As a surveyor there are many common writeups when inspecting a vessel's propeller shaft seals, but today I want to talk about one specific component of one specific but very common type of shaft seal.
Tides Marine 'SureSeal' Shaft Seals are quite common on pleasure craft and many sport yachts, and are quite easily one of the most common shaft seal types we come across. They utilize a lip seal riding on the shaft's surface to form a 'dripless' water seal. Most leakage starts from corrosion that develops on the shaft at the lip's contact area. Water leakage from the lip seal is typically quite obvious and easy to identify.
Less commonly identified, but even more prevalent, is corrosion and sea water leakage at the shaft seal's water injection fittings. These threaded/hose-barb connection fittings are commonly constructed of stainless steel, and since they have engine-warmed seawater continuously flowing through while underway, they are prone to corrode at a rapid pace.
Since these fittings are often tucked just behind the face of the shaft seal, the corrosion or common leakage stains below these fittings can often be overlooked. Failure of one of these fittings could be just as troublesome as a failed seal if the operator doesn't carry the tools to remedy on hand, which is why I always recommend that a few spare fittings be kept onboard. Even better, an early catch of this corrosion by a surveyor or attentive operator could prevent failure altogether!
Here's an example of a 'Quick Insert Option' phrase that I commonly use when I come across this finding. I have this phrase saved under 'Propeller Shaft Seals' - feel free to copy/paste this phrase into your version of InspectX and adjust to your liking.
Both of the dripless shaft seal cooling & crossover hose's stainless steel water injection fittings were corroded, indicating prior leakage (or possible current leakage over a more extended period of time). Trace any leakage and service or replace the fittings, as necessary. These fittings should be routinely monitored for porosity corrosion leakage.