Click the picture for the source.
If I log and plot my boatspeed, why can’t I make my own polar?
Issues
- Most of the time you aren’t performing optimally.
- Most of your logs include eating lunch and other stuff that pollutes the data.
- Note taking showing the good spots is very hard to do.
- Boat dynamics (new heading with a boatspeed above or below polar speed before acceleration or deceleration has happened).
- Wave effects (both upwind and down) messes things up your boatspeed with respect to polar speed.
- A boatspeed point at 12.3 knots and 47.8° true wind is between the lines. How would you handle it?
- You probably will never experience all the conditions needed to create a curve.
- The resulting polar is lumpy and full of holes. This makes it impossible to derive important data about Vmc sailing (i.e. you can’t derive differential speeds. Read about the Wally).
You will wear out your boat and sails before you have a usable polar. It is better to start off with a “theoretical” polar so you can have something to compare to. If it turns out to need tweaking (beyond say calibration), the Vpp guy can do it a lot faster and better than you could.
Q&A
| Q | If the boat goes faster than polars, why isn’t it the truth? |
| A | It could be that the polar is wrong. But more likely it is because of wave action or boat dynamics or wrong true wind speed. |
| Q | How can theory trump reality? |
| A | Polars are models. All models are wrong but some are useful. In this case, polars provide a smooth consistent number that you use to compare performance to. This includes what-if where you find out whether heading off your rhumbline will increase your performance. Hand-made polars with their lumps and holes do not allow this important function. |
How do I get a polar?
You can get one from US Sailing, or better, learn about the NeoPolar.
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