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F18 Downwind Control in Gusty Conditions #211862
05/25/10 05:57 PM
05/25/10 05:57 PM
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Vancouver, BC
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westcoaster Offline OP
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Recently I've had a capsizes when sailing downwind with the spin up in gusty conditions on a Nacra F18. Winds were about 10-15 knots, with gusts up to 20-25 knots that were accompanied by a header with the wind shifting about 15 degrees.

Can I drop my traveller as the gusts hit to depower the boat? If the mainsheet is still tight, will dropping the traveller risk me breaking the upper part of the mast?

Is there some better way to deal with these sort of gusts?

What I've found is that if we're sailing with the windward hull kissing the water in the lulls, when we get hit by the gusts the boat heels over almost instantly. Once it isn't fairly flat, the rudders (well, the one that isn't already mostly out of the water) are fairly sluggish, and the boat won't bear off quickly enough. Then we get to swim.

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Re: F18 Downwind Control in Gusty Conditions [Re: westcoaster] #211865
05/25/10 06:26 PM
05/25/10 06:26 PM
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A foot of traveler should get you enough ruddr time to turn down.


Richard Vilvens
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Re: F18 Downwind Control in Gusty Conditions [Re: F-18 5150] #211871
05/25/10 07:06 PM
05/25/10 07:06 PM
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Brett Goodall Offline
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You need to get your crew sheeting the spin much more... this sounds like the northerly we get at Port Melbourne. Crewing in these conditions I'm constantly sheeting a good 3-4 foot of sheet.

Re: F18 Downwind Control in Gusty Conditions [Re: F-18 5150] #211929
05/26/10 12:50 PM
05/26/10 12:50 PM
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westcoaster Offline OP
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Originally Posted by hobie18rich
A foot of traveler should get you enough ruddr time to turn down.


Thanks, so dropping the traveller 1-2 ft doesn't take away too much support from the top of the mast that there's a risk of damaging anything?

Originally Posted by Brett Goodall
You need to get your crew sheeting the spin much more... this sounds like the northerly we get at Port Melbourne. Crewing in these conditions I'm constantly sheeting a good 3-4 foot of sheet.


I'll certainly try to get my crew to trim the sheet a bit more. Is this a situation where having the spin out of trim is leading to more heeling force on the boat?

Re: F18 Downwind Control in Gusty Conditions [Re: westcoaster] #211938
05/26/10 01:43 PM
05/26/10 01:43 PM
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mikekrantz Offline
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you'll be fine dropping the traveller, it's easing the mainsheet that is the big no-no.

Another problem is bearing away after the hull rises, the angle of the rudder at that point becomes a down plane, and drives the bow down. Your trimmer needs to call the puffs so you can turn down at the beginning of the puff, not after its already on you.

Re: F18 Downwind Control in Gusty Conditions [Re: mikekrantz] #211944
05/26/10 02:21 PM
05/26/10 02:21 PM
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westcoaster Offline OP
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Originally Posted by mikekrantz

Another problem is bearing away after the hull rises, the angle of the rudder at that point becomes a down plane, and drives the bow down. Your trimmer needs to call the puffs so you can turn down at the beginning of the puff, not after its already on you.


Yeah, I figured that was a large part of the reason that the rudders become ineffective once the boat is heeled over. They are largely generating lift on the stern once the boat is inclined to 45 degrees.

Calling the puffs upwind is pretty easy, but downwind I find it somewhat more challenging. I'm definitely working on getting better at it, but I'm happy to use the traveller to cut down the amount of swimming I have to do while I learn.

When the traveller is dropped, I'm letting more air spill off the leech of the mainsail, reducing heeling motion, right? In addition to this, since the main isn't generating as much force on the boat any more, am I also moving the center of effort for the boat forward? Would this result in more lee helm, and help the boat bear off?

Re: F18 Downwind Control in Gusty Conditions [Re: westcoaster] #211956
05/26/10 04:23 PM
05/26/10 04:23 PM
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correct


Richard Vilvens
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Re: F18 Downwind Control in Gusty Conditions [Re: westcoaster] #211959
05/26/10 04:35 PM
05/26/10 04:35 PM
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Originally Posted by westcoaster

Calling the puffs upwind is pretty easy, but downwind I find it somewhat more challenging. I'm definitely working on getting better at it, but I'm happy to use the traveller to cut down the amount of swimming I have to do while I learn.

When the traveller is dropped, I'm letting more air spill off the leech of the mainsail, reducing heeling motion, right? In addition to this, since the main isn't generating as much force on the boat any more, am I also moving the center of effort for the boat forward? Would this result in more lee helm, and help the boat bear off?


If you find it difficult to know which direction the puffs are coming from, you might want to put some yarn on the side stays. They will point to the direction that the puffs come from.

You have the effect of letting out the traveler ocrrect. One thing that use missed though is that you will be closing the slot between the spin and main. Although more dangerous, in theory, letting out mainsheet (don't drop it!) should be faster because it twists off the top and flattens the spin by decreasing the luff tension.

If it is gusty, you may not be able to react fast enough on the mainsheet because it requires you to let out and pull in a lot of rope.

I found that weight distribution makes a big difference. Getting the crew on the trap makes the hull come up slower. It also makes turning down more effective because you are going faster and have a higher center of gravity. if you can get the crew to crouch in lulls and stretch out in puffs, you can control the puffs better too.

Re: F18 Downwind Control in Gusty Conditions [Re: westcoaster] #211963
05/26/10 05:31 PM
05/26/10 05:31 PM
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Err... thats what a bloody nF18 does!

One thing that you can do is make sure that you have a decent kite. Any sign of a tight leech and gust response goes out of the window.


Paul

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Re: F18 Downwind Control in Gusty Conditions [Re: TEAMVMG] #211987
05/26/10 11:24 PM
05/26/10 11:24 PM
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Thoughts on spin trim in response to the puffs? Are you sheeting out or in, as(before?) the puff hits?


Dave

Re: F18 Downwind Control in Gusty Conditions [Re: TEAMVMG] #212058
05/27/10 12:14 PM
05/27/10 12:14 PM
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westcoaster Offline OP
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Originally Posted by TEAMVMG
One thing that you can do is make sure that you have a decent kite. Any sign of a tight leech and gust response goes out of the window.


Our sails are a couple of years old, but still in ok (though not great) condition. Would having the luff a little too loose have a serious effect upon gust response? The tack line we're using has a bit of stretch to it (probably 1-2 in. when we heat up in strong winds) and I've been meaning to replace it, but haven't got around to it yet.


Originally Posted by davefarmer
Thoughts on spin trim in response to the puffs? Are you sheeting out or in, as(before?) the puff hits?


When anticipating the puffs, (particularly the ones I'm describing which were accompanied by a header) I'd say we were sheeting out the spin a little and bearing off before the puffs hit. Once the puff hits we're heating up enough to keep the windward hull out of the water.

In the case of when we didn't anticipate the puff at all, probably we're sheeting out a little and *trying* to bear off as the puff hits, but mostly we're just going over.


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