Watertight compartments question

Discussion in 'Fiberglass and Composite Boat Building' started by JohnMarc, Jan 24, 2019.

  1. JohnMarc
    Joined: Feb 2018
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    Location: Knysna South Africa

    JohnMarc <--- My ultimate goal

    Hi All
    I could start with the usual apology in advance for my ignorance but I am sure you will make up your own mind as you read this.
    I am busy with a 6 meter cat (using the PC20) as a base plan. I want to create several watertight compartments in the hull. With it being trailerable there is a good chance we be travelling a lot with it. I live on the coast and will be taking it up north which is at 1753 metres (5751 ft) above sea level. I will be building the boat from vacuum infused epoxy resin with 10 mm foam.

    This might be a silly question but should I be allowing a pressure release or pressure neutralisation valve of some sort.

    Thanks in advance

    John Marc
     
  2. The Q
    Joined: Feb 2014
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    Location: Norfolk, UK

    The Q Senior Member

    I've never come across a boat that didn't leak at some point into it's watertight compartments, even if a minute amount. If it were mine there would be a sealable hole at the lowest point so you can open up at any time to drain.
    Then a proper sealable inspection hatch somewhere you can either see in or get a camera in to do a proper inspection..
    Oh a quick check shows if you are starting from sea level then at 5751Ft you have about an extra 3psi in the compartments..
     
  3. JohnMarc
    Joined: Feb 2018
    Posts: 93
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    Location: Knysna South Africa

    JohnMarc <--- My ultimate goal

    Many thanks for the info Q, yes it is one of the issues I am trying to address , drainage ..... but I am trying to research a system that I can with a single bung release all the water from all the watertight compartments.... but am trying to find a system that will maintain the watertightness along the length of the hull through all the compartments, but release any ingress of water by opening a single plug. Seems I might be trying to find the impossible
     
  4. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Every void should have an access of some sort. As a trailer sailer I would have inspection ports that I would leave open
    (if placed the out of the weather)
    while on the trailer to allow the space to breath and then install them when sailing. Opening the ports and checking the voids just becomes one of the pre-sail checklist items.
     
    JamesG123 likes this.
  5. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    I can with a single bung release all the water from all the watertight compartments.... but am trying to find a system that will maintain the watertightness along the length of the hull through all the compartments, but release any ingress of water by opening a single plug. Seems I might be trying to find the impossible[/QUOTE]


    By definition you are looking for the impossible.

    One drain equals one compart. Even if it is divided be baffles. If water from one space can drain (flow) into another space, there is no watertight barior. Effectively one compartment.
     
  6. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    Remember Mr. Murphy. He especially likes the excessively clever/lazy.

    You need to differentiate:
    Compartmentalization - How you separate sections of the boat where the crew inhabit, usually with raised door sills to inhibit flooding.
    Water tight storage spaces - Spaces with small(er) opennings that provide mainly buoyancy reserve, but also storage spaces for (ideally) light but bulky items.
    Flotation - Spaces specifically allocated to emergency floatation. Usually foam filled.

    Generally, a boat with enough structural integrity to be "sea worthy" will be stout enough to tolerate being pressurized to 1.5 bar. Its a non-issue.
    The advise of opening the hatches as part of the haul-out proceedure is a good one. It will elleaviate a lot of on the hard storage concerns without the un-fun suprizes of forgetting to close a seacock when putting in.
     
  7. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    As for the pressure differential I wouldn't worry about it. Boats with watertight compartments are found at all habitable elevations and I haven't heard of any collapsing compartments (or vice versa). However the idea of one bung or valve to drain water from all of these compartments (shouldn't be any water in a watertight compartment, but then Murphy's law applies) would be extremely difficult to do. The idea of a water tight cover is a good one and they are readily available. They are in common use on canoes and other small boats.
     

  8. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Interesting question, I guess for boats at sea level the pressure may build up when in a hot sun, or fall on a cold night. What kind of pressure differences, difficult to say. 3PSI sounds like a bit, if the compartments are not that robust.
     
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