Since ship propulsion shifted from sails to propellers, preventing seawater from getting into the hull via the stern tube has been one of the most fundamental engineering challenges of designing and operating vessels. Without reliable sealing, even the simplest marine operation can become time consuming, costly and complex. Today there are new challenges to reliability, including greater forces at play and an environmental focus on preventing fluids from escaping the hull as well as getting in. But the stern tube seal remains a basic building block of safe and secure sailing.
Beyond the need for vessels to be seaworthy, the drivers of reliability differ depending on the nature of the operation. For commercial vessels, time is money. At a low level, unreliable seals can place an excessive burden on the vessel crew by increasing the demand for day-to-day maintenance and inspection, driving up manpower and maintenance costs. More serious reliability issues can result in reduced availability or failure to meet charter conditions alongside significant expense.
For naval vessels, availability for missions and the ability to complete missions is the overriding factor. A ship that unexpectedly has to return to dock for repairs can jeopardise the success of a mission. Likewise, with limited capacity spread across a wide theatre of operations, redeployment of vessels from other areas to cover essential missions can cause significant delay. Vessel systems that are robust, reliable and easy to maintain in the field are therefore critical.
With decades of experience in the design, servicing and integration of stern tube seals, bearings and shaftlines, Wärtsilä Shaft Line Solutions has extensive insight into the design and operational considerations that go towards maintaining maximal seal reliability.