Prop = planeing?

[gam6682]

O.K here we go. Got a 14' flatbottom jon boat with a 15 horse evinrude motor. The motor has a 9.5x10 prop on it and I added a hydrofoil. When I am in the boat by myself it gets up on plane very quickly and I can run at about 17 mph. Problem is when I add a person the top speed drops down to about 10 mph and I can't get it to plane no matter where the person sits. Would a different prop help or should I be looking for a larger motor?

 

[Spidybot]

Re: Prop = planeing?

Both. Your prop obviously is right for the one person load but cannot handle the extra load.<br /><br />Not knowing what rpm you run at WOT under he mentioned circumstances, it is impossible to guess if another prop pitch would do. Might and might not.<br /><br />If you repower with a motor matching whatever max. hp your boat is rated for (more than 15?), you will be better off in all respects related to performance. Ofcourse the new motor would have to be correctly propped as well.

 

[gam6682]

Re: Prop = planeing?

Thanks UU, don't have a way of getting max RPM on this motor but have been trying to convince "She who must be obeyed" that I NEED a bigger motor. The boat has a 30 HP rating and that is what I will look for.

 

[rickdb1boat]

Re: Prop = planeing?

Gam6682,<br />The Michigan site recommends a 9"X10" Prop for your set-up. You might try dropping down to a 9"x9", and see how that works! Here's a link! Of course, like UU said, nothing beats HP!!<br /><br /> Prop

 

[Spidybot]

Re: Prop = planeing?

As you are running 50% of max rated hp, you're bound to suffer somewhat when carrying extra load, being out in rough weather or trying to pull toys.<br /><br />A 30hp will bring you a 'new' boat and, dare I say, MUCH more boating fun & pleasure.<br /><br />For HER: Trying to make the old motor cope will stress it, cause heavy fuel consumption and in worst case make it fail when you need it most. (Well, not completely true, but a try..)

 

[ndemge]

Re: Prop = planeing?

Drop a nice shiny chevy Big Block right in the center! <br /><br />....just don't stop or y'all sink!

 

[Solittle]

Re: Prop = planeing?

Wait just a dog gone minute - Keep the bucks in your pocket and go for a lower pitched prop. My wife and I have a 13' alum boat with a 74 9.9 John long shaft. It gets up on plane easily - no I ain't a 75 lb kid - I am 200 lbs and my lady is 5' 9" (she dosen't talk weight) - I don't know the specs on the prop but it is a standard Johnson. I was surprised at the performance as it is a 20" shaft (originally for a sailboat).<br /><br />You may also have to adjust the vertical angle of the engine. In fact I would try that first.<br /><br />If you really want a new engine go for a higher pitched prop, adjust the engine way out of whack and tell the wife you have done your best and it is time to buy a new one.

 

[Spidybot]

Re: Prop = planeing?

I took it from your initial post, that you considered getting a larger motor and in that respect I'd still shop for the max rated hp.<br /><br />Respecting a budget, I'd agree with the suggested and check your setup (motor mount, trim angle) and test a lower pitch. Even if it doesn't solve the problem it will give you a good knowledge of your gear which will come in handy in all cases.

 

[steelespike]

Re: Prop = planeing?

G, Here is another angle If your jon has a narrow<br />bottom it may have a difficult time planing with a load. When I changed from my bare bones 15 ft Lone Star utility to my bare bones 18 ft Crestliner utility my 25 hp could plane easily with 5 or 6 average size adults wasnt even close to planing with the 15 ft.