Dangerous Outboard oscillation, does not bank on plane.

[Chotu]

This is a thread about the new 9.9 Tohatsu Outboard I got.

It is replacing an 8 hp Tohatsu outboard that died.

The 9.9 is 10lbs heavier.

I have a West Marine rib inflatable.

I’m having some problems with the configuration and wondering what I should adjust.

When I get up on plane and I am near top boat speed at half throttle or above, if I try to initiate a small course correction, I end up with a severe oscillation on the Outboard. The tiller wants to flap back and forth violently and roll the boat.

I have another problem that I think is related. If I try to do a hard over bank turn while on plane, The motor does not Bank the boat to the inside of the turn. It leaves it flat and it feels very precarious. Like I could catch the outboard edge and flip it.

What do I need to adjust on my motor to fix this situation?

[rslifkin]

Do both outboards have the same shaft length?

[rbk]

Trim the ob down with the set pin. See if that helps

[Bill O]

Not sure what you are describing with "The tiller wants to flap back and forth violently and roll the boat."
Is the tiller loose? (if so tighten nut to reduce tiller play)
Or are you saying the motor is too loose when you are trying to point it straight? If this is it, there should be an adjustment collar that will stiffen up the motor's ability to turn too easily (don't remember the name put refer to owner's manual to location usually on shaft under motor block)

Re: the turning issue, maybe slow down a bit until you are familiar w/the new motor.

[s/v Jedi]

I think you’re too far nose down. Adjust the engine to the next pin position with the tail further away from the transom.

Is this a rib 310?

[Chotu]

Ok. Thanks. I'll try these when we get in in a few days. I have already stowed the tender for our trip South.

Due to plenty of buyers trying to but our boat but no available surveyors in Maine until late August, I'm moving the boat to more populated areas to have access to more available surveyors.

Bill:. The oscillation is a side to side oscillation of the motor on plane. You make a tiny course correction and a harmonic oscillation builds up with the outboard starting to violently shake side to side.

It's the same motor I had before. Just 1.9hp and 10lbs more.

[Chotu]

Originally Posted by s/v Jedi

I think you’re too far nose down. Adjust the engine to the next pin position with the tail further away from the transom.

Is this a rib 310?

That’s what I was thinking. That I have an adjustment problem like that. I will try adjusting it further away from the transom. And good guess! This is the boat.

https://www.westmarine.com/buy/west-...85?recordNum=7

[rbk]

Sounds like you're nose up and riding a small aft part of the hull which causes oscillation as the back end of most planning hulls are flat and provide little directional stability. Get the nose down and into the water to a)slow the boat by pushing more water and b)letting the forward V part of the hull to bite the water and provide directional stability. Tightening up on the collar might help but it can also make steering jerky.

[JoeRobertJr]

Originally Posted by s/v Jedi

I think you’re too far nose down. Adjust the engine to the next pin position with the tail further away from the transom.

Is this a rib 310?

+1

Around the middle of this article seems to be a pretty good description of the effects of having the screw pointed too far up or down.
Boating Performance

[ttex]

May I also suggest the possibility that the ob is not centered and level on the transom?