I’ve heard quite a few experts say that the Yanmar 3GM30F tachometer
reads high, by as much as 100 rpm.
Until now, I have accepted that as gospel, and even repeated it to
others. No more!
But today I used my handheld optical tachometer in a calibration
exercise. And found that the boat tach is accurate to within 3% (ie
the error never exceeds 70 rpm) and for engine speeds in the range of
usual operation (2500 - 2900 rpm), the accuracy is quite good (within
1%). At the very top end of the range (>3300 rpm), the tach does read
high, but only by 50 - 70 rpm (1.86% at 37 hundred rpm on the tach).
The low end has inaccuracies of around 3%, but the errors aren’t
consistent (sometimes high, sometimes low).
If you’re interested, I’ve uploaded my findings as
Yanmar3GM30Ftach.pdf (about 84 K) and placed it at
http://finance.groups.yahoo.com/group/bcc/files/BCC/Yanmar3GM30Ftach.pdf (you likely need a Yahoo identity to access the file).