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TOPIC: Spinning Prop while Anchored - 4788/2" Shafts

Spinning Prop while Anchored - 4788/2" Shafts 17 Sep 2017 16:03 #1

  • higgins_jr
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Hi guys. Got a call from a friend tonight who's on the hook in an anchorage that has a 4-5 knot tidal flow. After a while he heard an unusual noise and thought some pump was running, so he went hunting for it. However it wasn't a pump, it was the port prop shaft rotating from the current flow. The starboard shaft doesn't move and there doesn't seem to be a mechanical issue with the functioning of the gearbox and nor do the dripless shafts leak during the rotation.

I've never heard of the issue and thought a cutlass shaft bearing had too much play and needs checking. Has anyone heard of or had experience with the same issue.

Thanks much. Cheers

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John H
Brisbane QLD Aust
"Harbor-nating"

2000 - 4788/Cummins 370's

Spinning Prop while Anchored - 4788/2" Shafts 17 Sep 2017 16:08 #2

  • Pcpete
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In my experience, it's perfectly normal. I can't explain why only the Port prop is spinning except that there is probably less friction in the system.

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P/C Pete
Edmonds Yacht Club (Commodore 1993)
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Spinning Prop while Anchored - 4788/2" Shafts 18 Sep 2017 18:53 #3

  • BerettaRacer
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Check to see if the transmissions have a trailing (not Trolling) pump. Should be in the specs, or call mfg with serial #'s to find out. A trailing pump works off the output shaft to keep the bearing lubed in this situation or when being towed or operating on a single engine. If equipped he'll be fine in any of those situations. If not equipped I wouldn't do it for very long. Quite easy to lock the shaft with a bar or length of chain, just be sure to tag the motor/ignition lockout so you don't forget it's there.
A trolling pump is another issue completely, don't get them mixed,

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Spinning Prop while Anchored - 4788/2" Shafts 18 Sep 2017 19:57 #4

  • WhiteRockMike
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Wow, that's a pretty good tidal flow through the anchorage - must have a pretty good anchor set to hold that. Would be similar to holding both engines in idle reverse when setting the anchor. Does the current swap 180 degrees when the tide changes?

Assuming he has the ZF Hurth 800-A2 transmissions, if you check the manual they are fine freewheeling at that speed. Agree with Pcpete that starboard engine probably just has a bit more friction in the cutlass bearing. There is quite a torque on the props at those speeds so I'm a bit surprised it's not turning. An easy way to check is to try motoring single engine with each engine and see what speed it takes to make the off engine prop start to rotate. It shouldn't be much more than the 4-5kts for ithe starboard prop and shaft and if it doesn't spin at speeds close to that, I'd check the cutlass bearings, alignment, etc.

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Mike
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Previous: '97 4788
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