Stern Tube

[davidla]

Next question to burden you all with.
The stern tube/gland where the shaft exits the boat does not seem to have a bearing. There is one at the skeg but not in the tube. Surveyor is of the opinion that it was either never there or removed due to an alignment problem. This casts doubt on the quality of previous maintenance IMHO. There is some very slight movement at the shaft seal underway but not a real concern and the engine is smooth. I did note the shaft is not in the exact centre at the exit of the stern tube. Given the length of the shaft I would expect a bearing in the tube??
Regards
David

 

[psneeld]

Next question to burden you all with.
The stern tube/gland where the shaft exits the boat does not seem to have a bearing. There is one at the skeg but not in the tube. Surveyor is of the opinion that it was either never there or removed due to an alignment problem. This casts doubt on the quality of previous maintenance IMHO. There is some very slight movement at the shaft seal underway but not a real concern and the engine is smooth. I did note the shaft is not in the exact centre at the exit of the stern tube. Given the length of the shaft I would expect a bearing in the tube??
Regards
David

What is inside the boat?

If one inside, just a hole through the glass keel is all that will be there.

 

[davidla]

What is inside the boat?

If one inside, just a hole through the glass keel is all that will be there.

Thanks for the reply. The only thing I saw was the shaft seal.
Regards,

 

[davidla]

Another photo from the port side. The water line seems to be okay in relation to the exhaust? This photo also shows the stern tube after a clean.

Edit: Oops starboard.

 

[psneeld]

Thanks for the reply. The only thing I saw was the shaft seal.
Regards,

Still, a bearing could be inside the tube that enters the boat covered by the shaft seal.

Slide the shaft seal off and put a bright light in there.... that will show if there is a bearing.

Also.... if from the shaft coupling to the first (or only) strut bearing is a certain distance, it may be within specs for that size shaft. A bearing at the hull protrusion that is too close to the shaft coupling is not needed and could be bad (hard to make alignments). In that case maybe there should be 2 struts with bearings and one relatively close to the hull protrusion.

Did the surveyor not explain/explore all this?

 

[PM]

The answers so far seem to miss the point. If the shaft is not in the center of the tube the situation needs to be further investigated, something is amiss.

pete

 

[psneeld]

The answers so far seem to miss the point. If the shaft is not in the center of the tube the situation needs to be further investigated, something is amiss.

pete

Didn't miss the point, the shaft has to be centered on the strut bearing, not the hole through the hull.

Very common that the shaft is not in the exact center and doesn't have to be, just can't be rubbing.

Any wobble could be many things not related to the non-centered in the hole shaft...not that there is no bearing or shaft tube on the outside.

 

[davidla]

Thanks for all the responses, I really appreciate the input. If I proceed with the purchase the mechanical inspector has already suggested the shaft be pulled and checked for alignment. There is an issue with some delamination of the stringer/engine bed at the stbd fwd engine mount. I am concerned it is all connected.

 

[rgano]

At cruise speed I want to see absolutely NO movement of the shaft seal.

 

[mvweebles]

At the Sea Trial, was the engine run WOT for at least 5-mins (preferably 10-mins)? Any vibration?

Peter

 

[BruceK]

Thanks for all the responses, I really appreciate the input. If I proceed with the purchase the mechanical inspector has already suggested the shaft be pulled and checked for alignment. There is an issue with some delamination of the stringer/engine bed at the stbd fwd engine mount. I am concerned it is all connected.

You could be right. Your surveyor seems to have given it some thought.
Removing and truing a shaft takes time, in Sydney they usually go to DH Porter to repair. Porters make up new bearings too, prop gets inspected, etc. Boat has to be hauled to remove, maybe plugged to go back in pending shaft repair, and hauled again to fit it. Plus fibreglass repair work. This will cost $$, be sure it`s well costed/allowed for or maybe done at sellers expense with the work checked by the surveyor. Probably better done before it goes by water to Gold Coast.

 

[davidla]

At the Sea Trial, was the engine run WOT for at least 5-mins (preferably 10-mins)? Any vibration?

Peter

Hi,
yes it was run at WOT (3300) for about 10 mins. There was no discernible vibration at the engine or hull. There was visible movement at the lip of the Tides Seal. This is a concern and I am currently negotiating to reduce price to allow for a full removal and examination of the shaft and replacement of the seal. I prefer PSS seals is that what most people use???
The downside of the engine WOT run was I only saw 11.5 knots on the gps but was not aware of tide and wind.
Cheers

 

[mvweebles]

Hi,

yes it was run at WOT (3300) for about 10 mins. There was no discernible vibration at the engine or hull. There was visible movement at the lip of the Tides Seal. This is a concern and I am currently negotiating to reduce price to allow for a full removal and examination of the shaft and replacement of the seal. I prefer PSS seals is that what most people use???

The downside of the engine WOT run was I only saw 11.5 knots on the gps but was not aware of tide and wind.

Cheers

Interesting. Not sure how much wobble is acceptable. Sounds like you have some concerns about this boat. All I can say is listen to your gut. Tough to offer much valuable input from afar from pictures.

As a side note, I recently changed from PSS to Tides. Ability to carry a spare seal as warm-standby was a notch in its favor. But both are good.

Good luck

Peter

 

[lwarden]

A PSS seal cannot tolerate much shaft movement and it's very important the graphite seal is concentric with the shaft. Sometimes this requires some offsetting of the bellows on shaft tube, but if the shaft tube and shaft are very far off you may not be able to center the graphite seal well enough to prevent it from touching the shaft during rotation. If it touches the shaft it can bounce and cause some spray.

 

[Duetto]

fwiw, we've had both tides and pss on another boat. tides is a lip seal which relies on the seal being perpendicular to the shaft. pss is a face seal which relies on the 2 surfaces to stay in contact. we had tides initially but any shaft wobble kills them in short order. we switched to pss and though not perfect is a lot more tolerant. i would not use tides on a shaft which has long unsupported lengths or one with any wobble/whipping.

 

[psneeld]

The PSS on the assistance towboat I ran was very far out of line after a new shaft strut was installed.

It took a few to six months before the wear on the carbon faces became so bad we had to do something.

At rest it did not leak, but did throw a lot of water when running hard as time went on.

So some wobble may not be a problem for years depending on how many hours the boat is run, average RPM and how much sediment is in the water.

 

[davidla]

Thanks for all the observations, some great information here. Probably will proceed to purchase but haul out immediately and get the shaft sorted for true and go from there.

 

[RickyD]

Just adding here that my 1991 Californian 55 has two struts and six cutlass bearings. My friend has a 1989 model and he as four bearings. He bought the boat last year. Now, maybe the stern tube bearings were removed as he had an alignment problem that was initially assumed to be a possible bent shaft. He could run up to max 1400 rpm until the wobble became scarry. After purchase, both shafts were removed and checked to be true. Upon re-installation it was determined that the middle strut needed to be moved inboard 1/2 inch. This strut is stout and stubby. I can't imagine that it could have been bent. Could it have been like this since construction?? How could engine alignment be the problem. It runs sweet now.

 

[paramount]

I'm not sure if this will help, but here's a great propeller shaft bearing calculator that will give you an idea of how many cutless bearings you should have based on ABYC construction standards.

As far as a reliable shaft seal that's designed to withstand extreme environments and use, check out the self-aligning shaft seals from RE Thomas Marine Hardware.

 

[davidla]

An update on my purchased boat. In January 24 finally managed to get the prop shaft pulled and aligned as well as the prop balanced. The shaft had little bend in it, 5 thou at most and this was taken out. A new bearing was made for the shaft log but was not able to be made to fit due to the engine, tube and hanger not being perfectly aligned. There was no bearing in the tube to start with.
Engine alignment was achieved using a couple of shims on the engine mounts and the vibration on the shaft is almost 100% eliminated and I am running a new PSS seal. This will spray very small amounts but only if I run the engine hard. I normally cruise at 2200 rpm and all is performing very well.
Very happy indeed.
For BruceK, we are now on the Gold Coast and we did use Porters to do the shaft and prop.