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Ask K. Kergan Your Own Question
K. Kergan
K. Kergan, Marine Mechanic
Category: Boat
Satisfied Customers: 1031
Experience:  24 yrs exp. Inboard/Outboard mechanic Mercury/ Mercruiser, Volvo Penta and OMC, Johnson/Evin.
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What causes the boat the feel like it's slipping or hitting

Customer Question

What causes the boat the feel like it's slipping or hitting something underneath when u accelerate ?
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
Underneath the hull when u accelerate it feels like a slip or a bump underneath almost like you run over something but didn't it's been doing it allday
Expert:  K. Kergan replied 2 years ago.
Hi, my name is Kerry
It sounds to me like your propeller is slipping.
I would say, pull your propeller off and examine it.
The propeller has metal blades and body, a rubber hub
and splines inside a metal center tube.
The rubber hub is attached to the center splined tube (the splines mate with the prop shaft), the hub assembly is pressed into the propeller
Look to see if the propeller has shifted on it's hub so that it's blades hit the trim tab.
Also check to see if the rubber of the hub looks smooth and not chewed up.
Let me know what you find.
Customer: replied 2 years ago.
No the engiene doesn't do anything it's just a shake or a bumpy feeling like a slipping feeling underneath the boat u can feel it through the floor as well it even done it while waiting in line at boat ramp just putting around almost like a feeling as if you were running over something I don't know if it could be a problem with the prop or foot or propeller?
Expert:  K. Kergan replied 2 years ago.
What make and model is your engine and drive?
Check the gear oil in the foot, see if there is water or metal bits in it.
A bad u-joint could produce these symptoms, if the prop and gear oil look good, you should remove the drive and check the u-joints.
Let me know what you find.
Customer: replied 2 years ago.
The boat is a wellcraft nova 23xl with a Chevy 350 5.0 liter
Customer: replied 2 years ago.
Expert:  K. Kergan replied 2 years ago.
Does the thumping and vibrating get worse when you turn hard?
Customer: replied 2 years ago.
Yeah it's gotten worse I've noticed it a few times lately when've we have been on the lake and yesterday It was like we were running over trees or something but we weren't u could feel it all over the boat floor it's worse when u turn and when u punch it! We were pulling a knee board yesterday when it got really bad
Expert:  K. Kergan replied 2 years ago.
You need to remove the drive and check the u-joints and gimbal bearing, it sounds like the u-joints are on the way out.
You can leave the question open and not rate the answer until you check if you like.
Expert:  K. Kergan replied 2 years ago.
Is it a Mercruiser?
I can get you a parts diagram if you like.
Customer: replied 2 years ago.
Chevy car engine also have you ever heard the term bagging?
Expert:  K. Kergan replied 2 years ago.
Mercuiser and Yamaha and several others use chevy engines in front of their out-drives, it's the make of the out-drive I was looking for.
Mercruisers are black when new.
OMC Cobras are charcoal color as is Yamaha.
Anyway, all of the ones I mentioned use a similar set-up, they have a shaft with u-joints on it that plugs into an engine coupler on the flywheel.
The shaft is held steady by a bearing called the gimbal bearing.
Either bad u-joints or a bad gimbal bearing can cause vibration that gets worse when you turn, the harder the turn, the more it vibrates.
I haven't heard the term 'bagging', what do you mean by it?

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