Rattling noise from propeller area

[goodoldwoody]

Hi All,

This must have happened to many others.
Recently about 2 months ago I had the cutlass bearing replaced and an engine re-alignment. The old cutlass bearing had lasted 10 years and wasn't at all noisey. Clearly it was worn. (This is the novastene type with the rubber bearing surface inside).
On picking up the boat I noticed a rattling noise from the prop area when going astern. Now a few weeks later I'm getting the noise while going forward.
The mechanic mentioned that the shaft - engine was quite a bit out of alignment. I'm wondering if it is now so well aligned that it's allowing the prop end to whip a little.
My crew dived under and couldn't see anything amiss. We will dive on it again on Friday and take a detailed look.
My guess is to put the engine slightly off alignment and see how it goes.

The prop is a stainless steel Slipstream 3 blade, it's only about 18 months old and it replaced a Gori 2 speed 3 blade.
The slipstream seemed a lot heavier than the Gori at time of replacement. I must say the Gori was great but after 12 years it wore out and very expensive to replace. (You get what you pay for).

The boat is 34 ft double diagonal Kauri about 6 tonnes.
Engine Bukh 32
Shaft 1".

All this just in time for holidays when we want to go south.

Thanks for any clews.

Woody

[Paul L]

A GoPro on a stick while underway might give yku some insight. Can't deliberately misaligning your engine as ever being a good solution. Have you recheck the alignment are the mounts still good?

[goodoldwoody]

Thanks Paul,

Very merky water here. If we don't find anything I'll try it

Thanks
Woody

[goodoldwoody]

Hi Paul

We dived on it found nothing worn or loose.
But we did note the noise only appeared while the engine was cold soon as it warmed up the rattling (from the propellor) disapearred.

Cheers Woody

[Pete7]

How about checking the engine alignment again now it has been launched. Any back lash in the gearbox and is it full of oil? are the engine mounts still in good condition? Use a crow bar under to lift and see if there is movement. Does the engine shake when cold but when warm settle down?

Is there a rope cutter fitted and adjusted to allow enough room for the shaft to move forward and backwards and you accelerate in gear etc?

Is there a P bracket and is it still firmly attached with no movement? Is the new cutlass still firmly located or has it come loose?

Whilst the above may not identify your problem it will eliminate some items.

[DougR]

Sounds like the noise may be coming from the torsional damper on the flywheel or gear rattle from the transmission. When the engine is cold it runs rough and loads and unloads the drive line (damper, gearbox & prop) causing rattle, but upon warming up the combustion is much smoother and the system smooths out. Raising the idle a bit might also cause less noise because the frequency of the impulses increases and they become smoother.

Sometimes this rattle is also evident when in neutral but disappears in gear, as the driveline backlash is absorbed and smoothed out by the resistance of the water on the prop.

DougR

[goodoldwoody]

Originally Posted by Pete7

How about checking the engine alignment again now it has been launched. Any back lash in the gearbox and is it full of oil? are the engine mounts still in good condition? Use a crow bar under to lift and see if there is movement. Does the engine shake when cold but when warm settle down?

Is there a rope cutter fitted and adjusted to allow enough room for the shaft to move forward and backwards and you accelerate in gear etc?

Is there a P bracket and is it still firmly attached with no movement? Is the new cutlass still firmly located or has it come loose?

Whilst the above may not identify your problem it will eliminate some items.

Hi Pete 7

Thanks for those checklist items.
I didn't check the p bracket. The only movement detected is slight movement in blades at the point where they unfold from. All the rest feels good.
There is more vibration from the engine when it's cold and when it warms after about 5 minutes and runs more smoothly the noise disappears. So I think getting the crowbar under the mounts & see if there's any movement.

Thanks for the help.

Woody

[goodoldwoody]

Originally Posted by DougR

Sounds like the noise may be coming from the torsional damper on the flywheel or gear rattle from the transmission. When the engine is cold it runs rough and loads and unloads the drive line (damper, gearbox & prop) causing rattle, but upon warming up the combustion is much smoother and the system smooths out. Raising the idle a bit might also cause less noise because the frequency of the impulses increases and they become smoother.

Sometimes this rattle is also evident when in neutral but disappears in gear, as the driveline backlash is absorbed and smoothed out by the resistance of the water on the prop.

DougR

Hi Doug,

I checked the gearbox oil and it's ok.
I'm going to check the flywheel as that's one thing that didn't even enter my head. I do hear a little rattle in neutral and seems to come from the driveline only obvious when standing on he dock it can't be heard from inside the or even on the boat.
I'll check all this next week.

Thanks

Woody.

[gmakhs]

If it happens on natural can be a bearing of the reverse .

[ejjawhite]

A friend of mine had a similar issue... it turned out that the Allen screws that hold the cutlass bearing in place were not tightened down properly... as simple as that maybe....

[goodoldwoody]

Hi All,

I'm just updating you with what I found!
Would you believe. When the mechanic re-aligned the engine he neglected to align the pilot holes in the shaft that position the shaft in its correct fore & aft position. The shaft was set 1-1/2" too far forward into the coupling which caused the prop to pass too close to the Skeg and that resulted in turbulent flow around the prop. Repositioning the shaft corrected the problem.

Thanks for everyone.
One for the record.