Knocking noise, could it be fouled propeller? Help

[adhdan]

Inboard diesel through shaft not stern drive .
took my new (new to me) boat out for a weekend run down the river , I’ve got a knocking noise in forward gear that increases with rpms, it’s like someone tapping on the bottom of the hull on the starboard side of where the propeller would be under the boat . In reverse gear the tapping stops. My first thought was rope or something which is fouled & banging on the bottom when it spins but It seems to have gotten progressively worse & reverse bursts haven’t cleared anything , what could it be? The boat was running smoothly at all speeds this morning. I did notice a quiet tapping this afternoon but which I thought must be something fouled (plenty of debris floating by) by later evening just before I tied up for the night it’s gotten very bad & forward propulsion seemed to be suffering. Engine is running smoothly & transmission shift is smooth as usual .

not sure what to do & I don’t fancy jumping in the river to give it a fondle

 

[Seastoke]

Does it make a noise when revving ,and out of gear

 

[adhdan]

Does it make a noise when revving ,and out of gear

No only when in forward gear, in reverse gear it stops banging

 

[harvey38]

Before worrying about the gearbox, I'd get a camera/Endo unit down there and inspect the prop, P bracket, shaft or other anode bolted to the hull in the vicinity of the prop/shaft or trim tabs if fitted.

 

[oldgit]

cutlass bearing ?

 

[Chris_d]

Engine mounts?

 

[SimonD]

I have had a boat where the prop shaft was so out of alignment, it was knocking on the stern tube. Agree that the first step is a check underneath though.

 

[sarabande]

Is the clearance between the deadwood and the prop enough ? If not, then has the shaft slid forward somehow. Check the shaft where it goes into the thrust bearing to see if there is evidence of movement.

Also see if there is movement in the shaft when changing form ahead to astern.

 

[DavidJ]

Interesting that the boat was running ok when you bought it (presumably?) then the question is what has changed?
What has the previous owner done to temporarily solve the problem?
…..a heavy grease up of something?
To my taste this is a bit too coincidental for a new owner to discover.
The previous owner will probably go into hiding but worth having a friendly chat.
…..stay cool!

 

[adhdan]

managed to get endoscope dropped off, couldn’t see anything obvious , quite difficult getting the thing in position for a decent view . Couldn’t see anything wrapped around. It does have a rope cutter so I wonder if that’s banging as it goes round . Im going to untie & start heading back toward Homebase. The boat was out of water when I bought it & the cutlass bearing & prop all seemed fine, no play or anything . I have had a few short trips and never had any issues .

 

[DavidJ]

Also see if there is movement in the shaft when changing form ahead to astern.

That’s a really good test. In problem solving terms the only clue you have at the moment is the forward/reverse change in situation. Keep working with that.

 

[Clancy Moped]

Lose prop shaft anode?

 

[Alicatt]

This was taken with a cheap Aldi action cam as I wanted to see what type of drive was on the boat and how it was fitted.

Volvo Penta MD7A through a S110 Saildrive to a 3 bladed 14"x12" propellor.
Now the water in the canal is even murkier than the above

 

[adhdan]

The only thing I can think for now is it’s the rope cutter or anode rattling , I’m on my own so it’s hard to watch the shaft when forward/reverse is changed. I’m having a leisurely drive back to my marina & will have to get boat lifted, I want a new thru hull transducer so I can tie in with that

 

[James jameson]

Inboard diesel through shaft not stern drive .
took my new (new to me) boat out for a weekend run down the river , I’ve got a knocking noise in forward gear that increases with rpms, it’s like someone tapping on the bottom of the hull on the starboard side of where the propeller would be under the boat . In reverse gear the tapping stops. My first thought was rope or something which is fouled & banging on the bottom when it spins but It seems to have gotten progressively worse & reverse bursts haven’t cleared anything , what could it be? The boat was running smoothly at all speeds this morning. I did notice a quiet tapping this afternoon but which I thought must be something fouled (plenty of debris floating by) by later evening just before I tied up for the night it’s gotten very bad & forward propulsion seemed to be suffering. Engine is running smoothly & transmission shift is smooth as usual .

not sure what to do & I don’t fancy jumping in the river to give it a fondle

Rudder flapping in the prop wash possibly

 

[iantomlinson]

We had exactly same problem. Only tapping when in forward gear. Loose rope cutter. The grub screws holding it on the shaft had come loose/worn. Take them out and use something like threadweld.

 

[adhdan]

We had exactly same problem. Only tapping when in forward gear. Loose rope cutter. The grub screws holding it on the shaft had come loose/worn. Take them out and use something like threadweld.

I think that might it , unfortunately it’s a lift out job to check, I just hope it’s not gauging the shaft … I’m sure it is but… glass half full

 

[iantomlinson]

I think that might it , unfortunately it’s a lift out job to check, I just hope it’s not gauging the shaft … I’m sure it is but… glass half full

Tapping in stbd side locker fits also.presume the noise travelled up the p-bracket. Like a small fishing weight quickly knocking the hull.

 

[adhdan]

I got some better pictures & found the installation booklet for the rope cutter in the folder. The Center ring has the knife that doesn’t spin with the shaft & should have an anti friction bearing which I’m guessing has worn out letting the blade bounce around . I recon back at the marina I’ll be able to back upto the slipway & get the Allen bolts undone on the ring before I die of hypothermia & then head to the showers & a victory pint.

 

[Timeless 2]

I assume you are planning on removing the rope cutter completely. When I serviced mine it was done with the boat on the hard. The cutter rotates with the shaft and the fixed blade er doesn’t. The nylon washers are there to give clearance to the rotary blade.The service kit was just nylon washers and Allen bolts. I wouldn’t try refitting under water. I can’t be see worn washers causing a noise although a damaged cutter would. The clearance between the fixed and rotary blade is only about 3 mm