Log Calibration ST50

[dprice]

I will apologize in advance for the confusing nature of this question.

Suspecting that my knotmeter was under reporting I performed 2 calibration runs this eve.

Chart distance was 2.15nm and the log showed 1.65nm as the average for both runs.  This should give me a correction factor of 1.3.

When I went to enter it I saw that the unit had already been setup with a correction factor of 1.27.  

I then made the assumption that to compensate for the fact that the unit already had a factor when I did my calibration run I could multiple the original factor by the new factor.

This gives me 1.65.  If I enter this number my boat can suddenly motor along at 7.4kt at full throttle (2400 RPM) M35B.  No Wind, Flat seas.

This seems a bit fast to me.

Anyone know what I am doing wrong ?.  Can the boat do more than 7.2 kts under power.

Thanks

[sail4dale]

I think it can with a clean bottom.  I've motored frequently at 7.5 k. and it checks with my gps.  I have a fixed three blad prop   so I do suffer under sail.

[dprice]

I have a fixed 3 blade as well.  So maybe my math is correct then.  

I also have another excuse to go get a GPS.

Thanks