evaluating of an old aluminium boat

Discussion in 'Materials' started by urisvan, Sep 28, 2022.

  1. urisvan
    Joined: Nov 2005
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    urisvan Senior Member

    hi guys ,

    I will just start to work on an aluminium boat as captain. the boat is a "maxi class" boat.
    normally when i start a job as captain i try to survey the boat (hull, engine,rigging, electric system, plumping etc)

    but i dont have experience about aluminium hulls. If you guys can tell me how to check the aluminıum hull, where to look, i will be very glad.

    I am sure there must be many details but at least some basics things, common flaws, some potentially problematic areas or some indications etc that can give an idea about the condition of the hull...

    of course, as a suspicous person, I worry about electrolisis and also i think maybe there is a corrosion at some local places so some pin holes can grow and can be enough to sink the boat!
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Which Maxi class yacht is this - is she a former Whitbread Race boat?
    Do you have any photos of her that you can post please?

    Is the boat currently out of the water, so that you can check the hull bottom? If so, check the condition of the zinc anodes and the paint system (in addition to the usual stuff like if there is any play in the propeller and rudder shafts).

    Check the bilges (if accessible) for any signs of corrosion such as pitting. Are the bilges painted, or not painted?
    Similarly check the condition of the transverse frames and longitudinal stiffeners, and the bulkheads where they are joined to the hull.

    Marine grade aluminium is an excellent material for boatbuilding, but you do have to be aware of the potential for corrosion - even a slow drip resulting in local salt accumulation on the ally plate can cause localized corrosion under the salt. Keep your bilges clean!
     
  3. kapnD
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    kapnD Senior Member

    “Old aluminum boat”
    There’s certainly cause for concern re corrosion, it’s inevitable, and most likely to flourish where it can’t be seen or treated.
    Proceed with caution Captain, you are responsible!
     
  4. urisvan
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    urisvan Senior Member

    Hi,
    unfortunately the boat is on the water, not on hard.
    it seems like a boat from late 70' or early 80's, fairly good made IOR boat.
    do they paint the bilge and interior side of the hull normally? as i know aluminium create a white layer and this will protect the material.

    so i think i will try to check all the hull as much as i can.
     

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  5. bajansailor
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    bajansailor Marine Surveyor

    Here is some more info about Nirvana -
    Days of Nirvana https://www.sailingworld.com/story/racing/days-of-nirvana/

    She certainly has an impeccable pedigree, designed by Dave Pedrick, and built by Palmer Johnson in 1982.
    Palmer Johnson do have a very good reputation for aluminium boatbuilding.

    She has a Facebook page - but I am guessing that was probably with her previous owners, as it has not been updated since 2020 -
    Log into Facebook https://www.facebook.com/profile.php?id=100062922866666

    And a thread on Sailing Anarchy 8 years ago, in typical anarchist fashion -
    IOR Maxi 'Nirvana' on Yachtworld https://forums.sailinganarchy.com/threads/ior-maxi-nirvana-on-yachtworld.161679/

    Re the bilges, I would think that generally they would be left unpainted, however they do then need to be inspected periodically (and ideally washed down with fresh water) to get rid of any evaporated salts (and any rubbish like copper coins).
     
  6. urisvan
    Joined: Nov 2005
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    urisvan Senior Member

    thank you Bajansailor,

    I checked the links you posted. there are very useful informations.

    I think the best thing i can do is to find a thickness gauge and check the thickness of all the hull...

    there is a myth saying that if you drop a copper coin or stainless steel screw in time, it will make a hole in your hull. I dont think it can be true unless thjere is an electrolyte at the enviroment to create galvanic corrision. right?

    regards
    Ulas
     
  7. gonzo
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    gonzo Senior Member

    Water in the bilge is the electrolyte. Salt water would be worse. Although is true that pure water does not conduct electricity, there is likely to always be some contaminants; even for rain water. Aluminum, copper and an electrolyte are not a myth, but a battery.
     
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  8. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    However testing the hull randomly with an ultrasound thickness gauge is probably not going to tell you if you have localised pitting corrosion, unless there is a lot of pitting, and the pits are deep, and the ultrasound beam actually encounters a deep pit.

    I think that your best bet initially would be a general visual inspection of the hull structure (where accessible) on the inside, and especially the bilges.
    If you see any areas of concern, please post some photos here on this thread.
     

  9. Flotation
    Joined: Jan 2020
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    Flotation Senior Member

    If' you are going to captain this vessel and want to know more about corrosion on aluminum boats, here's a good primer:

    Corrosion – Mayhem for an Aluminum Boat https://www.fishalaskamagazine.com/corrosion-mayhem-for-an-aluminum-boat/

    I'd pay special attention to the "Electrolysis and Stray Current – Hot Boat and Moorages" part, some relevant pieces from this section:

    "For moored vessels, a galvanic isolator is a device installed in series with the AC grounding conductor of the shore power cable to block low-voltage DC galvanic current flow but permit the passage of alternating current (AC) normally associated with the AC grounding conductor. This device helps combat corrosion caused by electrolysis and stray current found in moorages."

    "The best protection from a boat’s stray current is a well-maintained bonding system that meets ABYC standards. Unfortunately, these systems tend to get overlooked when it comes to maintenance and haphazard accessory installations. The purpose of bonding (different than grounding) is to equalize the electric potential of dissimilar underwater metals by tying them all together with wire. The benefits of a bonding system are to dissipate stray current leaks. Twelve volts of current focused on a small piece of metal will result in rapid destruction, whereas the same 12 volts spread over a much larger surface causes less damage in proportion to the size of the water-exposed surface of metal."

    I'd also get a copy of this book:

    https://www.amazon.com/Metal-Corrosion-Boats-Nigel-Warren/dp/1574090542

    Edit, newer edition of the same book:

    https://www.amazon.com/Metal-Corros...p-0713678178/dp/0713678178/ref=dp_ob_title_bk
     
    Last edited: Sep 29, 2022
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