Aluminium boat galvanic corrosion - pitted bronze prop

Discussion in 'Metal Boat Building' started by Cruisingsailor, Jun 11, 2024.

  1. Cruisingsailor
    Joined: May 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Malaysia

    Cruisingsailor New Member

    Hi to all,

    Thinking of buying 1980's aluminium hulled yacht.

    Boat is on the hard, there are no anodes on the hull and no fixtures for anodes... Somewhere else on this forum I read from one poster in particular that anodes were not necessary on an aluminium hull? I would love to hear more about this theory or fact?

    I suppose in the case that the aluminium hull was fully isolated with multiple epoxy coatings there would be no possiblity of galvanic corrosion or electrolysis? But as soon as there was a scratch correct me if I am wrong the bare aluminium would get eaten in that area whether from galvanic corrosion (bronze prop for example) or from electrical leaks.

    Also the boat in question has no anodes on the shafts, the props are terribly pitted, this would seem a classic example of galvanic corrosion between prop and stainless shaft (see photo ).Could the pitting also be from electrolysis as the boat doesn't have a galvanic isolator or isolation transformer?

    It would then be crucial to check that the engine/shaft connection is insulated and that the engine is floating and not grounded to the hull ? Would that be correct otherwise there could be serious consequences for the hull?

    Any further thoughts on the pitting of the prop and whether under the coat of antifoul I may find thousands of small pits like on the prop?

    Inside of the boat is severely pitted in the bilges but seems fine above where bilge water sat... I am trying to determine if cutting and welding new plates will make a sturdy new boat or if this is a risky business with possibly thousands of further pits to be found on the hull under antifouling.

    Thank y0u in advance for any thoughts.
     

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