Originally Posted by goboatingnow
In practice in the open sea there is little difference.
That's true in theory. If there is no current
their is no difference (in theory)
In practice there tends to be a big difference.
Most cruising boats have poorly calibrated logs
. They very often read a bit different on different tacks, upwind and down. Even if they start out OK a few months at anchor sees some growth on the transducer or on the hull
that disturbs the water flow and the calibration becomes inaccurate.
Yes you can pull the transducer and clean it, or dive and also clean the hull
around the transducer, which is better, but few cruising boats bother until the readings become poor.
the advantage that its always in perfect calibration. It does suffer some random speed errors, and the update rate it is a little lower, but in my experience it provides better wind information than using the log on a cruising boat.
units are much better,a sat differentional signal makes a huge difference, and you want to use it this way get one of the 5hz models when the GPS needs replacement.
For a race
boat the situation is reversed. They will typically place the log in the optimum position, keep the log and bottom spotless clean and of course recalibrate the log regularly.
Assuming both are equally acurate, true wind is also probably a more useful number for a racing
sailor where ground wind is useful for a cruising sailor.
The ultrasonic logs
should solve some of these problems, but at the moment they expensive and have been a little unreliable.
If you are a cruising boat give ground wind a try.