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| Sail Shape, effieciency. http://www.hobie.com/au/en/forums/viewtopic.php?f=13&t=16879 |
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| Author: | jmecky [ Thu Nov 12, 2009 8:32 pm ] |
| Post subject: | Sail Shape, effieciency. |
In an attempt to perfect my sailing ability, I have a few questions. When sailing downwind should I travel out or sheet out. Or combination of both. Lets say I'm only going downwind a little, is it better to travel out until a luff forms and keep the sheet relatively tight? Or keep the traveler in and sheet out until a luff forms, or both how much of each. I know you can't say exactly so if you have a mental rule of thumb you use spill it. (once I see luff I pull tighten sheet/traveler until its gone) Letting the sheet out changes the shape of the sail, for better or worse? |
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| Author: | ncmbm [ Fri Nov 13, 2009 7:26 am ] |
| Post subject: | Re: Sail Shape, effieciency. |
You lost me at "a luff forms"! What does that mean? Are you talking about luffing the sail by going head to wind? Do you have tell-tales on your sail? It depends on how deep downwind you are trying to go. If you are going dead downwind a wing on wing approach is best but that is very slow on a cat which can jibe downwind faster. You need to get Rick Whites book "Cat racing for the '90s", I think is the title. There is a complete section there from Hobie Alter Jr on racing the H18 and how to sail the boat. You need to understand reading your tell-tales, mast rotation and jib traveler positioning. Its not hard but there are basic principles that once you have them they will apply to any boat you get on. |
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| Author: | srm [ Fri Nov 13, 2009 9:15 am ] |
| Post subject: | Re: Sail Shape, effieciency. |
Downwind sail trim on the 18 is highly dependent on true windspeed and angle. Speaking from a course racing standpoint, we generally run a slightly deeper angle (probably about 90 to 110 degrees on the bridle fly) and correspondingly looser sheet tension in light wind. As the wind comes up, bridle fly angle is probably more in the 80 to 100 degree range and sheet tension is increased. There seems to be a noticable point when the windspeed increases enough that you can take advantage of the aparant windspeed increase and sail a little higher/tighter to an advantage (around 15mph and more). Below that point you'll be sailing too high/too much extra distance, so sailing deeper is better. The traveler position corresponds to the mainsheet tension. Again, in light wind we'll sail downwind with the traveler all the way out and the mainsheet quite loose. The mainsheet is almost never touched in lightwind, the speed comes from good steering and constant jib trimming by the crew- including holding the jib out and down to keep the upper and lower telltails streaming. As the windspeed increases, the traveler can be brought in slightly (maybe a foot or so, never farther in than the hiking straps) and the mainsheet tension increased. When sailing this way, you have to pay a lot of attention to your bridle fly angle and look for puffs/lulls. Changes in windspeed require immediate changes to sail trim. Having a set of telltails at the top of your mainsail (second and/or third panel down from the top) really helps with the trimming. In light wind, they'll probably be forward no matter how you trim- this is when you want your mainsheet loose. As windspeed increases, they'll start to start to blow up and back, and this is when you can start sheeting in. Having a good crew that constantly trims the jib to keep telltails flowing also makes all the difference downwind. Proper jib trim equates to at least 50% of downwind speed, even more in light wind. sm |
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| Author: | Skipshot [ Fri Nov 13, 2009 9:21 pm ] |
| Post subject: | Re: Sail Shape, effieciency. |
I think what srm is trying to say is, experiment a little to find the fastest point of sail and sail adjustments. In general, a broad reach is done with the traveler out and some of the main out, but play the sail to see what works best for the conditions. |
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