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

I have a 12.5 inflatable with a 9.9 four stroke and initially I had the same issue. Basically, as your boat planes, the prop is occasionally pitching out of the water and grabbing air. This is harmful in two ways as you can overrev the engine and also wearing the prop due to cavitation.
The fix is to tilt your prop down 1 notch lower on the outboard. This slight extra angle was enough to correct it on mine. In addition, install anti-ventilation plates on the outboard. This will aid in faster planning and also prevent the air from reaching the prop. You can find this for about $35 in Walmart.

Rather common problem with inflatables. Most models require a short shaft outboard but then tend to cavitate a lot. Try tilting the outboard before adding the planning plates as they require drilling.

When I run mine with a 9.8 long shaft, cavitation was never an issue. Now with the 15 HP short shaft I need to be wary of tilting all the time.

Good luck,

Omar