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Death Roll and how to avoid it...?

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G.R.F. View Drop Down
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Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Topic: Death Roll and how to avoid it...?
    Posted: 20 Jun 12 at 7:22pm
So, my jolly EPS showed definite signs of doing this joyous manoeuvre this avo in a bit of a hectic gybe in the run up to a mark rounding so I wondered if this is another example of kicker fiddling I should have engaged in.

It was quite puffy today probably a good force four on the sea of joy which translates to 2 - 4 inland, so off wind (which it never seemed to blow choosing only to puff up on the upwind legs)I left the kicker on, so I'm wondering if it had a contributory effect on the side to side roll that once started engages a life of its own.

So what's the story, it's tedious I don't want it to happen, fix it someone. Wink


Edited by G.R.F. - 20 Jun 12 at 7:22pm
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pondmonkey View Drop Down
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Post Options Post Options   Quote pondmonkey Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 7:58pm
tack round
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tim grasse View Drop Down
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Post Options Post Options   Quote tim grasse Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 8:13pm
head up a bit 

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G.R.F. View Drop Down
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Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 8:22pm
Tack round what? Head Up? 
It's a downwind leg the boat starts rolling from side to side, it hasn't anything to do with gybing it's just some sort of speed wobble, I used to think it was to do with wave action in the Blaze, this is a billiard table, it's got to do with the leech of the sail I'm sure of it.
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pondmonkey View Drop Down
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Post Options Post Options   Quote pondmonkey Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 8:38pm
put a kite on it and sail hot angles

or, squat down in the middle of the boat, tuck your head under your arse and kiss it goodbye... 
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sargesail View Drop Down
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Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 9:05pm
Oscillation "Death roll" is caused by the flow on the sail reversing (Because teh leech is sagging forward, the boat heels to leeward, the wind shifts or you get a funny wave), usually it starts at the top, and works down until more of the sail is affected, with each roll.  As you heel to windward the flow goes back to normal, so you roll to leeward, and it reverses again, and so on until you swim.

The tendency is to be react by moving weight to counterbalance but you can't be quick enough - so you tend to be out of phase increasing teh oscillation.

Finally at extreme angles of heel the rudder will work in a horizonatl (or part horizontal) plane not a vertical one.  So when you head up to correct the bear away it pulls the boat to windward too.

So what should you do:

Use more kicker(may not be fast of it depowers you be bending teh mast).
Sit more still - you can't beat the oscillation.
Sail in a safe by the lee fashion with stable reversed airflow from leech to luff.  (Often fast)
Sail in a stable broad reaching position.
Use a combination of the two to achieve your required heading.
When you roll to windward do not try and head up to correct.  Instead of pushing the tiller, pull it, thus pushing the boat flat with the rudder.

Finally buy the Rooster Downwind Sailing DVD.  Better than borrowing it because all thought it will cost money and you will feel a bit dirty, no one will know.  It shows it all really well.
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fab100 View Drop Down
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Post Options Post Options   Quote fab100 Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 10:06pm
What Sargesail said

Also, board down to go with kicker on and sheet in a bit.
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maxibuddah View Drop Down
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Post Options Post Options   Quote maxibuddah Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 10:48pm
Got to say that I always thought it was more to do with the rig accelerating faster than the hull and in so doing it caused the sail to lift, tilting the mast to windward. You counteract it and the rocking started. When I started in lasers in would rock you about 3 time before you went swimming but once I got better it seemed to be down to one. 

As the gust hits sheet in a bit and as long as you are not running by the lee this will depower it. If you are running by the lee you will need to steer into it (I think) to get the flow of the wind over the sail rather than into it.

To start with until you get used to it don't let the main out so far, say only 70 degrees rather than 90. This effectively sails it by the lee as sarge said. When a gust hits the wind tends to funnel out of the front of the sail rather than accelerating it which means the boat don't rock. It ain't fast but its safe and then once you have the hang of this then you can start letting the main out further as you get more confident. 

If you apply too much kicker the end of the boom is going to hit the water pretty damn quick in the gybe and you'll swim. If you have too little then even if you pull the main in the top of the sail is twisted and still presents itself square to the wind and in so doing still generates lift and movement of the mast to windward. 

My version is not a master class at all, and Steve DVD will show you how to do once you have mastered the getting along safely but slowly method I have suggested, but it is somewhere to start you and hopefully stop the death rolls that may put you off


Edited by maxibuddah - 20 Jun 12 at 10:57pm
Everything I say is my opinion, honest
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G.R.F. View Drop Down
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Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 12 at 11:26pm
I'm not about to buy Rooster anything never mind curing something like this, I knew it had to be the leech doing it, figured as it rolled up it was getting momentum until the power leaves then with no power support it falls back then starts again. It was a shift I think that set it off, I gybed and stopped it with a mark rounding before it could really get a grip, but I'm not happy about stuff like that, being the control freak I am, I dont really like stuff to happen unless i make it do it.

So, I already had a fair amount of kicker on, not an awful amount because it had been quite puffy up wind and I'd de powered a bit with downhaul, that of course could have been a contributory factor, if the downhaul did let the top of the leech twist off a bit, which tbh it didn't appear to.

I get the sheet in a bit, that's what i used to do with the Blaze, but it slows you down, then again so will death rolling right in I guess. The boom digging in isn't the issue it is on other boats, it's quite a high boom the racks go in before the boom does, and that's a whole other can of worms I bet.

I can only see it being a really serious problem in a force five and above and I'm seriously thinking of trying for the smaller sail for the winter, I was already racked out five holes, not sure how many more knotches there are.

Has anyone tried standing up to stop that rolling about? Just a thought.


Edited by G.R.F. - 20 Jun 12 at 11:27pm
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maxibuddah View Drop Down
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Post Options Post Options   Quote maxibuddah Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 12 at 7:17am
if you do stand I reckon you'll fall in quicker grf.
Everything I say is my opinion, honest
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