A new pipe configuration
HMS Endurance had been experiencing oil leaks to sea and oil ingress to its sterntube lubricating system and Deep Sea Seals(DSS) were called in by the MoD to supply and install new outboard and inboard seals and all the necessary pipework to connect with the tanks for the inboard lubricating system. DSS fitted an AC/Mk2 Coastguard anti-pollution seal system which differed from the existing system and required substantially modified pipework. Previously, only a single barrier seal had been used which was fed by a gravity lubrication system. The new AC system needed to be pump fed.
The new pipe configuration necessitated through-hole access holes in the aft and forward prop shaft bearing bosses, and new drilled and tapped holes for the outboard AC seal. This work was contracted to the Metalock Engineering Group who, in addition, undertook responsibility for the new pipework(seal pipes) and necessary tanks installation.
For the outboard seal, Metalock drilled and tapped 24 new M20 tapped holes equispaced on a 710mm PCD. The new seal pipe arrangement had to pass through the 5940mm long sterntube itself and to provide pipe access, four 20mm diameter holes had to be drilled through the 1030mm of the aft bearing boss and four more through the 400mm of the forward bearing boss.
The holes were positioned 30º either side of top and botton dead centres on a 680mm PCD in the aft bearing boss and a 640mm PCD in the forward bearing boss. Additionally, a 32mm diameter though hole was drilled at bottom dead centre on similar PCDs in one boss inward end to accept a larger diameter pipe to drain oil from the sterntube.
Sterntube pipe connections
Connections from the sterntube pipe runs to the various lubrication oil tanks was achieved using a spigotlocated MK2 adaptor ring secured by 12 x M20 hex head screws. The system uses three tanks, one for the inboard seal, a main header tank and a void space header tank, all of which were fitted by the Metalock Engineering Group.
Commenting on the project a Deep Sea Seals spokesperson said that they were contracted to supply the entire system, including its fitting which was outside their expertise.
However, with the assistance of the Metalock Engineering Group who not only carried out the necessary machining but also installed the seal pipes and tanks, the task was successfully achieved. HMS Endurance is now back on station in the South Atlantic with its new antipollution seal system.