martin.langhoff

Stable spinnaker on Foiling/Apparent Wind runs?

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I am having a blast on my Whisper cat. One are I am finding it tricky is stable runs on spinnaker, from reach or tight reach.

Lately we've been having light winds (~8kt); in these winds under spinnaker we build up nice speed -- flying in apparent wind -- to about 8kt, which is for me easy takeoff speed. And we do take off :-) -- but as we speed up (ie 13kt, perhaps with an assist from a gust) we get to the point where the spinnaker luffs. Even if we avoid a complete luff -- we lose speed quickly, and the apparent wind is gone.

As things stand, we have exhilarating runs of a few minutes, followed by a slowdown. We pick ourselves up and go at it again. 

Is there a technique to get to a stable dynamic?

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Not that I've found other than a recut of the spinnaker to that of a Screecher.

The F16 spinny I had on my sea hugger A did exactly what you describe even though it was as flat as a sail conforming to spinnaker rules would allow. Getting the leech as tight as a drum and bringing the clew inwards and backwards helped but I never really got to a point where I could get the front 100mm not folding unless running at really low angles which was slow, that would then dump the whole sail.

The S1 design now has a really really really flat spinnaker which they maintain is spinnaker measured but you have to look at it and do wonder if its a Screecher. It doesn't really matter now as SCHRS has a measurement rule if its not.

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Just curious, You ARE falling off as your speed increases, right?   Your description sounds like what would happen in my non-foiling cat in a gust.....

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Ya, you need to bear off to keep your apparent wind far enough back. Or ease your main to keep the speed down, so you apparent stays back and you don't collapse the kite. 
Kind of a knife edge. 

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Yup. Fast cats (and tris) need to steer S shaped courses unless the wind is very steady. You're an apparent wind machine.

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Drive down in the gusts and back up in the lulls. You may also try going without the spinnaker.  Many foiling boats are finding that unless running a screecher in very light winds, the spinnaker doesn't work downwind.

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The faster boats accelerate way faster than us mere mortals can bring the sheets in, have a look at the vid on the other thread, watch the crew, then watch both crew and the tension on the tack. The tack and leading edge are already folding as the boat begins to speed up, the crew still hasn't bought the tension on the clew to tighten the sail for the new increasingly tighter apparent wind angle. Its not until the leading edge has folded that the crew has then thought about the tension on the clew. Too late Ethel.

It happens in seconds and unless you really are on the ball with that tension on the clew, the sail will fold. No steering will compensate and if you want to think that you can steer to keep the sail from folding, nah you haven't experienced a very light weight boats acceleration level. Once fully up to speed then you can steer a little but beware at those speeds probably in excess of 25 knots, the merest movement on the stick means lots of G force. The number of times I have been spat off when trying to control both spinny and rudder and getting it just so slightly wrong. But good fun though.

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@Waynemarlow spot on. I posted this topic right after the outing in the video :-)

There's stuff for us to improve upon -- the tack could have been tighter, both on the tack line and on a trimming/tension line in the sail, we sometimes do better trading sheets so crew can work the spinnaker sheet faster and with both hands. Overall we need to react faster. We are already easing off the main aggressively (as we need to keep the boat flat to foil); and the spinnaker is screecher-ish in shape.

Still... the essential dynamics are speed up -> luff to a standstill, repeat. With main+jib, luffing against the apparent wind can be a stable dynamic - speed up a bit, luff slightly, slow down, lose the luffing, speed up...

With the spinnaker's leading edge folding... the luff is nasty.

In most of that video, we are against a lee shore, so bearing away isn't a winning move...

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Sort of sounds like your out running the cut of your spin, when I was two on the wire with spin on my Taipan 5.7, the tack had to be a lot tighter due to the apparent wind we could generate, if you could find a way to play your tack from the wire you might be able to tighten once you get going and then maybe work out a good setting to leave it at, if you cant find a setting it might be time to look at getting a flatter spin cut

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