How big motor needed for 10 horse jonboat?

[RDK]

I have a beat up old 10' grumman jonboat (rated for 3 Hp) and a 3 horse Sears Gamefisher (Tanaka) air cooled outboard.<br /><br />Motor runs semi-OK (though I've invested more than it's worth in parts), but it won't get the boat up on plane (I weigh 200 lbs). Not that I'm lookin for a speedboat, but without planing, top speed is about 2-3 mph. I've tried various trim angles, no improvement.<br /><br />Any ideas? Am I expecting too much?<br /><br />Thanks,<br />Russ

 

[rodbolt]

Re: How big motor needed for 10 horse jonboat?

yep<br /> a 3hp will never plane a grown man. maybe a light 8 year old. my 5HP eska worked great for me on an old sears 10ft. but I was a lot lighter then. I doubt it would work now. course that was 30 some odd years back speed was more relative then

 

[pwiseman]

Re: How big motor needed for 10 horse jonboat?

Last year I was running a 15 foot grumman sport boat rated for 5 HP and a 1963 Evinrude lightwin 3 HP. It would get on plane but run around 4 MPH perhaps 5. I am just under 200 lbs. I also had a Evinrude 6 HP fisherman, that pushed the boat very well. Never clocked it with GPS, but I am guessing it was around 10 MPH. Problem with the sportboats and square stern canoes is they ride real high in the bow. I thew a 80 lb bag of sand in the bow and that helped out and did not slow me down much with the 6 hp motor.

 

[steelespike]

Re: How big motor needed for 10 horse jonboat?

If your boat is rated for 3 hp you should stick<br />with that.A 3 hp evinrude/Johnson will do a better job than your Sears.And will be smoother and quieter.If you get an extension handle and sit in the middle seat it will run faster.Not likely to plane.Probably if you run that boat at planing speeds you will start getting problems with leaking rivets and cracks anyway.

 

[Mercathode]

Re: How big motor needed for 10 horse jonboat?

Is this motor running properly? It should do a tad better!

 

[north40]

Re: How big motor needed for 10 horse jonboat?

A 200 pounder shouldn't be in a 10 foot jon boat. I had a 10 foot Sears (my first boat) with 6 hp merc. Ran great. I weighed about 130 at the time.

 

[AJ168]

Re: How big motor needed for 10 horse jonboat?

I have a 12ft flat bottom that I run a Johnson 5.5 Seahorse on. At first i couldn't get it to plane, the bow just rose up real high. I ended up moving the portable fuel tank up towards the middle seat and moving myself forward. It moves really good now, planes with me and my dad in the boat. (about 350lbs) It moves pretty good, maybe 18 mph with just me in it. (checked with a gps)

 

[AJ168]

Re: How big motor needed for 10 horse jonboat?

Forgot- check out the fuel mixture and play with the main jet adjustment. It can make a huge difference. When I first bought my motor it wouldn't plane my boat and didn't seem to have all the power that should be there. I did a carb rebuild and found that the "mechanic" had installed the main jet incorrectly. Every day that I use my motor I do a quick adjustment on the carb, just to make sure that it's perfect.