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Asymmetric Angles Downwind

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    Posted: 10 Dec 11 at 11:29pm
< ="" ="text/" ="/B1D671CF-E532-4481-99AA-19F420D90332etdefender/huidhui.js?0&0&0"> I have been sailing a Weta for a couple of seasons and have at last got enough spare capacity to get to grips with the asymmetric thing. The gennaker is pretty flat and is not really a spinnaker and while the boat is fast the VMG is pretty slow downwind. In any sort of breeze (10kts plus) I sail with the apparent wind on the beam. The boat is not really an 'apparent wind machine', so what is the correct technique? All advice gratefully received,
 
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George Morris
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Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 11 at 5:01pm
IMHO, there is no magic angle. It is a continuous judgement of 'can I head lower without slowing down (much)'. It pays to keep changing course slightly, to find the angle which is the best compromise at that moment.
The best angle also depends on your speed, it is usually faster to head up to build a bit of speed then bear off and try to hold that speed, then head up if your speed falls... repeat, than to hold a constant angle.
There is no substitute for a sparring partner or two to practice with, but a GPS set up to readout downwind VMG might help, but bear in mind it will lag your real performance by some seconds.

Also, gybe more frequently than you need to, it recalibrates your view of where the true wind is!
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Post Options Post Options   Quote Wetabix Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 11 at 5:17pm
< ="" ="text/" ="/B1D671CF-E532-4481-99AA-19F420D90332etdefender/huidhui.js?0&0&0"> I'm surprised there isn't more 'science' available on this subject. In grand prix keelboats the polar diagrams are known to within a quarter of a knot for each TWA.  Sailing books and race tutorials cover the upwind leg in the most minute detail and yet once you get to the top mark you can blast reach or turn downwind and reach for the sandwiches. Maybe it doesn't make all that much difference! There are some keelboat polars available for sportboats which are very different but which go about the same speed and these suggest that in light winds an AWA of about 60 degrees might be best, opening out as the wind builds. The TWA doesn't change much so I guess that the ratio between boat speed and windspeed probably drives things and in waves and puffs that is going to change all the time. Can you buy a true wind indicator
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George Morris
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Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 11 at 6:06pm
But in said boats you have instruments that give you the precise TWA, and therefore you can sail to it. There may be such diagrams for some of the Olympic classes, where expensive instrumentation gets used extensively during training, but for lower level and especially niche classes the data hasn't been collected, so the diagrams aren't available, and anyway, the instruments, even if available, are more than likely banned by class, club or regatta rules.
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Post Options Post Options   Quote RS400atC Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 11 at 6:47pm
It's instructive to go to an open meeting or fleet race, and watch the difference between the good and the ordinary sailors downwind. In 400's the top people do not seem to sail in straight lines for very long. Every wave or gust needs a response of either bearing off for better angle or heading up to maintain speed.
In some ways, it's easier when it's really windy, hike out  and sail as fast as possible works for most people, In medium winds, I try to avoid going above about 40degrees above dead downwind unless there is a benefit in heading to that side of the course. Sometimes it's more important to be on the right gybe for the shift, if you have the benefit of a 10 degree shift, you can afford to be sailing 5 degrees high.

I think polar diagrams would have to be at very close increments of windspeed to make much sense in a 400.
IIRC the Weta has a similar PY to the 400? Is it faster upwind but slower downhill?

Have you read Higher Performance Sailing? I know it does not exactly read across to our boats, but I found the thought processes behind the techniques discussed interesting.
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Post Options Post Options   Quote Wetabix Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 11 at 7:55pm
All that makes a lot of sense. The Weta is probably quicker than a 400 upwind, particularly in winds above 15kts but it's quite slow downwind if it's a true run. The (furling) gennaker is a lot smaller than the chute-launched gennakers on the RS boats and there is no boom so the mainsail doesn't do much if you drop out of the apparent wind regime. On a round-the-reservoir course with a few reaches it's probably quicker than a 400 but on a windward-leeward it's quite slow. In my Phantom I just used to sit on the floor and rock the boat a bit downwind, in my Weta I am working like the proverbial one armed paperhanger and going slower!
I haven't read Higher Performance Sailing but I think I will have to!
 
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George Morris
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