omc prop differences

danray35e

Petty Officer 3rd Class
Joined
Jun 30, 2010
Messages
86
I have a 1976 55 hp johnson on a 69 Mckee Craft 14 fiberglass trihull. I was given the boat and motor, as they were going to scrap it. I have not had it in the water yet. After 3 months of work on the hull and motor. It is getting close. Just need a few more things. Primarily a prop. The motor has an aluminum 12 1/4 x 15 with 13 spline but it is chipped and bent.
I can either get it repair or buy another prop. I ran across a used stainless I can get for cheap. The size on it is 12 1/2 x 13 with 13 splines. While it is one of the sizes listed that can be used with this motor. The part number on the prop is not the same as the one on the evinrude johnson outboard parts catalog for that size. For example the part number for that size listed for my motor is 0038682 however the number on the prop I am looking at is 390849. I assumed that because it has 13 splines it will work, but I know just only slightly more than jack $#*$ about props. I assume the change in size and pitch will give me different characteristics on the water than the current size I have, but since ive never had it in the water, I doubt I will notice a difference lol
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: omc prop differences

Can't speak specifically to the numbers. Numbers could be different because material is different and the diameter and pitch are different. The ss prop will likely add about 400 rpm just with the pitch difference.And we don't have any base line to work, with.
You could get the ss prop with the idea if performance is wrong you can allways resell it.
I feel your best bet is to get the 15 repaired and do some test runs carefully evaluating motor height and trim as well as the response of the boat to the motor changes. The antivent plate just above the prop should be visable on plane.
 

danray35e

Petty Officer 3rd Class
Joined
Jun 30, 2010
Messages
86
Re: omc prop differences

Thanks for the information. I am starting to think that the prop I am looking at might be for the larger diameter gearbox. As it seems there are two different size gearboxes for this size and year. If that were the case, then the diameter of the hub would most likely stick out beyond the diameter of the torpedo section of the gear box.
 

SparkieBoat

Captain
Joined
Aug 17, 2009
Messages
3,643
Re: omc prop differences

you never mentioned your top speed or RPMs at WOT and trimmed out.
 

danray35e

Petty Officer 3rd Class
Joined
Jun 30, 2010
Messages
86
Re: omc prop differences

you never mentioned your top speed or RPMs at WOT and trimmed out.
Thats because I don't know the wot, top speed, or rpms. I've never had it in the water. Ive not even had the engine running. I am trying to stay ahead of the game so that once I get it running I won't be waiting a week for a prop to come in so I can get it on the water.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,082
Re: omc prop differences

Thats because I don't know the wot, top speed, or rpms. I've never had it in the water. Ive not even had the engine running. I am trying to stay ahead of the game so that once I get it running I won't be waiting a week for a prop to come in so I can get it on the water.

Ayuh,... So, put on a prop that fits, 'n Try it to develop some numbers to work with, aka; the wot, top speed, or rpms...

Go by prop Pitch,.... Diameter plays a tiny role in the overall grand scheme of things...
 
Top