12x36 houseboat on encapsulated foam

Discussion in 'Boat Design' started by livenlearn, Sep 13, 2020.

  1. livenlearn
    Joined: Sep 2020
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    Location: dallas

    livenlearn Junior Member

    Want to build a floating cabin nut I'm no expert and wanted to run it by you guys...
    What I have designed is:
    12'x36' frame of 2x6 c channel

    12' floor joists 2"x2" 11ga square tubing tied across with 1" angle iron to hold square.

    (5) 7' 2x2 11ga on each side to hold up the upper deck same as lower except perimeter being 2x2 rather than c channel.

    The reason for the steel superstructure is so there are no load bearing walls but also due to height restriction...the slip is 14'.5"

    And this is why I'm here....
    The cabin will be 28' front porch 6ft and rear 2ft 80" tall to accommodate a sliding door.

    I want a bedroom on top 12' so made centered atop the 28ft cabin.

    This will bring my height close to 14'

    My calculations show that in the end the floatation will be submerged close to halfway..so 12" and the deck will be pretty close to flush with the slip deck.

    I cannot find anyone to tell me is 2x2 11ga ok on 12' span? I've tried deflection calculators online but cant comprehend them intelligibly.
    I figure the bottom will be fine as they will be supported by 4' per side floats but the top may bounce....which I could compensate by walls for head and stateroom....not exactely loadbearing just bounce proofing.

    Next I think about it being 2ft taller than width...but only 12' so 1/3 total length and almost centered...dont want to tip over!

    It will be a cabin...not ever moving in the water.

    It will be clad in 3/4 ply so I think itll be sturdy but what do u guys think?
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Livenlearn.

    This sounds like an interesting project - however it is difficult to try to visualise what you are proposing, without any drawings or sketches.
    I presume that you must have created some drawings so far - can you maybe post (some of) them on here please?
    Even if they are just sketches, 'a picture is worth a thousand words' of description.
     
  3. livenlearn
    Joined: Sep 2020
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    Location: dallas

    livenlearn Junior Member

    Ok I only have basic sketches. I suppose this may not be the correct forum for the steel part but I'm wondering about the width height issue...about 8 inches of floatation will be submerged...two sides 48" with 48" inbwtween so similar to pontoons. 12 ft width and 14ft tall... I feel like will be fine but want to be sure.
     

    Attached Files:

  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Assuming a covered slip since you have a height restriction of 14'5", are you sure the water level doesn't fluctuate?
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    D7029D56-9510-4AD5-A166-BC970897F63F.png
    Attached a picture. 100 pounds loading is a deflection of just under 1/8", but you didn't mention how close the tubes are to each other.
     
  6. livenlearn
    Joined: Sep 2020
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    Location: dallas

    livenlearn Junior Member

    Yes the water fluctuates but the dock is on floatation so is constant...however if there are some big waves I may take a beating. I'm working on this issue. Ad for spacing the 2x2 will be spaced 2' apart..
     
  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    That is pretty far.

    What do you intend to use for a floor atop the ceiling and how will you attach it? Even 3/4" ply has a span rating of 16" typ.
     
  8. livenlearn
    Joined: Sep 2020
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    Location: dallas

    livenlearn Junior Member

    3/4 osb and 1/8 vynil should be fine on 2ft centers. Walls should def be 16" centers.
    At this point I'm wondering about being 12 wide and 14 high if itll try to tip? Itll be a foot in the water...
     
  9. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    I am a bit confused by the hull shapes shown in your sketches.
    The main deck appears to be 36' long, and 12' wide - ok, so far so good.
    I would be a bit worried though about the height being 14' - try doing a midship section sketch to scale, to see what it looks like.
    Especially as you appear to have a sort of 'transverse trimaran' hull form 36' wide and 12' long with three hulls - but these hulls are described as '4' x 8' x 24" ' - so are the pontoons actually only 8' wide, in relation to the overall width of 12'?
    If so, then you will definitely have a stability problem!
    I would be looking at a catamaran hull form, with two hulls each 36' long and 4' wide - this will give you twice the buoyancy of what your 'trimaran' sketch can provide , and much better stability.
     
  10. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I won't entertain the hull designs. I was only trying to help you calc the 2x2 deflection.

    personally, my gut tells me you are overweight and the 3/4" wall sheathing means you haven't thought out weights and buoyancy well enough

    I don't have the required credentials to comment further here.
     
  11. livenlearn
    Joined: Sep 2020
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    Location: dallas

    livenlearn Junior Member

    Thanks for all the input guys. Sry for the bad drawings. To clarify...the flooring on each deck will be 3/4 osb treated to keep moisture out of course. The walls will be 1/4in and then panelling. This will be a stationary unit so my thought is heavier will be more stable.
    The hull is the most affordable I can figure..6 encapsulated dock blocks spaced 4ft apart on each side.. my neighbor has thos set up and your right it's not stable at all but it's aarima with a break wall so not too bad just wish was better.
    I figure I can take any deflection up bt using inner walls.
    I have yet to see any boats that are taller than wide and in my head seems to be good reason for this. But then I think it would be really hard to tip a boat that's 12ft wide would have to be alot more than 2 feet tall keeping in mind it's a stationary cabin.
     
  12. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Re your 6 'dock blocks', each 8' long x 4' wide x 2' deep, I think that you will need a lot more than this in order to get the necessary buoyancy for all the heavy superstructure and outfit equipment that you will be installing above them.
    Can you go up to 40' from 36' hull length?
    If so, then you could use 10 of these 'dock blocks' - that would be a 70% increase in the buoyancy available.

    Have you seen the Rolling Barge website?
    Their pontoon design could work for your application?
    https://rollingbarge.com/floating-dock-kits/
     
  13. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    Sounds like what is often called a 'float-home'. May not be an issue but check with the city/district you are mooring in to see if you have to comply with any building codes.
     
  14. NomadOmad
    Joined: Aug 2020
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    Location: Uk

    NomadOmad Junior Member

    I think it’s a brilliant idea

    looking forward to seeing the to scale model
     

  15. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    @livenlearn I just came across this neat house boat on the Kasten Marine site and I saw similarities to what you are proposing.

    This boat is also 36' long, and has a maximum beam of 12', to fit into a marina slip.
    There is a good description of her, outlining all the factors that the designer had to take into account.

    36' DRIFTER - Houseboat for Inland Waterways http://www.kastenmarine.com/houseboat.htm

    The cost of the plans is $1,950 - it sounds like a lot, but it would only be a small percentage of the final cost of the boat.
    Our Plans List - Kasten Marine Design http://www.kastenmarine.com/plans_list.htm
     
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