space normally given to the sterntube. This new space, big enough for engineers to stand up in to maintain or replace propeller shaft components while the ship is afloat, has been created by trimming stiffeners and cutting an opening into the bulkhead.
“This is a very a big advantage because you don’t have to drydock the ship and withdraw the shaft or propeller to monitor and maintain seawater-lubricated bearings and seals. We can now do this from inside the ship while the vessel is operational,” said Mr Leontopoulos.
The sterntubeless ship, he said, also negates the need to realign the shaft throughout the vessel’s lifetime, mitigating the risk of shaft damage or indentation, which can result in substantial downtime and expenditure.
Going on to reveal the cost benefits of a sterntubeless ship, Mr Leontopoulos acknowledged that although the estimated CAPEX for additional components could add about US$10,000 to $30,000 to the cost of a newbuild depending on shaft diameter, the ROI is quick given the reduced operational expenditure. This is where the real financial gain is to be made. He told conference delegates that aside from immediate savings of US$350,000 in lubricating oil, operators could save more than US$1 million in through-life operational costs. This is based on reduced fuel consumption, reduced drydocking and maintenance costs, and associated loss of earnings; shaft alignment optimization, lower bearing wear rates, better EEDI; and an increase in cargo carrying capacity. The arrangement also reduces to zero the risk of environmental fines related to sterntube oil pollution.
Summing up he said, “There’s no pollution risk, no oil changes, and no need to drydock to change the bearing. A shorter shaft line and smaller engine room space increases cargo space and improves EEDI ratings; there is no barred speed range and no fatigue concerns. It complies completely with all existing class rules.”
On that latter point, ABS has now published a Requirements for Sterntubeless Vessels with Water- Lubricated Bearings guide, bringing together in one document all existing applicable rules for the design. ABS is also introducing a new notation for the sterntubeless ship design, for which the classification society awarded an AiP in June 2022.
Neil McDonald, Thordon Bearings’ Regional Manager – Northern Europe & Africa, said, “The sterntubeless ship design proposed by the Blue Ocean Alliance is truly a milestone development for the global shipping industry. This part of the ship hasn’t changed since the advent of steam propulsion.
“Simply by remodelling the sterntube space and replacing an oil-lubricated bearing system with one lubricated by water, newbuild ships can be substantially more environmentally and operationally sustainable, without the need for new class rules and notations. It is significant design intervention.”
Chris Leontopoulos believes the first sterntubeless ship with a Thordon seawater-lubricated propeller shaft bearing system, probably based on a SDARI design, will be ordered within the next twelve months.
The ABS guidelines for a sterntubeless ship can be downloaded in PDF format at
https://bit.ly/4chk1KY.
THE REPORT | SEP 2024 | ISSUE 109 | 109
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