Prop Recommendation For 1978 35hp Evinrude

beermunk

Petty Officer 2nd Class
Joined
Jun 20, 2004
Messages
146
The boat: 13' Boston Whaler (1968)
The motor: 1978 Evinrude Short Shaft 35hp 2cyl

A little history here: The motor was bought NEW by my grandfather for his old school ski boat. It was one of those awesome boats of the 60's and 70's that had the closed bow with the full windshield. It was the first boat I was ever in and the first I skied behind!

Anyway - about 10 years ago my step father bought the motor from my grandpa and put it on the Boston Whaler. Soon after I got my hands on the boat and it's been mine ever since. I've done some pretty extreme modifications to the interior to change it into a bass fishing boat, but that's another thread.

So about 5 years ago I ran the prop up onto a sunken bridge piling and had to put on the spare that we kept in the boat. I kept the old prop because it reminds me that you never know what lies beneath the murky river water.

Back to the prop now... That original prop that was on this motor (the one that was destroyed) was a 10x15. The spare I put on that day was a 10.5 x 11. I've ran it since with this prop and it works great for two people. Add two people and some gear or a dog and it's tough to get up on plane.

As I think back I remember never having that issue with the old prop. Since I can buy a new 10x15 for about $65 from iboats.com, I was wondering if that would be a smart purchase. What are ya'll general feelings on this?

I've read a lot of prop threads and went through the sticky but that was really geared towards bigger motors/boats with longer pitches. Any help is very much appreciated!
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop Recommendation For 1978 35hp Evinrude

It works the same for little boats as it does big boats. If you will give me your gear ratio, recommended WOT RPM and boat weight I can tell you what to expect RPM and speed.

H
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop Recommendation For 1978 35hp Evinrude

Beermunk, you need to change to a 10 x 13" prop in the same model you have now. This will bring your RPM into the right place and your speed up to about 30 MPH and carry the load. That extra 1/2" in Diameter is eating up your thrust from the prop, with no useful purpose. Here are the numbers assuming the 11" pitch is close to WOT RPM.

This is the 10 x 13" prop.
BeermunkPropChange.jpg



These figures represent your total boat weight with 2 people and gear with a total weight of about 1,200 pounds and your motor gear ratio is 2 to 1.

H
 
Last edited:

beermunk

Petty Officer 2nd Class
Joined
Jun 20, 2004
Messages
146
Re: Prop Recommendation For 1978 35hp Evinrude

Beermunk, you need to change to a 10 x 13" prop in the same model you have now. This will bring your RPM into the right place and your speed up to about 30 MPH and carry the load. That extra 1/2" in Diameter is eating up your thrust from the prop, with no useful purpose. Here are the numbers assuming the 11" pitch is close to WOT RPM.

This is the 10 x 13" prop.
BeermunkPropChange.jpg



These figures represent your total boat weight with 2 people and gear with a total weight of about 1,200 pounds and your motor gear ratio is 2 to 1.

H

Thank you so much for the advice sir! Buying it now.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop Recommendation For 1978 35hp Evinrude

Beermunk, please let me know what your WOT speed is and what RPM you are turning. I need that information for my database.

H
 

beermunk

Petty Officer 2nd Class
Joined
Jun 20, 2004
Messages
146
Re: Prop Recommendation For 1978 35hp Evinrude

So I just ordered a 10.1" x 13" pitch prop. The difference in price between the 10.1 and the 10 was about $20 - unreal! I figured that 1/10th of an inch couldn't be that bad. I'll be happy to get this boat back on the water with my new prop!
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop Recommendation For 1978 35hp Evinrude

You are right it won't matter. It is the same manufacturer and model right.

H
 

beermunk

Petty Officer 2nd Class
Joined
Jun 20, 2004
Messages
146
Re: Prop Recommendation For 1978 35hp Evinrude

You are right it won't matter. It is the same manufacturer and model right.

H

Probably not the same model or manufacturer - I just used the prop finder on iboats.com when I purchased.

I'll look up my WOT for that engine (no tach) and try to get a gps speed later this week.
 

beermunk

Petty Officer 2nd Class
Joined
Jun 20, 2004
Messages
146
Re: Prop Recommendation For 1978 35hp Evinrude


Hey man - according to a manual I found for evinrudes it's 35hp @ 5500rpm. PM me if you want a copy - it's too big to upload here.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: Prop Recommendation For 1978 35hp Evinrude

Great, that is what I used.

H
 
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