Wärtsilä Underwater Mountable Steerable Thrusters
Wärtsilä Underwater Mountable Steerable Thrusters (UMT) are azimuthing bow thrusters that can be installed fully underwater and serviced without dry‑docking, offering 360° continuous steering and a power range from 700 kW up to 6.5 MW depending on the product line.
Inspector Detail
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Common issues
- Shaft seal wear allowing water ingress into the gear housing
- Gear or bearing wear in the steering and propulsion drive train
- Hydraulic steering system leaks or loss of pressure
- Controllable-pitch mechanism seal leakage on CP variants
- Fouling and corrosion of the underwater-mounted housing and propeller
- Anode depletion accelerating housing corrosion
- Sluggish or inaccurate steering response from slewing drive wear
Inspection checklist
- Gear oil sampling for water content and wear metals
- Check seal air/barrier system function and pressure
- Diver or drydock inspection of propeller, housing and anodes
- Check hydraulic system pressure, filters and oil cleanliness
- Verify steering accuracy against commanded azimuth
- Check mounting/hull interface bolts and seals for corrosion and tightness
- Monitor bearing temperature and vibration trend
- Function-test local and remote/emergency control modes
Service intervals
| Gear oil sampling | every 500-1000 running hours or per the maker's PMS |
| Seal barrier system check | daily to weekly during operation |
| Anode inspection/renewal | at drydocking or per condition, typically every 2.5-5 years |
| Underwater housing/propeller inspection | per the maker's approved underwater service procedure, which is this unit's key feature relative to drydock-only designs |
| Hydraulic filter/oil change | typically every 2000-4000 running hours per the maker's PMS |
Critical spares
- Shaft seal set
- Sacrificial anodes
- Hydraulic filters and seal kits
- Gear oil of the maker-specified grade
- O-rings/gaskets for the housing and hull interface
Safety
- Underwater servicing must follow the maker's approved diver/ROV procedure with full electrical and hydraulic isolation and lockout
- Hydraulic stored pressure hazard before opening any component
- Confined space entry into the thruster room requires standard gas-free precautions
- Diver safety protocols are required around the propeller and steering mechanism during any in-water intervention
Class survey
Class surveys steering/thruster systems at drydocking or via an approved alternative survey arrangement; for underwater-mountable designs, class may accept in-water inspection/maintenance records in lieu of a drydock opening where the maker's service procedure and class's alternative survey approval cover it - confirm the specific approval basis with the vessel's class society.
Components & Design
Component data being added…
Technical Data
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Common failures & inspection points
Perform visual inspection and NDT (non-destructive testing) according to OEM and classification society standards. Polishing in combination with edge damage repair increases operating efficiency by 2-5%. Check for pitting, erosion patterns and corrosion spots; document severe pitting areas.
5-year overhaul: Disassemble and inspect all seals. 10-year overhaul: Complete replacement of blade foot O-rings. Check for water penetration in jet thruster assembly. Seals are critical for system protection.
Measure propeller shaft wear with poker gauge (between last two stern tube seals). Perform complete inspection of tooth clearance, tooth pattern and shaft seals. 5-year overhaul: seal replacement. 10-year overhaul: comprehensive replacement.
5-year overhaul: Check bearing clearance and wear. 10-year overhaul: Complete bearing replacement, reset preload, perform NDT inspection. Check main bearing axial clearance wear with feeler gauge (0.1 mm); maximum wear limit 2 mm. Use Wärtsilä bearing wear measurement system for remote monitoring of propeller shaft shoulder.
Check gear oil regularly. At critical wear limits: partial change (bleed-and-feed) or complete oil change. Monitor water content in oil (critical >1000 ppm). Check fine filtration system and redundant filter options. Continuously filter out water ingress. Use all Wärtsilä-approved spare parts. 5-10-year overhaul: Perform oil change and filter maintenance.
Check for oil leakage at outer seal. Inspect inflatable emergency seal and inner rope guard. Fully serviceable underwater without habitat or discharge. Measure seal gap and wear. Check retrofit compatibility with other seal types. Confirm compatibility with EAL and mineral oils.
Type-general inspection and maintenance points for this equipment category — not model-specific.
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