For the Speed Over Ground (SOG) we use a generic polar based on the Waterline Length (LWL) of your yacht. Ultimately the plan is for savvy navvy to learn how you sail, so it can optimise that polar as time goes on, improving the accuracy of ETA calculations. 

We are also thinking about adding additional controls for sailors in case the current polar is slightly off. There are a number of ways we can do that, so we plan to run some user studies on the best approaches for this, stay tuned...

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