Stern tube seals are a critical component in a ships propulsion system, sealing the shafts penetration through the hull. Stern tube seals can result in a significant maintenance burden when they are unable to handle the operational conditions of the vessel. Current systems are also lacking a capability to be able to operate through a primary seal failure, something that should be critical to the United States Navy. The United States Navy's Independence-class littoral combat ship (LCS) has challenging operational conditions including the need to survive shock loads, high shaft speed and significant galvanic corrosion potential. Through a five-year effort Midé developed a stern tube seal for LCS that could handle the challenging operational conditions and provide the Navy with new critical capabilities such as the ability to operate propulsion systems through a primary seal failure without the use of packing and to extend maintenance windows to reduce vessel downtime and associated cost. This paper will present the limitations and challenges of existing stern tube seals, followed by the design improvements that have been developed to improve performance and reliability while also reducing the total ownership cost for vessel owners and operators.

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