Fore deck locker floor drainage

Discussion in 'Multihulls' started by UpOnStands, Dec 19, 2016.

  1. UpOnStands
    Joined: Nov 2015
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    UpOnStands Senior Member

    how about 3 degrees high forward and 3 degrees down inboard.
    Enough angle to clear leakage or more is needed? no angle is needed at all?
    Two small sail lockers forward of the cross beam, one on either hull, so drainage is inboard.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    What boat? Where is this draining? How much water do you expect in a worst case scenario? Draining inboard on a cat, where to, etc., etc., etc. 3 degrees seems plenty, assuming your drains are sized well enough, to remove the water quickly.
     
  3. UpOnStands
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    UpOnStands Senior Member

    normally only wet stuff and bit of seepage.
    each hatch opening is 48cm by 38cm.
    drain is in-board side of hull quite high as it sits over a crash space just aft of the stem.
     
  4. PAR
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    PAR Yacht Designer/Builder

    3 Degrees will be fine, again assuming the drain is large enough to get a fully swamped locker empty in a minute or less. This would be the worst case situation, possibly after a hatch was torn away or flipped open for some reason.
     
  5. UpOnStands
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    UpOnStands Senior Member

    great image, but worst case. So now to calculate volume and determine the outlet size for 1 min. This type of info is great. Many thanks
     
  6. UpOnStands
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    UpOnStands Senior Member

    a rough calculation indicates that each locker is 1 cubic meter in capacity
    this equals 1 ton if filled? and to drain this in 1 min would take what, a 10cm dia hole?
    How many yachts have properly sized drain holes then?
     
  7. PAR
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    PAR Yacht Designer/Builder

    How did you perform this calculation, as it's not difficult though pretty unusual, for the novice to fully understand? If you can provide the dimensions for the enclosed volume, I can recommend an appropriate drain diameter.
     
  8. UpOnStands
    Joined: Nov 2015
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    UpOnStands Senior Member

    sorry, been busy but returned. Averaging out the dimensions yields 1m x 1m x 1m.
    The basic equation makes the rate of discharge proportional to the drain area and the sq root of the height of water but then a lot of real-world fudge factors creep in.
    Appreciate the help.

    edit: I put the eq in a spreadsheet and find for discharge coefficient of 0.6 a 2 inch dia hole yields a 6.1 min discharge time
    a 1 inch hole gives a time of 24.7 mins.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Two 50 mm drains will handle 990 lt. of water in less than a minute, assuming no pressure, which is as you've stated, proportional to the square root of its height (Torricelli's Law). This assumes no or very low pressure and no rotational considerations (and other stuff). I suspect you'll have more than a little pressure in this compartment and velocity/flow rates will improve. Use a 50mm drain and run a test. Ideally, you'd want this 1/2 ton of water out of there fast or as fast as practical, considering its location. A single 50mm drain (scupper) will handle all but the worst case scenario. You can have a bow wallow around for a couple of minutes while you wait for it, or install the second scupper, just in case. If this is a ocean crossing passage maker, I'll use two 50mm drains per compartment. If this is a weekend warrior, I'd use just one.
     
  10. UpOnStands
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    UpOnStands Senior Member

    thanks, for calc. seems we cross posted.
    two drains then per locker with one inboard and one outboard.
    I might just screw the damn lids down and give up on the idea of casual storage up front. I still need access for deck fittings but only at haul out time.
    Given the size constraints on the lid not much is going fit in there anyway and the image of wallowing bow down mid ocean is not reassuring.
     

  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A 1/2 ton in a bow may not be that big a concern, depending on the craft's size. Ground tackle can easily exceed this on some boats.
     
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