14' Inflatable Planing Problems

[mark_74]

I'm running a 9.9 Johnson on my 14' inflatable. Whenever I reach planing speed my boat starts to thrust intermittently. I think that when I start to plane my propeller is momentarily out of the water causing my speed to change drastically. Anyone know what I'm talking about? Any comments? Any help would be appreciated.

 

Thanks

 

Mark

[fishforfun]

Does it have an inflatable keel? Will it only do it when your solo? My 11' er does the same, sometimes water under the floor or the keel needs more air or you need weight forward.

[mark_74]

This happens both when going solo and when I have someone on board. I do have inflatable keel, I thought it had plenty of air but I'll check. Is it possible that the shaft is too short and is catching air? What is the theory about water under the floor boards?

Thanks for the reply

 

Mark

[fishforfun]

The water is pushed against the boards while on plane and will move to the stern when your getting up then shoot forward when you hit plane causing the boat to surge almost like a stall, weird feeling when it happens and the bow dives lifting the stern causing the motor to cavitate. Remove the stern board and drill 2 1 1/2" holes 6'' from the tube and maybe 8" from the stern, sand them nice and smooth and paint. you use these with a manual bige pump to remove the water you cant get with your bailing can because it's trapped between the hull and the floor.

[mark_74]

Now I understand what you mean, it makes sense. From your desription I think we're talking about the same thing but not sure. I'll build up speed and start to plane and for a second or two I feel like I'm talking off and then practically come to a stop with the motor screaming away and it's back and forth like that until I get the throttle under control. There's probably a surprisingly large amount of water under those floor boards.

I'll cut out the holes for the bilge pump as you suggested, it's a great idea regardless, you would think the manufactuers of these boats would have thought of that.

 

Thanks for you help

 

Mark

[Jonny]

Have you tried changing the angle of the motor? Is it possible you're porpoising?

 

Seems to me the first thing I'd try is moving the motor one notch in toward the transom to bring the nose of the boat down a bit. But that's just a guess.

[boatman]

The water is pushed against the boards while on plane and will move to the stern when your getting up then shoot forward when you hit plane causing the boat to surge almost like a stall, weird feeling when it happens and the bow dives lifting the stern causing the motor to cavitate. Remove the stern board and drill 2 1 1/2" holes 6'' from the tube and maybe 8" from the stern, sand them nice and smooth and paint. you use these with a manual bige pump to remove the water you cant get with your bailing can because it's trapped between the hull and the floor.

 

I think fishforfun has it. Its common on leaky inflatables for this too happen. Don't run it wide open until you get it sorted out. The cavitation could cause run-away and blow your motor. 9.9 hp is a little small for a 14' inflatable. What is your max hp rating?

[mark_74]

My boat is rated for 30HP. I went for the 9.9 so I could easily handle it myself especially since it is my first outboard. I'm most likely to going to upgrade to a higher HP maybe this summer definitely next. It's a 1997 Johnson, if anyone's looking for a trade let me know. Thanks to all for the info, it's a relief to know that it's a common problem and that there are solutions.

 

Thanks

 

Mark

[Jonny]

There's that other thread about getting hooked in various parts of the anatomy.

 

Make sure you don't hook your boat... or keep the chewing gum handy!