Results 1 to 5 of 5

Thread: Structural integrity of a boat hull

  1. #1
    Join Date
    Nov 2012
    Location
    Cambridge NZ
    Posts
    72

    Default Structural integrity of a boat hull

    Would it be fair to say that a completed (Plywood) boat hull is effectively a "stressed-skin-girder"? Can it support its own weight suspended at the transom and bow stem? In other words, is there any extra structure required in the hull of a boat like "Sealegs"? Just curious. Thanks. Norm.

  2. #2
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
    Posts
    35,259

    Default Re: Structural integrity of a boat hull

    When you consider that the hull will be bouncing about on waves, which may be supporting the bow and stern and the middle not so much, it should be OK.
    If you support it right at the bow and transom and bounce it about or drop it, it may well crack.

    It is a stressed skin girder and can be analysed as such to check the scantlings. As the bottom and lower sides are designed for wave slap and slamming they will probably be OK, but the deck might need to be stiffer to stop it from buckling.
    It really is quite difficult to build an ugly wooden boat.

    The power of the web: Anyone can post anything on the web
    The weakness of the web: Anyone can post anything on the web.

  3. #3
    Join Date
    Sep 2002
    Location
    Hamilton New Zealand
    Posts
    3,972

    Default Re: Structural integrity of a boat hull

    Quote Originally Posted by normil View Post
    Would it be fair to say that a completed (Plywood) boat hull is effectively a "stressed-skin-girder"? Can it support its own weight suspended at the transom and bow stem? In other words, is there any extra structure required in the hull of a boat like "Sealegs"? Just curious. Thanks. Norm.
    The Sealegs amphibious RIBs have considerable framing between the vee bottom and the cockpit sole, designed to carry the loads created when the boat is suspended between the bow whee and the two at the stern.

    Plywood boats are indeed stressed skin girders, I prefer to view them as a monocoque structure and design them to have reinforcement built in where the stress paths are, that reinforcement being frames, stringers, bulkheads, seat fronts and tops. Each one carrying the load out to the skin or preventing the skin from changing shape. Grab a shoe box and take the lid off, twist and flex it then tape the lid on securely and try that noting the difference. A good plywood boat, one intended for more than just lightweight use, may, ( there are other ways of doing this) in a structural sense be essentially a linked series of closed boxes.

    John Welsford
    An expert is but a beginner with experience.

  4. #4
    Join Date
    Nov 2012
    Location
    Cambridge NZ
    Posts
    72

    Default Re: Structural integrity of a boat hull

    Quote Originally Posted by Peerie Maa View Post
    When you consider that the hull will be bouncing about on waves, which may be supporting the bow and stern and the middle not so much, it should be OK.
    If you support it right at the bow and transom and bounce it about or drop it, it may well crack.

    It is a stressed skin girder and can be analysed as such to check the scantlings. As the bottom and lower sides are designed for wave slap and slamming they will probably be OK, but the deck might need to be stiffer to stop it from buckling.
    Thank you Nick. That's sort of what I was thinking.

    Cheers

    Norm

  5. #5
    Join Date
    Nov 2012
    Location
    Cambridge NZ
    Posts
    72

    Default Re: Structural integrity of a boat hull

    Quote Originally Posted by john welsford View Post
    The Sealegs amphibious RIBs have considerable framing between the vee bottom and the cockpit sole, designed to carry the loads created when the boat is suspended between the bow whee and the two at the stern.

    Plywood boats are indeed stressed skin girders, I prefer to view them as a monocoque structure and design them to have reinforcement built in where the stress paths are, that reinforcement being frames, stringers, bulkheads, seat fronts and tops. Each one carrying the load out to the skin or preventing the skin from changing shape. Grab a shoe box and take the lid off, twist and flex it then tape the lid on securely and try that noting the difference. A good plywood boat, one intended for more than just lightweight use, may, ( there are other ways of doing this) in a structural sense be essentially a linked series of closed boxes.

    John Welsford
    Thank you John. The "Sealegs" thing bothered me some. I've only seen one up close briefly, it was an inflatable-side, rigid bottom thing (rigid dirigible?) and came away thinking you wouldn't want a gaff (of the landing large fish variety, not the rigging?) on board though the inflatable bit seemed quite sturdy.

    Cheers
    Norm

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •