Watertight compartments

Discussion in 'Fiberglass and Composite Boat Building' started by Scuff, Sep 28, 2020.

  1. fallguy
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    fallguy Senior Member

    I am building a 10M cat in foam and did some calcs. My watertights will help deal with all those things that don't float like glass/epoxy/engines/beams/etc.

    And forward, in the event of collision with an underwater object; those watertights will also keep the boat from flooding higher so it can limp to safe harbor or shore.
     
  2. Rumars
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    Rumars Senior Member

    Unless you are hauling bricks most multihulls are unsinkable. The problem is how it will float full of water.
    Scenarios: you hit something with the rear. Aft watertight compartment(s) flood the boat sits nose up with half or all of the transoms submerged. Limping home is mostly unlikely. Same thing if you have a hole forward, now the boat sits bow down with the transoms in the air. If only one of the hulls is affected the boat has a diagonal trim.
    The only way to limp home flooded is if the boat sits more or less level longitudinally and transversly wich means either you have the hole in the middle, or the whole boat fills evenly on all hulls, or you arranged foam flotation so that bow and stern can not fill with enough water to significantly affect trim. This means foam flotation at least up to the waterline (or higher) in all ends. If you don't want foam you need many small compartments.
     
  3. Scuff
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    Scuff Junior Member

    That's what I was looking to achieve. The watertight bulkheads do segregate the floats into 3 areas. Figured out I had to have an app to resize the pics I posted them.
     

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  4. DogCavalry
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    DogCavalry Senior Member

    Indeed, I wrote too quickly. I was unclear. Nothing in Canadian regs saying that there can't be watertight bulkheads. Just that their volume is not used during swamp tests as part of flotation. Since the boat could be swamped by hull damage that would breach those compartments, if they were the only thing keeping you afloat, you would sink. For a swamp test there must be solid flotation. Generally that means foam.
     
  5. DogCavalry
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    DogCavalry Senior Member

    And building on what Rumars just said. A swamp test, which I'm assuming is more or less universal, means that the boat must float level, even if machine gunned full of holes. For a multihull with outboards, that would allow you to return home slowly but safely.

    Or as is far more likely, I run over a huge log thats almost awash, doing 30 knots with a load of bricks on board. That would tear up the entire length of my bottom, and really test the transom when both outboards smashed into the thing.
     
    Last edited: Sep 29, 2020
  6. fallguy
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    fallguy Senior Member

    I don't think mine would; quite honestly.

    I did the weight estimates and tried to tie back and no way am I buoyant enough to run machine gunned. But I think I could limp in on some.

    The Skoota has 9 boxes starboard and 8 boxes port. 17 compartments-lotsa footage, probably ? 100 cuft and at 2 pound foam, 200 xtra pounds per hull; no thanks
     
  7. DogCavalry
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    DogCavalry Senior Member

    Fallguy, what's your loaded weight?
     
  8. DogCavalry
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    DogCavalry Senior Member

    Fun fact: I read on similar threads, discussion of how to make a compartment air and water tight. If you actually accomplished this, it would wreck itself or the boat, next time the ambient temperature changed. Thermal expansion of hot air. Just a few psi, and Pop!
     
  9. BlueBell
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    BlueBell Ahhhhh...

    A pressure compensator is required.
    A small fitting with a length of surgical tubing, sealed at the far end, works without compromising the compartment seal.
    Some put a pin hole near the "top" to ensure pressure equalizing without undo compromise to watertight integrity.
     
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  10. Rumars
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    Rumars Senior Member

    GoreTex pressure equalization vents. Cheap.
     
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  11. fallguy
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    fallguy Senior Member

    9000? We will see.
     
  12. DogCavalry
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    DogCavalry Senior Member

    Having tried to weld a cube, it would actually be impossible to do this without one of you fella's suggestions. The heat generated by the curing epoxy would cause the air to steadily bubble out of the space. Then as the reaction slowed, the temperature would fall, sucking back in through the bubble hole. But I'm just being goofy from acetone fumes.
    I suppose it's common knowledge that canola oil will clean epoxy from your skin just as well.
     

  13. fallguy
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    fallguy Senior Member

    I was told they were not waterproof by gore.

    And one of my watertights expanded in the heat or shrunk in the cold unvented. So, still a bit uncertain here.

    Have you actually applied gorevents?
     
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