Prop shaft wobble through dripless shaft seal

[MattS]

I was having a good look at the engine running tonight, and noticed that there is some wobble where the prop shaft enters the dripless shaft seal.

The engine itself doesn't seem to be misaligned particularly, but maybe the prop shaft isn't quite straight.

How much wobble is too much wobble? ?

Video:

 

[pvb]

That's quite wobbly!

 

[Graham376]

How much wobble is too much wobble? ?

That's too much.

 

[MattS]

I was worried that might be the case. How urgently do I need to be worrying about it? i don’t really know what the risk might be from this.

I'm having some keel work done in September, so I’m wondering whether it could last until then?

 

[cherod]

it would appear that the engine is out of alighn with the stern tube rather than vice versa ,, ( poss ? )

 

[cherod]

I was worried that might be the case. How urgently do I need to be worrying about it? i don’t really know what the risk might be from this.

I'm having some keel work done in September, so I’m wondering whether it could last until then?

would depend on how much you wish to use it .

 

[MattS]

Let’s say once a week until then?

What’s the impact of having a misalignment like this? presuming it gradually does damage - but not really sure how!

 

[Graham376]

Shaft vibration not good and will increase wear on the cutless bearing. If you have an R & D flexible coupling, easy enough job to check alignment but then comes the more difficult bit. In an ideal situation, the gland needs sliding forward to check the shaft is centralised in the stern tube before altering the mounts but of course that would let water in when afloat. I would measure the position of the shaft close to the gland and make small adjustments to the engine without altering the position of the shaft.

 

[Ardenfour]

I'm having a similar problem. But can someone explain how a misaligned engine can cause the shaft to wobble?

 

[nortada]

I'm having a similar problem. But can someone explain how a misaligned engine can cause the shaft to wobble?

Any misaligned two rotating objects will induce wobble and stress; the centres of rotation do not line up. Fact of life.

Out of interest, when did the OP first notice the wobble and is it getting appreciably worse

It can’t get any better and if the engine is used it could rapidly get worse with the seal starting to leak uncontrollable. Depending how bad the leak is, this could result in the vessel sinking, with no comeback through insurance.

Were it me, even if it means hauling (or if a bilge keeler, beaching), I would get it resolved immediately; if necessary I would call in professional assistance.

 

[Daydream believer]

My take on it is this. Others will comment & may/maynot agree
The 2 faces of the coupling should meet square to each other. There are youtube vids of this on prop suppliers sites. If not properly aligned it will put a side force on the 2 parts. The flexible coupling will take up the distortion but will impart a force as the shaft rotates. Eventually this will cause wear on the forward part of the cutless bearing & this will allow the shaft to move from side to side.
The OP suggests using the engine once a week. This can be an hour or 8 hours so one is still not sure of use. Personally, I would just keep an eye on it if only a few hours & then get it fully sorted on dry land at the end of the season. It will not be catastrophic provided it is checked each week for drips on the seal & even then a jubilee clip round it in emergency would help until the boat was bought ashore
The situation has not happened overnight & has built up over time. Just needs monitoring closely until the end of the season with limited engine use.
Just keep the batteries topped up & an automatic bilge pump working

 

[Deleted member 36384]

Let’s say once a week until then?

What’s the impact of having a misalignment like this? presuming it gradually does damage - but not really sure how!

Nuts and bolts on couplings are being cyclicly stressed and at a higher probability of failing. I had a coupling bolt shear, that bent the prop shaft resulting in being driven onto a lee ashore mud bank in a F9, inside a marina. If that was not bad enough, the shaft and coupling had to be replaced and to do that the engine had to be lifted out the boat.

You have identified an issue and have been advised that it is significant, perhaps you should deal with it now instead of waiting later as damage usually just gets worse if left to its own devices. At a guess, perhaps your insurance requires you to make good damaged once identified.

 

[Tranona]

Let’s say once a week until then?

What’s the impact of having a misalignment like this? presuming it gradually does damage - but not really sure how!

If this is in a Moody then the only real bearing surface is the cutless in the P bracket. With the amount of wobble you have that bearing will wear more rapidly - it may even already be worn which accentuates the wobble. The Volvo seal seems to be taking the movement OK, but the lip seals may wear more quickly and lead to water leaking past. Good idea to apply extra grease to the seals if continuing to use the boat. Doubt anything will fail catastrophically with a few more hours use so keep an eye on it.

 

[cherod]

is it " wobble ", ( movement caused by wearing within the retaining unit ) i suspect not , more likely " run out " which is cause by the misalignment ..
At worst this could cause fatigue failure to the cutless bearing throo hull support ( pea bracket ? )

 

[cherod]

is it " wobble ", ( movement caused by wearing within the retaining unit ) i suspect not , more likely " run out " which is cause by the misalignment ..
At worst this could cause fatigue failure to the cutless bearing throo hull area support ( pea bracket ? )

 

[Graham376]

If this is in a Moody then the only real bearing surface is the cutless in the P bracket. With the amount of wobble you have that bearing will wear more rapidly - it may even already be worn which accentuates the wobble. The Volvo seal seems to be taking the movement OK, but the lip seals may wear more quickly and lead to water leaking past. Good idea to apply extra grease to the seals if continuing to use the boat. Doubt anything will fail catastrophically with a few more hours use so keep an eye on it.

Some models of Moody such as ours have a second cutless bearing in stern tube. Always struck me as an odd arrangement where the shaft is constrained but the engine can move on flexible mounts. Flexible coupling allows for the movement.

 

[[70521]]

If my interpretation is correct you have two threads running at the moment, this one and a porous exhaust.

If it was me I'd get the boat lifted today work on her over the weekend and splashed on Monday, if you have the skills for a DIY fix, or find somebody who will give you a firm commitment to do the work over the weekend or next week.

 

[Graham376]

If my interpretation is correct you have two threads running at the moment, this one and a porous exhaust.

If it was me I'd get the boat lifted today work on her over the weekend and splashed on Monday, if you have the skills for a DIY fix, or find somebody who will give you a firm commitment to do the work over the weekend or next week.

Sounds reasonable, I would be far more worried about the exhaust than the shaft.

 

[Gixer]

To the OP, Is this boat new to you?

If it is i'd want to get a professional to have a look around the engine and fittings before going any further. Looking at your three threads on here is making me concerned for your understanding of marine mechanics. No offence intended (I'm learning myself) but wouldn't want you to go out and get into trouble.

 

[ianat182]

Assuming the engine and shaft were al igned correctly at some time it seems to me that your problem may lie in the condition of your engine mountings. When I first had my Tiget and Volvo MD1b she ahook all over the place ; I renewed the cutless bearing to no avail, then inspected the mountings of which two had been perished by oil over years ,and the rocking was due to this fault . I'd had a rumbling of the prop shaft to draw attention to it in the first instance- one thing obvious , the other not so.

ianat182