ABS AIP for "Sterntube-less" Ship

Thordon Bearings said ABS issued an Approval in Principle to the “sterntube-less ship” concept developed in cooperation with the Shanghai Merchant Ship Design & Research Institute (SDARI), the National Technical University of Athens (NTUA) and Thordon Bearings Inc.

The design replaces a vessel’s sterntube with an irregular shaped chamber that allows a shorter, water-lubricated propeller shaft to be inspected and maintained while the vessel is afloat, without having to withdraw the shaft in drydock.
While the concept completely eliminates the need for oil-lubricated sterntube seals and bearings.

Anthony Hamilton, Technical Director, Thordon Bearings, said the concept revolutionizes the ships’ traditional sealed propeller shaft. “We started wondering why a vessel with a water-lubricated shaftline needs a sterntube. Why couldn’t the shaft simply run in the larger space outside the sterntube? This space is designed into virtually all vessels where an oil-lubricated sterntube is traditionally exposed to seawater for cooling. With a water-lubricated shaft this space still exists but it’s wasted space.”

Hamilton said the space could be used to access the shaft for inspections, and a lot of the shaft installation and operational challenges “completely disappear”.

A sterntube-less ship features a shorter shaft with the prime mover further aft the vessel. An additional bulkhead seal and a torsional vibration damper would be required but there is no aft seal and Thordon’s COMPAC seawater lubricated bearing replaces the oil-lubricated bearing aft.

“ABS and the Technical University of Athens have done the math and the engineering behind it. They’ve looked at system pressures, temperatures, loads, noise and vibration levels, shaft alignment – everything works,” said Hamilton.