Propshaft Alignment (again)

[DOILY]

There is plenty of advice here and elsewhere, on how to align the end of shaft with gearbox etc. But how to align the other end with the fixed but resilient, cutless bearing?
What is the best way to combat the effect of gravity on the mass of the shaft to ensure the centre line of the shaft lines up with the centre line of the bearing? Surely, that is the starting point before adjusting g the eng

 

[Caraway]

Doesn't the alignment rely on the stern tube being aligned with the output flange of the gearbox and by inference the centreline of the gearbox/engine.
If looking through the empty stern tube doesn't give you an accurate view of the gearbox flange, just inserting the bearing isn't going to alter anything. Don't you need to pack and adjust the engine/gearbox to aim at the sterntube.
I speak as someone who hasn't had to set up a propshaft/engine.

 

[lusitano]

How long is the shaft ?
Any support bearing
Stuffing box or deep sea seal ?

 

[DOILY]

How long is the shaft ?
Any support bearing
Stuffing box or deep sea seal ?

36 inches long approx. Rigid stuffing box. No support bearing, just cutless bearing and R&D coupling.

 

[lusitano]

Providing that you are out of the water and all bits are in good condition, good cutlass bearing, shaft not bent etc, dismantle the stuffing box remove all packing .
Bring in the shaft and with stuffing box ring loose on the shaft, and flange connected, offer up to gearbox flange. Using wood blocks and wedges, at the gearbox end, centralise the shaft in the stuffing box ID - exactly. Adjust engine mounts so that both flanges align.
Connect shaft and reassemble all parts. Repack stuffing box.
Recheck alignment of flanges with feeler guages once back in the water and with a few hours running,
(Car jack and wooden blocks are handy for moving engine gearbox assembly around)

 

[Bilgediver]

Doesn't the alignment rely on the stern tube being aligned with the output flange of the gearbox and by inference the centreline of the gearbox/engine.
If looking through the empty stern tube doesn't give you an accurate view of the gearbox flange, just inserting the bearing isn't going to alter anything. Don't you need to pack and adjust the engine/gearbox to aim at the sterntube.
I speak as someone who hasn't had to set up a propshaft/engine.

No it doesn't . On many boats the seal/Gland sits sits on a flexible attachment to the shaft log. This can allow the shaft to drop, pushing downwards a front bearing until the shaft rests on the ridged shaft log or stern tube front end Before any alignment can take place the coupling end of the shaft must be raised till it sits in the middle of the shaft log or in some boats the built in shaft tube. Failure to do this will be knocking sounds when the shaft strikes the shaft log or stern tube. It is not difficult to do but necessary.

 

[Graham376]

There is plenty of advice here and elsewhere, on how to align the end of shaft with gearbox etc. But how to align the other end with the fixed but resilient, cutless bearing?
What is the best way to combat the effect of gravity on the mass of the shaft to ensure the centre line of the shaft lines up with the centre line of the bearing? Surely, that is the starting point before adjusting g the eng

You're overthinking it. If the cutless bearing is in good nick, the clearance is so small you don't need to worry about trying to centre the shaft there. As others say, the important point is to centralise the shaft with packings where it exits the forward end of the stern tube and then adjust engine & gearbox mounts so the two flanges mate within about 5 thou all the way around.

 

[Caraway]

No it doesn't . On many boats the seal/Gland sits sits on a flexible attachment to the shaft log. This can allow the shaft to drop, pushing downwards a front bearing until the shaft rests on the ridged shaft log or stern tube front end Before any alignment can take place the coupling end of the shaft must be raised till it sits in the middle of the shaft log or in some boats the built in shaft tube. Failure to do this will be knocking sounds when the shaft strikes the shaft log or stern tube. It is not difficult to do but necessary.

I think that is what I said. Perhaps I didn't express it properly.