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RayTech Navigator User’s Guide
5-68
Figure 5-22. Twa Corrections Screen
It’s important to note that depending on your instrumentation system’s
damping, the Twa value can take up to 30 seconds to “settle down”
after a tack/gybe. Whether you add or subtract the value depends
upon whether the instruments have either lifted or headed during the
tack. The same convention applies to a downwind gybe, whereby a
lift takes you away from, and a header takes you closer to, the bottom
mark. If you apparently get a lift after tacking, you must subtract that
correction and add a header correction to the table.
Here’s an example of Twa calibration:
After tacking five times, the average wind direction changes 6 degrees
tack-to-tack in 10 knots of wind. This has the effect of showing a lift
and therefore 3 degrees can be subtracted from the upwind correction
table for 10 knots of wind. Keep in mind that some tacks/gybes can
yield an incorrect calibration value if the wind has actually shifted, so
this must also be factored into the calculation process. Additionally,
calculations will be affected if the boat has been set up differently
tack-to-tack (such as varying runner loads, more backstay, etc).