14 foot boat with 15 hp Johnson planing issues

[Mcflyfisher]

My Dad has a 14 foot deep V aluminum fishing boat. It has been tricked out with flat floors and casting deck. We estimate that the "improvements" increased the weight by about 300 lbs. The engine is a 1991 Johnson 15 hp with a 9.5X10 aluminum prop. He bought this rig used, and I don't know the manufaturer of the prop. This prop is not in excellent shape, as it has a burr around the exterior of prop. We installed a tiny tach today, and with just me in the boat (250 lbs) I got 7.6 mph on the gps and 4500 rpms at WOT. I am given to understand that this motor should run between 6 and 7k. Adding my dad (another 250 lbs) to the boat makes little difference in either speed or rpms. The boat is not planing. Are we chasing our tail trying to make this boat plane? I think we need to pitch this down, but I don't know just how much. The typical load for this boat will be about 500 lbs of people, and maybe another 100 lbs in gear. So two questions: will this rig plane, and how much pitch should the new prop have?

 

[hidef]

Re: 14 foot boat with 15 hp Johnson planing issues

I would put a 4 blade 8" pitch prop on it and call it good. The max RPM for that outboard is 6000 RPM.

 

[clemsonfor]

Re: 14 foot boat with 15 hp Johnson planing issues

Yea your either over propped or your motor has an issue with fuel or timing. I think you need to go wot and squeeze the fuel ball and see if it goes faster.

But forget it dude that boat wont plane with that motor let alone 500lbs of people in it. My brother in law has a 14 ft v hull tricked out like yours and with 2 people it barely wants to plane. I think forget about planing and try to get your motor to 6k or whatever wot in the book says.

 

[steelespike]

Re: 14 foot boat with 15 hp Johnson planing issues

My info from 2 sources is 7,000 I think the 9.9 is 6000.
I also feel an 8" pitch will help.
While you will be very lucky if you get it to plane: check that it is running on both cylinders.
Try a tickle of choke at speed.Check that the stator advances as it should and the cartb is opening all the way.
7.2 mph is barely above displacement speed Electric trollers can reach 6 mph in just the right conditions.

 

[Mcflyfisher]

Re: 14 foot boat with 15 hp Johnson planing issues

Thanks for the info. We will order an 8 pitch prop tomorrow. The boat seems to want to get on plane with just one person. . . here's hoping.