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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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Old 07-14-2011
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Velocity Predictions Polar Diagram

Can anyone help me find a polar diagram for my C&C 25. I'm looking for the velocity predictions of boat speed vs true wind angle. Its time to learn to sail smarter !!!
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Old 07-14-2011
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Quote:
Originally Posted by CowbaySailor View Post
Can anyone help me find a polar diagram for my C&C 25. I'm looking for the velocity predictions of boat speed vs true wind angle. Its time to learn to sail smarter !!!
I'd say, trace your own! It would be a fine entertainment and you'd get to know your boat a lot better...
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I have started to do that Pedro. That doesn't give me the best velocity made good (VMG) for my boat.
In your mind which is better. you sail into a puff and the apparent wind angle increases, do you chase the tell tails and heat up immediately or steer straight or bear off slightly ease the sails at the same time. When the boat comes up to speed then head up slightly at close-hauled sail trim ?
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Old 07-15-2011
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CB, did you get my earlier from before the server crash? Just draw horizontal lines tangent to each curve to find the upwind or downwind VMG. It works for any wind angle, but straight upwind VMG is most directly meaningful to your questions, and incidentally the simplest to find.
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I got a message saying you sent one but didn't receive it. Thanks for the info I will plot my collected readings.
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Old 07-15-2011
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During the server crash, I send a message that US Sailing sells polars, but they are expensive.
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They are not too difficult to create, but it does take time.

Simply take many data points and plot with Excel as a circle plot.

Sail Delmarva: Speed Polars

You have to play some games with interpolation and smothing, since wave conditions and load will vary over time. In someways the targets of others are better (depending on how they were developed) and in some ways your own are more valid.

I found I mostly worked on this during long, dull watches.
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I found and old book called championship tactics with Gary Jobson and Tom Whidden. In it they have Jim Marshall talking and explaining polar charts. As a radar plotter in the navy I'm pretty sure with a rel vel chart I can figure it out.

Now my question is will I have to plot are each jib in my inventory?
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Yes, for every sail combination and reef...

Quote:
Originally Posted by CowbaySailor View Post
I found and old book called championship tactics with Gary Jobson and Tom Whidden. In it they have Jim Marshall talking and explaining polar charts. As a radar plotter in the navy I'm pretty sure with a rel vel chart I can figure it out.

Now my question is will I have to plot are each jib in my inventory?
... but most only plot the largest sails in the inventory.
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Old 07-16-2011
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Thanks for the article on the pdq speed polars that gives me all the info I need. The wing on wing was interesting also. All good stuff.
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