Sailboat speed versus sailing angle

I nabbed this image off Pinterest via (https://hobiecat16.wordpress.com/2010/09/23/points-of-sail-vs-boat-speed/). It is a pretty good image that represents the speed of a sailboat versus the sailing angle to the wind.

It is pretty easy to read – at dead downwind in a 10-knot breeze the fastest you can get this boat to go is slightly less than 5 knots. Whereas if you came up 45 degrees to 225 degrees off the wind you’d be doing around 8.5 knots.

Applying a little trigonometry: this means that for a dead downwind destination, if you chose to go 45 degrees off of downwind and do a few gybes – while your friend chose to aim for the destination, you would win significantly.

The graph is called a polar plot.

Many boat manufacturers produce this graph for each boat model. Often times the trig works out so that dead downwind is not the fastest angle to a dead downwind destination. Also you need to take into account sail configuration, i.e. spinnaker or no spinnaker.

Catamaran Polar Plot
Catamaran Polar Plot

So here is a Puzzler for this week

The boat below is a Volvo Ocean Racer 60: Given a destination that is 170 degrees downwind. As the navigator, what angle would you tell the helmsperson to steer? Post your answer on our facebook page under the same article. Otherwise check back here in a week or so.

Polar Plot VO 60
Polar Plot VO 60

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