How to make catamarans to carry heavy weight

Discussion in 'Boat Design' started by Steptepha55, Nov 7, 2011.

  1. Steptepha55
    Joined: Nov 2011
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    Steptepha55 New Member

    I'm a beginner. I have read some catamaran history in wikipedia, so I found somethings that interesting.

    some ferry(passenger) uses design of catamaran.

    I want to know, how can they carry much weight or how to make catamaran to carry as much as possible weight.

    I'm building small catamaran for sailing (about 2.4m length) so I found some problems that my boat can't carry as much weight with my own design, I hope that your answer will impove it.
     
  2. rxcomposite
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    rxcomposite Senior Member

    Increase displacement.
     
  3. lewisboats
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    lewisboats Obsessed Member

    Bigger hulls...wide or deep or long (or a combination thereof). To carry weight they must displace a weight of water equal to the total weight of the boat/ship and its cargo, passengers etc. 1 cubic foot of salt water is 64 lbs and fresh water is 62.4 lbs. 1 cubic meter of salt water is 1025 kilos and fresh water is 1000 kilos. Generally most "designers" tend to set the displacement very early in the design as it is a key ingredient in shaping the boat.
     
  4. eyschulman
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    eyschulman Senior Member

    The things you have to do to make a cat a pack horse should make you think about why the complications of a cat?
     
  5. lewisboats
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    lewisboats Obsessed Member

    I like that!
     
  6. Wavewacker
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    Wavewacker Senior Member

    Answered my question too, LOL, make them fat, deep and long, but then they won't be efficient, make them efficient and keep them skinny, shallow and still long....:rolleyes:
     
  7. Submarine Tom

    Submarine Tom Previous Member

    Finding a proven design for your requirements will put you farther ahead in the long run.

    -Tom
     
  8. Richard Woods
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    Richard Woods Woods Designs

    The only sailing beach cats under about 12ft long are beach toys. Because, as you have discovered, smaller catamarans cannot take the weight of even one crew and still sail in a satisfactory manner

    The Livingston yacht tender is an 8ft catamaran powerboat but I doubt if it would sail well

    I believe Sea Eagle, amongst others, make a small inflatable sailing catamaran. Only for use on lakes though or in very gentle conditions

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  9. Wavewacker
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    Wavewacker Senior Member

    Might check "Jack's Plastic Welding" for inflatable tubes, rafts and cats. One called the Big Daddy. They also have frames. They can go beyound the local lake, how far might be based on nerves and skills.

    While I have never seen one, they can add different shapes welding them to a basic tube to form flat or curved areas that might make them more than just a O pontoon. But I'm sure most all you guys knew that....
     
  10. tom28571
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    tom28571 Senior Member

    The scaling factor is of great importance in all boat design but nowhere is it as important as in a performance catamaran. Displacement varies as the cube of the size ratio of two same design hulls. Increase the size of your 2.4 M (8') by 26%, which is 3 M (10'), and its total displacement doubles. That is how you control carrying capacity and how the big cats can haul 700 or more people and their cars.

    Once you decide what the boat is intended to do, the first design step is to calculate the displacement required to do that. Only then can you look at the other factors. It seems the natural thing for most beginners go at this backwards. Not a real problem as long as you learn how it really works. Everyone wants to design a boat and that is the most fun part of the addiction that affects us. There is a large learning curve though and that will take time and effort, which is also fun as the secrets become visible.
     
  11. yipster
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    yipster designer

    as said above go big keeping the cat's lines
     
  12. Wavewacker
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    Wavewacker Senior Member

    Yipster, I guess you mean blow up the plans proportionately.

    A rough cat sold on Ebay not long ago that was a motor cat, it appeared to have about 4' deep hulls @ maybe 30", bet there was little rocker, about 20' long with a simple deck and a small outbaord. IMO, rather crude looking, barge like, but it sold and guess it worked. So I guess two long boxes with pointed ends will work for some. I bet a car could have been floated on the thing, but not my car!

    While I could build something similar in my garage without plans, I wouldn't. Even though it would work, it wouldn't work as well as a professionally designed boat for sure and if I'm putting any real money in it, I'd get a design.
     
  13. yipster
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    yipster designer

    may i agree on that and thank you for the translation my expressions sometimes need "blow up the plans proportionately" as that was exactly what i meant
    have looked at those cheap landingcrafts thinking it would fit a camper but discarded that idea before, can still imagine a sailing big bus / riding boat tho ;-)
    ofcourse weight makes displacement grow but block coefficient can remain when upsizing and although weight is important i belive a cat's advantages over a monohull may still be there
    if you know what i mean, than again maybe i'm wrong, but that should be not so hard to calculate when needed
     
  14. Baloo
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    Baloo New Member


  15. Ad Hoc
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    Ad Hoc Naval Architect

    Baloo

    What you're looking for, from that link, is what is referred to as a Pontoon Boat. These guys may help you with what you're after. (But there are plenty, just google "pontoon boats"):
    http://u-fabboats.com/
     
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