mercruiser shaking after hitting a stump

[Donzi Vol]

Ok, question for you Merc guys. A friend of mine has a ski boat powered by a 4cyl merc. He takes ridiculous care of it and rarely runs it hard. He had it out for the first time this past weekend, and said it ran great until he got into some shallow water. He said he was running about 10 mph when he felt a thump. He stopped, trimmed up the drive, and the only damage he saw were a couple nicks in the prop. He trimmed back down and headed home and said that it started shaking as he accelerated. He's curious if he might have screwed something up in the lower unit. Any thoughts?

[thehow33]

Ok, question for you Merc guys. A friend of mine has a ski boat powered by a 4cyl merc. He takes ridiculous care of it and rarely runs it hard. He had it out for the first time this past weekend, and said it ran great until he got into some shallow water. He said he was running about 10 mph when he felt a thump. He stopped, trimmed up the drive, and the only damage he saw were a couple nicks in the prop. He trimmed back down and headed home and said that it started shaking as he accelerated. He's curious if he might have screwed something up in the lower unit. Any thoughts?

i'm guessing bent prop shaft

[Conquistador_del_mar]

He needs to check the shaft and prop like normal. It could be both, but almost certainly the prop blades. I have actually had great luck bending shafts back to straight with a 6' long cheater pipe and calipers. Bill

[MOP]

Run it on the hose it could a bent shaft or a tweaked prop blade, throw in gear and see which is doing what!

[z33donzi]

yupp bent a prop or picked up fishing line and it wrapped the prop shaft to throw it off balance

[RedDog]

When I saw the post, I thought it was going to be about your boat - whew!!!

[LKSD]

I too would venture to guess bent prop or prop shaft.. ;)

[DonziJon]

I seriously doubt that a prop strike causing a "couple of nicks" on the prop would bend the prop shaft. My Old Alpha I had a prop shaft that had 1/8 inch of runout at the end and ran without any vibration at all. If you hit something hard enough to actually Curl the blades of a SS prop, then that might bend something. :bonk:

On the other hand, if you were to say ..jam a piece of 2x4 between a prop blade and the cavitation plate at slow speed...say enough to actually STOP the engine.. I could see that bending a prop shaft.

[BUIZILLA]

I seriously doubt that a prop strike causing a "couple of nicks" on the prop would bend the prop shaft. Don Sierra just did the same thing, couple little nicks, and grenaded a Volvo drive recently..

[Cuda]

Bent prop. There were logs all over the place a few years ago when we went to the Oklahawa River through the locks. I lot of people hit logs (trees were down from 3 hurricanes the year before), and yet nobody broke a drive. You just needed a log splitter prop.

[RedDog]

I bet the boat in question has an aluminum prop. I also bet that in addition to the few nicks, a blade was warped and he hasn't visually noticed it yet. Take the prop to East TN Propeller just off of Cherry Street

[Donzi Vol]

Thanks for the input guys. I've passed it on and he is going to take a better look at it when he gets home next week.