Heavy vibration

[Wiggo]

Saturday last we were cruising past Lymington when we felt some vibration. At first, I thought it was just the sort of strange feeling you sometimes get in the overfalls at Hurst, but we were too far away for that. So we stopped and went astern, thinking it must be a rope or net, but it didn't clear when we brought the revs back up. We limped into Lymington on one engine and stuck her on a hammerhead in Berthon.

When we looked with the underwater camera, the prop, P-bracket, shaft and rudder were all clear, so we cast off again, but the vibration was still there. We tied up again and ran the engine in gear to confirm the engine didn't move excessively on its bed when we put her into gear. At this point, we assumed that it was just a blade out of alignment and bimbled back on one engine.

The boat was lifted yesterday at Shamrock Quay, but according to the engineers, there's no visible damage to anything, and apart from barnacles they 'look like they're brand new'.

We're pulling the raw water impellers to run her up on the hard and check for vibration next week, but dies anyone else have any ideas? KAMD43P's, HS63 gearboxes and conventional shafts/P-brackets...

 

[sarabande]

vibration ahead and astern ?

 

[DAKA]

As a rough engine alignment check you could try to turn the shaft by hand, it should rotate freely.

check for cracks in the flexible coupling which might only open up when under load.
PS

I have a spare HS63 gearbox
2.5 : 1

Hope its nothing serious but happy to loan it to you to try if you think it might be that.

 

[Wiggo]

Didn't try astern from memory, or if I did I didn't really notice any vibration. It wasn't noticeable at tickover, but as soon as the revs came up to maybe 1100-1200 rpm we could feel it up on the flybridge. The shafts turn freely, apparently, and have no bends visible by eye.

 

[Nautibusiness]

Cutlass bearing given up the ghost?

 

[Wiggo]

Cutlass bearing given up the ghost?

In the space of a few yards with no warning?

 

[jhr]

Washing machine on spin cycle?

 

[DAKA]

In the space of a few yards with no warning?

I have seen the rubber insert of the cutlass bearing slide out which wouldnt give any warning but you would have thought the engineers would have noticed play in the cutlass bearing and the insert would normally just sit behind the P bracket.(as it happens the one I saw was on a sealine F42)

 

[Wiggo]

Washing machine on spin cycle?

That's what it feels like, yes... Sadly, we have no washing machine on board.

 

[oldgit]

"no bends visible by eye"


Surely having taken the trouble to oik the old girl out, the very least would have been to stick a dial gauge on both shafts ?

 

[Wiggo]

Not sure, OG, to be honest. I only had a brief conversation with the yard. They may well have run a dial gauge for all I know - I know they didn't pull the shaft as they said it wasn't anything obvious. As we discussed, it would have almost certainly have been a noticeable bang to have bent a shaft, and we felt nothing (apart from someone turning the non-existant washing machine on)...

 

[MarieK]

What type of shaft seal do you have and did you notice any ingress of water from it?

 

[oGaryo]

Graham, I had severe vibration on the Fletcher when I first took her out... turned out to be the water pickup tube had become misaligned and water was going places it shouldn't go within the leg.. Not sure what setup you have but as there's nothing visibly wrong externally, then maybe a split or something in the pickup causing similar symptoms? With the Fletcher it was more noticable coming on to the plane under max load.

 

[Divemaster1]

Flexible coupling a possibility... been there & done that...

Could also be engine mounts..

 

[harveymae]

I had this happen turned out to be a injector

 

[Divemaster1]

Think an injector may be noticable at idle as well...but happy to be proven wrong.

 

[nicho]

Think an injector may be noticable at idle as well...but happy to be proven wrong.

Could it be an engine misfire caused by an injector problem?? Think of the vibration you get in the car when a spark plug drops out and you lose a cylinder.

 

[Divemaster1]

Could it be an engine misfire caused by an injector problem?? Think of the vibration you get in the car when a spark plug drops out and you lose a cylinder.

Petrol different from diesel... Diesel open fuel at given timing and inject diesel. if incorrect atomisation (sorry if spelling is wrong) from injector, you'll still have combustion (result of heat & pressure), but incomplete.... and will result in white smoke at start up, diesel sheen from exhaust and incomplete combusstion at idle will mean mis-fire. As temperature rise with increased RPM, mis-fire will decrease and as such injector problems should be less noticable at higher RPM .... but once acain happy to be proven wrong..

Pump/Injector and valve timing may of course give grief though..

 

[aquapower]

An air leak on the fuel system between tank and lift pump can cause misfire at certain rpm, if you hit something and damaged the underwater gear to the extent of causing vibration like this there is a good chance you would have felt it at the time, make sure shaft is checked with dial guage inside as well as out, I wouldnt bother removing impellors and running up out of water as this will tell you nothing as it will vibrate a lot worse than in the water and probrably damage something.

 

[oGaryo]

Isn't the first thing to do to narrow this down is to run her up and visually check if the engine's rattling about on the mounts on the presumption that if it's something to do with leg, it'd not have such a marked effect on the movement of the engine as say, a misfire would?