Stern Tube/Stuffing Box Hose Failure

[pencema]

I had a near-catastrophic failure the other day while motoring my '75 Catalina 30. Found several inches of water on the cabin floor, well outside the bilge. The stuffing box hose had come off the stern tube, allowing major flooding. I got back to the marina using the engine water pump as an emergency bilge pump. When I was able to get the hose back onto the stern tube, I found that it looked like it had been wrenched off violently, and was in bad shape. It's holding for now, but I need to haul the boat and replace it.

Problem is, the hose was new last summer, when I replaced the engine and almost everything associated with it. I used (supposedly) the proper hose, as recommended by the yard where I did the work, and used stainless T-bolt clamps that are still in good shape.

I did some internet searching and found a couple of articles that said the stuffing box and stern tube should be "castellated" or keyed together so the box/hose can't rotate with the shaft, and they described the resulting kind of hose damage I found in mine. My stuffing box and stern tube were not keyed in any way that I could tell. Any words of wisdom, anybody?

I reused the old stuffing box that appeared to be in good shape, and the old hose was also intact, just a bit worn/frayed at the ends, with some minor surface cracking. The new hose was an inch or so longer than the original, which in hindsight, was probably not the best idea.

MAP

 

[Anonymous 121765]

Pen,

There could be several reasons why this has happened. Here are some of my thoughts.

The longer hose?, that doesn't seem right as a packing gland fitting should not tear up the hose if installed correctly. Check the shaft log tube for any problems. Check the tube OD with a micrometer to establish exact and uniform OD. Also verify the hose type & ID. Not all hoses are created equal.

Another possibility would be misalignment of the shaft/motor, but for this to happen you would be experiencing alot of vibration, especially at slower speeds. Engine mounts do loosen/wear, motors go out of alignment, so I would look at this. If hauling the boat, misalignment should be evident at the cutlass bearing rubber insert.

Finally, it might be the "T" hose clamps. I had an exhaust hose to my muffler inlet that always leaked. I used a "T" bolt thinking I could really tighten the hose enough to stop the leak. What I did find was that improper tightning without a very tight fit between hose ID & tube OD was the culprit.

What I did see was that with the above scenario, directly under the "T" assembly the hose actually pinched together slightly killing the seal.

If you are going to haul the boat, Iwould suggest a new PSS shaft seal. This would be the ideal time to do it. No more having change flax. In addition, you will be able to confirm the hose culprit.

CR

 

[pencema]

Thanks for the prompt reply. I haven't had a chance to really look into the problem area yet, but will do so tomorrow. The marina mechanic said the hose looked "tortured", and I could feel that it was distorted somehow. Just seems weird that the original setup lasted at least 24 years and possibly 36, yet my replacement failed in about 9 months. All I can guess at this point is that the increased engine power, torque and rpm transferred a lot more torque to the stuffing box, which twisted the longer hose excessively. The new hose was maybe 2 inches longer than the original, but that could have doubled or even tripled the space between the ends of the stern tube and packing gland inside.

 

[Stu Jackson]

I agree with CR. You should check to make sure you got the right hose.

http://www.pbase.com/mainecruising/stuffing_box

Scroll down to the picture of the type of hoses that should be used.

 

[Anonymous 121765]

Pen,

Stu sent a good link for showing stuffing boxes. Take note that the only contact with the shaft is the flax. I doubt that an over packed/tightened nut could cause the hose to fail. A real strange situation.

Remember, opinions are like..........everyone has one. If someone gives you their opinion, do your homework. It will cost you $$ to pick & splash, along with yard (pirates) charges. It would be sad to go thru this based on a wrong asumption.

The hose length if too long, may have a tendency to twist (?) but like I said, all hose is not equal. My hose is heavy duty wire re-inforced. You never said what type of hose you have.....

CR

 

[pencema]

Thanks to Stu and CR. I don't recall the brand of hose I used, but I still have a piece lying around somewhere - just haven't been able to find it yet. I bought a foot of it, and used less than half. It was pretty massive, like the upper one in Stu's pic.

In hindsight, I may have had the shaft resting on the bottom of the stern tube when I aligned the engine. There wasn't a lot of play, but I'll recheck it next chance I get. I had no vibration, so alignment wasn't too bad.

One other symptom was that I was only able to get about 3,000 rpm the day the hose failed. Previously, I was getting 3600. I thought maybe the prop was starting to collect barnacles, but maybe something got up the stern tube and caused extra drag(?).

 

[pencema]

I replaced the failed stuffing box hose today, with the boat in the water, after getting tired of waiting for a haul-out date. It was kind of scary, seeing the flood of water, but I managed to stem most of it with towels packed around the shaft. I had a very hard time getting the new hose (Buck-Algonquin, 1.5" ID x 4" long) over the stern tube, but finally got it on and clamped tight.

Had to lift the back of the engine to pull the shaft coupling and stuffing box/hose combo, but from there, it went pretty straightforward. Saw a question somewhere on-line about the hose diameter. It's definitely 1.5" ID.

 

[jrowan]

You did not metion what type of engine that you replaced your presumably A4 Atomic with? I would contact the manufacture & explain your problem. Also this is the kind of situation where it would be worthwhile to contact Catalina Yachts directly & ask for their advice. If that hose slips off when you're not around after an extended motoring then tied up in your slip /mooring you could come back to a sunken boat. Hopefully you still have the origianl 1975 era hose lying around somewhere? It would be good to compare the inner diameter of the two hose sections & make sure that they are identical. Perhaps the longer length of the new hose is suffering from a suction action that occurs inside the hose as the prop turns within it. I would run the engine while tied at the dock for a good while, build up to operating temp. & see if this hose gets hot, or starts to cave inwards on itself. If it rubs the shaft in any way it will overheat & eventually fail from chafe, etc.

 

[Anonymous 121765]

MAP,

You did mention alignment. If you have enough room, An easy way to do this would be to remove the bolts in your coupling flange. You will be able push the shaft back buy pushing and rotating it back & forth. You may have to loosen
the packing nut somewhat.

You only need to back to where the keyed sections fit into one another. The prop flange may have a tendency to be alittle lower, that's not a problem.

Next, check to see how closely the flanges line up while turning the shaft 360 deg. Get ready to adjust your motor mounts to acheive the closest fit. The secret is when pushing the flanges together, there is no hangup with the keyed slots. It should fit together smoothly. While doing this, remember to rotate the shaft and check it every 90 degrees.

I've always beed advised not to do alignments while on the hard as the boat may be a bit flexed.

CR