Engine 70hp Evinrude 3cyl 2stroke.

Old prop was 13.75 X 15 aluminum. With normal load the engine maxxed
out at 5000 rpm which is the redline for this motor.

I put an identical size 13.75 X 15 stainless Rapture prop on with the
tuning vents full open. The boat yanks me up on skiis in about half the
distance it used to take. Boat hits plane and full speed in about 120
feet with no skier.

Here's the problem. The engine will hit 6000rpm at W.O.T. and that is
way to much, I have to keep an eye on the tach, and throttle back once
I am up on plane.

The factory 17 pitch prop is smaller diameter slightly 13 3/8 (13.375)
and I think smaller diameter is less efficient.

It seems thus,
Choice one, repitch my 13.75 X 15 up to 16 or 16.5 if they can go
that far, and keeping the larger diameter.

Choice two, sell the prop I have now, and buy a 13.375 X 17 factory
prop, which is a bit smaller in diameter.

(or just leave it alone, be careful with the engine rpm's, and enjoy
the fact that it nearly rips me out of my skiis on takeoff)

What do you folks think? Something differant entirely?

Something is not right. Either the old aluminum is not a true 15 or the new
one is not a true 15. Take both props to a prop repair place and have them
measured. Then you will know what is really going on. If they are both 15
then you may be trimming out too far and the prop is slipping. Try trimming
back down a little and see if the rpms come back down. You might also try
installing the vent plugs and see what that does.
Assuming the new one is indeed a 15 and it is not a problem as indicated
above - you will need a 19 to get your rpms back close to 5000.
That is going to kill your now fantastic hole shot. But it will give you
great top end and cruise speed compared to what you have now.

The slightly smaller diameter is not going to be a factor. Larger diameter
w/ smaller pitch gives you more ability to carry a heavy load. Your boat is
probably not heavy enough to make a difference.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com

-
"Gudmundur" wrote in message
...
Engine 70hp Evinrude 3cyl 2stroke.

Old prop was 13.75 X 15 aluminum. With normal load the engine maxxed
out at 5000 rpm which is the redline for this motor.

I put an identical size 13.75 X 15 stainless Rapture prop on with the
tuning vents full open. The boat yanks me up on skiis in about half the
distance it used to take. Boat hits plane and full speed in about 120
feet with no skier.

Here's the problem. The engine will hit 6000rpm at W.O.T. and that is
way to much, I have to keep an eye on the tach, and throttle back once
I am up on plane.

The factory 17 pitch prop is smaller diameter slightly 13 3/8 (13.375)
and I think smaller diameter is less efficient.

It seems thus,
Choice one, repitch my 13.75 X 15 up to 16 or 16.5 if they can go
that far, and keeping the larger diameter.

Choice two, sell the prop I have now, and buy a 13.375 X 17 factory
prop, which is a bit smaller in diameter.

(or just leave it alone, be careful with the engine rpm's, and enjoy
the fact that it nearly rips me out of my skiis on takeoff)

What do you folks think? Something differant entirely?