Closed end rivets

Discussion in 'Boatbuilding' started by danilo, Jan 18, 2012.

  1. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    What do you think shall happen when you place the boat in the water...no stresses?! If the structure and joints cannot withstand this simple test, then you shouldn't be out in the boat.

    Water inside or outside....same result.
     
  2. Frosty

    Frosty Previous Member

    How do you work that out, it will be less stress not same result. Filling a small boat with water --say 15 foot would be many tons of water. Putting the boat in water will displace only the weight of the boat which could be a few hundred kilo.

    Not to mention the boat being designed more for external compression rather than internal expansion.

    If you filled it with water the rivets would be in tension as the pressure tries to push the skin from the ribs. If the pressure is on the outside the rivets are under no stress as the skin is being pushed to the ribs.

    However I agree the boat should be able to withstand the test but its not same same.
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Don't forget the people onboard and equipment too, thus a bit more than a few hundred Kg's.

    But this is why it is a good test. The amount of water, depending upon how much you fill the boat and if it has any dividing BHDs, (my little fishing boat had 2, one fwd, for the anchor/flares etc, and aft, for the engine catch-all), provides a good "over-load" test. If it passes, you're fine. If it doesn't, then the whole structure under "normal" loading conditions would be very suspect indeed.

    Compression and tensile strength of ally is the same. So this wont affect the rivet, other than the magnitude of the load.

    As for the internal structure, as these being "designed" for compression. Therefore, there must be something, ie a bit of structure, that is required to resist that compression load, otherwise it'll just collapse, that would be in tension. So that "something" is the weak link, as that must now resist compression loads rather than tensile loads.

    However on very small boats, there is a limiting case for this and the reverse loading may be detrimental as you point out. But i'm not 100% convinced from all the small boats I've seen built this way.
     
  4. L'eau.Life
    Joined: Jan 2008
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    L'eau.Life Junior Member

    I started my career as an aircraft sheet metalworker where in some instances there is no choice but to use mandrel-formed rivets but for pressurized areas these have aa alloy steel locking ring to prevent the mandrel backing off and are made from aluminum alloys that are not saltwater-friendly. There are some all alloy versions but they are low shear, low tensile formed and again made of a material not suitable for marine use.
    Regular aluminum "pop" rivets also have a steel mandrel that breaks under load leaving the head in the rivet tail so not only would you risk leakage from a poor seal but also ferrous oxide on the mandrel head and corrosion in the aluminum rivet from dissimilar metals immersed in saline.
    Short answer; you'd be mad if you do
     
  5. cor
    Joined: May 2008
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    Location: Alaska

    cor Senior Member

    Where I live lots of people run riveted Lund boats on the ocean. After a few years of overloading and pounding in the waves the rivets come loose.

    The easiest way to find the leakers is to pull the boat up the beach on a few rollers (pipe, logs, etc) and fill it with water. Look underneath and see where the drips are.

    Most people use a small machine screw and nut (if you are lucky you might have stainless ones) to replace the bad rivet. If you put a little bit of your favorite goop on the screw before you tighten it down they don't leak a bit. Be sure to use nyloc nuts to prevent them from coming loose.

    C.O.
    http://whatsintheshop.blogspot.com/
     
  6. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Huh ?? Put a boat on the hard and fill it with water and you point load every contact point between boat and hard. Ive seen jackstands push into the hulls of boats and garboard planks detach when flooded out of the water.

    . Filling a boat with water is a bad idea.

    Bed your rivets in the correct diameter hole and you should have no problems. If the holes are out of round, redrill and upsize the rivet.
     
  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Please show me where i state to put a boat on the hard?
     

  8. cor
    Joined: May 2008
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    Location: Alaska

    cor Senior Member

    Don't FILL the boat with water, just put a little in the bottom to find where the leak is.
     
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