Stern tube seals, mounted between the propeller and the stern tube, are vulnerable to damage due to the hazards present in the subsea environment. Operating with a damaged seal risks environmental pollution and failure of the stern tube bearings, either of which can result in a vessel being unable to sail, costing the owner time and money.
Failure may occur when a stern tube seal is compromised by a foreign object such as fishing line or by environmental abrasion. When this happens, the seal must be repaired or replaced before the ship can sail again. Such incidents often occur when the vessel is far from its home maintenance port.
When damage occurs, a ship operator needs a seals and bearings partner who can manage and fix their problem quickly. A partner with expert supply chain management can offer shorter lead times for stern tube seal repair or replacement. In other words, the partner is able to engineer a seal for the customer’s need; then manufacture, deliver and install it – all within a few days’ notice, around the world.
Stern tube seals can even be repaired underwater, which is sometimes a smart alternative to dry-docking an offshore vessel, which can cost tens of thousands of dollars per day. Underwater servicing means that a team of diving engineers conduct the repair either in open water or in a de-watered hyperbaric chamber. Working in the hyperbaric chamber resembles working conditions in a normal dry dock. The vessel needs only to be secured at a location where sea conditions allow for safe underwater repair.
According to Wärtsilä, its seal engineers react within minutes when a customer reports a problem. Chris Rowlands, Director, Wärtsilä Seals & Bearings PC Sweden, commented, “We design a seal that suits the customer’s vessel by using 3D parametric CAD tools to reduce the risk of error. Next, the main components are cast by our in-house foundry and machined using our state-of-the-art CNC machine tools. Finally, the finished seal is assembled and tested. In most cases, this stage is performed by the engineers who will actually install the seal on the customer’s vessel, helping to ensure the highest quality.”
Wärtsilä Sternguard SeaQual seals are designed for long life running in demanding operating conditions, the manufacturer said. They are fully-split, meaning that they can be fitted without costly and time-consuming propeller shaft withdrawal. Additionally, Wärtsilä Sternguard SeaQual seals are shorter in length than other seals, meaning that they can be easily retrofitted.