Stern gear and underwater fittings

The parts of the boat that you rarely get to see include some of its most vulnerable points, and because they are below the waterline, any failure can have catastrophic effects. You might not be able to see the outside of a skin fitting, but you can usually check its integrity from the inside. Any sign of a leak, either from the skin fitting itself or from the seacock, should be dealt with immediately.

  • For shaft-engined boats, the other significant point of vulnerability is the stern gear. The stern tube is moulded into the hull, with the propeller shaft rotating inside it, and the gap between the two is sealed with either a cutless bearing or a stern gland packed with grease. If the latter, the packing needs to be topped up from time to time, whenever there is any sign of seepage.
  • All underwater metal fittings are at risk from galvanic corrosion. Ignore this at your peril! There are essentially two points to watch out for: one, that all fittings are connected to an internal bonding system; and two, that enough sacrificial anodes are fitted. Check the state of the bonding wires – that the anodes are zinc for salt water and magnesium for fresh water. As the boat moves into higher concentration they should be swapped accordingly (i.e. when salt water exceeds 50%, change to zinc).


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Sterngear and underwater fittings