STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

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adreno1981
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STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby adreno1981 » Wed Mar 07, 2018 2:24 am

Hi Fellas,
anyone has any write up or material regarding high stern tube bearing temperature..Consider , you are in maneuvering in congested waters and heavy current from ahead .Vsl Observe high stern tube bearing temperature on both sensors , checked oil level in tanks to be normal. Stern tube cooling water tank level also good..Stern tube oil Pump pressure also normal..Can u pls assist on action to be taken and other checks to be carried out to ensure satisfactory condition of stern tube..Any links/write up or assistance on matter will be highly appreciated..
Thanks'
Regards

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JK
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby JK » Wed Mar 07, 2018 8:45 am

is this an actual occurance or are you doing a paper?
Anytime I’ve seen this in practice, the ship has to be docked, but you have no details in your question.

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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby The Dieselduck » Wed Mar 07, 2018 7:54 pm

Is your cooling pump sucking up the bottom?
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Big Pete
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Big Pete » Thu Mar 08, 2018 1:07 am

If the oil temperatures goes up, either the cooling system isn't working properly or the the prop shaft is generating more heat.
So first check the cooling system, simple things first, are all the valves fully open, clean any filters, check the current drawn by the pump motor, it will INCREASE as the pump becomes worn and the water recirculates from the discharge side back to the suction side inside the pump, increasing the mass flow produced by the impeller even as the mass flow outside the pump falls, if you have no record of the motor current from before the problem started, you may have to open up the pump and check it.
Is there a thermostat? is that full open, bypassing the cooler or has the inside corroded away? ( I saw that on one ship where the crew had decided to dose the the Domestic Fresh Water with Swimming Pool Chlorine Tablets, the chlorine corroded away all the Brass thermostats in the Fresh Water Cooling systems and also the the Domestic Fresh Water pressure was maintained by pumping water continuously against a relief valve and the relief valve dissolved.
Have you logged readings of the oil and water temperatures before and after the cooler? Those might give a clue. Was the change in temperature sudden or gradual?
If the shaft is generating more heat, the friction has increased, so most likely either the bearings have failed or the shaft is bent, or the prop is out of balance, have you grounded or has the prop made contact with submerged debris or anything that might have caused prop damage?

Those are the things that I would be looking at.
Good Luck.
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Merlyn
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Merlyn » Thu Mar 08, 2018 3:03 am

Wonder why the high temps. only seem to happen when maneuvering ?
Higher rpm when underway in cruising mode and yet no mention of higher temps?
Could it be because shaft turning both ways thereby aggravating white metal or shaft bearing premature breakup?
Something must be generating the higher than normal temps?
Sensors /display head displaying correct readings?
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby camshaft » Thu Mar 08, 2018 3:48 pm

Hi adreno,

This is a theoretical scenario right? Of course the biggest worry is shaft/bearing damage - but as BP mentioned first find out if it's excessive heat from the bearing or much more likely a cooling problem. If this is a real situation you're probably alongside now but I'd check all the oil & water temps going in and out to determine where the heat is coming from and to gauge the efficiency of the cooling system. What are the oil temps in and out of the stern tube? Like Merlyn says don't trust the sensors and get readings from everywhere possible. From that you should be able to tell if it's a plugged or bypassing cooler, or a pumping problem. I can't think of why the vessel driving against a heavy current would raise shaft brg temps but as Martin says sucking debris up from the bottom is a definite consideration. Maybe if the shaft brg is really excessively worn then the lower rpm has trouble keeping the oil wedge and there's actual metal-to-metal contact but that's not the first thing I'd think of.

Regarding docking the vessel - if this is an exam question or especially if it's an actual scenario, make sure you've eliminated any other possibility before suggesting docking her. You have to be absolutely sure before doing something like that, otherwise you may be looking for another job or at least fail this exam question. Divers to inspect the shaft/seals, weardown readings if possible, shaft vibration noted, and analysis of the oil come to mind for sure (not necessarily in that order). I actually know of an instance where a vessel was docked for a CPP problem which turned out to be a plugged filtre. I would expect shaft bearing damage to show up more at full away and brg problems will show up in the oil analysis - usually long before a failure.

How to assess the cooling system temp & pressure readings is a bit of a longer dissertation and depends somewhat on the specific installation (one shaft or two, one pump or two) but it's basically thinking about temperature & pressure drops across coolers and pumps. It's possible to get debris like sand in the stern bearing but that usually results in a longer-term aft seal wear issue rather than an immediate failure and will probably show up as oil leaking out.

If this is an exam question they'll want more than this, more of a discussion about general troubleshooting and condition monitoring of stern tube bearings...Cheers

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Merlyn
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Merlyn » Fri Mar 09, 2018 12:54 am

I find personally in cases like this that our magic ray gun comes to the fore.
For exactly pin pointing an overheat problem shine the infra red two rays on the target, move forwards or backwards to align the dots as one and hey presto, exact reading in C or F in the display window.
Use in both sides of a thermostat for example to see if it's opening to max. or only 90%, trace pipe work/ water rails blockages instantly.
In this case tank reservoir temps, output pipes / flow rails, flanges / in and out of filters temps, all flows and returns throught the installation.
Sometimes lagging etc to be removed but like when doing exhaust systems both upstream and downstream of sensors/ internal obstructions pin pointed exactly without dismantling.
As long as you can shine the light as they say this bit of kit is invaluable and certainly is a vast improvement on the old days of using the pinkies as a sensor.
Cheap as chips nowadays to buy.
Removes all doubt.
Never used in underwater though.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby D Winsor » Fri Mar 09, 2018 5:39 am

I've seen this issue on some vessels, especially those with CP Props where the HP Servo oil is fed through the shaft to the hub. Depending on CP system, part of the cooling of the CP Servo oil is sometimes dependent on the transfer of heat generated while maneuvering from the shaft to the sterntube cooing media be it oil or water. One particular solution especially if the sterntube passes through a normally empty After Peak tank would be to add just enough water to the cover the sterntube. The water then creates a static means to transfer heat from the sterntube to the outer hull.

Overheating issues with both oil and water cooled sterntubes became a common occurrence on Great Lakes vessels with the advent of the CP Propeller. Especially when the ships ended up sitting in a lock with the shaft turning for extended periods with little water movement around the hub and high water temperatures especially in summer. On these vessels covering the sterntube with water in the After Peak helped solve the problem and is now considered a standard operating procedure.

I also heard of an issue where a sterntube would overheat while maneuvering again on a vessel with a CPP where the pipelines supplying oil to the tube were connected incorrectly reversing the flow of oil through the system
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby adreno1981 » Sat Mar 10, 2018 4:34 am

hey fellas ,
Thanks for ideas and guidance..
This was scenario on a colleague's vessel which was sailing with much less than normal propeller immersion , as they were just coming out of a repair yard, following a take over of this vessel in china..On coming out vessel encountered adverse current and they had to suddenly increase rpm on Pilot's command...Engine room observed high stern tube bearing temperature on raising rpm and checked all parameters such as oil temperature on local gauges , pressure of oil in system , pump pressure gauges and sound , oil flow in sight glass , cooling water tank level , and stern tube oil tank level.All was observed to be absolutely normal..Engine room informed bridge to reduce rpm else they may face complete bearing failure.Speed of vessel was reduced once the vessel came out of congested waters , and observed alarm to become normal and remote temperature sensor readings to come to normal value after operation at reduced rpm for sometime ...

Checks Carried out :
Vessel was then finally stopped and checks made by turning engine by turning gear , and keeping stern tube pump running in system after changing over the pump.Filters of the pump were checked for white metal presence and cleaned and put back after finding no metal presence..Vessel aft peak tank was ballasted and vessel brought to value for proper propellor immersion..
Once all done , engines were restarted and vessel sailed safely with no high bearing temperature alarm again..
This was the sequence of events received from vessel...
Pls share if Any comments or suggestions are there regarding the checks that were carried out or better way to check system for bearing condition except taking the vessel to dry dock, which will undoubtedly be required if bearing is in bad shape..
Any other suggestions about what could have led to this situation are welcome...
Thanks again fellas..
adios

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JK
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby JK » Sat Mar 10, 2018 7:05 am

Forgive me if the are simplistic questions.thinking out loud here.
So not Thordon bearing. Was heat observed at the gland? Do you know definitely how hot the oil got?
Is your shaft seals damaged?
Not all systems are plumbed in equal. I sailed on a ship, same thing happened and we took out the bearing in 5 minutes, on my watch :cry: despite the fact we were on it immediately, reducing speed and declutching. We actually had thordon showing up in the strainers. It was a long involved problem after I left the ship and breaking my arm, what what it come down to was the system itself was problematic and difficult to fill so that oil flow was correct.

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Big Pete
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Big Pete » Sat Mar 10, 2018 10:02 am

If the prop was only partly immersed it would vibrate like hell, all that sideways thrust on the bearings would heat things up Nicely!!
If they caught it in time they may have been lucky and no further damage done, if not, it could be a big dry Dock job.
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby camshaft » Sun Mar 11, 2018 1:58 pm

Oh yeah the prop out of the water is a good piece of the puzzle. For starters the reduced prop efficiency may be why they needed to increase the shaft RPM to begin with, and more than normally required. Good reason not to let those tugs go too early if you have them. Also as mentioned above if the aft peak was empty the stern tube loses that bit of extra cooling. If the shaft was jumping around, and I expect it was, that would have increased friction & therefore heat from the bearing - maybe even the oil film breaking down (boundary contact). "...just coming out of a repair yard" - maybe the oil pump temporarily lost suction for some reason (air lock)? I think oil bearing lubrication works ok at slow speed with no oil flow as the brg is immersed in oil but reduced flow reduces the cooling effect required at higher load/speed.

Sounds like no damage done, but lessons learned and I would watch it carefully for a while, and get an oil analysis.

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Big Pete
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Big Pete » Mon Mar 12, 2018 12:06 pm

I have sailed on a couple of ships where it was a design requirement to keep the aft peak partially ballasted to provide Stern Tube Cooling, and this requirement was firmly stated in the stability Booklet for use by the Deck Officers in stability calculation.
As a practical measure to ensure sufficient water in the Aft Peak there were "High" and "Low" Ballast suction valves on the Aft Peak. The High suction valve being used for normal Ballast operations and the Low suction valve kept padlocked shut and only used when the tank had to be completely emptied for Tank Inspections etc.

Easy to miss, when taking over a new ship in Dry Dock!! But definitely something to be aware off.

BP
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Merlyn
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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby Merlyn » Tue Mar 13, 2018 2:14 am

Maybe those cheap old Chinese rubber gloves are obstructing the return flow to the tank.
I think the too high freeboard could be the main part of the answer?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.

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Re: STERN TUBE HIGH TEMPERATURE DURING MANEUVERING

Postby D Winsor » Tue Mar 13, 2018 6:06 am

Big Pete wrote:I have sailed on a couple of ships where it was a design requirement to keep the aft peak partially ballasted to provide Stern Tube Cooling, and this requirement was firmly stated in the stability Booklet for use by the Deck Officers in stability calculation.
As a practical measure to ensure sufficient water in the Aft Peak there were "High" and "Low" Ballast suction valves on the Aft Peak. The High suction valve being used for normal Ballast operations and the Low suction valve kept padlocked shut and only used when the tank had to be completely emptied for Tank Inspections etc.

Easy to miss, when taking over a new ship in Dry Dock!! But definitely something to be aware off.

BP


As mentioned in my previous post about operating with water in the after peak to aid in sterntube cooling
I forgot to mention that when operating in very shallow water 1-2 meters from the bottom combined the use of steerable Kort nozzles instead of a rudder dredging mud and silt off the bottom while maneuvering, vibration caused by cavitation can cause major issues as well with respect to sterntube cooling
Troubleshooting 101 "Don't over think it - K.I.S.S. it"


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