Beach Cat Spinnakers

[Bill Roberts]

I have been looking at the Ronde Texel Race results/pictures etc lately and the size of the beach cat spinnakers jumped out at me, They are so small! Why? Why aren't beach cat spinnakers trimmed to the rear beam? They would be much wider and larger in area. They could sail deeper and faster than these little toy spinnakers we have today. What's going on? How did we end up here with these small chutes? Does anybody know? Tell me about it.
Bill

[gahamby]

That's a great question. What are the specifications for spinnakers on our various cats? I would like a light air off the wind sail for my SC15. Is there a source of information on what I need? Is this a stock item?
Thanks GH

[Bill Roberts]

Hello gahamby,
Back when sailmakers and sailors were experimenting with spinnakers on beach cats, early 1980s, there were no rules, no specifications. A sailmaker simply measured the three sides of the spinnaker triangle on the boat and then made a sail to fit. This is the way sails are made for non one design boats everyday.
There is a basic technical reason why beach cat spinnakers are the size they are today. It has nothing to do with rules (except maybe some scientific laws/rules).
The size was determined/selected/proven before there were any class rules.
So, beach cat sailors, what's the reason? How and why have the beach cat classes arrived at the
size and shape spinnakers we have today?
Bill

[fjviola]

Bill
I have ARC 21 #2101 that I bought from Eric Arbogast, who bought it from original owner Daniel Sassman (2001). Eye-straps on the rear-crossbar suggest it was set up for a 'Large' spinnaker, but the chute I got (good 'training wheels' for me to learn as I am a spinnaker novice) is cut for a Tornado. In fact, I have purchased an identical chute (foot 13'6", luff 25'7", leach 29'6") for when the old spinnaker is completely blown out. I am sure a 'Large' spinnaker as you described would be a ROCKET, as this Tornado chute lifts the ARC 21 out of the water in light air!

Might that most cats are now using the mid or end pole snuffers (vs trampoline launching) have anything to do with deploying/retrieval of a 'Large' rear-crossbar-clew chute'? I posted the 'continuous loop' system I installed on my ARC 21 at viewtopic.php?f=3&t=643 as I have a mid-pole snuffer. Before doing so we almost always 'shrimped' the spinnaker while trying to retrieve it as it drops much faster than we could haul it in.

I am currently in Panama for 6 months and missing my cat! Would very much appreciate the opportunity to speak to you direct as I would like to discuss the 'shared lift' of the forward daggerboards (wonderful design!). If possible, please send me your email and/or phone# to photo@violaphoto.com We have Vonage here on the island (radio internet/telephone) so I can call 'local' from a Houston 713 area code.

Thanks again for designing such incredible cats. First time I trapped out on a SC17 it just simply "fit" me!

franklin j VIOLA

[Mac M]

I thought that the newer spins were cut flatter than the older ones and reached better? If you could sail faster a little higher wouldn't that make up for not being able to go as deep? I know on the F16 I race when the wind picks up we downhaul the main more which flattens the sail, depowering the boat and allowing us to go faster. Wouldn't the flatter cut spinnakers follow suit and be able to handle bigger winds better than the large full cut spin sails?

[Bill Roberts]

Hi Mac,
It is true that the new spins for beach cats are flatter than they used to be or at least what they were for me, 1980s. Note that flatter also means much narrower because wide and flat doesn't work. Wide and flat has large radial wrinkles coming out of each corner of the spin. The fix for the large radial wrinkles is put much more shape back in the spinnaker and we have already been there and that doesn't work for beach cats. So we are left with the only other possible solution, "make the spinnaker more narrow". Why doe this work on beach cats and not work on keel boats?

[whalerman]

Is there a spin setup from say a Nacra or Hobie that I could rig on my 17? Some downwind help would be good.

[Bill Roberts]

Whalerman,
You can get the spin pole and spin sail and all blocks and lines etc needed to put a spin on your SC17 that fit perfectly from the SC17 factory, Aquarius-Sail.com. If you like, they can ship them to you tomorrow blue lable.
Call them at 651 462 7245.

[havliii]

So we are left with the only other possible solution, "make the spinnaker more narrow". Why doe this work on beach cats and not work on keel boats?

is the answer the apparent wind? catamarans these days don't seem to have a downwind point of sail anymore, they are moving so fast that the apparent wind is always on the nose. A dragging sail (spinnaker) would be of no use if the apparent wind is from the bow.

[Bill Roberts]

YES, YES, YES, Devloping, you have it right.
The keelboat monohull will not develop a sufficient increase in boat speed by reaching up or heating it up, as beachcat sailors put it, from a downwind run to offset the additional time required to sail a longer course. Therefore the keelboat sails straight for the downwind mark to minimise elapsed time for the leg. The downwind sailing keelboat's relative wind speed simply equals the wind speed minus boat speed.
The downwind sailing beach cat is so easily driven with the flat chute that it can develop a boat speed even greater than true wind speed sailing on a relative wind speed vector that it created with its own boat speed. This relative wind speed vector crosses the boat at an angle forward of abeam while the true wind is from the rear quarter. To sail on this point of sailing requires a flat chute, acting like a big jib, and the mainsail is trimmed to boat centerline. The rig looks like it is sailing to windward but the boat is going downwind, not dead downwind but within 30 degrees or so of dead downwind. The boat is sailing faster than true windspeed, sometimes twice true wind speed, and this method of sailing a downwind leg will minimize elapsed time.
Sailing downwind on relative wind also opens the window for smart tactics. Normal windshifts now can have a major effect on boat positions sailing downwind on relative windspeed.

[SC15Av8or]

Is this and could this be the reason why we are seeing Gennakers on the America's Cup AC45 verse a true Spinnaker ?? If so then the question goes to why are we even using spinnakers on these boats to start with when we should be using a Gennaker type sail?? Is there a Gennaker set up then for these cats ?? What modification would need to be done to fly a Gennaker??

[Bill Roberts]

Professional,
Gennakers are faster than flat spinnakers in a very narrow window. My experience is that a Gennaker will make my boat go 1 knot faster out of 20 knots when I am sailing downwind but high relative wind angle and I can hold the boat down. The spinnaker is faster sailing deeper and the window is much wider. Also to make the Gennaker work, the luff must be very tight, minimum luff sag, and this drives mast loads, axial compression, through the roof. We would all would have to have bigger, stronger, stiffer, heavier, masts. I have broken a mast flying a Gennaker. Also the shape of the race course can favor one type of sail or the other. The other driver is how much relative windspeed can the boat develop? If the boat can develop a large amount of relative windspeed, this in itself takes the relative wind angle far forward on the boat. In this situation it will let the boat sail deep easily. Then it is possible to get by Gennaker all the way. A boat doing this succesfully would have a 30 degree or so jibing angle. Our beach cats won't get there. We are better off with flat spinnakers. In a light air situation, close reach, the Gennaker is fast and you probably can't fly a spinnaker without it pulling mostly sideways and then the Gennaker is faster.

[whalerman]

So if we are looking for larger, flatter jib type of sail why not put a large roller furling jib on the end of a spinnaker pole? This solution would make management of the sail much easier as well as provide the larger surface area required of a down wind sail. Just a thought....

[Bruiser]

So if we are looking for larger, flatter jib type of sail why not put a large roller furling jib on the end of a spinnaker pole? This solution would make management of the sail much easier as well as provide the larger surface area required of a down wind sail. Just a thought....

You can. Check out the AC 45's and 72's that is exactly what they are doing. I think what Bill is saying is that the platform (boat) has to have the speed potential to build the apparent wind forward enough to then drive the boat with speed on very deep (down wind) angles. If your boat has that potential then it will work out better than a spinnaker. My guess is almost all of the RC and ARCs could do it. I would think most of the Supercats can as well. Hard to tell until some boats go head to head to see. However over the years multihull spinnakers have continued to be built flatter and flatter so that we are at that intersection right now. The new spinnakers I am seeing now are basically big jibs.

[Bill Roberts]

Hey Guys,
As the downwind head sails become flatter, they are also becoming narrower and smaller in AREA. In the limit the smallest downwind headsail is the Gennaker trimmed to the rear beam. The Gennaker will produce more force per square foot but the square feet are down
in the Gennaker. A flat spinnaker is significantly larger in area than a Gennaker. A big deep spinnaker is larger in area than a flat spinnaker. The flat spinnaker will work with the air flowing across the sail like a jib and produce much more force per square foot of area than the big deep spinnaker. The result is more sail thrust and speed out of the smaller flat spinnaker on the easily driven beach cat. Also the loads in the rig are less with the flat, small spinnaker than with the Gennaker.