Eliminating the traditional sterntube could reduce construction costs, create additional space on board and remove a major source of oil pollution risk according to Thordon Bearings. But while shipowners see the benefits, few want to be the first to adopt a new approach to the shaftline.
In this episode, Janne Silden speaks with Craig Carter, VP Business Development at Thordon Bearings, about T-BOSS®, the company’s sterntubeless shaftline concept and the challenges of introducing a different approach to a traditionally conservative part of ship design.
T-BOSS eliminates the traditional sterntube and uses a seawater-lubricated bearing. According to Carter, interest among shipowners is strong, particularly because the concept removes the risk of oil leaking from the sterntube into the sea. The main obstacle is not whether owners see the potential, but their reluctance to be the first to put the new design into operation.
One question is whether such a change comes at an additional cost. Thordon commissioned Hydrus Engineering to examine the capital expenditure implications for a 157,000-dwt Suezmax tanker. The study compared a conventional oil-lubricated arrangement with the sterntubeless concept and concluded that the T-BOSS design could actually reduce the vessel’s build cost. Carter also points out that the required changes at the naval architecture stage are relatively limited.
Removing the sterntube has implications beyond the shaftline itself. A shorter propeller shaft allows the main engine to be moved further aft, potentially creating additional engine-room space for equipment such as a shaft generator or freeing up more space for cargo without increasing the overall length of the vessel.
Maintenance and inspection are another part of the argument. With T-BOSS, seals can be accessed from a dry chamber inside the vessel and the bearing can be inspected internally. This means shaftline inspection and maintenance can be carried out without dry-docking the vessel, reducing both operational disruption and risk.
Yet introducing a new shaftline concept requires more than convincing shipowners. Shipyards, design companies and classification societies all play a role, and busy yards can be reluctant to change established designs, drawings and construction procedures. Thordon has therefore worked with partners including ABS, the National Technical University of Athens, Wärtsilä Shaft Line Solutions and SDARI on the development of the concept.
For Carter, getting the first vessels into operation will be a crucial step. Once shipowners and yards can see the concept working in practice, he believes the barriers to wider adoption could begin to fall.
As Carter puts it: “Everyone likes the concept and the idea and the benefits that come with a sterntubeless design. […] But the strongest point that I’ve heard from shipowners is that they say they don’t want to be first.”
