Đóng tàu Industry Bearings: Codes & Applications

Shipbuilding industry bearings are specialized rolling bearing assemblies engineered for harsh marine environments—where salt exposure, high humidity, constant vibration, and dynamic loads destroy standard industrial bearings in months rather than years.

Vietnam's shipbuilding sector—spanning Hai Phong, Da Nang, and Vung Tau shipyards—operates thousands of cargo vessels, fishing trawlers, service boats, and offshore supply ships. Each vessel contains dozens to hundreds of bearing locations. Selecting the wrong bearing code or using materials incompatible with saltwater corrosion means offshore failure—rescue and downtime costs typically run 10–20 times higher than scheduled bearing replacement.

This article analyzes each major application by specific bearing codes, material criteria, and operational reality at Vietnamese shipbuilding facilities.

What are shipbuilding bearings?

The term "shipbuilding industry bearings" encompasses three major categories:

1. Propulsion shaft bearings — propeller shaft, rudder stock, intermediate shaft supports.
2. Deck equipment bearings — anchor windlass, deck crane, cargo hatch assemblies.
3. Auxiliary machinery bearings — seawater pumps, diesel generators, engine room ventilation fans.

The distinguishing factors versus standard industrial bearings center on three critical elements: (a) bearing rings and cages must withstand seawater pH 7.5–8.4 with elevated chloride ion (Cl⁻) concentrations; (b) internal clearance must accommodate thermal expansion in engine rooms reaching 60–90°C; (c) lubrication must maintain an oil film under hull vibration cycles spanning 2–50 Hz frequency range.

SKF Rolling Bearings Catalogue, 2018 documents that equivalent dynamic load (P) on a mid-size cargo vessel propeller shaft can reach 40–80% of the bearing's basic dynamic load capacity (C)—substantially higher than most land-based industrial applications.

Propeller shaft—the vessel's power transmission spine

Load characteristics

The propeller shaft transmits full engine power to water. Combined loading includes:

• Radial load from shaft weight and hydrodynamic thrust vector.
• Axial thrust load transmitted through thrust bearings as the propeller drives the vessel.
• Low-frequency vibration (5–30 Hz) from propeller cavitation and hull resonance.

Mid-size cargo vessels (3,000–5,000 DWT) typical at Vietnamese yards operate with shaft diameters 80–160 mm, lengths 6–12 m, supported by 2–4 journal bearings.

Common bearing codes

Why use SRB (Spherical Roller Bearings)? Long shafts deflect under distributed load and thermal gradients. SRB self-centers up to ±2° misalignment without stress concentration. Using ball bearings or tapered roller bearings on long shafts without flexible couplings creates edge loading—the leading cause of inner-race fracture on marine propeller shafts.

Shaft seal system (seawater exclusion)

Propeller shaft bearings never contact seawater directly—a shaft seal system (mechanical face seal or lip seal with air cavity) maintains the barrier. At Vietnamese yards, the predominant design is a lip seal with air pocket or mechanical face seal assembly. When seal integrity fails, seawater infiltrates the bearing housing within hours. Monitoring seal compartment pressure on the lube-oil pump at 250-hour intervals is mandatory.

NSK Technical Report, 2022: propeller shaft bearings with ISO VG 460 mineral oil and intact seals achieve calculated L₁₀ life = 50,000–80,000 hours under average loading conditions.

Anchor windlass—high shock, short duty cycles

Load profile characteristics

An anchor windlass (mooring winch) operates in short intermittent cycles: raising or dropping anchor 10–30 minutes, then idle for hours. Shock loads when the anchor hits bottom or the chain jerks create a defining characteristic—peak transient load can spike 3–5 times the nominal rated load. Typical mid-size cargo vessel windlasses use 15–30 kW hydraulic motors with sustained torque 5,000–15,000 Nm.

SRB and thrust bearing pairing

Anchor windlass bearings consist of a pair:

• SRB 22216 EK/C3 (d=80, D=140, B=33, C=166 kN) — windlass shaft journal bearing, absorbs radial loading and axial shock during anchor deployment.
• Thrust bearing 51316 (d=80, D=140, B=44, C₀=340 kN) — axial load bearing when anchor chain tension loads the shaft.

A common design error is placing an SRB alone to carry full axial thrust under combined loading. Spherical roller bearings can tolerate axial load only to a limit (typically Fa/Fr ≤ 0.55×e). Exceeding this threshold causes roller skidding on the raceway—spalling (false brinelling) is the inevitable outcome.

Windlass lubrication

Anchor windlasses typically use EP2 grease (NLGI #2 with extreme-pressure additives). Grease replenishment occurs at 500-hour service intervals or after extended voyage legs. At Vietnamese ports, windlass maintenance often falls outside scheduled preventive maintenance routines—the majority of SRB failures on anchor windlasses stem from inadequate lubrication.

Deck crane—eccentric load, smooth slew requirement

Crane bearing assembly configuration

A deck crane (ship's derrick) on cargo vessels integrates two main bearing systems:

1. Slewing ring (turntable bearing) — large-diameter ring bearing 500–2,000 mm, with integral teeth meshing with the slew drive motor. Combined loading includes radial force from crane and cargo weight, overturning moment from the boom extension, axial force from the crane superstructure.
2. Boom hoist axis bearing — SRB 23028 EK/C3 (d=140, D=210, B=53, C=470 kN) at the boom pivot joint.

Slewing ring—technical characteristics

Slewing rings have no unified ISO standard designation—each manufacturer (Rothe Erde/ThyssenKrupp, IMO, Kaydon) uses proprietary codes. Core technical requirements are:

• Breakaway torque (initial torque to start rotation) ≤ 2% of the static torque capacity.
• Radial runout under nominal load ≤ 0.5 mm.
• Design life ≥ 10 years with 20,000 rotation cycles per year.

Slewing ring lubrication uses specialized grease: Klüber Barrierta L 55/2 or equivalent—polyurea-based grease withstanding heavy loads and not washed away by rain or saltwater spray. Inject grease through nipple ports around the ring circumference until fresh grease appears uniformly at the outlet.

SRB at boom hinge

FAG/Schaeffler Industrial Bearing Solutions Guide, 2023: marine deck cranes mandate SRB with brass cages versus steel or polyamide cages—brass withstands shock impact and remains ductile at low temperatures in northern coastal waters.

Corrosion resistance—mandatory in the marine environment

Three primary corrosion mechanisms

Galvanic (electrochemical) corrosion: When carbon steel bearings contact saltwater with elevated Cl⁻, a corrosion potential develops between different steel phases (ferritic/martensitic). Corrosion rate increases 3–5 fold versus freshwater industrial environments.

Crevice corrosion: Occurs at the contact interface between bearing ring and housing—the tight gap where salt brine condenses and dissolved oxygen depletes. Surface degradation at the press-fit interface accelerates faster than oil-lubricated raceways.

Stress corrosion cracking: Combined dynamic loading in a corrosive environment initiates micro-cracks originating from the raceway stress field into the ring body—dangerous because no warning signs precede sudden fracture.

Material solutions

Stainless steel 316L (AISI 316L): Used for small to medium bearing sizes (d ≤ 70 mm) with direct seawater contact—seawater pump impeller shafts, through-hull valve spindles, subsurface monitoring equipment. 316L contains 2–3% molybdenum, enhancing Cl⁻ resistance. Limitation: raceway hardness is lower than standard bearing steel (52100), so allowable loads drop 20–30%.

Zinc plating or Geomet (zinc flake coating): Applied to bearing housings and shields—not to raceway surfaces. Sacrificial zinc protects the base metal cathodically for 3–5 years before recoating becomes necessary.

Ceramic hybrid bearings: Hybrid bearings pair ceramic balls (Si₃N₄) with 52100 steel rings coated with nitride. Ceramic balls are non-conductive (blocking stray-current-induced corrosion common on electrified ships), 40% lighter than steel, and immune to electrochemical corrosion. Cost runs 3–4 times higher than standard steel bearings but operating life doubles in harsh marine conditions.

Brands and market selection for Vietnam

ZVL—operational field experience on Vietnamese vessels

ZVL (Slovakia) manufactures bearings to ISO 492 and ISO 15:2017 standards with CE certification at European testing labs. ZVL's marine product line includes SRB series 222xx and 223xx with C3 clearance and welded steel cages—suitable for propeller shaft journals, windlass bearings, deck equipment, and auxiliary machinery.

On-site experience across Vietnamese shipyards: ZVL bearings see widespread deployment in Hai Phong, Nam Dinh, and Vung Tau repair facilities. Competitive pricing versus SKF and FAG for equivalent bearing codes, with stable domestic distribution channels.

Note: ZVL does not manufacture slewing rings or ceramic hybrid bearings—these specialized product families require sourcing from Rothe Erde (ThyssenKrupp) or dedicated suppliers (NSK/SKF).

SKF Marine Range

SKF offers a dedicated marine bearing portfolio: EXPLORER spherical roller bearings with advanced raceway geometry and cage design, plus shaft seals in V-ring and SPEEDI-SLEEVE formats. The SKF Marine catalogue (PUB BU/P1 10000/2 EN) lists over 200 bearing codes approved for marine vessel applications per class society standards (DNV, Lloyd's, Bureau Veritas).

Quick brand comparison by application

Real-world case study

At a mid-size ship repair facility near Hai Phong port, the engineering team documented premature failure of SRB 22320 EK/C3 on the main propeller shaft journal bearing—failure occurred at 8,000 hours, well short of the design life expectancy of 40,000+ hours.

Root-cause analysis following ISO 15243:2017 identified fretting corrosion at the raceway-to-housing interface. The housing was gray cast iron GG-25 without protective coating—the press-fit surface corroded, opening micro-gaps that permitted micro-slip between the bearing outer ring and housing under hull vibration.

Corrective actions implemented:

1. Applied Loctite 648 (anaerobic retaining compound) to the press-fit surface, filling micro-voids and preventing micro-slip.
2. Replaced the housing with GGG-40 (nodular graphite cast iron) exhibiting superior hardness and corrosion resistance compared to GG-25.
3. Adjusted vibration monitoring frequency from 1,000 hours down to 500 hours per ISO 10816.

After 14,000 operating hours post-replacement, the new SRB assembly showed zero signs of degradation. Initial corrective cost (new housing and surface treatment) equaled approximately 30% of a single offshore emergency repair and downtime event.