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Polars

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Quoddy

.
Apr 1, 2009
241
Hunter 260 Maine
How are polars made? Are they derived from actual conditions or calculations? If they come from actual tests, how can you have the same sea state at wind speeds from low to high?
 
Jan 22, 2008
1,483
Hunter 37 C sloop Punta Gorda FL
The polars you buy from US Ailing are calculated from their Velocity Prediction Program (VPP). Some people have done actual sailing and recording. There are Observed polars for S-2 7.9' s on their fleet web site.
 
Oct 25, 2005
735
Catalina 30 Banderas Bay, Mexico
How are polars made? Are they derived from actual conditions or calculations? If they come from actual tests, how can you have the same sea state at wind speeds from low to high?
They are calculated. The Velocity Prediction Program that is used for ocean racing handicaps (used by US Sailing) includes calculated sea state for each true wind speed. The model gets better all the time and the results are a better reflection of true performance than they used to be.

Observed polars for a boat are totally dependent on the quality and calibration of the instruments. Boat speed is a tough one. If you spend time with instrument calibration you will find that most boats do not have a linear speed calibration. If the knot meter is calibrated for 3 knots it will probably have an error at 6 knots. GPS speed is completely irrelevant for creating polars or for knot meter calibration.

Wind speed and angle measured at the masthead must be adjusted for height over the water and for leeway angle and for the upwash from the sails.

Getting all this right is very time consuming and most systems have no way to calibrate for more than one boat speed or wind speed much less for different sailing angles and sail combinations.

In other words, don't expect to hit the polars from a VPP all the time. Use the best angles as guidelines after you have your instruments calibrated as closely as you can get them. Then make notes as to best observed performance at different speeds and angle to use as "personal best" targets to beat. If you are constantly faster than the polars ... your knotmeter is not calibrated correctly. :)

Randy
 
Jan 22, 2008
1,483
Hunter 37 C sloop Punta Gorda FL
This is NOT first hand knowledge. but it is my understanding that the Americas Cup guys with Bazillions to spend on instruments and VPP formulas use polars and "Target Speeds" as guidelines, then they look over at the comepetition with their bazillion dollar infra red FLIRs and adjust.
 

Quoddy

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Apr 1, 2009
241
Hunter 260 Maine
Polar thanks

Thanks for the details on polars .I now have a better understanding of what they might be able to do for me.
 
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