Pitch and diameter question.

[Mudbugger]

Sincere question
I'm dealing with a vintage (OK old) engine, a 1963 Johnson 40 HP, and the prop that is on it has been beaten to death. Probably an inch or better, smaller than what's specified and the edges of the blades are all flat.
There's not a lot of selection out there, I've found two, 10 3/8 X 11 1/2 and 10 1/2 X 12.
It's on an old Manark, 18', aluminum VEE bottom.

Which, if either would be preferable?

 

[racerone]

On an 18' with that 40 HP you will want / need the lowest pitch.------There may be a 11 " or 10 1/2 " available.-----Remember in 1963 the choice of boats motors was different than today.----A 75 HP electric start was considered " top of the line " in those days.

 

[Mudbugger]

The lowest pitch, even though this is basically a lightweight jon type boat?

 

[racerone]

Sorry-----I have no idea what an ---" old Manark 18' VEE bottom " ---Looks like or how much it weighs.----Ask your friendly dealer to help you.----Using the wrong prop can damage a fine motor.

 

[Mudbugger]

It's just a vee bottom, aluminum, fishing type boat. The motor probably weighs, almost as much as the boat, if not more.

We have no dealers, within probably 50 miles or so, and they weren't interested in helping much on an old, obsolete boat and motor.

BTW, thank you for your answers.

 

[jimmbo]

OMC did make an 11" X 9" for that Motor, OMC part # 376738

 

[Mudbugger]

Only 2 hours, I consider myself lucky, if I can find stuff the same day, sometimes the same week!
Our location is North Central, IN. About 1 1/2 hours north of Indy.

 

[jbcurt00]

.....

Check your PMs

 

[Mudbugger]

I did find a deal on a 10 1/2 X 10. I also found out that I have two other engines, that will take the same props. A 1957 & 1958, Johnson 35 Horse. So an extra or two, won't hurt. I need to see if I can Identify, what those have on them.

 

[Sea Rider]

Would you say that the beaten prop was a nice water performer ? If so, send it to a prop shop and have it fully repaired. After that will need to tach it to know if the motor runs safely inside its wot rpm range factory stated, can go from there for a prop repitch in the -0.5, -1.0,- 2.0 sizes to up the wot revs as requiered.

Happy Boating

 

[Mudbugger]

No idea, I bought the boat & motor this way and I've never had it in the water.

The prop is bad enough, I didn't want to wait until season, only to find props hard or impossible to find. Plus, I have severe doubts about the balance.

There is no tach in the boat, it's a mag system, so I'll need to find one to use. That makes me wonder, what did everyone do, before tachs (especially cheap ones) became readily available?

 

[Sea Rider]

I guess that you could install a cheap induction tach to any of the spark plug cables as assume won't matter which type of electrical system the motor runs with.

Before the standard and induction tachs became popular, nobody knew at which wot rpm the motor were running at as loaded. Motors with factory delivered props were usually medium pitched ones for the factory to remain safe in case the motor experienced an unwanted kabooom issue while over revving badly.

Used to have an Evi 96-15 HP motor, at that time there were only 3 OEM props to suit different loads and applications. My current motor has 7 different pitch sizes to extensively play with.

Happy Boating

 

[JimS123]

That makes me wonder, what did everyone do, before tachs (especially cheap ones) became readily available?

When I bought my first outboard motor it came with the promise that the dealer's chief mechanic would tach it out for me. After the initial 10 hour break-in I made an appointment and he met me at the launch ramp for a boatride. The rpm was spot on, just as they had suggested when they mounted the motor and gave me the prop they did.

A few years later, when I got my second outboard, I had them order a dash mounted tach and compass, and actually I installed them myself. Once again it was spot on, so I didn't need to have them help me or exchange the prop.

That was 50 years ago. To their credit that same marine dealer is still in business and still going strong. See, customer service helps you stay in business.

I though tachs were always available. I don't know about cheep, but as a poor college kid at the time I don't remember it being all that expensive.