Need an opinion or suggestion about catamaran design

Discussion in 'Multihulls' started by catfahmi, Jun 10, 2014.

  1. catfahmi
    Joined: Jun 2014
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    Location: Malaysia

    catfahmi New Member

    hello everyone.
    i'm a final year student that need help about my final year project. i am doing a water wheel turbine for my project that need to use catamaran design as base or floating platform because we are designing a minihydro (hydrocat) water wheel turbine on running river water. This is an upgrade from the previous design of water wheel turbine and i need to use catamaran concepts as it platform.

    i need some suggestion about the calculation and basic design that i can start off. how much the design can support and what else do i need to consider related to the design. with the attachment of the previous design of the water wheel floating platform(pontoon boat).

    i hope that,anyone here could give some idea about the new design hull. the ideal length,beam and draft of the hull

    Attached Files:

  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Is your platform going to be stationary (anchored) in the river?
    If so you don't need any rocker to the hull, that will just reduce the bouyancy and weight carrying of the design, for a given draft.
    Why the rounded v shape for the hull cross section? Unless you will be trying to prevent sideways movement due to wind, like on a sailboat, it will be better to have a round crossection.
    On any catamaran design, having walking platforms at the extreme ends is a poor choice, there is no bouyancy at the ends to keep the "boat" level. Move them in as much as possible - closer to the turbine.
    To keep the boat straight in the current, have the stems of the boat slightly underwater. 1 1/2" each will do.
    To determine how much the platform will support you will first have to estimate the total weight required with the turbine, platform, and anyone standing on it. Then do a bouyancy calculation on your initial design hull. If the platform is sitting too high in the water or too low, then change the dimensions of your platform, re-estimate the weight, and recalculate the bouyancy (and how high in the water the waterline is).
    This recalculation will probably need to happen a minimum of 4 times as you refine the weight of the platform and turbine and person/ tools, etc. If you are really trying to get it right you might recalculate a lot more times.

    Don't forget that symmetric boat hulls cause waves from the bows. The waves from each bow will meet in the middle, raising the water level right where your turbine is. Since the turbine will also cause a wave the water level in the middle of the boat could be quite high, possibly washing over the deck. You might want to make a model scaled in size and weight and watch what happens in the water. Your platform might need to have wider separation as a starting point.

    Good luck, any design is a lot of work.
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I think skegs may help too. Sidewinds will tend to make the boat shift and not be aligned with the current.
  4. catfahmi
    Joined: Jun 2014
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    catfahmi New Member

    Yes, the catamaran is going to be anchored in the river and will not move.(not sailing)
    Second one is i didn't understand what is the mean of rocker to the hull and how they will reduce buoyancy. Is the rocker means the keel or the sharp edges under the v shaped.
    Did you mean the semi circular cross section? Or wider shape than the v shaped? Means that, not the narrow shape.
    the turbine blade is at the middle of my catamaran design which is length of 2400mm. that why the is hollow a the middle of my platform. Do i need to increase the length of catamaran hull?
    Are stems and skegs is a same thing?

    River flow at 1.3m/s only. Do I need to consider for symmetric boat hulls?

    The previous water turbine is weight 1000kg. For this new design I estimate to support 800kg for total. Based on design that I made for hull is weight at 126kg/hull and platform at 240kg which is total of 492kg. how much the weight for a simple catamaran?
    What is the thickness of the hull normally used? i use 16mm thick for my design
    Fb =ρVg
    Ρ = 1000kg/m3
    V(displace volume) = 126.643 kg/0.427 m3 = 296.588 kg/m3 (both hull = 593.176 kg/m3)
    Gravity =9.8 m/s2
    Is it correct if I got the value of Fb =5812.703 KN….
    The immersion depth is about 0.457m
  5. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Since the thing is stationary, I think it would be a good idea to shape the hulls so instead of just support the load they actively channel and force water into the the turbine wheel for more power.
  6. catfahmi
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    catfahmi New Member

    SamSam do you have any idea or sketch of the hulls?
    here i attach the water turbine that inspired my design

    Attached Files:

  7. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    If it's going to be in a small stream it would probably be easier to drive a piling or two than build a hull to float the generator. If the boat part is necessary...

    My guess would be to go deep and narrow with the hulls. With the outboard edge of each hull being board flat and the hulls angled to push water into the channel between the two hulls. This will increase the pressure of the water flow thru the tunnel to help spin the generator a little faster. This may or may not have any real benefit, and it is beyond my engineering capability to run the numbers.

    Assuming that trying to accelerate the water thru the tunnel doesn't work out then just some aluminium pontoons would probably work fine.
  8. Leo Lazauskas
    Joined: Jan 2002
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    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    My colleague Dr. Brian Kirke has worked on hydro-kinetic turbines
    with his (Malaysian) student, M. Anyi. Their work uses different
    turbines, but if you look up the following papers you should get a
    contact address for Mr. Anyi who might be able to give you some
    advice. Or write to Brian who can give you Anyi's email address. See:

    Anyi, M., Kirke, B.K. and Ali, S.,
    "Remote Community Electrification in Sarawak, Malaysia",
    Renewable Energy, Volume 35, Issue 7, July 2010, Pages 1609-161.

    Anyi, M. and Kirke, B.K.,
    "Evaluation of small axial flow hydrokinetic turbines for remote communities",
    Energy for Sustainable Development 14, 2010, 110-116.

    Anyi, M. and Kirke, B.K.,
    "Hydrokinetic turbine blades: Design and local construction techniques for remote communities",
    Energy for Sustainable Development 15, Issue 3, Sept 2011, 223-230.

    Good luck with your project!
  9. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Here's both the idea and a sketch provided by "HydroCat".

    At around 0:55 you can see the funnel effect of the hulls along with the extra depth and close side tolerances to the turbine wheel that maximize the water flow.

    In the original sketches you provided, say the platform was 6 feet wide and the wheel was 1 foot wide. The wheel is only using a 1 foot wide piece of river. If all the water from the 6 foot wide front of the platform was directed inwards and into the wheel, I imagine you could have a 2 or 3 foot wide wheel and capture at least 2 or 3 times more energy.

    Since the platform is going to be anchored or tied to something, you don't need any kind of efficient 'boat shape' that will move smoothly through the water. You need something that will float whatever load is put on it and after that it's only purpose is to enhance the working of the turbine wheel by funneling water to it.

  10. catfahmi
    Joined: Jun 2014
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    catfahmi New Member

    thank leo i will try contact Dr. Brian Kirke

    thank samsam for the video.I only seen another video version of hydrocat which do not show the sketch of it
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