Propellor size: 1996 mac 26x with a Johnson 50 HP 2 stroke

[walker127]

I am out in Malaysia and want a new prop for my Mac 26x.

I have a 1996 Johnson 50HP 2 cylinder 2 stoke but the local outboard shop haven't a clue what size I need........and neither do I. I guess I could just replace the damaged prop on my boat but there is no guarantee that is the correct size. I don't have a tachometer.

I have found info on this site for Honda props but not Johnson 2 stokes.

Is there anybody else on this forum out in Asia and if so where do you buy your parts? I have to import most of my stuff from the states and Singapore, which is expensive.

Martin

[walker127]

Ok maybe nobody is running a 1996 2 stroke Johnson, but I guess the propellor sizes for all 50 HP 2 stokes should be similar.

Anybody got any suggestion as to what size prop I should be buying?

[Moe]

A 50 HP motor is typically used for a 15-16" aluminum fishing boat and most of the props available for it are sized for that load. What you need for a Mac is the prop that would be used on that motor for pushing a barge. That is, the largest diameter, and the lowest pitch possible.

Here's iboats.com's listing for a 1996 Johnson with 13 tooth spline prop shaft. You'd want the lowest pitch, 10" by 14" diameter, if you have the large gearcase that can take it... and depending on the gear ratio, a 10" pitch may not be low enough.


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Moe

[walker127]

Thanks for the reply Moe

I have been in touch with a Johnson dealer in Hong Kong and they recommend an aluminium prop 12.25 x 15, part No. 778774 but I don't think they are familier with Mac 26x's.

I am not after the perfect match, just something that doesn't over rev the engine at WOT and gives reasonable gas mileage.

Would this be ok?

[mark,97x]

on my yamaha F 50 i use a 3-12-10 solas prop(3 blade,12 inch dia,10 inch bite)

[ferd johns]

I have a 10 x 14 on the same boat/motor combination. Good low end power, good rpms.

[Frank C]

Hoping not to confound your problem, but you can use some foundation advise. You'll either choose a 12" or 14" diameter prop, depending upon what the motor is designed for. Next, you'll choose pitch, something from 7 to 11 inches (max).

You must first determine if your motor has a 12" or 14" prop. Use a ruler to measure the distance from center of prop shaft to cavitation plate ... if it's 7" (plus a little) then your prop is 14." But if that distance is about 6.25 inches, then you'll choose a prop in the 12" diameter range. The Mac is a relatively heavy load for any 50hp motor, and the biggest prop diameter is usually the best choice. It would be a rare motor that was routinely fitted with either or both.

Secondly, you'll choose a pitch measurement. You're correct, the guys in Hong Kong suggesting 12.25 x 15-pitch don't know your boat. Regardless of diameter, you should choose a 11-pitch at maximum. If you frequently expect to be heavily loaded, or if you plan to motor with ballast full, then 8 or 9 pitch is better. Hope it helps ...