30 Hp M-35 Max RPM underway

[n624ma]

I have a question for the later Mk I (Mk. 1.5) drivers with the 30 Hp M-35.

At Wide Open Throttle (WOT) what numbers do you see for RPM and Speed through the water (not GPS, Speed over ground) and what prop do you have?

I was on a friends boat recently and with a 15x10 3 blade we were 600 RPM short of WOT in neutral when underway with calm seas and a pretty clean bottom.

I'm looking for some data.

[cmainprize]

As others have stated before, unless each engine has been checked with a laser tach, all readings from the boat tach are useless.  Calibrate the tach then start to compare speed.  And I would use a gps in calm water and no tide verses the boat knot meter.

[Ken Juul]

Joseph,
I think what you are saying is at WOT in gear, the boat is 600 RPM less than in neutral.  That could indicate many things. Depending on the type of prop your friend has, it might be a bit over propped.  Or it could be fouling on the prop, dirty injectors, fuel flow or airflow restrictions, etc.  You have reason to be concerned.  WOT RPM in gear should be within a couple hundred of WOT in neutral.  What you describe could indicate a problem.  But need more data to help troubleshoot.