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oak and ferrous metals

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  • oak and ferrous metals

    Users swear by the strength of oak but beware! American white oak is non durable, fine for interiors or furniture but that is all. European, English or green oak are strong but may be subject to movement or shakes. A greater problem I found is that over time oak and steel or iron are not compatible. What looks like a bit of rot around a seemingly reasonable bolt reveals itself to be a major problem, The steel bolt has reduced to hairpin thickness where in contact with the oak and the oak has rotted to such an extent that you can knock out the bad and put your fist through the hole. An old blacksmith advised the following if combining oak with ferrous metals. Heat a rod to red hot, put inside the drilled hole in the oak to char the wood. This should prevent the tannic acid in the wood corroding the metal so violently You can choose to use an alternative wood or stainless steel (which actually can still rust, depending on the grade). Any other users found this problem?

  • #2
    One of my mates owned several wooden boats over many years. He did all the maintenance and some of the restoration himself - he comments:


    "Yes, I have heard of this and oak certainly turns black over time in way of iron. However on our old 1930s boat we never encountered any problems with the oak wooden floors. I am nearly sure that the wood keel was oak and she had an iron ballast keel with iron keel bolts through the wood keel and the floors. Doubtless there would be some good old fashioned sealer between the two faces...

    What I believe is a very much bigger problem is the reaction between mahogany and iron. Mc Gruers
    (high quality Scottish boat builders on the Clyde, now defunct) built many boats with galvanised iron strap floors and almost all of them ended up with either wooden "diamonds" in way of the fastenings or some new bottom planking. That problem did not occur with either teak, larch or pitch pine bottom planking.

    Interesting that "Twister of Mersea" had a pitch pine bottom and the planking was perfect, but the bottom of the frames which were oak, I think, showed signs of degradation when we took out the strap iron floors for re galvanising. They were fastened to the frames with galvanised bolts.

    Frames are almost always fastened with either bronze screws and/or copper rivets or more unusually and cheaper with copper clenches i.e. No roves, just the end bent over and battered with a hammer!

    I notice in quite a lot of wooden boat adverts state that the iron floors have been totally replaced with bronze ones using bronze bolts. Apart from no degradation of the timber, the bilges will never show rust when bronze is used."


    The enclosed shot shows Twister of Mersea winning the Scottish Series in 1993 - a blast from the past - yours truly trimming the spinnaker
    Attached Files
    Last edited by Mike Lunch; 05-05-17, 05:28 PM.

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    • #3
      Quite understand your point about Oak and Steel Stephen. There are of course some occasions when that is useful. In model railways, cast chairs are often pinned to wooden (sometimes Oak) sleepers and brass pins work their way out, whereas steel ones stay put because they rust in. I guess the pins we use to fix mouldings to wooden carriages never go in as far as the Oak framing, so the issue doesn't arise there, but I have seen carriages where these pins have worked loose and broken the surface.
      Mike

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      • Stephen Middleton
        Stephen Middleton commented
        Editing a comment
        I like that, turning a problem in to an attribute!

    • #4
      I just spotted a most interesting article on Classic Boat Magazine's website about the restoration of Sir Robin Knox Johnson's yacht Suhali. The article describes in detail the problems of iron fastenings interacting with the timber of the planking and the problems of replacing these iron fastenings with bronze.
      The article is enclosed as a pdf file and also a link to it on Classic Boat Magazine's web site...
      Attached Files
      Sir Robin and friends set about bringing Suhaili to sailing condition three years ago. This is their story After one solo circumnavigation, two transatlantic crossings, a voyage to Iceland and five years drying out in the clinically clean air of the National Maritime Museum in Greenwich, Sir Robin Knox-Johnston’s Suhaili was in need of restoration. …

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      • #5
        Fascinating article, amazing that the wood stood up to the vigorous bolt removal techniques.

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