wrote in message
...
On Sat, 10 Apr 2010 10:37:13 -0400, "mmc" wrote:


"Tim" wrote in message
...
I'm familiar with two cycle motorcycles, and they're power band. Some
are really finicky and doggy untill you hit a certain rpm, then can be
almost uncontrolable. (Motocross) while some have less power yet a
wider range of usable torque.(Streetbikes) and some have the tuning
at the absolute bottom of the rpm ranges (trials bikes)

But concerning a v-4 johnson/evinrude etc. Is there a powerband where
you run a set range rpm for maximum efficiency? too little rpm labors
the engine, and too much gaines little except sucks more fuel?

Well, my experience is that just enough throttle to keep a boat on plane
is
the most efficient (get somewhere) setting but this doesn't work for a
normal, round tube pontoon boat.


A pontoon still has a step where the hulls level out a bit higher in
the water than pure displacement. More speed generally raises that up
a little but at a pretty good increase in fuel consumption.
If the motor and boat are well matched it will be up on the step and
leveled out at 3200 - 3400 RPM. Bumping that up to around 4000 RPM
gives you a good cruise speed and a healthy RPM for a 2 stroke engine.
.
I'm just happy to keep my prop deep enough in the water to keep the
cavitation down. When cruising around the Banana or Indian Rivers, any chop
at all will cause it to cavitate at 3,000-3,800 RPMs and if almost can't run
at over 4k at all.
It's a long shaft 50 Force and the cavitation plate is just under the
surface. Should I move the motor lower? Probably involve a either one of
those brackets used to move an OB out from the transome (name escapes me
this morning) or chopping the crap out of my outboard mount, something I'd
really like to avoid.