Laser 140101 Tynemouth |
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Rossiter Pintail Mortagne sur Gironde, near Bordeaux |
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Laser 28 - Excellent example of this great design Hamble le rice |
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List classes of boat for sale |
Ramblings on Dinghy Development |
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Dougal ![]() Really should get out more ![]() ![]() Joined: 23 Sep 09 Location: England Online Status: Offline Posts: 556 |
![]() ![]() ![]() ![]() Posted: 11 Feb 13 at 9:12pm |
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One point that I think is particularly pertinent is a design of boat that performs consistently throughout the wind range. Maybe it is just me, but it seems that a lot of boats perform very well in certain conditions, but very badly in others. If that could be evened out I would certainly find sailing a lot more enjoyable. Also, thanks JimC - your explanation of how assymetrics have evolved was very informative (and has led me to change my views somewhat) |
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What could possibly go wrong?
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Xpletive ![]() Far too distracted from work ![]() Joined: 28 Jan 06 Online Status: Offline Posts: 320 |
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How about a twin sock chute system which allows a choice of 2 kites, reaching or running, launched on the same pole? (Not at the same time, of course...that would be ridiculous)
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pondmonkey ![]() Really should get out more ![]() ![]() Joined: 12 Aug 11 Online Status: Offline Posts: 2202 |
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LMFAO... almost as amazing as when you described some Bloody Mary cold hands as 'frozen w**king claws' |
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SoggyBadger ![]() Really should get out more ![]() Joined: 26 Oct 10 Location: The Wild Wood Online Status: Offline Posts: 552 |
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I believe that's been done in the FDs. |
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Best wishes from deep in the woods
SB |
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Do Different ![]() Really should get out more ![]() Joined: 26 Jan 12 Location: North Online Status: Offline Posts: 1312 |
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Twin chutes used by Rodney Pattisson, I think for trialling different kites on Supercalifragilisticexpialidocious
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Xpletive ![]() Far too distracted from work ![]() Joined: 28 Jan 06 Online Status: Offline Posts: 320 |
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O bugger....I can take innovative off my cv then......
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pondmonkey ![]() Really should get out more ![]() ![]() Joined: 12 Aug 11 Online Status: Offline Posts: 2202 |
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So could most people... Just cos it didn't go mainstream doesn't mean it's a dumb idea, but that'd be a lot of dead weight and hassle factor carrying all that around a course, no to mention expense if you were to commercialise it.
The Weta screacher looks good, and I'd be quite tempted to boat on boat the Vareo's kite options RTC- the new radial might just prove useful in a club race. |
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JimC ![]() Really should get out more ![]() ![]() Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6662 |
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A bit more on the theory... This is my model of the theoretical performance of a boat with no drag and no righting moment limits, so is limited only by how far you can sheet the sails in and still have them set... 20 degrees for the outer curve, 25 for the other. Wind speed is 5 whatevers. It might be ******, but I think the model is reasonable. Could be wrong though.
![]() As hopefully you can see the max speed is on a reach of 90 degrees plus sheeting angle, where the apparent wind is at its max, and the craft is going several times wind speed. You can also see that on a dead run the boat can only travel at windspeed, so the best downwind speed is at a pretty hot angle. Of course in the real world there's drag and righting moment, but actually the shape is about right for an efficient single sail boat, its just that the benefits of apparent wind drop off... One of the interesting things about this, which real world polars back up, is that running absolutely dead square is just about never advantageous. To see some real world data look at these links... http://www.j24blog.com/wp-content/uploads/2007/05/j24_polar.pdf Page 7 of this second one includes Laser polars, both real and mathematically modelled. http://eprints.utas.edu.au/7388/1/BinnsBethwaiteSaunders2002.pdf OK, what happens when we put a kite in the mix... For this I've sketched on a line onto my theoretical curve, which is a simulation of real world... ![]() Going deeper than the ideal vmg you see there's a huge hit in performance as the kite starts filling badly and the apparent shuts off. Going higher there's an equally big cliff in performance as the boat gets blown flat and the kite refuses to set. So what does this tell us if we want even performance round the polar? The first thing is that apparant wind is the enemy, so the less apparent wind affects you have the better. An example of that is the IC - a low dragboat with lots of righting moment which I suspect in some conditions at least is faster on a 45 degree beat than on a 135 degree broad reach. The next thing is you want a slow boat, and the slower and draggier the better. And if it can't plane that's better yet... And this is a point about pole kites versus sprit kites. Your typical Northern hemisphere pole kite is a complete drag fest. Because its symmettrical the shape tends to get blown aft so its horribly draggy, and because the pole is typically comically short then its even baggier and draggier. And as hopefully is demonstrated above the more drag the less apparent wind and the more even the polar curve. Given a tight luff and a very long pole a symmettric kite isn't that much worse than a asymm for speed, and will have similar effects on polars. But the biggest puzzle of it all to me is why people object to sailing hot angles. They do, because I've had this discussion time and time again, and I never get folk to agree with me. By all theory and logic, the hotter the angles you have to sail to get best vmg, then the more legs of the course you will need to put gybes in on, and the more time you will spend sailing your boat as fast as possible. As far as racing is concerned it really doesn't matter if the vmg isn't that great because in class racing its the same for everyone and in PY racing the handicap will sort it out sooner or later. But when it comes down to sailing in practice almost everyone seems to think they'd be better off with a soddin' great kite sailing lower and slower but nearer the mark... |
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fab100 ![]() Really should get out more ![]() ![]() Joined: 15 Mar 11 Online Status: Offline Posts: 1005 |
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This is all very well, but ever tried running against the tide on a river, or getting away from the wind shadow of the trees on a pond - the ability to aim where you want to go is strategically essential
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rb_stretch ![]() Really should get out more ![]() Joined: 23 Aug 10 Online Status: Offline Posts: 742 |
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Jim, I'll have to re-read your very informative post in the morning, but from what I gather the answer to a more rounded polar is to have a very high drag spinnaker that minimises the apparent wind effect, but helps the boat speed in very deep angles, where drag is a good thing. Just like old fashioned spinnakers really.
Also surprised from your referenced document that a Laser is not faster straight downwind than sailing the angles, cause I never see a Laser sailing the angles. Maybe that's because the document does not consider sailing by the lee?
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