Yes,another prop size question

[hila2006]

Well our prop fell off last night while taking a sunset ride around our lake. We don't know how, can only assume. We've looked at forums here, looked a quite a few mfg. specs as well. We own a 1986 Monark Mcfast v16 bassboat with a 1986 Evinrude 70hp vro. Our aprox. weight is 1150-1200 pounds with the motor. The gear ratio from the original owners manual is .414(12:29), and our WOT is 5500 rpm. We live on a small 120 acre lake so we're not trying to set any speed records, but we were currently running about 40mph with 2 adults on board nearfull throttle and the tilt up to the top line on the tilt gauge. If we could get at least 35 mph we'd be happy with that. We're the fourth owners of the boat and have no way of contacting any of the previous owners for info. We know the ss prop that just fell off was put on by the owner we bought the boat from. We also do not have a tac on the boat. With the research we've done we're thinking of a 13.25x17, or a 13.50x15 prop. We are also trying to figure out gearcase size because a couple things we've seen say we have a large gearcase, and a couple said we had a small gearcase. We bought a Quicksilver prop today at West Marine with the Evinrude hub kit, but the end of the prop that fits into the motor was too big to tighten down at all, it was the same diameter as our motor. The diameter outside of the opening where the spline is is around 3 3/4". We need to get back into our boat asap, and just need a general, but safe prop to finish out the year with. Much thanks in advance.

 

[steelespike]

Re: Yes,another prop size question

I'm pretty sure you have the small gear case and I'm guessing a 15" pitch prop.
The diameter will follow if the prop is intended for your motor.
Stainless props are too expensive for guess work so go with an Aluminum to start with.
Even if it turns out to be the same pitch the al prop will perform differently than the ss prop.
Your motor needs to be able to operate freely within its rated wot rpm range, probably in your manual.
Thats regardless of the typical speeds you cruise at.
You need a tach to check the wot rpm.