Polars

[bigal.nz 60]

We recently sailed to Fiji and I took the chance to generate a set of polars for our boat using the OCPN plugin.

Pretty neat I thought until it dawned on me that these polars are probably junk - every time we surfed down a wave it recorded the peak speed as the value for that wind angle. 

Has anyone else experimented with this plugin - is it only to be used on flat water or am I missing something?

[Island Time 1,286]

You can’t (shouldn’t) be recording for polars in surfing conditions. Your trying to record the boats best possible sailing speeds, for every angle, and every wind speed. It takes a lot of sailing over a long time to get them pretty right….

[K4309 369]

The easiest way to come up with a set of rudimentary polars is to get an ORC handicap certificate. The certificate comes with design polars for your boat. They aren't going to be as flash or accurate as the boat designers polars for a modern GP racer, but to enable basic weather routing for a middle aged NZ cruiser they are ideal.

I don't know what they cost now, I did mine about a decade ago, and it was maybe $100. Substantially cheaper than the nonsense with IRC.

The below link is a current certificate for a First 50 based in Aust. Shows you the level of detail you can get. Just type in the polar figures to Open CPN and you will be away with weather routing and what ever else you want to fiddle with using polars. Once you have a base set, you can refine it and improve the accuracy with open CPN I beleive. I never got to that level, I just used it for weather routing on predict wind.

ORC Certificate for 51ST Project

PS, these certs also give righting moment data (theoretical of course) that can be used for certain CAT certificates. I think I used this to get CAT 3 for my log of wood. Fairly sure you need better data for CAT 1, but the ORC cert can be handy for certain other issues, basically if you have an old cruiser and want to do the Coastal Classic / CAT 3.

[Island Time 1,286]

Alternatively install the weather routing plugin if you dont have it, then look in ProgremData\Opencpn\Plugins\Weatherrouting\Polars and select a boat similar to yours. Modify that to suit...