Evinrude 50 prop revisited

[bigrockets]

I have a 17 ft Cobia center console boat with an 89 evinrude 50. When i got the boat it had a 17in pitch aluminum prop. It would not get up on plane very well and at Wot would sometimes pull air and over rev. I measured the engine height and trim angle and adjusted both to get the cavitation plate aligned with the hull and adjusted the trim angle down one notch. My marine dealer using a manufacturers calculator recommended a 13 in pitch prop so i bought it and put it on the boat. At Wot of 5500 rpm the gps speed is 21 mph. It gets on plane better but i think it should go faster considering the boat is fairly light weight. I'm thinking i should have a 15 in pitch prop. I thould i would get other opinions here before spending another hundred on another prop. Thanks in advance for your help.

 

[DJ]

Re: Evinrude 50 prop revisited

Your RPM is right on the money.

Any larger pitch and you'll lug the engine which will lead to a premature failure.

 

[steelespike]

Re: Evinrude 50 prop revisited

I agree your rpm is right on and a 15 will likely drop the rpm too far and definately will slow hole shot.What year is the boat?Do ypou have a model number?The lightest 17 I found was about 900lbs fairly light for a 17 but not a light boat in my mind.
I do feel that your speed should approach 30 or so.
Motor height isn't really measured.The antivent plate should be visable on plane.
I usually suggest you raise the motor to a point just before venting becomes a problem.
You should definately play with the trim angle as well for the best speed.

 

[bigrockets]

Re: Evinrude 50 prop revisited

The boat is a 1989 Cobia 17 ft. I guess it is around 900 lbs. When I had the 17 pitch on it it was venting at WOT. It was also trimmed out one hole on the plate. The previous owner had moven it because he was mostly towing his kids in tubes. You could see by the paint wear that the motor had always been trimmed down to the first hole. I thought it was riding bow high. With the 17 prop it would suddenly over rev when up on plane. I thought the hub was spun and thats why I got a new prop. It doesn't have a trim/tilt. I'm looking for an aftermarket trim/tilt like a CMC or Atlas but am also toying with the idea of a jack plate. Of course I get fifty different opinions on the pros and cons of either. All I know is that either one would make life easier when trailering and running in shallow water. I just think the boat should be a little faster at WOT than 20 MPH but I could be wrong.

 

[steelespike]

Re: Evinrude 50 prop revisited

The NADA used boat guide doesn't list a 17. there is a 172XL that is 16 ft and a
1700 that is 16 ft.Couldn't find any with letters that might indicate a center console
CC. No matter, the 16 footers I checked were 1100lbs Again no matter In my opinion the boat should approach 30 mph.
Is the bottom clean and smooth?Is the throttle opening all the way at the carb?
Did it still vent with the new prop? Generally for speed your better off with the bow a little high,less surface in the water.Is the antivent plate visable on plane?
Prop selection can help control venting.
You might confirm the tach is accurate.