FlexoFold Prop - Noise

tdw · #1 10-01-2012

We hauled the old girl last week for her yearly tart up and anti foul. No problems and she went back in on schedule.

but but but .....

Ever since she has a rather strange rumbling noise when motoring in reverse. Nothing in forward only reverse. Definitely not related to gearbox, shaft or gland. I crawled into the space behind the gearbox and there is no unusual noises in there.

Anyone have experience of this or any ideas as to what has gone awry ?

(In case you need to know the Womboat is a Malo 39 Classic with a Yanmar naturally aspirated 56hp donk and a two blade FlexoFold prop.)

HUGOSALT · #2 10-02-2012

Rumbling, but no vibrations? Would still dive on prop to make sure
she not working loose and both blades are fully opening.

tdw · #3 10-02-2012

Quote:

Originally Posted by HUGOSALT

Rumbling, but no vibrations? Would still dive on prop to make sure
she not working loose and both blades are fully opening.

Nope, no vibration, only the noise.

chef2sail · #4 10-02-2012

Rumbling when tranny is set under reverse when sailing or under power. You Probably only set the tranny is forward when sailing, but see if it makes the noise when set in reverse. Is the prop close to any of the aperatures ( not suyre what you confiuration is (( spade rudder, protected skeg rdder etc.)

MarkSF · #5 10-02-2012

Did they touch the transmission fluid? If so, did they put new fluid in, or just drain the old stuff out?

tdw · #6 10-02-2012

Chef ... only occurs under power. We have had this girl for about 18 months now and the problem has only popped up after this haulout. She's fin and skeg btw. See below.

Mark .... nothing mechanical was touched. Haulout was for bottom clean, antifoul and anodes. I checked all anodes before she went back in and they were all good and tight.

Now ... further information .... six months or so back we managed to get our signals mixed when dropping mooring and ran over the dinghy painter which was tied to the mooring buoy. Buoy and dinghy met up at the prop shaft. Luckily I realised what was about to happen and had her in neutral by the time the line reached the shaft but there was still some turn in the prop when the line arrived. Problem was resolved by rotating the shaft from inside the boat in the reverse direction until line cleared. Dinghy was somewhat the worst for wear as was the buoy but that was six months back and there has been no problem with shaft or prop in that time. We are out and about pretty much every weekend other than for family occasions. This includes right through (our admittedly very mild, albeit not very windy) winter when we do a lot of motoring.

Hartley18 · #7 10-02-2012

TD, did they grease the prop internals before she went back in?? I'm guessing the answer is "no" and that it's been a while since that was done.

You can also get rumbling in reverse-only from the stern gland if it's not being properly lubricated. In forward, the prop thust pushes up against the end-plate, but in reverse the prop is trying to pull the shaft out of the gland ('tow the boat'), potentially causing metal-on-metal grinding noises from around the back of the prop.

What kind of stern gland has she got?

EDIT: The instructions on-line say the prop is water-lubricated, so ignore my initial question. They do seem to be rather fussy about thread lockling compounds though... I wonder if you have a screw loose? Unlikely..

tdw · #8 10-02-2012

Quote:

Originally Posted by Hartley18

TD, did they grease the prop internals before she went back in?? I'm guessing the answer is "no" and that it's been a while since that was done.

You can also get rumbling in reverse-only from the stern gland if it's not being properly lubricated. In forward, the prop thust pushes up against the end-plate, but in reverse the prop is trying to pull the shaft out of the gland ('tow the boat'), potentially causing metal-on-metal grinding noises from around the back of the prop.

What kind of stern gland has she got?

EDIT: The instructions on-line say the prop is water-lubricated, so ignore my initial question. They do seem to be rather fussy about thread lockling compounds though... I wonder if you have a screw loose? Unlikely..

I do wonder about the stern gland though. I was about to say Aqua Drive but duh that is the coupling not the gland. Memory fails me but it is dripless and I don't recall seeing any form of grease nipple. Hmm ... will check it out when next on board. I did btw give the gland a good looking at before we left the boat on Monday evening and there was not a hint of water coming in. Nonetheless the noise could well be what you describe.

FSMike · #9 10-03-2012

Quote:

Originally Posted by tdw

I do wonder about the stern gland though. --- Memory fails me but it is dripless and I don't recall seeing any form of grease nipple. ---

Some types of dripless seals require "burping" when first launched to fill the bellows with water. Even if yours is one of those not sure why that would produce noise only in reverse.

tdw · #10 10-03-2012

Quote:

Originally Posted by FSMike

Some types of dripless seals require "burping" when first launched to fill the bellows with water. Even if yours is one of those not sure why that would produce noise only in reverse.

This isn't the first time we've hauled her and I know I didn't need to 'burp' the gland last time but i'll check it out nonetheless.