Looking For Educated Feedback on Design

Discussion in 'Boat Design' started by baboon, Feb 16, 2011.

  1. baboon
    Joined: Feb 2011
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    Location: Arizona

    baboon New Member

    OK...here goes. Over the last few years I have helped build and weld a couple of aluminum commercial gillnetters and I am now more interested in the technical aspects of hull design.

    So I have been playing with Carlson.hul to produce a simple developed hull with what I think will be desirable dimensions. Then imported into Delftship to get better modeling visuals and would like to further develop bulkheads, decks, and house using its layering capability. However, before I spend several more hours I would appreciate any and all feedback from those that are more educated than I am about this boat designing business.

    Attached are a couple of photo/images, as well as the Delftship file if you are interested in taking a closer look.

    My questions include, but are not limited to the following:

    Reverse Chine: At first I did not include a reverse chine but only a hard flat chine. Then I want to produce some lift to keep the boat able to go faster when not loaded, so I put in an 8 degree reverse chine at the stern and flattens after it rises to the bow. The Chine is only 6 inches wide, is that enough, not enough?? My dead rise at the stern is 12 degrees.

    Sheer: Again at first I put a sheer in the top of the hull (6"), and the chine and keel also rise about 4-6" from the deepest point. I have reduced the top sheer line to about 4 " and I am not sure if any rise in the chine or keel is adding any efficiency to the design. My thought was that the stern would dig when power was applied, so a sheer to the chine would maximize the lift and stability while under power?

    Beam: related to the above sheer. I have narrowed the beam at the stern about 4 inches from the maximum (near midship) Thought is that narrowing it would give better efficiency through the water, but is it just a cosmetic?

    Tunnel for shaft and prop: I have not "cut out" a tunnel from the keel/design yet. Not sure if a simple flat/delta with a keel dropped vs. gullwing/trapezoid, vs. a nice rounded tunnel would be ideal? I have seen all and many others. The tunnel is necessary to keep the boat relatively shallow.

    That is a start. Thanks for the feedback and comments. (I am new to the forum,so please forgive any and all of my ignorance and shortcomings). Look forward to learning a few things.

    Attached Files:

  2. Tad
    Joined: Mar 2002
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    Tad Boat Designer


    Designing boats is a curricular thing........

    First you need to guess the weight (operating displacement) based on the size (structural weight) and loading (fuel, fish, ice, etc) of your boat. The weight and installed power will give you the operating speed....which defines the hull shape and location of your centers (LCB, LCG, etc)......

    No one can say much useful about your hull until you define the displacement, dimensions, centers, coefficients, and expected speed......

    See this for some ideas.....http://www.tadroberts.ca/about/pdf/power-boat-design-form-and-function.pdf
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  3. baboon
    Joined: Feb 2011
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    baboon New Member


    Thanks for the reply and the article, it is very informative and I am keeping a copy for future reference.

    The beauty of using Delftship is that it does most, if not all of the calculations mentioned in your article. The Hydrostatic reports are attached. Hope this helps formulate some comments.

    Attached Files:

  4. baboon
    Joined: Feb 2011
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    baboon New Member

    Also.... here is a link to a Fiberglass gillnetter, with roughly the same dimensions I am using, with the engine that I would like to design for (Cummins QSM11 660hp), planing at over 20 knots. With 4,500 lbs of fish onboard, I am guessing that total displacement of that boat to be approximately 25-28,000 lbs.

    The link is: http://www.youtube.com/watch?v=MDsKewoM2vs&feature=related

  5. Perm Stress
    Joined: Sep 2009
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    Perm Stress Senior Member

    Do not want to sound negative,
    The weights have to summed up first, and than hydrostatic software used to design a hull to support the sum total of them.
    Just as it is in real physical world: hull will keep sinking and trimming until weight of displaced water is equal to weight loaded on to this hull, and center of volume is directly below center of gravity, no matter where Design Water Line is drawn by builder or designer.
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