Downwind rolling - how to react

dpearson

New Member
I'm a bit confused -- when on a broad reach or when running in stronger winds, when the boat goes into a death-roll, and the boat is rolling to windward, I know that one should pull in on the mainsheet -- the outward force on the sail then counteracts the windward rolling. But what does one do with the tiller/rudder? Tim Davison's book says to push on the tiller and head up. That doesn't seem intuitive. Does he have a misprint or can you provide some rationale?
 
dpearson said:
I'm a bit confused -- when on a broad reach or when running in stronger winds, when the boat goes into a death-roll, and the boat is rolling to windward, I know that one should pull in on the mainsheet -- the outward force on the sail then counteracts the windward rolling. But what does one do with the tiller/rudder? Tim Davison's book says to push on the tiller and head up. That doesn't seem intuitive. Does he have a misprint or can you provide some rationale?

ref: above (The Laser Book, Tim Davison, 4th ed, pg 60-62).

But note also that in Ben Tan's "The Complete Intro to Laser Racing", p45, the recommendation is to sheet in and pull the tiller towards you (bear away).

Thoughts?
 
Good question. I death rolled about 3 times last week. I read the rooster sailing article which indicates bearing away is better. This didnt work for me. Perhaps I wasnt forceful enough. All I know is I remember saying stupid rooster sailing site, as I crashed into the water.

My gut feel is that heading up into the wind for a beginner is probably better.
 
Skipper Johnson said:
Good question. I death rolled about 3 times last week. I read the rooster sailing article which indicates bearing away is better. This didnt work for me. Perhaps I wasnt forceful enough. All I know is I remember saying stupid rooster sailing site, as I crashed into the water.

My gut feel is that heading up into the wind for a beginner is probably better.

I just pull the sail in some. Works for me.
 
Let go of the tiller and wail on the mainsheet with both hands. If you are fast enough, you will keep the mast from whacking the water.
next >>>
1. As the boat starts to level you grab the rudder and begin to drive again. If the boat starts to heel to leeward..ease. With practice, you will learn to come out of almost slam dunks looking as though you did it on purpose.
2. If the boat continues and dumps to weather. DO NOT LET GO OF THE MAINSHEET!!! As you are washed off the boat, it will come to a stop and usually flip to leeward. All you need to do is hand over hand up to the boat, climb on the board, struggle on to the deck, sit up, scream a few times, and sail away.

UNless you are super coordinated, do not try to climb to the high side. The result of that move is:
The boat slams over to weather
The mast tip is used as a brake for the full speed boat and YOU!!
The mast is bent by this stupid stunt.
You slide doen the rail and cut your hands on the edge. Then you fall off and smash into the back of the centerboard and break off a chunk.. You also tear your hiking pants and foulies o the fractured board.
Net cost for being a dumbass and climbing to the high side of a slam duinking boat??

New top section, new foulies, new hiking pants, Dr visit and pain killers, divorce from spouse who is sick of all your money going to the sailboat.

Learn to trim your way out of a slam dunk and you will sail better for life. try a slick coordinated move to get out of a slam and you might make it a few times.
 
Here's a thought.

Just think of running as a mirror image of tacking. When you hit by a gust in tacking, you ease the mainsheet and head up. So when running, I guess it makes sense to pull in the sheet and bear away.
 
Attached is a copy of an article I wrote for my local club newsletter a couple of years ago and still reflects what I believe is going on in this situation and how best to react. It is based on material from Rooster, my understanding of the aerodynamic forces on the rig and what I have actually experienced sailing!
Cheers
 

Attachments

  • Avoiding the Death Roll in a Laser 2.doc
    714 KB · Views: 148
Clive Humphris said:
Attached is a copy of an article I wrote for my local club newsletter a couple of years ago and still reflects what I believe is going on in this situation and how best to react. It is based on material from Rooster, my understanding of the aerodynamic forces on the rig and what I have actually experienced sailing!
Cheers

Good one Clive.
 
I have conclusively proved to my complete satisfaction that it is possible to death roll the boat by pulling the tiller towards you or pushing it away from you.
 
i think a lot of it has to do with the timing of said stick pulling/pushing.

I know when i sail offwind, i really ease the vang - even if it's breezy, when running this causes the head of the sail to twist so that there is a significant lateral component of the force pushing the mast head over on top of me. When a gust hits, the twist is emphasised increasing that component and hence driving the boat on top of me which is why, I will always always always sheet in and head up which stabilizes the boat and then drive back downwind in the gust.

Now if you're really cool, you can eliminate this entirely by sailing by the lee offwind where the flow is from leech to luff rather than acting as a big kite before the wind. I've tried this in 15 knots or so and it's fast and stable... however... if the wind shifts by 10 degrees you will have gybed and therefore you will be wet.

So for me, less that 10knts breeze... by the lee... above 10knts... sheet in and push the stick bit...
 
I'm pretty positive that when the wind is up you don't ease the vang....come on that just isnt realistic, you want to choke down your sail a bit in the breeze.

Alot of your trouble downwind porbably deals with you seating position. When on Port tack have your right knee down in the middle of the cockpit, opposit when on starboard, have your left knee back. The reason for this is with all your weight pushing down (flattening) on the that back knee on the rising side of the boat (the high side) you will be able to stabilize the boat better than any steering or trimming techniques (why they say steer with your body down wind). I will trim hard while i push with the body to help steer.
 
For the first time last week I tried sailing by the lee in 20 kts+. I was amazed how stable it was. Only once did my sail flick but if you pay attention and steer you can avoid the accidental gybe.

QUESTION: Is it imperative to have the boat heeling to windward when sailing by the lee? In pictures that seems to be the way.
 
Hi Skip,
It isn't necessary to heel the boat to windward when sailing by the lee, sailing by the lee is when the flow over the sail is reversed or in other words from leech to luff instead of luff to leech. In my opinion you really don't need to or want to heal the boat to windward when there is moderate to big breeze blowing. In light airs yes, heeling the boat reduces wetted surface area.
Take care,
Fishingmickey
150087/181157
 
Being that type of guy, I'm in love with the physics of it all -- but I agree that some experimental data on my own part will do the most to really understand this situation. I appreciate taking advantage of your previous "flight history" though.
 
tomsinamerica said:
i think a lot of it has to do with the timing of said stick pulling/pushing.

I know when i sail offwind, i really ease the vang - even if it's breezy, when running this causes the head of the sail to twist so that there is a significant lateral component of the force pushing the mast head over on top of me. When a gust hits, the twist is emphasised increasing that component and hence driving the boat on top of me which is why, I will always always always sheet in and head up which stabilizes the boat and then drive back downwind in the gust.

Now if you're really cool, you can eliminate this entirely by sailing by the lee offwind where the flow is from leech to luff rather than acting as a big kite before the wind. I've tried this in 15 knots or so and it's fast and stable... however... if the wind shifts by 10 degrees you will have gybed and therefore you will be wet.

So for me, less that 10knts breeze... by the lee... above 10knts... sheet in and push the stick bit...



I drew a diagram that I hope will help a little. Probably not.
Blue lines are wind, arrows are direction, and black lines are force. Red circles are noted below.

anyway, on a normal run, the sail acts mostly as a wall to be pushed against, but it does attain a small amount of attached flow like a normal sail would, from luff to leech. This attached flow is dumped off of the leech, and the resulting reaction is a small amount of sideways/diagonal force (pushing to the right in diagram). This is much more pronounced when the vang is off, as it opens the leech to smooth flow instead of hooking in and cutting most of it off (note red circle). That small amount of force makes the sail want to slide in the opposite direction of the wind force, which happens to be right on top of you. It can be countered by either heading up (aiming sideways force into bow/changing direction of attached flow) or heading down (reversal of attached flow, initiation of sailing by the lee). sheeting in also changes the direction of attached flow.
When by the lee, as mentioned above, the small bit of flow is reversed. the wind attaches at the leech and leaves at the luff, which ends up being very turbulent as it exits off the mast instead of a nice flat sail. This coincidence is what keeps the boat from wanting to slip the other way (looking at the diagram, left), similiar to having an incredible amount of vang on. The resulting flow force still goes (looking at diagram) right, which can be countered by sitting on the leeward side (the recomendation of most books as to sailing by the lee).

That's all I got's
 

Attachments

  • Laser_Downwind_Diagram.doc
    72 KB · Views: 99
Have a look at http://www.roostersailing.com/ and click on Hints and tips, 4th dimension downwind sailing. I have found this helpful and really opens up down wind sailing in the Laser in high wind conditions as being something that is good fun rather than a frightening experience! The downwind DVD is also good.

Basically, Steve is saying, sail by the lee or broad reach, if you want the boat to be stable. In between (ie directly downwind), on a run in high wind, the flow over the sail can suddenly reverse and cause the deathroll instability. The diagrams and video clips show this very well. He also shows what to do with the rudder and mainsheet when the boat starts to roll on top of you.

Cheers,
 
You must'nt forget to yous your body... You must sit on the middle so you can torque your body on winward or leeward if needed. Simultaneusly rightly used body, sheet and tiller will avoid the deathroll... :D
 
Seems to depend on whether you are 'by the lee' or broad reaching/running in the conventional sense when the 'weather roll' occurs. Appropriate reactions can be different depending on this - if by the lee and rolling, sheet in and drive deeper by the lee (i.e. pull the tiller up to what is conventionaly known as the 'windward side' but is actually probably better described as the leeward side except that the boom is not over it when sailing by the lee) - confused yet??

probably best to conceptualise the main as a spinnaker when sailing by the lee - then conventional reactions apply,

GL
 
About one of lifes little mysteries....

Until a few years ago, when I was racing Lasers pretty much full time, I always went for the luffing up option. Just before I moved halfway around the world and changed class, I was competing in an OCR in NZ, sailing out to the start, which was a straight run, I was alongside one of the other front runners, and we were chatting away when we both got a gust of around 25kts, and started to roll in. I was windward, and luffed slightly/sheeted in, and caught a good wave, And glimpsed back to see how much distance I'd pulled on him....
Suprise!! He'd gone down, by the lee, caught the same wave, and pulled about 150m. That was a valuable lesson in downwind sailing! when we came back towards each other, he was still 150m in front!

Now I'm back in lasers (albeit a very old one) and despite being a bit saggy myself, IE fat, by using the lee thing in the bigger puffs I've been beating all those who take the high road on those windy runs.

Just remember to ease lots of kicker, which will allow you to get very far by the lee, to the point where the lower leech can actually fliick in and out, on the point of gybe, but the upper leech has enough pressure to stop the gybe. oh, and dont let the boom past 90 deg unless its light and you're using gravity to keep it out!
 

Back
Top