Beginner: shape for 78feet monohull?

Discussion in 'Motorsailers' started by Pancho, Aug 10, 2007.

  1. Pancho
    Joined: Aug 2007
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    Location: France

    Pancho New Member

    I want to design a 78 feet motored monohull capable of sailing in agitated waters. I wish the part of the boat under water to be as thin as possible. Is it possible ? What would be the shape I need ? Can I do long and thin or do I have to do it long and wide ? I wish the boat was aerodynamic.

    Thank you
  2. timgoz
    Joined: Jul 2006
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    Location: SW PA USA

    timgoz Senior Member

    Hello Pancho,

    Clarify something if you would. Do you want to design this boat on your own, or do you want a designer working with your thoughts as guidance do the work?

    Have you completed any succesful previous designs of smaller vessels? Is this boat design strictly theoretical, or do you intend to build, or have built, a vessel from the design?

    I'm just wondering because thats a huge & complex endevour unless you are already a competent designer. Anything over here 65' and up is legally considered a small ship. There could be certain regulatory standards that must be met with such a large boat.

    You certainly found a good forum here. Take care & happy research.

  3. Pancho
    Joined: Aug 2007
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    Pancho New Member

    I want to "design" this boat on my own. I don't know really how to use d softwares but I can sketch. So I would just like to sketch the boat, I need to know what would be the maximum width of the boat, how deep it is .... so that I can make plans.
    I don't intend to build the boat at least within the next 10 years .... so no.
    What I want to know is the dimensions and what would be the best shape for a polyvalent motored boat.

    Thanks a lot
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Typically, designers use well known vessels as reference for experimentation. By this, once the principles of yacht design are absorbed (books, education, etc.) you will find you've started collecting different designs. Some out of interest, others from historical value, maybe just to save a classic shape you like or other design elements that interests you in some way. After the concepts and engineering of these yachts is discernable by you, then you can speculate on improvements in the general "type" or model.

    Lets say you like the old fisherman style of coastal schooner, that worked the waters at the turn of the 19 -20th century, but don't like the high D/L and general performance envelope usually associated with them. Because of your new found understanding of building methods, materials, techniques, etc. you think you can lower the D/L considerably, improving the performance substantially. You work up a set of scantlings around a target displacement and see how good you efforts turn out. Maybe you see things in the underwater areas that could benefit from your knowledge, so you hone the ends down, modify the beam/length ratio, pair down the appendages to the minimum, incorporate clever foil sections, refine the waterlines, etc. All this work is little more then an educated opinion, based on the level of experience and education you have, in regard to the dynamics of yacht design and structure engineering.

    Once you've educated yourself enough to have the confidence to tackle a project like this (quite a substantial one in deed) then work up the drawings. Without the understanding of several engineering disciplines, you're pretty much helpless to perform this task with any reasonable hope of success. There are many schools and a few correspondence based courses available (so you don't even have to leave you easy chair) which can offer the education you need. You drawing skills will be helpful.

    To directly answer you question about beam/length ratios, there are a wide variety of options, based on many factors and no general guides in this vain. You'll find, more often then not, this is the case in yacht design.

  5. Pancho
    Joined: Aug 2007
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    Location: France

    Pancho New Member


    Thank you ! I'm going to wor on that !:rolleyes:
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