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Death Roll and how to avoid it...?

Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Technique
Forum Discription: 'How to' section for dinghy questions and answers
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=9529
Printed Date: 04 Dec 20 at 5:46am
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Topic: Death Roll and how to avoid it...?
Posted By: G.R.F.
Subject: Death Roll and how to avoid it...?
Date 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


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Replies:
Posted By: pondmonkey
Date Posted: 20 Jun 12 at 7:58pm
tack round


Posted By: tim grasse
Date Posted: 20 Jun 12 at 8:13pm
head up a bit 



Posted By: G.R.F.
Date 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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Posted By: pondmonkey
Date 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... 


Posted By: sargesail
Date 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.


Posted By: fab100
Date 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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Posted By: maxibuddah
Date 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


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Everything I say is my opinion, honest


Posted By: G.R.F.
Date 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.


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Posted By: maxibuddah
Date Posted: 21 Jun 12 at 7:17am
if you do stand I reckon you'll fall in quicker grf.

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Everything I say is my opinion, honest


Posted By: pondmonkey
Date Posted: 21 Jun 12 at 7:34am
Well actually isn't the standing up bit verging on rock star territory? Especially in something like a Finn where a combination of induced roll, pump and hard bearing off all contribute to the physicality and technical challenge of the boat at the highest level?


Posted By: G.R.F.
Date Posted: 21 Jun 12 at 8:36am
Well for me, standing is obviously more akin to what I've spent most of my racing life doing, our boards can wobble a bit especially if we leave the plate down, off wind, you simply counter by bending the knees.

The only issue, there's not much to hold onto, the wiggle stick doesn't provide much counter balance to the mainsheet, which is the only other stabilising do dah to hang on to, it does feel more natural though, but as you point out you do feel a bit 'rock star' tall poppy when all about you are seated.

Would it in itself counter that death rolling though, I seriously doubt it, sheeting in does sound the best answer I've read here...


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Posted By: sargesail
Date Posted: 21 Jun 12 at 8:46am
Standing makes it worse - the rig will still oscillate so you just add greater moment to it.  (and you're in the way when the gybe comes!).

Sheeting in is only one part of this equation - and its slow.  And unless used at the right time in the right way may still make things worse.


Posted By: maxibuddah
Date Posted: 21 Jun 12 at 8:54am
sarge, I know its slow but its a method for a beginner (and let's face in this respect grf is a beginner) to quickly and fairly simply stay upright. once he has got confident with that move onto the more advanced stuff as you suggested.

the important thing with being or starting to sheet in is that you ate not running by the lee. if you are then it is likely you will inadvertently gybe and then swim, which is why I said that you will need to steer into it.

one thought, is the EPS an unstayed rig or with shrouds?

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Everything I say is my opinion, honest


Posted By: pondmonkey
Date Posted: 21 Jun 12 at 9:29am
[tube]http://www.youtube.com/watch?v=hEQttj8E1b0[/tube]

[tube]http://www.youtube.com/watch?v=Hujuxvo3gLM[/tube]


Posted By: maxibuddah
Date Posted: 21 Jun 12 at 9:46am
that's all well and good Jimbo but wouldn't Graeme be better off learning the basics to get his confidence up with them then doing that. don't run before you can walk, unless of course he wants to jump straight in

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Everything I say is my opinion, honest


Posted By: G.R.F.
Date Posted: 21 Jun 12 at 9:50am
OMG how can they have the brass neck to accuse us of air rowing ffs...

And that other bit is wave surfing so not the same, I get that, can do it a bit on the sea, it's easier, more predictable if there are waves involved.

This was unpredictable without the benefit of an up slope of a wave to 'check' on.


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Posted By: G.R.F.
Date Posted: 21 Jun 12 at 9:55am
It's also probably not accurate to describe me as a 'beginner' per se, new to this type of craft maybe(boat without a spinnaker, they don't create this problem).

I clearly have been running before walking having only really spent much time on spinnaker driven off wind boats, except the Blaze which from memory wasn't quite as 'lively' off wind. Lively in a good sense, the EPS certainly appears to accelerate quicker than I remember my Blaze doing, then I never sailed it in the close confines of a lake where everything seems to happen faster.

Oh and the EPS has I guess what you'd describe as semi stayed rig, the lower section has a forestay and lowers, to about 2-3 ft above the deck.

Oh and another thing, you don't seem to see the Phantom doing this much, can't say I've noticed my chum (another ex racing windsurfer) having death roll issues, then he is a bit heavier.


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Posted By: pondmonkey
Date Posted: 21 Jun 12 at 10:06am
Is your Phantom buddy letting the rig go forward with adjustable lowers and forestay???  If not, then he won't be able to square the main, therefore he is in fact 'sheeted in a bit' as per Maxi's suggestion.

And Maxi, yep, the point of posting that wasn't for Graeme to start copying them, it was to highlight that an induced 'death roll' is actually fast in the most competent of hands.  As an ex laser sailor, you've probably experienced the upside of a fortuitous death roll survival... a shed load of speed and exceptional VMG to the mark on a dead downwinder.  Of course being able to initiate this and know you'll survive it, control it even... well that's a skill I never mastered LOL


Posted By: maxibuddah
Date Posted: 21 Jun 12 at 10:09am
that's cos we basically deep broad reach due tobthe shrouds and the boat has a flat aft section with hard chines round bottom bottom boats roll more. the beginner comment only related to death rolling experience

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Everything I say is my opinion, honest


Posted By: RS400atC
Date Posted: 21 Jun 12 at 10:24am
Originally posted by maxibuddah

that's cos we basically deep broad reach due tobthe shrouds and the boat has a flat aft section with hard chines round bottom bottom boats roll more. the beginner comment only related to death rolling experience


That's why most modern boats have chines.
Is the EPS one of the 'we don't need to design for ply wood' era, all rounded?

In my varied but selective experience, rolling is fiirstly caused by the top of the main driving the mast to windward.
It is kept in check by:
Kicker
Steering
Sheeting in and heading up a bit.
Possibly heeling to windward a bit, rig centre over hull.

I say kept in check rather than stopped, because in some boats, rolling a bit or being on the edge of it is not slow.
The real cure is to get the kite up, speed up, get the apparent wind off the stern.


Posted By: Rupert
Date Posted: 21 Jun 12 at 12:11pm
Before Lasers started doing it so well, this was called the "Firefly Death Roll", and once it started, the helm would be screaming at the crew (me) to sit still. The answer in a boat with shrouds was always to sheet in and drop the centre plate a bit, but with a shroudless rig like the EPS, bearing away to rebalance the boat certainly works, as the rig can go so much further forward.

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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: G.R.F.
Date Posted: 21 Jun 12 at 12:16pm
Originally posted by RS400atC

Originally posted by maxibuddah

that's cos we basically deep broad reach due tobthe shrouds and the boat has a flat aft section with hard chines round bottom bottom boats roll more. the beginner comment only related to death rolling experience


That's why most modern boats have chines.
Is the EPS one of the 'we don't need to design for ply wood' era, all rounded?

In my varied but selective experience, rolling is fiirstly caused by the top of the main driving the mast to windward.
It is kept in check by:
Kicker
Steering
Sheeting in and heading up a bit.
Possibly heeling to windward a bit, rig centre over hull.

I say kept in check rather than stopped, because in some boats, rolling a bit or being on the edge of it is not slow.
The real cure is to get the kite up, speed up, get the apparent wind off the stern.

Yes it has an edge to edge curve as well as a nose to tail parabolic rocker with what looks quite close to a shift to flat that we use windsurfing, sailed flat it really is as 'quiet' a wake as you could wish for, it doesn't like to be on its ear and all that rocking is not good news. The obvious answer is never dead run but then on a lake with a short buoy to buoy course, comes the time you have to point right at them and should that coincide with a shift.....

You don't get death rolls with kites, well not that I've ever experienced it seems to be the province of certain single handers, I bet that 300 would get five stars if ever death rolling were in the michelin catalogue.


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Posted By: pondmonkey
Date Posted: 21 Jun 12 at 12:25pm
Originally posted by G.R.F.

 I bet that 300 would get five stars if ever death rolling were in the michelin catalogue.

4.5... the reverse flare gives some crucial face saving opportunity... if you're alert (or have exceptional fitness LOL)


Posted By: maxibuddah
Date Posted: 21 Jun 12 at 12:42pm
never really used to death roll the 300. the hull accelerated as quickly as the rig meaning the generated lift on the sail didn't happen so much. of course if it got a little on the draughty side of things you could just move aft and dig both wings in to act as stabilisers, again slow but safe. the wings stopped an awful lot of rolling if needed.

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Everything I say is my opinion, honest


Posted By: RS400atC
Date Posted: 21 Jun 12 at 2:12pm
Originally posted by G.R.F......

You don't get death rolls with kites, well not that I've ever experienced it seems to be the province of certain single handers, ......
[/QUOTE




I've seen a keelboat roll with the kite up, to the point where it filled up and sank. So a kite is not a total cure. But a dinghy with a kite would have been going much fast


I've seen a keelboat roll with the kite up, to the point where it filled up and sank. So a kite is not a total cure. But a dinghy with a kite would have been going much faster, got the apparent forward etc.
Enterprises were always known for rolling, less chines that say a GP and no kite, and in the days I sailed them, mickey mouse kickers.
The 400 is certainly much happier with the kite up, at least until it's time to gybe.


Posted By: G.R.F.
Date Posted: 21 Jun 12 at 4:25pm
Originally posted by RS400atC

 So a kite is not a total cure. But a dinghy with a kite would have been going much faster, got the apparent forward etc.

It probably only has been in my case since I've only ever experienced assyms that are loaded to one side come what may.

It also occurred to me, the longer and lower the boom the more likely it must be, although I've not seen boats like Contenders engage in the habit, then they have flatter hulls.


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Posted By: pondmonkey
Date Posted: 21 Jun 12 at 4:36pm
how many contender sailors would run2run gybe?  I'd have thought it was be tippy as hell with the relatively high aspect rig, low freeboard and narrowish beam???


Posted By: fab100
Date Posted: 21 Jun 12 at 5:29pm
You could always just spray the mast-top with WD40, GRF. It repels water after all, so the effect should get stronger, the more the boat heels

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Posted By: Steve411
Date Posted: 21 Jun 12 at 6:11pm
Originally posted by pondmonkey

Originally posted by G.R.F.

 I bet that 300 would get five stars if ever death rolling were in the michelin catalogue.

4.5... the reverse flare gives some crucial face saving opportunity... if you're alert (or have exceptional fitness LOL)
 
The 300  may occasionally heel a bit to windward on a run in a blow, but so will any boat sailed incorrectly - the 300 just tells you quicker than most boats. Smile
 
As Sargesail mentioned, there is more than one way to get downwind safely. I love this picture as it's all there - http://www.chunkypics.co.uk/photoalbum/Sport/Sailing/2007/RS300%20Inland%20Champs%2001-12-07%20NSC/Saturday/Page%202/E5013673.jpg - http://www.chunkypics.co.uk/photoalbum/Sport/Sailing/2007/RS300%20Inland%20Champs%2001-12-07%20NSC/Saturday/Page%202/E5013673.jpg
 
Sargesail is in 506 - bit of kicker, boom well out, rock steady. I'm in 411, bit less kicker, boom in a bit more, rock steady. The thing in commom is that both of us have the top batten in line with the mast. Letting the top batten go in front of the mast is what causes death rolls -  http://www.chunkypics.co.uk/photoalbum/Sport/Sailing/2007/RS300%20Inland%20Champs%2001-12-07%20NSC/Saturday/Page%202/E5013590.jpg - http://www.chunkypics.co.uk/photoalbum/Sport/Sailing/2007/RS300%20Inland%20Champs%2001-12-07%20NSC/Saturday/Page%202/E5013590.jpg
 
 


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Steve B
RS300 411
D-Zero 11

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D-Zero page


Posted By: G.R.F.
Date Posted: 22 Jun 12 at 7:44pm
Now I look at that and see a badly designed craft, low nose volume going under in no waves to speak of.
You lot would all go on about it being a technical boat to sail and that fella is obviously doing it wrong, when patently he's not, the conditions are blowy enough for it to be fun, not a battle.
And the more you lot get blinded by that 'technical to sail' rhetoric, the more your sport will disappear to the margins.


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Posted By: sargesail
Date Posted: 22 Jun 12 at 9:56pm
And I just read your comments and extrapolate a bloke who simply doesn't know what he's talking about....

The 300 sailors (and ex-300 sailors) and a few others have told you how to solve your problem - you seem to know better, and then you sl*g off our craft.

And the stuff above is part of the fun.  And although Steve would tell you that his brother Nick is doing it wrong, I remember this moment: Nick didn't swim - which indicates just how wrong you are about the nose volume.

And I don't see my sport disappeearing to the margins other then in your head.


Posted By: G.R.F.
Date Posted: 22 Jun 12 at 11:12pm
Well since I feel argumentative tonight, the truth is sadly that boat like mine is already in the margins.

But one is in my mind a far better boat than the other, naturally we're going to disagree.

And as to knowing better, if I knew better I wouldn't have posted asking now would I?

And frankly I'm still not really any better off given all the variables.


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Posted By: Oatsandbeans
Date Posted: 23 Jun 12 at 8:23am
The way that I look at this is that there is a sector from a broad reach to dead downwind that is a problem because the air flow over the sail becomes unstable. This means that in the light it is slow to sail in this sector and when its windy the boats behaviour becomes unpredictable leading to death rolls or broaches. So I always avoid this "no go sector" and sail either on a broad reach or bye the lee. If I have to move through this sector I do it quickly. This works for me and the 2 angles give lots of tactical opportunities on the race course. The sail set up for the 2 modes is slightly different with less vang being favourable for the BTL sailing.


Posted By: Rupert
Date Posted: 23 Jun 12 at 11:22am
Originally posted by Oatsandbeans

The way that I look at this is that there is a sector from a broad reach to dead downwind that is a problem because the air flow over the sail becomes unstable. This means that in the light it is slow to sail in this sector and when its windy the boats behaviour becomes unpredictable leading to death rolls or broaches. So I always avoid this "no go sector" and sail either on a broad reach or bye the lee. If I have to move through this sector I do it quickly. This works for me and the 2 angles give lots of tactical opportunities on the race course. The sail set up for the 2 modes is slightly different with less vang being favourable for the BTL sailing.


That is a pretty sensible way of looking at things.

Of course, what it needs most is time in the boat, learning to control it.


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Firefly 2324, Lightning 130, Puffin 229, Minisail 3446


Posted By: robin34024
Date Posted: 31 Oct 12 at 1:57pm
from what i know, it seems the rs300 dude in the picture is doing it wrong; if you bear off rather than luff up when the boat tries to death roll, it comes flat again. if you luff up the rudder and the sail work together to drive the nose of the boat down, meaning that the rig becomes more and more powered up, leading to a death roll. anyways, thats what we did in the topper, although it may be different in other classes.

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Streaker 1837
RS600 638
Cherub 3201


Posted By: frow3n
Date Posted: 01 Nov 12 at 12:11pm
When I sail my radial, 
- I find its much easier to let of the cunningham but keep some kicker on. 
- also when the boat starts to heel on top of me I sheet in the mainsheet about 1.5 or 2 armfuls and move my weight slightly into the middle and then ease it out :)
sometimes the best thing to do can be to gybe :)
 


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Laser Radial 201357
29er 1907

Queen Mary SC


Posted By: Fraggle
Date Posted: 02 Nov 12 at 12:25pm
Originally posted by G.R.F.

I'm not about to buy Rooster anything never mind curing something like this,

 
Sorry GRF but you really would benefit from borrowing/buying the downwind dvd http://www.youtube.com/watch?gl=UG&feature=relmfu&hl=en-GB&v=JivVDWlNiaw - http://www.youtube.com/watch?gl=UG&feature=relmfu&hl=en-GB&v=JivVDWlNiaw .  Really explains how to stop the deathroll (and use it to your advantage).  Plus, you get to watch Lasernut capsize , as he briefly features in the DVD, which is always a giggle LOL
 
If you really can't stomach rooster than I think http://www.caribwind.com/ltc/laserdvd/ - http://www.caribwind.com/ltc/laserdvd/  also includes footage/tips downwind (its a little while since I watched my copy) and I think you know the guys running the centre so should be able to get hold of a copy.


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Posted By: iGRF
Date Posted: 02 Nov 12 at 12:48pm
You should be a training coach Fraggle, I learned more in the moments we had together rounding those marks than ever I would watching videos. Even if I watched the video I'd forget it almost immediately such is my propensity for watching films, ask the bread knife she just loves watching Dodgeball and The Hangover over and over and over...

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Posted By: Fraggle
Date Posted: 02 Nov 12 at 12:53pm
Glad to be of service Wink
 
I used to coach when I sailed at NSC, let all my RYQ quals lapse since moving south however.  Now just run the occasional laser training session with Lasernut at HHSC. 


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Posted By: iGRF
Date Posted: 02 Nov 12 at 12:56pm
Almost makes me sorry I sailed you past that mark pretending I wasn't doing it deliberately..

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