Bought motor w/ no prop, need help finding prop size

[flagflyfish]

Hi all,
I recently purchased a 50 HP mercury 2 stroke motor with rope start and a tiller handle serial # 56325XX. It has a jet unit on it right now as that is what is needed on most interior Alaska rivers, but it also came with the original lower gearbox but it has no prop on it. From what I have gleaned by searching, the motor is a 1981 with a WOT of 5000-5500 RPM. It is mounted on a 16 ft X 80" beam flat-bottom Jon boat, that will be used mostly on rivers. Can you help me with some ideas of prop size/ pitch? It has a 13 spline shaft. Thank You, Flagflyfish

 

[Fun Times]

Re: Bought motor w/ no prop, need help finding prop size

Below is the list of props that fits your engine size.

http://www.mercruiserparts.com/Show...nbr=290&bdesc=PROPELLERS(RIGHT+HAND+ROTATION)

http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=13287

 

[Bob_VT]

Re: Bought motor w/ no prop, need help finding prop size

Check iboats for a prop.....http://boatpropellers.iboats.com/

 

[steelespike]

Re: Bought motor w/ no prop, need help finding prop size

It would help if we knew the gear ratio.If you count the rotations of the input shaft for each revolution of the prop shaft it would help a little. Probably something like 1.80 a little less or little more.
Is the boat a lightly loaded bare bones boat?

 

[flagflyfish]

Re: Bought motor w/ no prop, need help finding prop size

It would help if we knew the gear ratio.If you count the rotations of the input shaft for each revolution of the prop shaft it would help a little. Probably something like 1.80 a little less or little more.
Is the boat a lightly loaded bare bones boat?

The gear ratio is between 1.90 and 2.00, probably closer to the lower side. The boat is a utility boat, and will be used for fishing, moose hunting, bear hunting, etc, etc......there will be times that it will be hauling a moose or a four wheeler, but those times will be few. It will mostly be used to haul myself and maybe a companion to the cabin, so I'm looking for a good all-around prop.......maybe a 10-10 1/2 pitch????? What would have come stock on that motor?

 

[pootnic]

Re: Bought motor w/ no prop, need help finding prop size

I take a guess and say somewhere around a 15" pitch.
Is the 80" gunnel dimension?
What brand boat is it or is it locally made?
Anyways,I think 10.5" would be to small,good maybe if your loaded down.
A tach is the only way to really figure it out...