You write "We have heading pointing to leeward of COG on both tacks". Could it also be that your heading (without leeway) is pointing to leeward of Course (with leeway) as well?

If so, it means your leeway has the wrong, opposite direction. The cause can be that heel has the wrong sign, the instrument system thinks the boat is heeling the wrong way and subsequently leeway also has the wrong direction.

Some instrument systems seem to handle the signs of parameters such as heel (and subsequently leeway) well and others don't.

Bad compass calibration does not affect performance data directly. However, compass calibration affects TWD. When doing the normal wind calibration trying to ashieve constant TWD through tacks, then you might end up with incorrect wind angles in your log files. 

I have seen occasional blips in heading (at least in the visual display) when using multiple sources in a NMEA2000 network. If you use an Actisense, make sure you ignore backup sensors until you actually need them. 

It should be possible to back-calculate TWA if you know your wind cal tables before (when using an incorrect table) and after (what the wind cal table should look like) but it is (A) hard work and (B) possibly still incorrect as correct wind calibration tables will look different depending on the daily conditions.

Last edited by barne (3/31/2022 11:04 am)