Designing and building a houseboat

Discussion in 'Boat Design' started by JohnMarc, Mar 13, 2018.

  1. jorgepease
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    jorgepease Senior Member

    Yeah, heavy stuff at lowest point is good idea...
    I wonder how everyone would feel about a flat bottom with a type of mini keel that you could put all the heavy stuff in, be easy to build and it would solve the drift issue plus increase stability.
     
  2. jorgepease
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    jorgepease Senior Member

  3. JohnMarc
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    Location: Knysna South Africa

    JohnMarc Junior Member

    Let me do a sketch of my thoughts and I'll throw myself at the mercy of this forum...unless of course someone suggests it not be a solution .....Just a thought if I go this route would it be better to have two outboards either side in "clean water" and would it give me better manoeuvrability (the way a rubber duck for example has the motor between the pontoons in clean water) or is that splitting hairs.
     
  4. JohnMarc
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    JohnMarc Junior Member

    jorgepease likes this.
  5. TANSL
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    TANSL Senior Member

    I think not, maybe just the opposite and it produces a worse use of the space available in the interior. If you do not want to sail with the pontoon, the "V" shapes are not necessary and complicate the construction. See what the drift area is, in red in the picture.

    original design 2.jpg
     
  6. JohnMarc
    Joined: Feb 2018
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    Location: Knysna South Africa

    JohnMarc Junior Member

    Okay thank you now I am beginning to understand the different concepts it is really making sense. I am busy with a altered design thanks to the advice given here. Will consider all the fantastic advice during the redraw. One quick question if I may, I am going to put in a centrepiece as advised by Jorgepease to act as a hold for the heavier equipment, would the sides of this new "box keel" act as a further drift area, effectively doubling the drift area, or is the fact that it will be totally submerged make it mute? Maybe the drawing makes more sense.... Regards
     

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  7. Heimfried
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    Heimfried Senior Member

    John, I'm not sure, if I understand this right. Incorporate these 8.5 tonnes only the stuff, gear, load, fuel, fresh water, crew and passengers or is the boat itself included?

    At this stage of planning you don't know very much about the boat, so it is difficult for you to estimate the light ship weight. Am I right?
     
  8. TANSL
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    TANSL Senior Member

    Yes, the area of the box keel must be considered as part of the total drift area, but this box keel will give you more buoyancy so reducing the draft.
    My advise, again, think on a catamaran only because, having less buoyancy, you will need more draft.
     
  9. JohnMarc
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    JohnMarc Junior Member

    Yes good point, the 8,5 tonnes comes from an exhaustive list that I did and I added 1,2 tonnes for the weight of the (unknown) hull. However the tonnage I calculated does include the weight of the entire structural elements excluding the hull .... (Don't know the correct term)
     
  10. JohnMarc
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    JohnMarc Junior Member

    One last stab at this design.....I beg you patience :p..... I calculated the volume of the box keel at about 3,6 m3 so if the battery bank and other permanently stored items...even thinking of doing an inboard, would it help to neutralise the additional buoyancy ..... you know as I am writing this I am beginning to think it best to go the catamaran route but limitations on overall height is still a concern.
     
  11. JohnMarc
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    JohnMarc Junior Member

    Tansl are you in fact saying I should go back to my original design as below and work out everything based on that..... (is this incidentally what you mean by a catamaran design) two hull as opposed to a mono hull.
     

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  12. JohnMarc
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    JohnMarc Junior Member

    As a very general question, please tell me if my logic is right, If I am looking at supporting lets say 8 tonnes then in very simplistic terms I am looking for 8m3 of pontoons, for e.g. it could be 8m long x 500mm wide x 2 pontoons (I appreciate salt water is different etc.but for now trying to keep it simple,) but the 8m3 would mean I am floating on the top like a cork? so no drift area.... if I am looking for a draft of say 400 mm then do I simply reduce the volume by the equivalent ratio.....i.e. make the pontoons narrower?
    I really hope this initial question makes sense. Its this fundamental principal I am trying to get my head around....:rolleyes:
     
  13. jorgepease
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    jorgepease Senior Member

    What are the conditions like, waves, chop ... That will determine how much clearance you need to avoid a slapping nightmare
     
  14. TANSL
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    TANSL Senior Member

    With your initial design you would obtain the following values :

    Draft (m) ..... Displacement (tons)
    --------------------------------------------
    0.26 .................. 6.96
    0.28 ................... 7.63
    0.30 ................... 8.33
    0.32.....................9.13

    Which means that with 0.30 m of draft you would get enough buoyancy to support the approx. 8.4 tons of weight.
    With that, you could build something similar to the figure. All I'm trying to do is give an approximate idea of the available heights

    Snap1.jpg

    Alternative solution with more draft :
    Snap2.jpg
     
    Last edited: Mar 14, 2018

  15. JohnMarc
    Joined: Feb 2018
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    Location: Knysna South Africa

    JohnMarc Junior Member

    Wow thank you so much for this, the conditions are very calm, it is an inland tidal lagoon, Knysna Lagoon on the Garden route in South Africa.
     
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