Foldable catamaran

Discussion in 'Boat Design' started by skatun, Nov 20, 2018.

?

Feasible?

  1. Yes

    2 vote(s)
    50.0%
  2. No

    2 vote(s)
    50.0%
  1. skatun
    Joined: Sep 2010
    Posts: 23
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    Location: Aachen

    skatun Junior Member

    upload_2019-1-24_13-59-57.png

    The critical point is the air thickness between the windows.. and that they are 100% air tight...

    10mm gap:
    upload_2019-1-24_14-1-48.png
    30mm gap

    upload_2019-1-24_14-2-8.png
     
  2. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    Attack of the Maths! lol
     
  3. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    The way you are calculating the thermal resistance of the air gap between the acrylic panels is not appropriate, because the convective flow of heat is not included. In engineering tables for heat energy calculations on buildings an vertical oriented air gap with a thickness of 10 mm to 20 mm is set to the value of 0.14 (m² K)/W (regardless if it is 10 mm or 20 mm or inbetween). Likewise an air gap of >20 mm to 500 mm is set to 0.17 (m² K)/W .

    In addition you should consider the heat transmission resistance between air and surface. The values are depending on wind velocity and the used value of (about) 40 W/(m² K) is for buildings in average climatic conditions in Germany. A boat is potentially prone to considerably more wind. And the heat transition resistance will decrease. Depending on how your heating will work it may be you will get different layers of air temperature, e. g. 16 °C on the floor and 28 °C and more at the ceiling, so your Delta T goes up and so does the heat loss. If you use a ventilator, this would be probably better but the same time you are increasing the thermal loss because of lowering the transmission resistance at the inner surface.

    So most probably your calculations will give you a too optimistic result.
     
    Last edited: Jan 25, 2019
  4. skatun
    Joined: Sep 2010
    Posts: 23
    Likes: 2, Points: 3, Legacy Rep: 10
    Location: Aachen

    skatun Junior Member

    Excelent, can you share these?

    Yes, I have included the nusselt number yet, I will get around to it...

    Was thinking about using a heatpump with saltwater and circulate heating coolant in the floor, any suggestion around this, links to where to get heatpump?

    At this stage I am just trying to figure out roughly if I can have windows all around, or if I should only have partial windows, lets say from 90cm and up to ceiling. Also if I can use windows with aluminium frame, because then i can weld them straight in and dont have to worry about leakages.(changing windows might be hard though). Glass windows does have better R values, but are heavier and I am not sure how well they are in heavy seas. So any tips around the window topic will be highly appreciated.
     
  5. skatun
    Joined: Sep 2010
    Posts: 23
    Likes: 2, Points: 3, Legacy Rep: 10
    Location: Aachen

    skatun Junior Member

    Updated numbers:

    upload_2019-1-25_11-22-8.png
     
  6. Heimfried
    Joined: Apr 2015
    Posts: 278
    Likes: 18, Points: 18, Legacy Rep: 37
    Location: Berlin, Germany

    Heimfried Senior Member

    Sorry, no, the tables are part of printed books.

    Searching the web "books.google.de" provided some pages of "Lehrbuch der Bauphysik", Jenisch, Storer et.al.
    A table there shows the resistance (exterior surface) decreases from 0.04 (m² K)/W for wind speed 4 m/s to 0.02 (m² K)/W for 10 m/s.

    Heatpumps I know, are electric driven an that is potentially a problem on board, because you need AFAIK about a quarter of the generated thermal energy as electric energy input.
    I'm building a kind of houseboat, but only for weekends and holidays, not to live on it. So heating is not a point for me (may be later for use in spring or autumn).
    This thread could give you some ideas about a liveaboard katamaran planning in many aspects (e.g. windows):
    boote-forum.de - Das Forum rund um Boote https://www.boote-forum.de/showthread.php?t=270807
     
    Last edited: Jan 25, 2019

  7. skatun
    Joined: Sep 2010
    Posts: 23
    Likes: 2, Points: 3, Legacy Rep: 10
    Location: Aachen

    skatun Junior Member

    So this weekend I ran into a guy from the car racing society, and he told me how he would make the glass panels:

    1 layer of thin glass(<1mm) laminated to 3mm acrylic and then darkening film, then air gap, then electrical film(for curtain), 3mm acrylic and final layer of thin glass for scratch resistance.

    Now I only need to figure out how expensive such a glass is and who can produce it...
     
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