Re hull shapes

Discussion in 'Multihulls' started by Matt.D, Feb 13, 2008.

  1. Matt.D
    Joined: Oct 2007
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    Location: gold coast

    Matt.D Junior Member

    Toying with the idea of building a 15m full displasment steel cat.
    Powerd by 2x 80hp outboards mounted inboard as a cheap alt to saildrives.
    Avg speed 10 kts aprox.
    Aprox weight 23 tones

    Ques. What shape is the best? Eg round chine or v ? canoe or square stern with a gragual point? or just a v point on the front?

    R these speeds attainable?

    Sorry i had some drawings but the failed to load!

    Thanks for your input!
     
    Last edited: Feb 13, 2008
  2. Spiv
    Joined: Jun 2007
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    Location: The Big Wide Blue Brother

    Spiv Ancient Mariner

  3. Guest625101138

    Guest625101138 Previous Member

    I put your constraints to Godzilla and it came up with the attached for the minimum drag ship. It would take around 30kW to push it at 10kts.

    The shape is not quite what I expected but Godzilla often gives surprises. I am reasonably certain that there were no other constraints that drove the shape.

    Rick W.
     

    Attached Files:

    1 person likes this.
  4. Matt.D
    Joined: Oct 2007
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    Matt.D Junior Member

    Thanks mate ! What an awesome read !
     
  5. Matt.D
    Joined: Oct 2007
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    Matt.D Junior Member

    Hi Rick , thanks for ur reply ,still a bit new but what is Godzilla? and u mentioned attachment ? cant seem to find any? and is that 30kw of trust or engine power? Full of questions arnt i!!! : )
     
  6. Guest625101138

    Guest625101138 Previous Member

    Godzilla is a hull optimising program.

    The 30kW is power as in about 40HP. Roughly 1HP equals 750W and 1kW equals 1000W.

    The attachement is a lineplan beneath post #3 on this thread. If you open the thread and click on the small image it will show up full size. Or to make it easier I will place a link here:
    http://boatdesign.net/forums/attachment.php?attachmentid=18842&d=1202978944

    Rick W
     
  7. Matt.D
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    Matt.D Junior Member

    Thanks Rick.
     
  8. yipster
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    yipster designer

    Rick, not an swift turner but allmost old fashioned keels, Rudy Choy ( and i ) would love to see those hulls sail boardless
     
  9. Guest625101138

    Guest625101138 Previous Member

    Yipster
    The draft is over 1.6m on a 15m WL so not the ideal foil but a lot more efficient than the typical rounded hull.

    I was surprised when Godzilla produced it so I checked that there were no other constraints unintentionally in play. I could not find any. Thinking about it and looking at current design trends for heavy displacement cats it seems reasonable.

    It is a heavy boat for 15m but it would not take a huge sail to achieve design speed.

    Rick W.
     
  10. Matt.D
    Joined: Oct 2007
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    Location: gold coast

    Matt.D Junior Member

    Hey guys im thinking of powered rather than sail and if i made the hulls 1600mm wide would this slow it to much?
    Want to keep all accom. in the hulls and leave the wing deck for a large saloon area with a seprate dining aft and galley midship.
    A little unconventional i know, but the salloon /dining area in standard cats just dosent seem inviting to me. whats ur thougts?

    Matt
     
  11. Guest625101138

    Guest625101138 Previous Member

    Required power goes up to around 60HP.

    Rick W.
     

  12. yipster
    Joined: Oct 2002
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    Location: netherlands

    yipster designer

    i tend to agree with that, think better interior design can make the difference
     
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