buoyancy of marine plywood box

Discussion in 'Boat Design' started by Shraddha, Mar 12, 2020.

  1. Shraddha
    Joined: Mar 2020
    Posts: 2
    Likes: 0, Points: 1
    Location: india

    Shraddha New Member

    Will a 4 ft x 4ft x 1ft marine plywood (thickness - 12mm) box float on water? The box is hollow. Also, will it sink if multiple boxes are joint and someone has to walk on it?
     
  2. BlueBell
    Joined: May 2017
    Posts: 1,273
    Likes: 247, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Shraddha,

    Welcome to the forum.

    Yes, it will float on water, and, it depends how big the person is...

    4 x 4 x 1 = 16 cubic feet x 62 pounds per ft^3 = about 1000 pounds buoyancy minus the weight of the box, is how big a person it will hold.

    Why do you ask? School project?
     
    bajansailor likes this.
  3. Ike
    Joined: Apr 2006
    Posts: 2,404
    Likes: 283, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    that's 16 cubic feet. its 48 square feet of surface 12mm thick (0.472 inches) which is approx 1.9 cubic feet of plywood. Fir plywood weighs about 55 lbs per cubic foot which means your box weighs about 104.5 lbs. However wood floats so the wood alone would support 85 lbs. 16 cubic feet of air will support 16 times 62.4 lbs per cubic foot in fresh water. If the box is watertight it will float approximately 978 lbs . 16 x 62.4 = 998.4 - 104.5 + 85 = 978.9 . Walk on a single box ? Yes, but it would probably roll over because your center of gravity is about 3 feet above the surface you are standing on and that would raise the CG of the box about 2.5 feet. If you sat down it would probably be ok. I may have made a math error somewhere but someone will come along and point it out .
    If you have multiple boxes that are joined together it could be walked on. That is the basic principle for floating docks and floating pontoon bridges.
     
    jehardiman, bajansailor and fallguy like this.
  4. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    If you are from India, the metric system is your friend.

    4ft (1.2 metres) * 4 ft (1.2) metres x 1 ft (.3 metres)

    = 1.2m x 1.2m x .3m
    = .432 cubic metres

    x 1000 (litres)
    = 432 litres

    1 litre = 1 kilogram

    So, that box will float up 432 kilos (952 pounds), less the weight of the box.
     
    bajansailor likes this.
  5. Shraddha
    Joined: Mar 2020
    Posts: 2
    Likes: 0, Points: 1
    Location: india

    Shraddha New Member

    yes university project.
     
  6. BlueBell
    Joined: May 2017
    Posts: 1,273
    Likes: 247, Points: 63
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    So, did I pass?
     

  7. jehardiman
    Joined: Aug 2004
    Posts: 2,763
    Likes: 357, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    As Ike said, stability is going to be your real issue. Just how the floats are constrained or joined can be problematic.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.