A Revolutionary Ship Design


Sterntube-less Ship with Thordon COMPAC

On June 9, 2022, classification society ABS granted Approval in Principle (AIP) to Shanghai Merchant Ship Design and Research Institute (SDARI) for the “sterntube-less ship” concept developed in cooperation with, the National Technical University of Athens (NTUA) and Thordon Bearings Inc.

This revolutionary design replaces a vessel’s sterntube with an irregular shaped chamber that allows for a shorter propeller shaft with a seawater lubricated single bearing and seal that can be inspected and maintained while the vessel is afloat, without ever having to withdraw the shaft in drydock.

Compared to a traditional sealed oil-lubricated shaftline, the sterntube-less ship concept removes the sterntube casting, reduces the shaft line length, moves the engine aft, and increases the cargo space in most ships.

This new design can better support simplified compliance with environmental-focused regulations, such as the Energy Efficiency Design Index (EEDI), and can enable more efficient use of the engine’s propulsive power, since the whole RPM range of speeds is available for continuous operation. And it completely eliminates the need for an oil-lubricated shaft line – a major source of marine pollution – the design can save shipowners hundreds of thousands of dollars in capital and operational expenditure over a vessel’s lifespan.

Key Ship Owner Benefits

More Cargo Carrying Capacity (Engine Moved Aft)

  • The design of the stern and the ship does not change, but by moving the engine further aft, more cargo space is created.

Improved EEDI

  • Shortening the shaftline and bringing the engine aft wards, minimizes engine room space and maximizes cargo space.
  • The lack of BSR (Barred Speed Range) is estimated to reduce emissions and fuel consumption only for those vessels that frequently pass through BSR, based on their operating profile and where a Torsional Vibration Damper has been installed.

No Shaft Withdrawal Needed for Bearings and Seals

  • Propeller shaft never needs to be withdrawn for bearing and seal inspection or maintenance. An open seawater lubricated propeller shaft, bearing, liner and seal can to be inspected and maintained while the vessel is afloat, without having to withdraw the shaft in drydock.

If oil-lubricated bearings require replacement, shaft withdrawal is necessary.

  • Class Societies consider a seawater lubricated propeller shaft bearing system to be technically equivalent to an oil-lubricated system. Based on monitoring criteria, shaft withdrawal periods for seawater lubricated systems can now be extended similar to oil-lubricated systems.

Lower Operating Expenses

  • Elimination of Environmentally Acceptable Lubricants (EALs) or oil propeller shaft lubricant as shaft lubricated with FREE seawater and there is no aft seal nor seal maintenance.

Zero Pollution

  • Lubricant is seawater (no oil is used) and is future compliant with all global regulations.

The Sterntube-less Ship System


COMPAC AFT Bearing with Tapered Keyset

Non-metallic homogeneous elastomeric polymer alloy COMPAC bearing is at the heart of the award-winning seawater lubricated propeller shaft bearing system. The COMPAC bearing has no grooves on the lower half of the bearing to promote early formation of a hydrodynamic film between shaft and bearing, comparable to oil. Given the unique elastomeric nature of Thordon COMPAC bearings, this concept is more tolerant to shaft misalignment with go home capability.

The COMPAC bearing is supplied split with a tapered keyset that allows bearing to be withdrawn inboard, inspected and re-installed in a matter of hours with the shaft in place.


Thordon BCM System

The Thordon Bearing Condition Monitoring System allows bearing wear measurements from inside the ship by pushing a button, supporting the Classification Societies’ bearing clearance requirements.


Thordon BlueWater Seal

An axial lip seal with Safe Return to Port (SRTP) capability that will deliver reliable performance and value to the shipowner with the low friction RENFORM main sealing ring.


Thordon Water Quality Package

A Thordon Water Quality Package delivers a consistent supply of conditioned water to the seal and bearing to ensure long predictable bearing wear life.

Today, a Sterntube-less Ship with a Thordon COMPAC propeller shaft bearing system offers considerable advantages to shipowners and shipbuilders, offering easy monitoring and maintenance of bearing and seal condition without shaft withdrawal, lower operational expenses, de-carbonization of the ship and elimination of oil emissions forever.

Contact Thordon for more information on Thordon products.

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