Polar diag for Sigma 362

[cagey]

Evening,
Anyone any idea where to find a Polar diagram for a Sigma 362 MH normal keel, many thanks. Keith

 

[sarabande]

K - I can't find one for your boat, but this site

http://www.blur.se/boats/

has lots of polars for various boats. Anything similar to the Sigma there ?


HTH

 

[cagey]

Thanks for that Tim, unfortuately I dont know if any are similar, am looking to complete routing program so dont even know what are important parameters, think my phone is a lot smarter than me. Perhaps repost on racing forum
Happies
K

 

[Tintin]

I know what you are up to....

 

[sarabande]

I'm a great fan of not re-inventing the wheel. For the extent of the accuracy that a routing system is going to give you (taking into account the accuracy of tidal rates, leeway and other variables), one of the polars available for a similar boat would be a good starting point, and take away the need to log your boat speed and wind angles, sails etc for months and months.


I am happy to ferret around to try and find some data.

 

[bitbaltic]

If you have a PC connected to your NMEA system PolAuto is excellent, and free. You can build a polar for your own boat in a surprisingly short time.

I recycle the polar data into PredictWind routing which I guess is something similar to what the OP is looking at.

 

[Ric]

I made my own polar using least squares method with the LINEST function in a spreadsheet.

Boat Speed can be modelled as a function of True Wind Speed and True Wind Angle to the nth power:
BSP=aTWS+bTWS^2...+nTWS^n+aTWA+TWA^2+...nTWA^n
In practise, you only need to go to 5th power to get accurate results.

To get the data, I set up a multi-instrument to show a screen with BSP, TWS and TWA, then just film it for a minute or so on different points of sail and different sail configurations. I then just freeze-frame the video on computer at home to manually input into a spreadsheet ten or so points from each point of sail to ensure that I get a good average. It really doesn't take long at all to build up a very accurate polar.

I then have this outputted into a table in exactly the layout required by Predictwind, so I can just copy/paste the figures directly into the website upload.

 

[sarabande]

here's a website for the software to log your polar data automatically. It's in froggish but the software is available in rosbif.

http://www.plaisance-pratique.com/polauto-mesurer-la-polaire-reelle?lang=fr