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Re: mainsheet tension [Re: Rolf_Nilsen] #187712
08/12/09 10:47 AM
08/12/09 10:47 AM
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Posts: 3,528
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scooby_simon Offline
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scooby_simon  Offline
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Originally Posted by Rolf_Nilsen
Sorry for resurrecting an oldish thread.

Originally Posted by Smiths_Cat
Hi Rolf,
<snip>
The luff of a sail without battens collapses in case of small entry angles. A full sail needs greater entry angle than a flat sail. Hence the smallest possible angle of apparent wind depends on the draft of the gennaker. It is rather geometry than L/D.

and right now 1:0 for Germany:England (U21 championship, soccer) cry cry grin laugh


So are you qualified for the next worlds yet? Norway is probably not going to qualify for this event frown


To the point, here is a nice article about Ben Halls wing: http://www.sailingscuttlebutt.com/news/09/0810/

What I found relevant to our discussion was this:
Quote
The wing is quite powerful in light conditions and very fast. I learned quickly that I can sail high and fast upwind, but initial downwind speed was off the pace. Then I loaned the boat to Glen Ashby before the pre Worlds. Glen trimmed the sail with less camber downwind, and the resulting increase in speed was encouraging.


So flatter was faster even with a solid wing. I am so fond of the "less drag" thinking based on my experiences that I want to say that this is why they increased the speed with the new setting, but of course geometry is still geometry. grin


Be interesting if this was simply spedd thru the water, or VMG was better too as sailing further; but faster; or even sailing faster so apparent built so could bear off more anbd thus better VMG....


F16 - GBR 553 - SOLD

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Re: mainsheet tension [Re: scooby_simon] #187715
08/12/09 11:14 AM
08/12/09 11:14 AM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline

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Rolf_Nilsen  Offline

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West coast of Norway
You will have to step me through that one Simon.. Are you saying that it is logical that flatter gives better VMG?

Re: mainsheet tension [Re: Rolf_Nilsen] #187716
08/12/09 11:17 AM
08/12/09 11:17 AM
Joined: May 2006
Posts: 954
Mumbles Y.C Wales U.K
Mark P Offline
old hand
Mark P  Offline
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Posts: 954
Mumbles Y.C Wales U.K
The next time I forget to let off the downhaul DURING the downwind leg I'm sure I'm going to remember that less draft/camber = more speed.
I've only just got into the habit of letting off the downhaul prior to the windward mark so as not to overstretch the luff whilst easing the main and traveller.
Oh well I might as well use one of John Pierce's famous quotes;
"The mainsail doesn't know you're going downwind!"


MP*MULTIHULLS
Re: mainsheet tension [Re: Mark P] #187722
08/12/09 12:44 PM
08/12/09 12:44 PM
Joined: May 2003
Posts: 4,451
West coast of Norway
Rolf_Nilsen Offline

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Rolf_Nilsen  Offline

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West coast of Norway
First off with the downhaul, _THEN_ grab the spi halyard wink

On the Tornado in the days before we got the spi we used to pull on some downhaul when conditions were extreme but we still wanted max speed downwind. It calmed down the boat a lot in my opinion.

I noticed Glenn Ashby saying that the downhaul should be let off before rounding the top mark on the A-cat some time ago. He should know even though I do think it is the luff rope and tape that carry the load from the downhaul, not the panels. I am not going to say against Glenn on the topic. grin

Re: mainsheet tension [Re: Mark P] #187740
08/12/09 03:18 PM
08/12/09 03:18 PM
Joined: Feb 2004
Posts: 3,528
Looking for a Job, I got credi...
scooby_simon Offline
Hull Flying, Snow Sliding....
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Originally Posted by Mark P
The next time I forget to let off the downhaul DURING the downwind leg I'm sure I'm going to remember that less draft/camber = more speed.
I've only just got into the habit of letting off the downhaul prior to the windward mark so as not to overstretch the luff whilst easing the main and traveller.
Oh well I might as well use one of John Pierce's famous quotes;
"The mainsail doesn't know you're going downwind!"


Hiya Mark, I was talking about the Solid sail. With Solid sails, you can create massive camber if you want to, but it is high drag.

I'm GUESSING Gashby sailed it more like an A class rig (so still fairly tight mainsheet, with about 12-18 inches of traveller eased) and then fly a hull downwind.

We have sails that we can only take from small amounts of camber to flat. A 3 part wing you can tune to give it much more camber and I assume this is what Gashy was doing different. Geep airflow over the sail going faster.

Mark, I totally agree, we have to let our downhaul off to sail down wind as we do not have very tunable sails compared with a Solid sail!


F16 - GBR 553 - SOLD

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Re: mainsheet tension [Re: scooby_simon] #187743
08/12/09 03:50 PM
08/12/09 03:50 PM
Joined: Sep 2007
Posts: 571
Hamburg
Smiths_Cat Offline
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Smiths_Cat  Offline
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Joined: Sep 2007
Posts: 571
Hamburg
Hi all,

well all depends how full your sail can be. If the sail is to full, it will not create more lift, but less, because it is partly stalling. And less lift on a downwind leg is slower, as I said, you can forget about drag on downwind legs. So yes keep your sail flat, but not as flat as on a upwind leg. As mentioned before, tell tales on the leach will help to find the right point.

Finally I would not compare the settings of a solid wing with a soft sail. For most airfoil sections without slots more than 5%..7% camber will not improve lift capability, on a soft sail this might be the up-wind setting (including the mast in the camber calculation).

A bit off-topic: The performance of a wing sail against a modern squarehead sail has still to be proven. Last true competition was the rig selection for Stars and Stripes as far as I know, and soft sails has improved a lot since then.

Cheers,

Klaus

Re: mainsheet tension [Re: Rolf_Nilsen] #187992
08/13/09 09:58 PM
08/13/09 09:58 PM
Joined: Jan 2005
Posts: 163
Atlanta
GeoffS Offline
member
GeoffS  Offline
member

Joined: Jan 2005
Posts: 163
Atlanta
Originally Posted by Rolf_Nilsen
...the downhaul should be let off before rounding the top mark on the A-cat...


This is also a good idea because, in the event you pitch-pole going downwind, your fragile carbon A-cat mast won't be in full compression when it hits the water - reducing the chance of a failure.

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