I. The "Dry Dock Conundrum" of Bearing Replacement in Ship and Marine Engineering

In the propulsion shaft systems, rudder shaft systems, deck machinery, hoisting mechanisms, of commercial ships, military ships, marine support vessels, tugboats, fishing vessels, and offshore platforms, bearings are the key components that support the operation of the core shaft systems. However, once the bearings of these equipment fail, the maintenance team faces a much more complex "dry dock conundrum" than that of onshore equipment - traditional overall bearing replacement requires the ship to enter a dry dock, wait for the dry dock period (usually several days to several weeks), discharge the seawater inside the dock, dismantle the propeller, extract the entire shaft system, dismantle the coupling and surrounding components, and then this series of operations mean weeks or even months of downtime, resulting in direct economic losses in the tens of millions or even hundreds of millions of yuan.

 

Take the stern bearing of the propulsion shaft system of a large commercial ship as an example: The traditional replacement plan requires the ship to enter the dry dock (waiting for the dry dock period of 2-3 days), drain the seawater inside the dock, dismantle the propeller (the heavy propeller blades weighing several tons require heavy lifting equipment), extract the stern shaft (several meters to several tens of meters long), dismantle the old bearing, install the new bearing, reinstall the stern shaft, reinstall the propeller, and re-centering - the entire dry dock repair period lasts for 2-4 weeks. During this period, the ship cannot operate, and the losses from rent, cargo delays, and ship schedule breaches are extremely huge. In response to the limitations of the traditional water-lubricated stern bearing type, the use of split stern bearings and adding split stern tubes can achieve inspection, repair, and replacement of stern bearings without disassembling the propeller or the shaft.

 

Typical pain points of traditional overall bearings in ship and marine engineering:

 

Must enter the dry dock - Traditional bearing replacement requires the ship to enter a dry dock, and the waiting period in the dry dock is often several days to several weeks, occupying valuable dry dock resources.

 

Large engineering volume for extracting shafts and removing propellers - Replacing a single bearing requires dismantling the propeller (several tons to several tens of tons), extracting the entire shaft system, dismantling the coupling and surrounding components.

 

Unable to operate at sea - Traditional bearing replacement must be completed in the dry dock or workshop, and if the bearing fails on the ship during navigation, it cannot be repaired in the anchorage or berthing state.

 

Risk of secondary damage to the shaft neck - During the extraction and reinstallation of large shaft systems, collisions are prone to cause scratches, wear, and deformation of the main shaft shaft neck, resulting in extremely high repair costs.

 

Losses in ship schedules amounting to hundreds of millions - The non-planned downtime of 2-4 weeks, rent losses, and operational costs are extremely huge. In adverse sea conditions, maintenance work may even not be able to be carried out.

 

Corrosive marine environment - Ships and marine equipment are constantly exposed to high salt fog, high humidity, and seawater erosion, requiring extremely high corrosion resistance performance of bearings and seals.

 

II. NMT Marine Split Bearing: Dry Dock Replacement without Dry Docking or Shaft Extraction

The NMT marine split bearing combines the core advantage of "axle-free installation" of split bearings with the special requirements of ship and marine engineering. The inner ring, outer ring, rolling elements, and cage of the bearing are split axially, and during installation, no core components such as the main shaft, propeller, rudder blade, or coupling need to be disassembled, and the assembly can be completed directly at the original position of the shaft. More importantly - the NMT marine split bearing can complete the replacement while the ship is berthed at the dock, at the anchorage, or even floating, without entering the dry dock, without extracting the shaft, or without removing the propeller, significantly compressing the waiting and operation time in the long process of "dry dock - extracting shaft - removing propeller - replacement - reinstalling - out of dry dock".

 

▸ Full split + corrosion-resistant structure: Each piece can "split apart, but rotate together", and resistant to salt fog and seawater erosion

 

Each component of the NMT marine split bearing is split - split inner ring, split outer ring, split cage with rolling elements, split sealing components. During installation, these semi-ring components are assembled around the shaft in sequence, locked and fixed with high-strength stainless steel bolts, forming a precise transmission unit with the performance of the overall bearing. The joint interface of the split bearing adopts a precise stepped对接 structure or V-shaped split opening design to ensure that the bearing after assembly has no inferiority in bearing capacity and rotational accuracy compared to the integral bearing. The split bearing can be quickly disassembled and replaced without disassembling the shaft system and the integrated equipment.

 

In terms of material， NMT provides a complete corrosion-resistant steel system for marine environments - marine corrosion-resistant bearing steel undergoes special surface treatment to resist the erosion of seawater and salt fog； fully stainless steel materials (316/316L) are suitable for highly corrosive marine environments， and the passivation film can self-repair， effectively isolating the erosion of salt fog and seawater. The excellent moisture-proof, corrosion-proof, and impact-resistant properties can withstand the high salt fog and high humidity corrosion environment of the ocean. Combined with marine-grade anti-corrosion coatings and sealing systems, the bearing can operate stably for a long time under harsh marine conditions.

 

▸ No-dismantling shaft installation： Dock replacement of shafts， no docking， no shaft extraction， no propeller disassembly

 

The core value of NMT's marine split bearings lies in - replacing the bearing does not require docking， no shaft extraction， no propeller disassembly. This means that the ship can complete the bearing replacement while berthed at the dock， in the anchorage， or floating. Maintenance personnel only need to open the bearing housing， remove the half ring of the old bearing， install the half ring of the new bearing， lock the bolts， and complete the replacement. Throughout the process， the propeller does not move， the shaft system does not move， the rudder blade does not move， and the coupling does not move. Compared to traditional solutions， the split bearings can reduce the installation downtime by up to 90%. Ships do not need to wait for a docking period， do not have to pay huge docking fees， and do not have to endure long-term downtime losses. For ships sailing in harsh sea conditions， this "no-docking bearing replacement" capability means that key maintenance can be completed at sea， avoiding the passive situation of having to find a dock nearby.

 

▸ Interchangeable with standard marine integral bearings： Seamless replacement， no modification required

 

The design of NMT's marine split bearings fully considers the interchangeability with standard marine integral bearings. In most cases， the outer diameter and the width of the outer ring of the split bearings are exactly the same as those of standard self-aligning roller bearings (222， 230， 231， 239， 240， 241 series). This means that shipowners can directly replace the existing integral bearings in the ship equipment with NMT's marine split bearings without any mechanical processing of the bearing housing.

 

III. Compatibility with a full range of marine split bearing types

NMT provides a split bearing product system covering various marine and offshore engineering conditions：

 

▸ Marine split cylindrical roller bearings

 

They use corrosion-resistant steel cylindrical rollers to bear high radial loads. The inner ring， outer ring， and the retaining ring with one or two rows of cylindrical rollers are all split into two halves. The outer ring can have a flange to withstand limited axial thrust， providing "fixed end" and "floating end" configurations. They are suitable for intermediate bearings of the propulsion shaft system， stern shaft tube bearings， deck conveyors， winches， etc.， for heavy-duty radial applications.

 

▸ Marine split self-aligning roller bearings

 

Designed for the shaft system of ships to withstand shaft deflection and skew caused by hull deformation， temperature gradients， and wave impact during navigation. The inner ring， outer ring， and the retaining ring with rollers are all split into two halves. The self-aligning performance is the same as that of integral self-aligning roller bearings， effectively compensating for shaft deflection and installation errors. They are suitable for stern bearings of the propulsion shaft system， intermediate bearings， rudder shaft bearings， marine platform lifting mechanisms， etc.， for heavy-duty impact conditions. The advantages of split tail bearings (with copper sleeves) and split tail tubes lie in that they do not require shaft extraction or disassembly in the shipyard， only the tail tube needs to be disassembled， the tail bearing pulled out， and then it can be smoothly inspected or replaced. The bearing housing is designed in a split form combined with spherical bushings， which can adapt to the bending deformation of the hull during navigation.

 

▸ Marine split conical roller bearings

 

Two rows of corrosion-resistant steel conical rollers can simultaneously bear radial and bidirectional axial loads. Designed specifically to handle combined loads and suitable for fixed-end bearing positions on shafts. It has unique advantages in difficult-to-reach applications. It is specially designed for applications such as ship propulsion systems, rudder shafts, Z-type propellers, and water jet propulsion devices. It can also be used for winches, deck cranes, anchor gear, and other deck machinery.

 

▸ Marine Split-Type Swivel Bearing

 

Designed for large rotating equipment such as marine platform cranes and ship cranes. The split structure enables the large swivel bearings to be installed and replaced on-site without the need to dismantle the upper structure or the boom. Suitable for offshore wind installation platform cranes, marine engineering ship deck cranes, port equipment, etc.

 

IV. Special Seals and Anti-corrosion Systems - Adapted to high salt spray, high humidity, and seawater erosion environments

Marine and offshore engineering equipment is constantly exposed to harsh environments of high salt spray, high humidity, and seawater erosion. The NMT marine split-type bearings are paired with exclusive seals and anti-corrosion systems:

 

▸ Marine-grade labyrinth seal structure - Non-contact design, using rotational centrifugal force to expel seawater, salt spray, and impurities, avoiding failure caused by wear of the sealing components. The patented triple labyrinth extended seal can effectively extend the service life of the worn shaft.

 

▸ Water-lubricated seal upgrade - For special applications such as water-lubricated stern bearings, NMT provides customized water-lubricated seal solutions, suitable for seawater or freshwater lubrication environments, ensuring the bearings operate stably in water media.

 

▸ Corrosion-resistant seal materials - Using FKM or special rubber materials resistant to seawater, salt spray, and marine organisms.

 

▸ Split-type seal components - The seal components also adopt a split structure, allowing for assembly without threading the shaft, completing the assembly synchronously with the bearing.

 

▸ Marine-grade anti-corrosion coating - External components such as bearing seats and locking rings are treated with marine-grade anti-corrosion coatings to resist high salt spray corrosion environments.

 

V. Installation and Maintenance - Efficiency Revolution from "Weeks in Dry Dock" to "Hours at the Wharf"

Installation time comparison:

 

Traditional marine integral bearings: Ship enters dry dock (2-3 days) → Drain the seawater in the dock → Remove the propeller → Remove the shaft system → Remove the coupling → Replace the bearings → Reinstall the shaft system → Reinstall the propeller → Re-centering → Departure from the dock. The typical duration is 2-4 weeks.

 

NMT marine split-type bearings: Ship is moored at the dock or anchorage → Open the bearing seat → Remove the old half-ring → Install the new half-ring → Tighten the bolts → Completion. The typical duration is only a few hours to 1 day.

 

Marine split-type bearings can reduce the downtime for bearing replacement by 80-90%. Taking the replacement of the stern bearing of the large ship propulsion shaft system as an example: Traditional integral bearings replacement requires 2-4 weeks in dry dock, with rental losses amounting to tens of millions of yuan; with the NMT marine split-type bearing solution, the replacement can be completed at the dock in 1-2 days, saving tens of millions of operational costs each time.

 

Maintenance convenience:

 

No dry-docking replacement - Cranes can be replaced at the dock or anchorage without entering the dry dock, without draining the shaft, without removing the propeller.

 

Can be inspected at any time - The bearing seat can be opened without disassembling the machine to check the operating condition of the bearing.

 

Split transportation - The bearings can be disassembled into smaller components, simplifying the lifting and transportation tasks, especially suitable for narrow engine rooms and steering gear compartments.

 

No on-site adjustment - The clearance is preset at the factory, no on-site adjustment or special installation tools are required.

 

Sensor reserved interface - The bearing seat is reserved for temperature and vibration sensor installation holes, facilitating condition monitoring.

 

VI. Quality Control - Triple Guarantee of Ship Split Precision, Corrosion Resistance Performance and Reliability

NMT implements a strict quality control system for marine split-type bearings:

 

Marine material certification - Each batch of bearing steel undergoes ship-grade material testing and corrosion resistance verification, meeting the requirements of marine standards. Finishing of the split surfaces - The inner and outer ring split surfaces are precisely machined using high-precision wire-cutting technology to ensure the concentricity and strength after the split surfaces are mated.

 

High-strength stainless steel locking system - The stainless steel locking ring and multi-bolt design ensure the stability and non-loosening of the split surfaces during operation.

 

Preparation for classification society certification - NMT marine split bearings can provide complete material reports, inspection reports and certification documents, supporting the requirements of classification societies such as CCS, DNV, and ABS.

 

Post-assembly precision inspection - Each set of split bearings is inspected for radial clearance, rotational accuracy and vibration values after assembly to ensure consistency with the performance of the integral bearings.

 

Seven, Stock Availability + Non-standard Customization - Quick response to ship emergency needs

Common marine split bearing models (marine split cylindrical roller bearings, marine split self-aligning roller bearings, marine split conical roller bearings) are in stock - covering 80% of the marine split bearing requirements in industries such as merchant ships, military ships, offshore vessels, and fishing vessels. Quick response to emergency failures, minimizing the downtime of ships.

 

Customizable projects - Special inner and outer diameters/widths (standard range 55mm to 630mm, expandable), customized marine materials (corrosion-resistant steel/316 stainless steel), special split structures, customized sealing solutions (marine labyrinth/ water lubrication/contact type), special clearance, classification society certification support.

 

Customization based on old bearings or drawings - Provide old bearing samples or equipment drawings, and NMT can quickly complete mapping and customized production. Affordable replacement of imported brands (SKF Cooper, Bowman, Timken), significantly reducing procurement costs.

 

Eight, Full Lifecycle Cost Optimization - No docking without shaft removal, saving millions of shipboard hours

Unplanned ship downtime of one day not only results in losses of ship rental but also involves cargo delays, ship schedule breaches, and customer losses, etc. As an example, for a large bulk carrier or container ship, the single-day downtime loss can reach several hundred thousand to several hundred million yuan, and a 2-4 week downtime means several hundred million to several billion yuan in operational losses.

 

Implicit costs of low-priced ordinary marine integral bearings:

 

Replacing once requires 2-4 weeks of docking, and the downtime loss is hundreds to thousands of times the cost of the bearing.

 

High docking costs (dockage fees, crane equipment rental, labor costs).

 

Axle damage during the process of removing the shaft and propeller, with extremely high repair costs.

 

Possible damage to the sealing device during disassembly, leading to subsequent oil leakage or water ingress problems.

 

Unable to operate at sea, if a failure occurs in the open sea, forced search for a dock is more costly.

 

NMT marine split bearings achieve "no docking without shaft removal, no shipboard downtime" in propulsion shaft systems, rudder shaft systems, deck machinery, and offshore platforms:

 

Downtime is reduced by 80-90% - from weekly to hourly/day, significantly reducing annual downtime losses.

 

No need for docking for replacement - mooring at the dock or anchorage can complete the replacement, saving huge docking costs.

 

No need to remove the shaft and propeller - the propeller and shaft system remain stationary, avoiding secondary damage during disassembly.

 

Corrosion-resistant material for long-term resistance to marine erosion - resisting salt fog, seawater, and high humidity environments, extending service life.

 

Extended lifespan of equipment (propellers, shaft systems, rudder blades) - reducing disassembly times, extending the major overhaul cycle of the entire ship.

 

For shipowners, ship management companies, naval vessel units, offshore operators, port enterprises, and fishing fleets, the comprehensive holding cost of NMT marine split bearings is far lower than the docking and disassembly costs of traditional marine integral bearings - what is saved is not the bearing price difference, but the huge operational risks and operational certainty of "one docking, one shipboard shutdown".