need help choosing ideal prop pitch for 85 merc

[stinkbait85]

i have recently bought an early model 85 merc. i plan to put it on my 16ft fisher bass boat. its dry weight is around 700 pounds plus the additional weight of the normal stuff(fuel, rods, anchors, tackle, ) im not sure which size or pitch prop to get for it. please advise

 

[steelespike]

Re: need help choosing ideal prop pitch for 85 merc

If it has a prop you should check the prop size(on the barrel or under the prop nut) run it to get a base of the rpm and speed.Otherwise there should be a long list of info required to help calculate a prop size at the top of the page.I believe your 85 was probably produced 73-77 wouldn't hurt to pinpoint the year."early model" is a little vague.

 

[stinkbait85]

Re: need help choosing ideal prop pitch for 85 merc

to be honest im not sure of the year model of the motor. it is actually a mariner motor. how can i determine the exact year model?

 

[Bondo]

Re: need help choosing ideal prop pitch for 85 merc

how can i determine the exact year model?

Ayuh,... By posting the Serial # in the Mercury outboard forum...

You might as well start with whatever prop is on it,... Just to get a baseline to work from...

 

[bryanwess2000]

Re: need help choosing ideal prop pitch for 85 merc

I've had a 1977 mercury 850 on two boats that weighed around 700lbs
one was a glasstream 1550 probass trihull, the other a 16' sylvan aluminum
v bottom, both ran 37-38mph with a 13X21P aluminum prop. No tach, but
at 10% slip or more I was turning 5000rpm or more. This was with the motor
sitting flush on the top of transom. I had no blowout no matter how hard
or fast I turned so the motor could have been raised, but I didn't want to drill
more holes in the transom. I would start with a 19-21p prop.