factory prop size for 1982 70hp johnson

[mrauschenfels]

anyone know the factory prop size on a 1982 70hp johnson? I am looking at buying a 16' aluminum boat that has a 13 3/4 x 15 prop on it. Seller says does not pull a tube very well. What prop size could I change to that would give more power (better hole shot) for pulling a tube? Thanks.

 

[SparkieBoat]

Re: factory prop size for 1982 70hp johnson

you get a prop that gives you the best WOT RPMs, you should prop it to run around 5800 at WOT. this will give you about the best hole shot you can get without chance of over reving your motor. you could try a 13 pitch prop, but without knowing your WOT RPMs with the 15, I am just guessing. also you can try raising your motor a hole or 2 or 3 this can make a world of difference sometimes.

 

[steelespike]

Re: factory prop size for 1982 70hp johnson

Standard prop was a 13 1/4 X 17 .Your prop should do better trhan a 17 at pulling.
Unless that boat is really heavy or hauling a load of people I would think it would pull pretty good with a 15. Do you have any indication of its rpm and speed?

 

[Texasmark]

Re: factory prop size for 1982 70hp johnson

With no statistics to go by, back in the early-mid '70's a 15'-16' tri-hull with several folks aboard and a couple of kids, or a fat......adult person on a pair could have a jolly good time with a 15" prop. We didn't have tach's back then...they were a novelty.....but nobody that I knew of ever lost an engine, but ME and I lost it because of a stuck OMC thermostat with no warning horn, not because of the prop. I run Mercs now................

Mark