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Another little conundrum for the hive mind..
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Daniel Holman View Drop Down
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Topic: Another little conundrum for the hive mind..
    Posted: 07 Jan 13 at 12:47pm
Another thing about board sails is that they generally operate at a much lower lift coefficient, which is equivalent to saying that the sail will be working in a state of much more overpower.
(lift coefficient is proportional to side force / (apparent wind strength squared x area)
I.e. a guy hiking out in a dinghy will be putting significantly more righting moment and hence side force on a 8m2 sail than a guy holding onto a an 8m2 rig on a board, even if wide.
The board will be going at least twice the speed, hence the speed squared term will be much higher.
This means that the board sail will need to be flkatter, more twisted, and with much more skin tension. Direct sheeting means that the quick response necessary with such flatness is possible.

Until its really windy, an unstayed dinghy will go upwind best with reasonable fullness all the way up the rig and minimal twist, with the aforementioned sheeting angles.


Edited by Daniel Holman - 07 Jan 13 at 12:48pm
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 5:26pm
That is such a nice sail particularly for those conditions. Not sure I entirely agree with your calculations, sure when breezy boards move quite fast but in sub 8 knots they're (Raceboards) moving at displacement Speeds and we're hanging onto 9.5 sq mtr rags not unlike that one, although in my case a little lighter weight perhaps but with just as much stand out at the head if I'm not running much downhaul.

And I note how close to the centreline that rig is hence it sailing higher and faster than mine imv.

Edited by iGRF - 07 Jan 13 at 5:27pm
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Daniel Holman View Drop Down
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 5:37pm
It's still not quite there, but good enough. May not look it but that is set at 9deg off centreline there - halfway between centre and edge.
Obv in 15kts the down haul starts coming on which flattens a fair bit esp at head and puts a lot of twist in.
What you up to Saturday Graeme?
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Daniel Holman View Drop Down
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 5:39pm
The point re lift coefficient is that there is only so much force / leverage that a little fella can derive from a sail when his feet are near the centre line.
Race board sails are halfway between rec free ride sails and dinghy sails I'd say. Can be firmed up for the light air work.
It's still a very different ball game though.
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 6:16pm
Originally posted by Daniel Holman


What you up to Saturday Graeme?


Depends, if the cloth arrives and my new sail gets cobbled together and the weather looks do able then I might do a last minute dot com Bloody Mary..
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iGRF View Drop Down
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Posts: 6499 		Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 6:26pm
Raceboard sails, depends who makes them and there are only two or three folk left who know how to do it.
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Chris 249 View Drop Down
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Posts: 2041 		Post Options Post Options   Quote Chris 249 Quote  Post ReplyReply Direct Link To This Post Posted: 07 Jan 13 at 11:45pm
Some interesting posts, chaps.
 
Re "even the most pointy board (an old Div 2) will still get stuffed by something as pedestrian as a Laser upwind". Sorry, no way do all boards suck upwind. I did a fair few races or trials between Canoes, lowrider Moths (Hungry Tigers), Lechner Div 2 and Mistral and other Raceboards, plus raced in or shared a course with the Raceboard fleet for years.
 
The Canoe and Moth were out-performed upwind from about 6 to 8 knots by the boards. The boards may have been a degree or two lower, but their VMG advantage was such that they could have been pinched to the same height and still probably have been at least as quick.
 
All of those involved in each class (apart from when there were actual fleets) had finished at least top 3 in that class nationally and the Mothies were 1 and 2 in the world at the time, so the standard of sailing was reasonable.
 
Some times the boats will kill the boards but in my experience that's when sailing in light and shifty stuff (where the boards lose in tacking) or in light winds funnelling out of a bay, where the boat's slight pointing advantage will allow it to hook into the lifts and the board's footing will just put it out of the shifts. The boards can normally stuff it to hang as high as a Laser etc but they don't because they get better VMG lower and faster.
 
FWIW I don't believe that windsurfer rigs are actually "better"; as others have mentioned, they just benefit from being able to be optimised to drive a very low drag hull, and the ones designed mainly for reaching are terrible upwind. A few years back the biggest UK windsurfing event saw 2nd out of about 300 in the "Sport" class go to an original Windsurfer with dacron "pinhead" sail and down here we have seen similar destruction of modern "funboard" fleets by original Windsurfers in some races - for all the furore the modern non-racing boards and rigs are incredibly slow at times.
 
Modern board rigs also suffer from being very heavy - they claim to be light and efficient but the original Windsurfer sail (6m and around 2.1 kg) is half the weight of a current sail, or less.  Fine if you are thrashing through waves or freestyle (when strength is vital) or blasting in steady winds, but a pain around the light and fluky winds of many dinghy courses.
 
It's not one being more advanced than the other, just different approaches created by different requirements and driven by different dimensions.


Edited by Chris 249 - 07 Jan 13 at 11:49pm
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