Prop does not let engine get to full rpm

[lou_ky_it]

Looks like I'm running a 12.5x22 prop on a 50 hp mercury big foot, serial is 0G836524. Problem is at full throttle I get about 3800 rpm out of the motor, top rpm should be 5500-6000. Any and all suggestions welcome. BTW it's pushing a smokerkraft sunsport 820 fish pontoon boat.

 

[steelespike]

Re: Prop does not let engine get to full rpm

I'm not an expert but that is way too much pitch.You probably want a little more diameter and pitch in the neighborhood of 12 inches.Should give you about 5,500 rpm.
Your badly over propped and shouldn't run that as you could damage the motor.

 

[180shabah]

Re: Prop does not let engine get to full rpm

Agreed, that is alot of prop for 50hp.

 

[Silvertip]

Re: Prop does not let engine get to full rpm

Merc makes a line of pontoon props -- they have a very large blade area. I agree, 22P is about double what should be used.

 

[gjblanchard]

Re: Prop does not let engine get to full rpm

I recently ran into the same thing with a Merc 50 HP (not bigfoot) on a Lowe FM165. The dealer supplied it with a 10x17 prop, and I was getting too low RPM (4800) and lots of break-out while cornering. I switched to a 10.25 x 14 and it made a world of difference. I now get 5300 RPM and it corners perfectly.

Cheers, Gary