1975 evenrude 70 hp prop

[ranger42]

im going to put a 70 hp even rude on a 17 ft bowrider. i know its to small but i havent got another motor. this boats weighs 1080 lb what size of prop should i use for best performance. it will be for riding and fishing with up to 4 adults.the prop thats on the engine now is broke so i want be able to try it.

 

[steelespike]

Re: 1975 evenrude 70 hp prop

delete

 

[steelespike]

Re: 1975 evenrude 70 hp prop

What size prop is on it now and what size boat had it been on?
It is possible the prop could be fixed and used for a test run and kept for a spare or sold.
I believe the motor was available with a small or large gear case.
The prop size will help tell the size.
The prop size may be under the prop nut.

 

[BonairII]

Re: 1975 evenrude 70 hp prop

13 1/4 X 17p seems to be a good "all around" prop for the 70hp....but boat weight/load will dictate which prop will work best. A tachometer is needed to determine best prop.

My boat is lighter than yours, but I use a 17p for general use....and a 15p when I'm carrying more passengers/gear. A tachometer will ensure that you aren't over revving or lugging your motor.

 

[Texasmark]

Re: 1975 evenrude 70 hp prop

13 1/4 X 17p seems to be a good "all around" prop for the 70hp....but boat weight/load will dictate which prop will work best. A tachometer is needed to determine best prop.

My boat is lighter than yours, but I use a 17p for general use....and a 15p when I'm carrying more passengers/gear. A tachometer will ensure that you aren't over revving or lugging your motor.

I see what looks like a Starcraft alum in your avatar. If that's your boat it is light by design. He didn't say what his hull material was. Could make a difference.

Mark

 

[ranger42]

Re: 1975 evenrude 70 hp prop

I see what looks like a Starcraft alum in your avatar. If that's your boat it is light by design. He didn't say what his hull material was. Could make a difference.

Mark

its a fiberglass boat. 1971 thunderbird 17 ft. with walkthru windsheild

 

[jestor68]

Re: 1975 evenrude 70 hp prop

I would say no more than a 15" pitch for that size boat and a 70 Evinrude; 70 hp @ 5500 rpm; with a range of 5000-6000 rpm.

Ideal WOT rpm to shoot for would be 5600-5800 rpm.

I assume your weight is the bare hull without the motor.

 

[BonairII]

Re: 1975 evenrude 70 hp prop

Do you have power trim?

I'm going to take a guess...and figure that a 15" prop will end up being the right one for your rig.

 

[Texasmark]

Re: 1975 evenrude 70 hp prop

I only saw one thunderbird in my life. I was fishing off Gulfport, MS. In an open boat behind Cat island. A rather large squall came up and a 21' Cuddy I/O came in with bimini and side curtains. He motioned for me to come over and get out of the rain....no wind as we were on the lee side of the island.

The boat I boarded was very well built and looked to have appropriate weight to go with it. As others have said the 15 P looks ok and if it's not, drop down to a 13 for when you have guests and run the 15 when you are alone.

Mark