For a description of polar diagrams have a look at Create a polar diagram
What information is in a polar table and diagram
The reason we want to have polar tables and diagrams is to get an indication on the the maximum speed we can achieve on a certain course. We can use this in a regatta or we can combine the polar information with weather (GRIB) files to make predictions for a trip.
For the Beat and Run, we only have to look for the optimum angle at a given windspeed, and trim if our speed is below the indicated speed.
For a free leg, look at the top speed and select the apropriate angle.
Below the optimum boat speed are the apparent wind speed and angle, use them as a check.
Large differences could be due to windshear (direction or speed)
What is a Polar Table
The polar table is divided into 3 seperate section: Optimal upwind(beat), different angles in between, optimum downwind(run).
The optimal up & downwind are the most simple, for instance:
at 06 knots of wind, head upwind at 43.6 degrees
at 10 knots of wind, head upwind at 41 degrees
at 20 knots of wind, head upwind at 37.7 degrees
If you sail higher, you will lose speed (have a look at VMG), if you sail lower, you will not get at your destination as fast as possible.
So when you are on a beat or a run, just sail these angles for optimum VMG
The next step is looking at the boatspeed at the angle you are sailing, for instance with 6 knot wind speed:
at 75 degrees wind angle, speed is 6.48 knots
at 90 degrees wind angle, speed is 6.43 knots
at 135 degrees wind angle, speed is 5.09 knots
So if you are sailing at 90 degrees and your boat speed is 6.10 knots, you are to slow, trim! You’re sailing at 95% of the optimum
what is VMG, Velocity Made Good, an indicator of your upwind performance. Don’t sail directly to this, VMG is not useful for steering, use the target angle and target speeds on an upwind course.
How do we create a polar
Use this Excel sheet to create a print version of your polar table.
We can download some polars from here: http://noordzeeclub.nl/rating/meetbrieven.php, select a boottype, press “ZOEK”.
From the list of results, open one and on the second page are the predicted polars.