Need help from the engineering gurus of gcaptain. We just pulled the shaft packing after clearing the first few rounds the engineer and I noticed that there is serious wear on the shaft. The dip is noticeable and the metal is clean and shiny. The opposite side has no visible wear on the shaft and the packing left a gummy residue for as far back as I can feel. Now my question is which side is the one with the problem. As far as I know both shafts were true when they were put in last year. And if it’s relevant were using a black graphite or silicone packing, (can’t remember which it is) not the old white flax stuff. If any other info is needed let me know and I will do my best to get answers. Thanks in advance.
Paddy
What size shaft? What rpm? Water cooled? Type of packing? (critical info) Lantern ring properly placed?
Shaft alignment correct? Shaft straight? Over tightened? What operating temperature? Drips or no drips?
Is this a little boat with a good old fashioned stuffing box on a propulsion shaft? Was the gland cocked?
Many details missing, grasshopper.
[QUOTE=Steamer;185407]What size shaft? What rpm? Water cooled? Type of packing? (critical info) Lantern ring properly placed?
Shaft alignment correct? Shaft straight? Over tightened? What operating temperature? Drips or no drips?
Is this a little boat with a good old fashioned stuffing box on a propulsion shaft? Was the gland cocked?
Many details missing, grasshopper.[/QUOTE]
6 in shaft, roughly 1600 rpm, water cooled, always a constant drip. Not sure of operating temp. As far as I know since being out of the shipyard a year ago everything was straight and true. Gland is straight. It’s a 70 foot tug 2200 HP. Had 14 rounds of 1 inch packing and it is 8000t packing from American braiding. It’s black stuff I think silicone. Hope that helps some if I missed anything or you think of something else let me know.
Paddy
Now I understand the head scratching … that shouldn’t have happened with that packing in that application.
The only thing I can think of is some kind of contamination during installation or the shaft riding well off-center. How wide and deep is the wear scar?
It’s about 1.5 inches wide just about 1/4 in deep.
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I haven’t felt a wobble. You would think if the shaft was that far off you’d get a bounce.
And since being out of drydock last July we’ve added 2 rounds of packing on that side. I’ve seen shaft wear like that in the past but not inside a year.
.25 inch deep on a 6" shaft? That’s a significant loss of cross section. Usually you can’t add packing without removing some. A gland usually has a designed number of turns. The side missing the metal is the problem but I think you knew that. Rather than a wobble you might not feel anything until it shears. Good luck.
The unit will need further disassembly and inspection to confirm the cause of failure and extent of the damage. Have your pocket book ready. When you take it apart you will be replacing some parts that’s a guarantee. Based on the photo rust / corrosion and deterioration may play a role in the cause of failure.
To put it simply. A shaft is simply a piece of metal that turns and will not wear due to packing if the packing is installed and lubricated properly. If the shaft is straight, balanced, not subject to lateral forces beyond its design and the bearings which support it are in good condition there will be no wear. When a shaft wears on it’s packing in one area only [not concentric] it is either bent not balanced or subject to a force such as an improperly ailgned transmission/engine or imbalanced screw/propeller. Might try some Grafoil ribbon packing in the area of the wear, wrap it on until flush with the non-worn part of the shaft. Then pack graphite inpreganted packing on top. Right after you do this run the shaft with little or no leak off for a few minutes then adjust for normal leak off. May take a couple of tries to get the right amount of Grafoil. At any rate it won’t hurt. This is only an effort to buy time until you find the root cause. This problem will not cure itself.
Are those axial fractures I see in the wear area? I have seen similar wear from over tightening packing and not getting enough lubrication (water) through the gland.
[QUOTE=cmakin;185470]Are those axial fractures I see in the wear area? I have seen similar wear from over tightening packing and not getting enough lubrication (water) through the gland.[/QUOTE]
I see what you are talking about and wonder the same thing. I have seen “Marks” like this after Yard Birds using more than a little force remove jammed packing rings.
While, I have never seen anything close to the size and depth of this grove, I have seen brand new shafts marked up right after a yard period due to the packing being jammed in there when the shaft was packed.
When in SY, I always tried to either pack the shafts myself or at least be there watching when they were packed. One time the yard packed the shafts on the 3rd shift without letting me know and we had nothing but problems. Hell, we were almost to the Bay Bridge near Annapolis, MD before I got water flow that I was happy with. We had a fire hose on the gland to stop it from smoking while I was pulling rings out.
I had to lock the shaft more than 3 times to pull packing out then have the wheel house back down hard a couple of times trying to get a flow out of that gland. IIRC, I pulled out 4 rings before I started getting flow. I was ready for what happened as it did not take long for the “Flow” to get almost uncontrollable. When this happened I started adding New Rings until I was happy with water flow and also enough packing where the gland was not bottomed out.
In all of the yard periods that I have been through, I have always been surprised with the number of CE’s that let the Yard pack the glands without witnessing it! Two things I always did was being there for the glands and NO tank was ever closed until I came out and either put the manhole back on myself or stood there while the yard di it!
After further disassembly and failed component inspection and replacement is performed, paying close attention to the support bearings. as you might already know - Whatever you do DO NOT over tighten after the initial installation. Adjustment takes time and break in. You will need to keep an eye on this after reassembly and normal usage. Never adjust to the at rest drip rate and always adjust to the “spinning” drip rate. You inadvertently got this shaft and box so hot you literally melted the packing you previously used and you have scored your shaft. Is the prop bent? or show any evidence of physical damage / impact? When your vessel is out of service for repair you are not making money so you might as well fix it right the first time, otherwise it will be an ongoing headache.
[QUOTE=DeepSeaDiver;185483]After further disassembly and failed component inspection and replacement is performed, paying close attention to the support bearings. as you might already know - Whatever you do DO NOT over tighten after the initial installation. Adjustment takes time and break in. You will need to keep an eye on this after reassembly and normal usage. Never adjust to the at rest drip rate and always adjust to the “spinning” drip rate. You inadvertently got this shaft and box so hot you literally melted the packing you previously used and you have scored your shaft. Is the prop bent? or show any evidence of physical damage / impact? When your vessel is out of service for repair you are not making money so you might as well fix it right the first time, otherwise it will be an ongoing headache.[/QUOTE]
Grafoil or similar ribbon packing will fill in the worn down area and can take some initial heat. The flax of your choosing or Teflon packing you put on top of the Grafoil will do the actual sealing and must have a proper drip rate for lubrication while turning, needless to say it needs no lubrication while sitting still. At this point the shaft is damaged and needs removing and repairing while you investigate the entire running gear. Anything you do now will just be buying some time.
Tugboat paddy please update the thread hows it going with this problem?
Why do new $10 million tugs, and tugs that have just $5 million overhauls, still have 19th century water cooled and lubricated shaft packing?
Isn’t it long past time for oil cooled and lubricated shafted bearings and seals on tugs? Why are we still allowing streams of water to run into the bilge which then must be pumped out? There is always risk of oil contamination of that water.
- Because it works.
- Because it’s cheap.
- Because, in the world we live in now, it is better that water trickle into the boat then oil trickle into the sea.
Water-cooled shaft seals are “always failing” (the water flows into the bilge. A seal with pressurized oil can fail “the other way”: oil leak out into the ocean. Instant pollution problem. And if no way of fixing at sea?
Worked on boats with both of these seals and they worked great with no drips.
I’ve worked on a boats with oil lubricated shaft bearings and seals. They don’t put water into the bilge that the has to be pumped out. They use tapered roller bearings that run smoother and quieter with less fuel consumption.
There are EPA approved biodegradable lube oils available where potential lube leaks are no big deal.
Cheap cheap and cheap pretty sad some outfits don’t spend extra to prevent failures down the line.
[QUOTE=tugsailor;188322]
I’ve worked on a boats with oil lubricated shaft bearings and seals. They don’t put water into the bilge that the has to be pumped out. They use tapered roller bearings that run smoother and quieter with less fuel consumption.
There are EPA approved biodegradable lube oils available where potential lube leaks are no big deal.[/QUOTE]
I think the company views it like this: Water in can be processed overboard, through a piece of equipment the vessel already has. Biodegradable oil lost through the seal is money lost. Who cares if the crew has to pump the bilge and fight the OWS? It’s cheaper than buying oil.
[QUOTE=Rafterman;188332]I think the company views it like this: Water in can be processed overboard, through a piece of equipment the vessel already has. Biodegradable oil lost through the seal is money lost. Who cares if the crew has to pump the bilge and fight the OWS? It’s cheaper than buying oil.[/QUOTE]
Oily Water Seperators are not required on vessels under 300 GRT, so very few tugboats have them. It’s been awhile since I’ve seen one.
About half of the tugs I’ve been on in the last few years have an “ecology well” to catch the water running past the shaft packing before it gets into the bilge. On the other half, the water goes right into the bilge. It’s a constant battle to try to pump the oil off the top, or use diapers to collect it and put all that mess into 55 gallon drums tied down on the 01 level, and to pump the bilge water off the bottom without putting any oil overboard. A very high risk and imperfect system.
Why take this ridiculous and unnecessary risk? In a $10 million boat after a $5 million overhaul? An oil lubricated system of smooth running, quiet, fuel saving, oil lubricated shaft bearings and seals, for an extra $50,000, sounds like a lot better, safer, and ultimately cheaper system to me.