Stern tube seal renewal procedure dry dock?

.stern tube seal renewal in dry dock

Stern Tube Seal Renewal Procedure in Dry Dock

Preparation Phase

System Familiarization

• Check maker’s instruction manual for key points, draining procedures, and service records
• Review previous records (dry dock reports, seal renewal records, wear down reports)
• Verify and update TALISHAFT MONITORING records
• Prepare dry dock specification and maintenance plan for office approval

Equipment and Supplies

• Check onboard spares and raise requisitions if needed
• Ensure sufficient environmentally acceptable lubricant (EAL) is available
• Verify safety equipment availability (gloves, helmets, safety harnesses)

Pre-Work Checks

• Review previous lubricating oil (LO) analysis results
• Check main engine crankshaft deflection and bearing clearances
• Verify onboard LO analysis records

Execution Phase

Safety Measures

• Conduct risk assessment before starting work
• Hold toolbox meeting with dock supervisor and service team

Initial Inspections

• Turn shaft to zero marking and check clearance
• Isolate and drain the system
• Measure propeller drop/stern tube wear down clearance using poker gauge
• Compare readings with previous records and maker’s limits

Chrome Liner Inspection

• Check for:
• Wear down
• Scoring marks
• Cracks
• Seal Replacement
• Decide whether to change seal in-situ or remove propeller
• If propeller is removed, inspect stern tube bearing for:
• Lacquer formation
• Signs of overheating
• Fretting marks
• Metal peeling

Reassembly and Testing

• Pay attention to alignment of stern tube and propeller shaft
• Replenish lubricating oil and conduct leak test
• Recheck poker gauge reading at ZERO mark with all main engine units in place

Key Points to Remember

• Perform leak test after flushing pipes
• Take wear-down readings before and after overhauling AFT seal
• Protect seals from external damage (sandblasting, painting, welding, chemicals, heat)
• Use stainless steel fitting bolts (SUS 316 or equivalent) for AFT seal installation
• Secure all fitting bolts and plugs with stainless steel wire
• Return all valves to “Normal Operating Condition” after testing
• Monitor oil level for sudden reduction due to air-locking dissolution

Explain the procedures of stern tube alignment checks in dry dock

.stern tube alignment .st alignment

• Dial gauge for radial direction:

o This gauge is set up to measure the radial movement of the shaft. Radial direction reefers to a direction that radiating out from the center of the shaft

o It is important to measure this to ensure that the shaft is perfectly centered & there is no excessive play or wobble which would indicate misalignment

• Dial gauge for radial direction (On another point):

o This second dial gauge is measuring the radial displacement likely at different point along the shaft to measure consistency in shaft alignment throughout its length

• Dial gauge for axial direction:

o the axial direction is along the length of the shaft. This gauge measures the end play or axial movement of the shaft. It is crucial to measure that the shaft doesn’t move too much back and forward along its length, which could affect in the operation of the seal and further lead to leak or wear

In a stern tube seal alignment check gauges would be used as follows:

• The dial gauges are positioned at a specific point on the stern tube and propeller shaft

• The shaft then to be rotated and the reading to be observed at the dial gauge

• By reading the gauges we can determine if there is any misalignment in the shaft. This is determined by looking for variations in the variations of the reading which would indicate that the shaft is not perfectly round or is not seated centrally within the stern tube.

• Any misalignment can lead to excessive wear in the seal & bearing and potentially lead to seal failure

• Therefore, it is crucial to adjust the alignment until the reading on the dial gauges are within acceptable limits as specified by the manufacturer.

Note: In case adjusting liner eccentrically by turning shaft isn’t available, then even clearance between liner bore and shaft surface by using feeler gauge must be achieved.

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

.stern tube water ingress

Causes: 

1. Seal Ring damage.
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.