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Richard Casady

On Mon, 18 Aug 2008 09:06:10 -0700 (PDT), wrote:

On Aug 18, 11:54*am, (Richard Casady)
wrote:
On Mon, 18 Aug 2008 05:33:47 -0700 (PDT), wrote:
If the prop is a little too small then there's not really much issue
as long as you are careful not to run at wot for any length of time.

At WOT the engine speed will be above redline. Don't do it at all if
you want the engine to last. Install a tach if you don't already have
one. Maybe you could trade the wrong prop for the right one. It is
like having a numerically large rear axle on a car. More engine speed
for the groundspeed. You have better accelleration at all speeds with
a slightly small prop. Watch that tach and figure on burning slightly
more fuel due to higher average engine speed.

Too large creates an additional load on the engine no matter what
speed you run at. *If it seems to be performing reasonably then odds
are good that the prop is in the ballpark.

Buy, borrow or rent a tach. Better yet, install one. The quick and
easy way is to email the boat builder. After all, what would he know?

Casady

Clearly from his original post he has a tach.

Most boat engine redlines are considered "sustained". I often run a
prop that allows me to exceed redline when the boat load is light so
that I still have a good holeshot when the boat is loaded. You just
need to keep an eye on the tach and not run it for long periods above
redline.

That is a new one on me. Every redline I have encountered in the last
fifty years has meant 'never exceed'. There may be a lower yellow line
marking maximum continuous. I do not believe boat engine redliines are
somehow different from all the rest.

Casady