Oil sealing:

how oil loss due to seal failure can be restricted while on passage

Under normal condition, seal activated through #3 sealing ring.

(valve V3 & V4 normally open).

If oil leakages take place, shut V3 & V4 respectively and drain line – #3S will be activated.

Pipeline connection to oil tank for chamber  #2 & #3 seal – prevent

oil loss into the sea.

sea water ingress into stern tube by draining into collection tank

If #3 & #3S sealing rings are both damaged, stern tube hydrostatic oil pressure

to be lowered – using temporary oil tank & vinyl hose.

Sealing arrangement

Itemise the factors which adversely affect seal life.

• Rubber seal harden/deteriorate
• Damaged due to foreign objects-rope, fishing nets, sand
• Cooling failure
• Lube oil contamination
• Loading condition – axial & radial movement, vibrations
• Distortion/rupture of seals due to high pressure differential

Air Sealing:

Sealing arrangements:

.stern tube

→System operates by spouting air into the sea.

→Leakage of system by sea water or oil in system is drain down to a collection tank (leakage tank)

→Air pressure passing through #2/3 seal is about 0.2~0.4 bar higher than sea water

→The S/T LO tank is set about 2~3 meters above the propeller shaft centre line. This tank is air tight and connected to air control unit. The air pressure in the tank is same as air pressure through #2/3 chamber.

→LO pump when running passes through #3/3S seal. A needle valve in system is to be adjusted to adjust the LO pressure to about 0.3~0.5 bar higher than air pressure in #2/3 chamber.

Oil filling:

→Close air supply

→release air pressure

→meantime sea water pressure on seal no-01 will prevent water from entering to engine room

→ fill required amount of oil and afterwards normalize the system

Troubleshooting:

Stern tube liner: Chrome liner

.stern tube

.chrome liner

Material:

High nickel chromium steel –

→  Excellent wear (abrasion) & corrosion resistance

→  Optional ceramic coating if applied on running surface, heavy duty rings are mandatory

Chrome liner fitting:

• Seal is gripping on to the chrome liner. Chrome liner is bolted on to propeller boss(aft). An o’ring is fitted between the chrome liner and propeller boss to prevent sea water ingress.
• Fwd chrome liner is fitted on to a clamp ring . Clamp rings are of 2 halves and have holes.
• Aft  sealing assembly consist of 2 main and 1 aux sealing rings. All sealing rings are spring loaded . Fwd sealing ring prevent oil leakage to sea .Lip seals hold oil within Stern tube and accepts small misalignment
• O ring fitted between boss and liner
• Chrome liner act as rubbing surfaces for lip seals. The chrome liner at the aft end protects the steel shaft from seawater and corrosion .Grooving will not happen on the shaft because of liner, so that the chrome liner can be machined or can be shifted axially by putting spacer. If grooving occurs leak will start.
• Seal no#2 and no#3 is connected to air supply system ,#3s is the spare seal
• If water content found on the stern tube that means along with #1 and #2 , then #3 seal is also leaking. Then we have to put #3s seal in use.

Stern Tube LO temp high / Running Hot

.stern tube temp high  .stht

Causes :

1. Sensor faulty or loose connection – check locally.
2. System LO temp high due to —-

• Cooler dirty – clean cooler
• Pump pressure low – changeover pump
• Filter dirty – changeover to clean one.

3. Poor Quality, insufficient or contaminated LO in the System.
4. Water or Foreign particles in the oil.
5. Excessive vibration, M/E running on critical speed for a long time – Avoid prolong running in critical speed.
6. Axial movement & vibration of shaft due to uneven loading & ballasting – Ensure proper ballasting.
7. Eccentricity of shafting due to bearing wear down.
8. High ambient temp.
9. Aft peak tk / Stern tube cooling water tk empty or less wa)ter.

• Propeller obstructed / unbalance due to broken blade.
• Uneven Trim / List – correct the Trim / List.

Actions:

1. Check temperature locally and manually by temp gun. Check the level, appearance of oil and cooling line.
2. Inform Master, Bridge if problem is real & Reduce RPM.
3. Start another A/E & keep eye on Boiler steam pressure.
4. Reduce RPM until it cools down.
5. Check Causes for running Hot & take necessary action.
6. Check stern tube cooling water tk level, if less water – fill up tk
7. If System LO temp high due to—-
8. iv) Cooler dirty – clean cooler
9. v) Pump pressure low – changeover pump
10. vi) Filter dirty – changeover to clean one.
11. If Uneven Trim / List – correct the Trim / List.
12. Avoid prolong running in critical speed.

• Check drain oil quality.

Causes & Actions in case of Sea Water Ingress in Stern Tube

.stern tube water ingress

Causes:

1. Seal Ring
2. Scored Chrome Liner
3. Seal Assembly loose & crack.
4. Oil line or air line leaking in aft peak tk
5. Fishing net caught in the Aft Seal assembly.
6. Bearing wear down will allow the shaft to drop, causing the seal to overload, clearance may develop between seal & liner.
7. Low LO pressure or air pressure
8. Misalignment & vibration
9. LO cooler sw side leaky.

Actions @ SEA:

1. Reduce engine RPM
2. Reduce Aft draft is possible
3. Check sea water cooled LO Cooler.
4. Increase oil pressure/air pressure in seal by raising height of gravity tk or adjust air pressure or increasing tk back pressure or using high viscous oil (Gear oil, mixing grease).

Actions @ Port:

1. Check seal, if damage renew.
2. If fishing net, removed by driver.
3. If Chrome plate liner scored, machined it (Dia must be within limit) / Shift seal position by changing the distance piece position.

Intermediate Shaft Bearing LO temp high / Running Hot

.intermediate shaft bearing

Causes :

1. Faulty & loose connection of
2. Cooling water temp high, less flow of cooling water due to choked valve, pipe leakage, if SW cooled—may be SW O/B valve choked.
3. Wrong grade, Poor quality oil.
4. Insufficient LO, oil leakage, seal broken, sump level may low.
5. LO Contaminated with Bearing / foreign particles – Replenish the oil.
6. Failure of LO supply mechanism.
7. Ambient temp high.
8. Misalignment of the shaft due to Shaft & Hull distortion or Internal bearing wear down.
9. Shaft got misaligned due to bearing wear down (rare to happen, can be detected by taking crankshaft deflection after engine is stopped).

• Others bearing wear down.
• Deformation of tank top due to excessive heating of DB tk ( Bilge tk, Sludge tk).
• Excessive vibration of shaft due to propeller damage.
• Excessive vibration, ME running on critical speed for a long time – Avoid running in critical speed.

14. Hogging & Sagging
15. If ship listed – correct list.
16. And also check trim condition – correct trim.

As a Chief Engr Actions :

1. Check temperature locally and manually by temp gun.
2. Check the level, appearance of oil and cooling line.
3. Inform Master, Bridge if problem is real & Reduce RPM.
4. I will instruct to 3/E to Start another A/E & keep eye on Boiler steam pressure.
5. Engine should slow down automatically, if not, need to be slow down manually until it cool down.
6. Check Causes for running Hot & take necessary action.
7. I will instruct to 4/E engineer to check cooling water supply and arrange extra cooling means.
8. I will tell 2/E to renew oil by flushing with new oil, Check drain oil quality.
9. If ship is listed, inform Bridge to correct the list.

• In extreme case, Ask bridge to stop engine if possible.
• If not possible to stop engine, continue with minimum possible rpm and strictly monitor the temp of int. bearing and other parameters as well specially the crankcase condition (as misaligned shaft may damage main bearings and can lead to crankcase explosion).
• In the meantime, investigate the cause of this high temp. if possible do troubleshoot.

13. When it is port, re-metal bearing & adjust chocks to give correct share of load. If overheating is frequent, check shaft alignment (Methods : Optical Sighting, Piano Wire, Gap & Sag Method, Jack-up Method, Strain Gauge Method), Check holding down bolt.