the boat..
More good photos demonstrating different shapes anybody?
I started a similar thread a few weeks ago. I take this opportunity to beg you to measure also the distance between end of pole to max halyard. It could be interesting to evaluate also if different sailmakers have a different approach into the "EXPLOITATION" of the distance available between mast and pole. I guess that the average distance between end of pole and max halyard is around 8,000 m (most likely slightly less). in fact class rules fix max hoist at 7,500 m and max pole lenght at 3,500 m then square root of (7,5x7,5 + 3,5x3,5) = 8,275 m
Re: F-16 spi shapes
[Re: Catfan]
#89407 04/16/0705:49 AM04/16/0705:49 AM
I dont think you can assume that there will be a 90deg angle between spi-pole and mast. Mast rake and spi-pole height will influence this, so a*a=b*b+c*c might not be correct.
The picture is of a Gran Segel mk-4 Tornado spi. Luff length on this spi is 9130mm while distance from bearing point on the spi-pole to bearing point at the mast is 9100mm. Max allowed luff length in the Tornado class is 9150mm. I just tought it was a good picture showing how they do the luff of their very good spis. It's definately what the sailmaker do with the allotted geometry that is important. E.g. last week I learnt that the radial panels should not be wider than 6deg. More than that and the cloth would not be able to withstand the bias loads in strong winds and the surface would be uneven = more drag, less good shape and shorter lifetime of the sail. This means that more panels are needed, but this brings the price up..
I find the subject of sail trim and design wildly interesting. It's very rewarding when sailing to know the whats, wheres and whys of the sailshapes you want for different conditions. It's a bit surprising that so few participate and show interest when these discussions pop up from time to time.
Rolf I am aware that more mast rake lenghtens the distance and more spi-pole height shortens the distance and that usually there is not a 90deg angle between spi-pole and mast (in the REAL world my guess the angle is less than 90deg). My indication was aimed only to enter in the ball-park. On a different note I appreciated very much yr info about the "correct" width of the radial panels. This is the kind of info that we should share on this Forum. I agree in full with you: it's VERY surprising that so few participate and show interest when these kind of discussions pop up from time to time. Only these discussions can make us better catsailors!
Hi Rolf here are a few snaps of my Landy kite. Definitely a different luff shape than the Gran Segel, as the luff appears straight but there is a lot of shape behind the luff as I couldn't fold the kite the same as yours to produce a straight line as a datum point.
Thanks for the photos Mark. Fun to see how much apparant draft there seem to be in Landys F-16 kites.
Having a right line in the first fold is nice and should be possible, but it's the second fold you need to work with. No wrinkles in the fold and let the luff tape take it's natural position. It looks like there is a rather severe crease at the bottom of the second fold, just to the left of the rather nice concrete brick you used to hold it down <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> I am unable to download the first image unfortunately. If you really want some useful information about the shape of the spi, try to get some photos of the spi while flying. Just lie down under the spi pole and shoot upwards into the trimmed spi. Easiest to get a good result if done on land <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" /> With such a photo, it's relatively straight forward to analyze hos much draft there is and where it is.
Got a question.... Are all (I guess most would be a better term) spins designed to have a luff that adheres to the 90 deg fist deal? Someone who knows what he is talking about once said that my spin (smyth, a little old) is designed for a "tight" luff. What would that mean? tighter than the 90 fist? What really happens if the luff is allowed to fall off some either by simply having the spin pole higher vs loosening the tack line? I am slow compared to other boats and am wondering why <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
Re: F-16 spi shapes
[Re: PTP]
#89413 04/20/0707:14 AM04/20/0707:14 AM
. . .I am slow compared to other boats and am wondering why <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
Join the club! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
I'll make a small wager that the main problem is sailing the proper course i.e. keeping 90 degree apparent wind. It takes time to develope that skill.
The cure is to get in all the time on the water you can. Happy sailing!! <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />
Re: F-16 spi shapes
[Re: fin.]
#89414 04/20/0707:39 AM04/20/0707:39 AM
Pete, you sail with the wind at 90deg apparant when going downwind with the spi? Is that a normal apparant wind for going downwind on a F-16? Have you tried going higher to build more apparant and drive off with the higher speed?
PTP: The 90deg rule is a very loose rule. I believe it originated in the Tornado class with a certain setup there, but the class have since gone to a tighter luff. How loose the luff should be depends absolutely on the design of the spi. The trend is for tighter and tighter luffs on fast boats (like your 18HT). I have never seen a Smyth spi, so I dont know how he does it, but why not experiment a bit? If you let out on the tack line or halyard, you loose much of the draft in the forward part of the spi and move it back. Leech will open more and likely flutter. You will be able to go higher against the wind with the spi like that, but sideways forces will increase a lot compared to your forward forces.
Why not supply some photos taken from below the spi while it's sheeted in its sailing position, and you will perhaps get some more useful responses. Post them here, and I'll run them trough Accumeasure. [quote]If you really want some useful information about the shape of the spi, try to get some photos of the spi while flying. Just lie down under the spi pole and shoot upwards into the trimmed spi. Easiest to get a good result if done on land With such a photo, it's relatively straight forward to analyze hos much draft there is and where it is. [quote]
Pete, you sail with the wind at 90deg apparant when going downwind with the spi? Is that a normal apparant wind for going downwind on a F-16? Have you tried going higher to build more apparant and drive off with the higher speed?
Yes and yes. But maybe I'm wrong! It wouldn't be the first time. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />
I know! <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" /> How 'bout a whole new thread!! <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Pete, you sail with the wind at 90deg apparant when going downwind with the spi? Is that a normal apparant wind for going downwind on a F-16? Have you tried going higher to build more apparant and drive off with the higher speed?
PTP: The 90deg rule is a very loose rule. I believe it originated in the Tornado class with a certain setup there, but the class have since gone to a tighter luff. How loose the luff should be depends absolutely on the design of the spi. The trend is for tighter and tighter luffs on fast boats (like your 18HT). I have never seen a Smyth spi, so I dont know how he does it, but why not experiment a bit? If you let out on the tack line or halyard, you loose much of the draft in the forward part of the spi and move it back. Leech will open more and likely flutter. You will be able to go higher against the wind with the spi like that, but sideways forces will increase a lot compared to your forward forces.
Why not supply some photos taken from below the spi while it's sheeted in its sailing position, and you will perhaps get some more useful responses. Post them here, and I'll run them trough Accumeasure. [quote]If you really want some useful information about the shape of the spi, try to get some photos of the spi while flying. Just lie down under the spi pole and shoot upwards into the trimmed spi. Easiest to get a good result if done on land With such a photo, it's relatively straight forward to analyze hos much draft there is and where it is. [quote]
Good idea... I will take some this weekend. I imagine a lot of it probably has to do with the spin being a little blown out, but I will get some pics.
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