The project fast lightweight power catamarans - is possible?

Discussion in 'Boat Design' started by romanewas, Jan 6, 2017.

  1. TANSL
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    TANSL Senior Member

    I agree with kilocharlie2. Some aspects on which SWATH has advantages, which may interest the OP:
    - ample space on deck.
    - less power needed to achieve the same speed, compared to boats of similar dimensions.
    - greatly reduces the effects of pitch and heeling due to the waves.
    It also has negative aspects that detractors can expose.
     
  2. kach22i
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    kach22i Architect

    I agree with others, this is an expensive specification and set of goals.

    One option is similar to a cat is an SES, it however has additional complexity and costs associated with flexible seals/skirts front and back and a fan to lift the hull out of the water.

    2013
    http://www.maritimejournal.com/news...nergy/design-for-surface-effect-ship-ses-wfsv
    http://www.maritimejournal.com/__data/assets/image/0021/512661/MJAUG13Renewables-SES-Dag.jpg
    http://www.uac.no/WEB/um200.nsf/pages/Composite components
    [​IMG]

    http://www.um.no/web/um200.nsf/pages/E8912C46BA
    [​IMG]
    http://www.um.no/WEB/um200.nsf/pages/mainframe
    [​IMG]

    I do not know of a existing specific model meeting the requirement outline, but it may be out there - do a search if interested.

    If the never scarped the old US Coast Guard SES models might work, maybe they can be restored?

    https://www.uscg.mil/history/articles/SurfaceEffectShips.asp
    [​IMG]
    https://www.uscg.mil/history/img/SES-Tied-up.jpg
    Sorry about the giant images, thought this forum had an automatic size reduction feature.

    http://www.navsource.org/archives/09/46/46515.htm
    [​IMG]

     
  3. kilocharlie2
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    kilocharlie2 Junior Member

    Regarding hydrofoils, there are 2 types. One type is completely submerged and has an automatic pitch control system, the other sticks out of the water at an angle and is somewhat self-righting.

    Under a SWATH in 6' waves, I'd choose the submerged type with the automatic control system.
     
  4. kerosene
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    kerosene Senior Member

    swath and hydrofoils?
    It has been discussed here and every specialists of swaths seems to slam dunk no to the lifting foils. You would get little to no reduction of resistance from lift until the pontoons would be up and that would require significant lift (and drag).

    stabilizing foils yes, lifting no.
     
  5. kilocharlie2
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    kilocharlie2 Junior Member

    You're right - I am thinking flat water.oops!

    The one I used to work on was a combination type. The pontoons were V-bottom in front, planing pad in back, lifting foil below with the wing foils outboard. It was only fast ("flying" in the skipper's terminology) in fairly flat water. The skipper ran it conservatively ("planing") in anything over 3', and deeper yet ("SWATHing") in rough stuff. I was just a substitute pinhead from another boat, not even a deckhand yet. I do recall it was fast, and comfortable. Nobody barfed. On my usual boat, chumming was the norm.

    I agree that it is a high-power application, not a low-power one.
     
  6. romanewas
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    romanewas Junior Member

    Colleagues interested me the concept SWATH. How big would have to be floats to swim to wave heights of 5 '(already give up swimming at 6')? I want to take on board from 25 to 35 people. I care that people do not have seasickness. Cruise is expected to last up to two hours at a speed of 20 knots.
    I think I found what I need: http://newatlas.com/stability-60-swath-superyacht/8877/
    Any comment?
     
  7. kilocharlie2
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    kilocharlie2 Junior Member

    Roman -
    That link to the Stability 60 yacht is right up your alley. If the performance of that SWATH design is within 70% of their claims, it still fits your needs exactly.

    Look at business plans and combinations that will put you in one of these things making money. I hope the market is there to keep you busy. You could really bring some important income to the Canary Islands during Tourist Season. Good luck!
     
  8. romanewas
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    romanewas Junior Member

    I asked them exactly the performance and videos from swimming. But after further reflection it seems to me that this is just advertising.
     
  9. romanewas
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    romanewas Junior Member

    The question is whether I can build the hull without advanced technology? I think about the construction of the hull and floats made of steel or aluminum (welding sheet metal)...
     
  10. kilocharlie2
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    kilocharlie2 Junior Member

    Do you think think they are floating an ad to see if they should go build the first one then test it out?

    If so, then maybe you can beat them to it if you KNOW you have the market for such a "budget gulper" - it sure looks expensive.

    My only criticisms are that the pylons connecting the deck to the pontoons should look more like sharp, airfoil-shaped inverted cones, and they should be taller. This is what gives the SWATH it's amazing stability, yet allows good speed in rough seas. The pontoons are either displacement type and built for a specific speed / Reynolds number / Froude number range, or planing type. Both types are volume specific. Tall, conic pylons allow big waves to pass through without disturbing the ships attitude much. Sharpening the leading edge and shaping the horizontal cross sections like airfoil sections help the vessel make speed indifferent to the waves up until they reach the bottom of the deck. Some of the better SWATH designs look like a boat hanging on a gantry crane or a trimaran with deep outboard pontoons. I far prefer the inverted cone pylon over the straight tunnel hull type, especially in very high seas. The bottom of the deck should be a rough-water, narrow, deep vee hull hanging up high and dry.
     
  11. romanewas
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    romanewas Junior Member

    Do you know how big would have to be the floats to swim 20 knots in a 5 'wave? What size is to have the hull? I'm talking about displacement mode. The gross weight of the boat (passengers, fuel, etc.) let say 8 tons.
     
  12. kilocharlie2
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    kilocharlie2 Junior Member

    4 forces to consider - gravity goes down, buoyancy goes up, thrust goes forward, drag (both water and wind) goes back. Forces are equal, boat sits still. Add force, boat moves in the direction of that force until acted upon by another force.

    So, 8 ton gravity, 8 ton buoyancy in the pontoons (there is more buoyancy in the pylons and the deck's hull that hangs in the air if the waves get up that high). Twist the throttle, the boat goes forward against sum of drags. Give it more throttle, the boat goes faster. Planing-type hulls generally need MORE THAN 7 times the thrust than displacement boats to "climb out of their own hole" and plane off on the planing pad (the flat area of the bottom in the back).

    If you are designing the whole thing, start with the requirements. Seating for 35 passengers, captain, and crew, moving space, outside space. Anchoring systems, all requirements on structures above waterline, safety equipment, everything on the vessel. Figure out the weights of these. Make some realistic drawings to start the brainstorming process. You could even make up some "fake" mock-up pieces of cardboard boxes to simulate the actual topside deck, complete with cabin, guwale, etc. It needs to be well-thought out, you'll finish it on paper before you build it.

    You'll probably get a marine architect with SWATH experience to help with the pontoon and pylon design, and power requirements. He'll figure in the weight of the engines. Money well-spent. You'll end up with a boat that others will want, so you can sell the design and the boat. Home made "cut and try" boats may float, but many usually die of old age in dry dock, unless the home boat builder is smart enough to start with a set of plans. New designs are best done from the known tables of knowledge that marine architects are familiar with. You'll get a lot of help here on the forums, but hire an architect anyways. There's a ton of details on a boat that all work - either together or against each other - and they all affect your ride. Easy to visualize flat water conditions, but what about 20 foot seas? Hurricanes? Those things happen out at sea. Well-designed vessels fare pretty well against rugged conditions, poor designs make you think, "I wish I had bought a better life raft."
     
  13. romanewas
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    romanewas Junior Member

    Of course, I will hire designer. But maybe someone knows such basic data on the basis of some approximations. Also, I'm not going to sail the boat with waves higher than 5 '. I will always be up to one hour from the safe harbor.
     
  14. kilocharlie2
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    kilocharlie2 Junior Member

    Pylon height is up to you, and has a lot to do with wave size tolerance. The pylon height - to - deck width ratio should probably be within something like the golden ratio, phi approximately 1.618034 to 1, just a guess. A SWATH owner should speak up and say, "No! 1:1 is better because X", or "No.! 3:1 is correct because Y".

    Pontoon design comes late in the game, after you have a good idea of what the weight is going to be. Volume of seawater displaced gives buoyancy, shape determines drag at speed. You need to draw and make real the deck and what the control room looks like. The architect will design a 20+ mph pontoon set that floats your SWATH, and give an estimate to the price to build the project.
     

  15. romanewas
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    romanewas Junior Member

    You say that if the deck has a 20 'width then the height of the pylon is expected to be over 32' ?? Somehow it seems to me impossible ...
     
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