I propose here an exercise to assess the practical effects of 2 corrections described in previous posts:
- correction of apparent wind angle vs heel
- correction for leeway
We will see the results displayed by 3 types of instrumentation system, for a sailboat on a tack in the following conditions (assuming no upwash, and no wind shear).
System A : basic system, no correction
System B : AWA corrected for heel
System C : AWA corrected for heel, and results corrected for leeway
System C is the only one reporting correct values in these conditions.
The following table presents the data that would be displayed by each of these systems.
|System A||System B||System C|
|No correction||AWA corrected||like B + corrected|
|for heel||for leeway|
We see that the most volatile figure is the true wind angle (TWA), and by consequence the wind direction (WDIR). We also see that systems without correction make you believe that your boat is pointing like a champion. It is possible to retrieve the correct TWA by taking the average WDIR over the 2 tacks and back-calculating the TWA. This is called ‘dewiggling’ and the poor upwash is usually identified as the responsible, even if it has often nothing to do with that.