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Old 08-16-2012
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Atomic 4 Shakes the Boat

I purchased a Cat27 last summer and am hooked. She has an Atomic 4 that runs like a horse.

Last weekend as i was headed back into port (under power at top speed) the boat suddenly lost a lot of speed and the motor got loud, the boat also started to shake. I throttled back on the gas and ran it at almost idle; the shaking stopped and i made it back into port.

I had a mechanic inspect it and he found nothing noticeably wrong with it.

I took her out for a test run to see if the issue persists; it does, when in low speed it runs fine, as soon as i gas her up she starts to shake and although the motor speeds up, the boat itself does not.

Does this sound familiar to anyone?
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Old 08-16-2012
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Check for something fouling the prop.
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Old 08-16-2012
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Does it shake when you Rev it in neutral?

Probably not.

Almost certain you have fouled shaft
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Old 08-16-2012
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Re: Atomic 4 Shakes the Boat

Atomic 4s are some notoriously smooth-running engines. If you're getting vibration on that scale it's something else than the engine.
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Old 08-17-2012
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+1 on the fouled prop or shaft. Also inspect engine mounts.

Fixed prop or folding?
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Old 08-17-2012
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Re: Atomic 4 Shakes the Boat

Prop, prop shaft (and cutlass bearing), engine mounts..
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Re: Atomic 4 Shakes the Boat

The mounts we're fine and no, there is no shaking while in neutral... It's surprising (or maybe not) that my mechanic didn't mention anything about the prop. I'm going to jump in the water this afternoon to take a peek, i'll post a follow up... thank god its a hot day; 91 degrees in Seattle.
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Old 08-17-2012
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Re: Atomic 4 Shakes the Boat

Bread knife works best IMHO.
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Old 08-18-2012
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Re: Atomic 4 Shakes the Boat

When you say that the motor got loud, did it sound like the exhaust got louder or was it more of a thumping/vibration? If it's the former then there may well be something wrong with the engine itself. If the latter, like others have said, it's probably a fouled prop, bad motor mount, bad cutlass bearing, or some combination of those.


BTW, I would look for a new mechanic if I were you.
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