Propeller Shaft Movement Fore and Aft. What Is Acceptable.

[RunAgroundHard]

I was looking at a boat with an associate and it was noticed that between forward and reverse the shaft slid in and out of a standard packing gland by about 3/4”. Evidence was the black smear on the stainless shaft. No water ingress, and standard engine mounts, with no CV joint and associated thrust bulkhead. The boat had a small Beta engine in excellent condition, clean looking mounts with no evidence of rust or degradation, folding propeller, LOA 34’. The cutless bearing and gland packing had just been replaced.

I have a Halyard Aquadrive, so longitudinal shaft movement is not what I experience, and it’s been a few decades since I looked at stern gear on the more traditional set up.

Is this movement normal?

 

[billskip]

about 3/4”.

Does seem a lot....
How is the shaft fixed inboard end?

 

[RunAgroundHard]

Does seem a lot....
How is the shaft fixed inboard end?

A flexible coupling, something similar to an R&D

 

[Tranona]

+/-6mm for soft mounts and big engine 2-3mm for a small Beta. 3/4" improbable unless the shaft is loose in the clamp type coupling and something is stopping it from coming out completely. What boat/engine is it?

 

[Plum]

I was looking at a boat with an associate and it was noticed that between forward and reverse the shaft slid in and out of a standard packing gland by about 3/4”. Evidence was the black smear on the stainless shaft. No water ingress, and standard engine mounts, with no CV joint and associated thrust bulkhead. The boat had a small Beta engine in excellent condition, clean looking mounts with no evidence of rust or degradation, folding propeller, LOA 34’. The cutless bearing and gland packing had just been replaced.

I have a Halyard Aquadrive, so longitudinal shaft movement is not what I experience, and it’s been a few decades since I looked at stern gear on the more traditional set up.

Is this movement normal?

3/4" total (3/8 each way) is about what I get due to the combined flexibility of both the flex coupling and the engine mounts from hard ahead to hard astern. Half of the movement is due to my Vetus coupling.

 

[RunAgroundHard]

+/-6mm for soft mounts and big engine 2-3mm for a small Beta. 3/4" improbable unless the shaft is loose in the clamp type coupling and something is stopping it from coming out completely. What boat/engine is it?

Not sure of the engine specification, it is a Beta, 3 cylinder and I assume 30 HP, mechanical gearbox, don't know the make and model of gearbox, boat is a Fastnet 34

 

[earlybird]

The mounts normally supplied with small Beta diesels are fairly stiff fore and aft. They would allow nothing near that sort of movement.

 

[Boater Sam]

I have seen movement on this scale in narrow boats frequently. The small Beta engines are very light and are often on softer mounts.
I does not seem to be a problem, in fact it would avoid the shaft wearing into a groove if it had a stuffing box.

 

[DownWest]

Humm;
I fitted a Beta 16 with the R&D mounts and the supplied flex coupling. For and aft movement was minimul, certainly noway near 3/4".

 

[Tranona]

Not sure of the engine specification, it is a Beta, 3 cylinder and I assume 30 HP, mechanical gearbox, don't know the make and model of gearbox, boat is a Fastnet 34

Same engine as I have. Usually a TMC40 box although I have a PRM90. The norm is to leave 15mm clearance between the face of the cutless and the front face of the prop to allow water in and out and enough for the small amount of fore and aft as it goes in and out of gear +/- 10mm which you are suggesting is excessive. With the normal gap 10mm would mean the prop hitting the P bracket in forward, although this boat has excessive gap between the cutless and the prop oceancompassgroup.co.uk/boats-for-sale/1988-fastnet-34/

 

[RunAgroundHard]

Thanks for the feedback everyone.

 

[ridgy]

oceancompassgroup.co.uk/boats-for-sale/1988-fastnet-34/

What is the grey contraption beneath the engine?

 

[stone beach]

Definitely something amiss with the shaft movement.
The grey contraption mentioned above is a hydraulic motor, which I believe is driving the shaft, the engine is driving a pump and hydraulics moves the motor. Engine mounts are not part of this equation.
If you are interested in taking it further you need to find where the shaft movement is occurring, i.e. prop loose on the shaft, (cant be that as you mention shaft moving in and out?), drive coupling loose on the motor, another coupling in the shafting which is loose, motor loose on its mounts, coupling cemtre element damaged or loose, or motor output shaft moving in and out. Moving prop back and fore with a lever while watching what happens inside should reveal all.

 

[stone beach]

I'm responding based on the link in post#10, maybe that's the wrong boat ? if it is please ignore