Gauge thickness for a 21 ft steel boat

Discussion in 'Metal Boat Building' started by flathead65, Jul 21, 2014.

  1. flathead65
    Joined: Apr 2014
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    flathead65 Jeff Thompson

    I'm sure if I searched long enough I could find some examples, but I will ask instead. What are the standard gauge thicknesses for a steel boat 21 ft loa?
    Bottom, sides, transom,decks, and cabins? I have only built in aluminum so I am in need of some guidance. Also if someone could suggest the best book about building small steel boats under 30 ft I would appreciate that as well. Thanks for your time.
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    There is no standard gauge. It depends on the shape and the framing. There are some designs for frameless boats that use a much thicker plating.
  3. pdwiley
    Joined: Jun 2008
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    pdwiley Senior Member

    There have, to my knowledge, been very few steel boats of that size built as the material is really too heavy.

    3mm is getting close to the practical lower limit for workability. 2.5mm is pretty hard to weld fair and has little margin for corrosion over time.

    I have a fairly extensive literature on small steel boats and I've never heard of one less than 25'. Mind you this is sailboats, I have no idea about power boats.

    At that length I'd stick to aluminium.

  4. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Classification society scantlings are what you need. You can buy ISO 12215-5 but I'd recommend Germanisher Lloyds aka GL there are links to the downloads under the heading "Class Societies"
  5. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    looks like 3mm is the minium, even for those Dutch steel workboats

    some good info here at

  6. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I can confirm that there were, and probably still are many hundreds of those small Dutch steel boats. However I would hesitate to call them work boats, most are recreational craft, from about 3.5 meters upwards, for rowing and sailing. In the 1970s' through to this side of the millenium I have seen loads of them on all types of Dutch waterways. Some were built in aluminium, but mainly the more serious offshore craft.
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