DIY dripless shaft seal

When I decided to give my homebuilt motorboat, Tudor Rose, a dripless shaft seal I could find no proprietary units that were suitable. I needed something to fit her stern tube, fit within the narrow moulded keel slot, fit the imperial shaft size, and not need burping after every low tide as she lives on a drying mooring.

Heaving a sigh of exasperation, I knuckled down to design and build a bespoke dripless seal. It’s essentially a simple device and not really difficult to build if you tackle the job with determination and forethought.

A question of design

I based my design on the setup in a little aluminium speedboat I once owned. It uses carefully specified lip seals in a tubular housing secured to the inboard end of the stern tube by