Watertight compartments

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

  1. Ad Hoc
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    Ad Hoc Naval Architect

    It is not applicable to this vessel - as this is a pleasure yacht.

    So quoting collision bulkhead and its associated requirements are a misnomer.
    It is also a Statutory requirement not a Classification requirement.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    A lot of boats have sunk, or capsized, despite having watertight compartments that should have prevented it. It is too late to find out they were not, after the event. One could make a case for an air valve on each compartment, to test they are not compromised, periodically. I'd like to see something like a resilient flexible liner, "blown" into the cavity like a plastic drink bottle is made, and possibly of a similar material, but, needless to say, a technical challenge. Or sprayed in to form a bladder, but not adhering so strongly that it breaks if the structure in penetrated.
     
  3. fallguy
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    fallguy Senior Member

    except one of the main draws of the watertight is reducing the weight vs foam, so a bladder adds weight
     
  4. DCockey
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    DCockey Senior Member

    Correct. But it entirely permissable to have watertight compartments which are not completely foam filled. In preparation for a floatation test:
    4.4.1.3.8 Where air chambers contribute to the buoyancy, the two largest shall be perforated so as to allow
    complete flooding.
     
  5. DCockey
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    DCockey Senior Member

    Do Classification Society regulations apply to vessels under 24 metres in length?
     
  6. Rumars
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    Rumars Senior Member

    This is a plywood multihull, it should be unsinkable by design. The two existing full bulkheads are under the crossarms, they serve primarily to tie those to the structure and only secondarily as crash bulkheads. Additional watertight compartments can be installed into the structure but will only work if they are not pierced, otherwise they have to be filled with foam. I only see the need for those if you want the boat to be sailable when swamped, in wich case you have to arrange them so as to mentain a level attitude, wich probably means giving up some space in the bilges and under the setees. You would have to actually model the swamped condition for different scenarios like "hole in the hull" or "front of ama/waka ripped off after collision" to see how it will float. If you don't want to go trough this exercise additional watertight compartments are just wasted work.

    This is a ply epoxy boat so you have two options: air filled buoyancy chambers that have pressure equalizing valves and inspection hatches for ventilation when in port, or foam that is completley glued to the ply on all sides.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed... but considering the max permissible volume is listed as 0.014m3... it is not a lot to worry about.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    It is a statutory requirement, not Classification.

    Noting Class rules, as a guide, is a misnomer...

    Edit:
    I assume you're still referring to the location of bulkheads, such as the collision bulkhead, already cited.
     
  9. DogCavalry
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    DogCavalry Senior Member

    Indeed, TC does not say you can't use watertight bulkheads, just that sealed compartments don't count in a swamp test. I replied in haste, using only half my axe. I should have used my whole axe. Careless of me, fortunately folks more alert than I am saved the day.

    For what it's worth, I have 3 watertight bulkheads in my 8m boat. And there will be extensive foam under all cabin soles.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    It's a complicated matter, yes, extra weight, but there is the matter of cost to consider, too. I would chose foam, but in large volumes, the cost is substantial. and it really needs to be strictly sealed against water, as it can lose its integrity to some degree, over time.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    It is a bit of an inexact science, the pouring foam, the theoretical expansion is when not restricted , when poured into confined spaces, it will be denser, to a greater or lesser degree. I would prefer polystyrene that is painted, but not practical in many cases.
     
  12. Scuff
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    Scuff Junior Member

    Tansl, is there any recommendation on how far up the waterline the compartment should be? The float is 24' so using the 7-9% the bulkhead should be a little over 2' aft of the bow.

    The boat is pvc foam and glass not wood. I did intend to put an inspection hatch in the compartments is that not a good approach?

    Thanks for the help!
     
  13. TANSL
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    TANSL Senior Member

    You know perfectly, or should know, that, in general, no. But there are boats, less than 24 m in length, in which watertight bulkheads must be installed.
     
  14. TANSL
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    TANSL Senior Member

    Although it is a pleasure craft, I think the OP is thinking about the convenience of placing watertight bulkheads in his hull and asks if there is any standard that recommends the number of watertight bulkheads required and, more importantly, their situation. It is about recommending something practical to @Scuff and not to demonstrate our immense wisdom.
    That's correct.
    In certain vessels, according to vessel type, regardless of their size, the so-called "floodable length" calculation is made, which allows obtaining the maximum length that each compartment can have. That determines the number of watertight bulkheads that the ship must carry.
    The compartments must be accessible so that openings, inspection hatches, with a watertight cover, are placed which allow the inspection of any space in the boat.
     

  15. Rumars
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    Rumars Senior Member

    So the boat has even more reserve buoyancy because foam construction should be lighter and has more volume even if not. So what do you expect watertight compartments to do for you? Give us a scenario.
     
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