1983 Mariner50hp4 cyl low speed

[ZenBasser]

I've put this motor on a 16 foot bass boat I built myself. I am running WOT at 5500 RPM but can only manage 20 - 23 MPH via GPS. With any additional trim,the propstarts to ventilate/cavitate.<br /><br />The compression is 110 in all 4 cylinders<br /><br />The anticavitation plate is about 1/2inch below the hull at the keel.<br /><br />Do you think this motor is too high? Should I consider a jack plate? What else would contribute to this low speed --the calculators suggest a speedcloser to 30.

 

[corm]

Re: 1983 Mariner50hp4 cyl low speed

So how deep is the keel? Also is anything in front<br />of the lower unit that would push the water from the prop? Motor hight seems fine.

 

[ZenBasser]

Re: 1983 Mariner50hp4 cyl low speed

Corm, thanks I'm slow getting back here because I found the source of my problem. a small hook in the hull acting like a giant trimtab. Fortunately, I'm still "under warranty"...I'll report back after the fix.