gear ratio 90hp evinrude

[mstevens61]

I have a 1989 90hp Evinrude V4 on a 17 foot boston whaler newport. I have been trying to fit a new prop to it. The engine is new on the boat and the only markings on the prop are "218 K" and "392E" I don't know what these mean so I dont know what the pitch and size of the propeller is. I also can't find the gear ratio of the motor. Without these two pieces of information I can't make a very educated decision on what prop to get. The boat will only do 27 kts, and 4800 rpm. The prop is aluminum and badly beat up, but there is no vibration. I think it should do about 34 with this boat motor combination and the right prop. Can you answer any of these questions?

 

[Dhadley]

Re: gear ratio 90hp evinrude

We usually run a 19 on those rigs. It depends on the load and set up. Something may be wrong with the motor, like running on 3 cylinders.<br /><br />The gear ratio is 2:1.

 

[mstevens61]

Re: gear ratio 90hp evinrude

Thanks, I was thinikng a 19 also, but actually went with a 17" stainless progressive pitch cupped propped. The boat is heavy as the foam is saturated with water. But by my calculation I expect about 32 kts with 15% slip. The motor was turning up to 5200 when the prop wasn't quite as beat up. So I don't think there is anything wrong with the motor. and with a 2:1 ratio and a 30% slip I figure the Prop I have is a 19" SO I hope a 17" is not going to be to weak.<br />Thanks again!