Design economies can lead to shaftline failures

Paul Gunton
Paul Gunton
ShipInsight

16 August 2019


Cost-cutting by shipowners and yards is leading to sterntube bearing failures, according to Simon Wiles, operations manager of Wärtsilä Seals and Bearings’ Shaft Line Repair Services.

Speaking to ShipInsight in an exclusive interview, he said that companies often reduce newbuilding costs by reviewing their shaft line design. “We’ve seen an increase in sterntubes with single bearings [and] seen increased failures of those bearings,” he said. This trend is also reflected in actions that have been taken by many classification societies, which have been updating their rules for single sterntube bearing arrangements, he added.

Operational factors also have an impact on bearing wear, with one common cause of bearing failure arising from ships sailing at a light draught with part of their propeller out of the water. “This changes the dynamics and the balance of the loads across the shaft line and that can often cause bearing failure,” he said.

These causes are contributing to an increase in stern tube bearing failures and were “a primary reason” for Wärtsilä Seals and Bearings launching its Shaft Line Repair Services last November. Now, with Mr Wiles recently appointed as its head of Operations, the department is expanding, including by hiring dedicated field service engineers worldwide.

They will work with Wärtsilä’s existing global network of service engineers and other centres of expertise within Wärtsilä Seals and Bearings to project-manage its response to bearing failures and other shaft line incidents. Those could include sudden damage caused by groundings, collisions or other major incidents.

Asked whether most of the incidents it deals with are unexpected, he said that the service is tailored to provide support for urgent needs but also offers preventative maintenance advice by, for example, providing diagnostic equipment and tools that can help shipowners avoid future problems. Shaft alignment errors, even those that cause just a noisy bearing, can turn into a major issue over time, he said.

To avoid these problems, he had some simple advice for chief engineers: “follow all the routine maintenance procedures, ensure that you are doing your oil sampling properly and that you’re operating within the parameters set according to the design and the operational profile of the vessel.”

To help engineers and superintendents check for potential problems, the company can provide its portable condition-based monitoring (PCBM) system that an owner can install for a typical sailing that covers all operating conditions. With sensors providing data, a subsequent analysis can reveal how the shaft is moving more accurately than by traditional methods, Mr Wiles said.

Shaft line problems can emerge when a vessel’s operating conditions change, he said, such as a different loading arrangement or a new operating profile, which can alter the load distribution along the shaft line. A change in lubricant can also have an effect: bearing problems are often associated with a switch to environmentally-acceptable lubes, he said.

Less obvious causes might include changes in the dimensions of the ship’s hull or in the engine room’s machinery foundations. “We can’t plan for everything,” he said, but “what we are doing is looking at how to organise ourselves to better support our customers when they experience these issues.”