sylvan mercury prop.

[rolmops]

I bought another boat just last week.It is a 1984 18 foot aluminum Sylvan with a 1984 75 horse 4 cylinder mercury.Although I know that this 75 horse takes a 12.5 prop,I do not know what the preferred pitch is using an aluminum prop for this engine.
I would really appreciate it if somebody can give me some advice about this specific combination.
Thank you.

 

[Silvertip]

Re: sylvan mercury prop.

There is no specific pitch for the engine -- that's why there is a range of pitches available. Without any wide open throttle rpm with an average load on your boat we can't be of much help unless someone has the exact same setup. That engine on your boat would likely take a different pitch than the same engine on a heavier or lighter boat. If you have no prop to test with, you might check with a Sylvan dealer and see what they recommend.

 

[rolmops]

Re: sylvan mercury prop.

I took the old prop off, brushed the soot off and came up with the following:
Michigan PM 3 CUP.
After cross referencing from old to new numbers I was left with the PM series which are 031042,43,and 44. (in the range that my boat is in)
These are 13.25 x 17,13x19 and 12.45 x21 (all aluminum)
I think I will try the 13x19 and see what happens.
The boat I have is aluminum and probably a lot lighter than fiber glass.Is it safe to presume that I can bump up the pitch because of that?

 

[steelespike]

Re: sylvan mercury prop.

I think a 15 is closer to what you need.If you go with a 19 and you end up overpropped you just plain can't use it if you go with a 15 I think you will be close and if you are under propped you can just throttle back if needed to stay within recommended rpm. The 15 will deliver hole shot and load performance.I think with the 17 or 19 you will struggle.From my research even though the aluminum boats are light they are not necessarily easy to push.And for 18 ft your a little under powered.