Engine / Shaft Alignment - Afloat with Tides Marine Series One seal

[Ammonite]

I'm helping a friend out and wondered if any one has any bright ideas of how to align the engine / shaft with the seal in place when the shaft seal used provides zero support at the inboard engine of the shaft? In this case a series one tides marine seal. The shaft has been centred / aligned on the hard using a top hat bush to centre the shaft in the stern tube but I'm concerned with the degree to which I've had to move the engine to line things up ashore and suspect things will be different afloat.

It's a way to check the alignment I'm looking for rather than resorting to an alternative shaft seal or flexible coupling at this stage.

Many thanks

 

[macd]

You'll often read (probably already have) that engine/shaft alingnment changes when the vessel's in the water. I believe this is particularly true of wooden boats. We re-engined our GRP boat on the hard two years ago. The shaft engine was aligned on the hard, then checked again after a week in the water: no change. I'm not suggesting this is universally true, but it certainly was in our case.

Your top-hat system sounds good. Wedges are also used in the same way, if perhaps less accurately.

Re flexible couplings, should you go that route: note that what is probably the most common type, the R&D, is principally designed to reduce the transmission of engine noise and vibration to the hull. It's ability to compensate for misalignment is minimal...I seem to remember a max of half a degree. Some other designs are more tolerant.

 

[Tranona]

Is the engine already attached to the shaft and you want to check the alignment? or is the shaft in the boat and you want to install the engine?

If the former then as macd says it is highly unlikely in a GRP boat that alignment has changed just because the boat is in the water, although over time it may be out because of mounts deteriorating. So, just slacken the coupling and provided the shaft and half coupling slide back easily you can just check the clearances. If it is way out it may not slide freely. If this is the case, and in the second situation you need to be able to block the shaft in the correct position, but you only know what that is if you have wedged the shaft central in the tube.

 

[vyv_cox]

When I suspected that my shaft was not central in the stern tube I simply disconnected the rubber gaiter from the tube to assess the clearance. Some water will come into the boat but the volume is not huge and your bilge pump should easily cope with it. Wrapping a rag around the tube and shaft reduces the flow considerably while you make any adjustments necessary.

 

[rogerthebodger]

I
It's a way to check the alignment I'm looking for rather than resorting to an alternative shaft seal or flexible coupling at this stage.

Many thanks

As you say the shaft seal does not support the shaft and if the engine is also flexibly mounted you should not fit a flexible coupling as with a shaft , coupling, gearbox/engine only 2 should be flexible and the third rigid otherwise you will have too many degrees of freedom causing possible vibration or worse.

 

[Ammonite]

Thanks for the input and reassurance that the alignment shouldn't change dramatically once afloat. Given that's the case I should be able to offer up the shaft and fine tune if needed. That's really helpful.

macd - fully appreciate what you are saying about the R&D not being used to compensate for any misalignment. I have one on my own boat and it's just there to allow for engine movement once running, not initial setup.

Tranoma - the former. Engine and shaft already connected

Rogershaw - thanks. That's my understanding too. I have flexible mounts on my own boat along with an R&D and a Volvo seal but I've heard / read on the forum somewhere that this is OK as the Volvo provides a fair degree of support and the R&D is a very rigid "flexible" coupling. It certainly seems to be OK.

Vyv - hopefully a shouldn't have to resort to this as there's circa 10mm clearance between the shaft and the stern tube and the cutless is mounted in a p bracket so I think the flow of incoming water would be substantial and I'm not sure I'm as brave as you!

 

[Pagetslady]

Thanks for the input and reassurance that the alignment shouldn't change dramatically once afloat. Given that's the case I should be able to offer up the shaft and fine tune if needed. That's really helpful.

macd - fully appreciate what you are saying about the R&D not being used to compensate for any misalignment. I have one on my own boat and it's just there to allow for engine movement once running, not initial setup.

Tranoma - the former. Engine and shaft already connected

Rogershaw - thanks. That's my understanding too. I have flexible mounts on my own boat along with an R&D and a Volvo seal but I've heard / read on the forum somewhere that this is OK as the Volvo provides a fair degree of support and the R&D is a very rigid "flexible" coupling. It certainly seems to be OK.

Vyv - hopefully a shouldn't have to resort to this as there's circa 10mm clearance between the shaft and the stern tube and the cutless is mounted in a p bracket so I think the flow of incoming water would be substantial and I'm not sure I'm as brave as you!

I have a split bush that fits into the stern tube around the shaft, I slide the Volvo stern gland off the tube a rush of water comes in but I quickly put the split bush in and slide the stern gland back on I am then able to align the engine and shaft with feeler gauges. Remember to remove the split bush before running engine in gear, bail out the water and with luck your shat will be in lign, however having had this system for 25 years on my boat, I don't believe it's possible to align a shaft spot on that is supported between a rubber bush at one end and an engine that is supported on rubber mounts at the other end.
I have seen pictures of a dial indicator being used I have never understood this with so many variables to contend with.
If anybody knows differently I would love to learn differently. Incidentally Beta marine recommend this method in their engine hand book.
Mike

 

[Ammonite]

I have a split bush that fits into the stern tube around the shaft, I slide the Volvo stern gland off the tube a rush of water comes in but I quickly put the split bush in and slide the stern gland back on I am then able to align the engine and shaft with feeler gauges. Remember to remove the split bush before running engine in gear, bail out the water and with luck your shat will be in lign, however having had this system for 25 years on my boat, I don't believe it's possible to align a shaft spot on that is supported between a rubber bush at one end and an engine that is supported on rubber mounts at the other end.
I have seen pictures of a dial indicator being used I have never understood this with so many variables to contend with.
If anybody knows differently I would love to learn differently. Incidentally Beta marine recommend this method in their engine hand book.
Mike

Hadn't thought of that. Great idea. I could easily modify the existing top hat bush to acheive that. Hopefully not not needed this time assuming minimal difference between afloat / on the hard but great if the engine had to be moved any distance while afloat. Many thanks