history

Ever since propellers were fist fitted to vessels, the seal around the shaft preventing (or rather restricting) the ingress of water has been a critical part of the vessel.  Failure of the seal was likely to prevent further trading until repairs were carried out.   Until the 1950s most vessels had water lubricated sterntubes with the shaft running in Lignum Vitae bearings.  On the inboard side there was often just a simple stuffing gland.  If this was tightened too much it would overheat, and if it was not tightened enough, water leaked past the gland. These glands often required  attention and the Lignum Vitae bearing needed to be changed on a regular basis.  The invention of oil filled sterntubes with the shaft running in plain white metal bearings and with two lip type seals one either side of the sterntube revolutionised ships’ maintenance schedules.  Over the years survey periods have been extended from five  years to ten years for most deep sea vessels.

Since 1948 when the first SIMPLEX seal was introduced to the market, there has been a steady progression in design and materials. The original seal, the SSS, was superseded in 1970 by the Simplex Compact seal, now known as the SC1, and this seal was replaced on 1992 by the SC2.  With each new design, technical improvements were incorporated into the  sealing ring design, to reduce wear on the liners and to make in situ maintenance easier.  Materials, both for the rings and the liners, have been improved, and special new designs have been developed for new applications such as pods. Nevertheless the basic modular design philosophy has been retained making it possible to offer all parts from stock with very short delivery times.

In recent years there has been a clear trend towards environmentally friendly designs using an airspace between the water and oil seals on the outboard seal.  Such designs enable any leakage to be brought back inside the vessel and so prevent  any pollution of the sea in normal operation.