Brian Sweeting wrote in message
...
The normal excuses for lack of revs a-
Bottom of the boat fouled
Prop fouled
Air intake blocked

Bear in mind also that if the boat is a displacement hull then its maximum
speed is only about 5.5 knots; trying to go any faster will overload the
engine giving the sort of sound effects that you are experiencing.

Hope this helps ;} Brian


I have the manual for the Vedette installation. There is no governor.

Generally speaking, engines of this period (late '50s/'60s) were not
designed to run at more than about 2000 rpm. Speed limitation is mainly due
to the boat hull (assuming the correct prop). If the hull is clean, expect
3/4 h/gallon at 4 mph. As the speed increases fuel consumption drops rapidly
until you are only getting about 1 h/gal at 7 mph.

My single Vedette in a Freeman 22 just about gets me up to 7 mph at 2000
rpm. A twin Watermota installation (very similar in power to a Vedette) from
the late '50s on a Freeman 22 will make 10 mph with both engines at 2000
rpm: so engine rpm is not the limiting factor.