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Righting moment on Bayline 3870-gctid405753

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    Righting moment on Bayline 3870-gctid405753

    I was hoping someone could give me this information.

    We are currently doing a lot of rough cruising and I am told the boat can handle more than I think it can.

    How do I determine the "righting moment" of our 3870 Explorer?

    Help please

    #2
    Here's a link to a paper discussing small boat stability:

    http://newboatbuilders.com/docs/stability.pdf

    You can get a good handle on the general inherent stability of your vessel by learning the terms designers use when assessing various hull forms and ballast configurations.

    For further information, do a Google search for 'righting moment'.

    In general, righting moment is the resistance to heel (tipping) inherent in a hull form. This resistance is influneced by the beam of the vessel, the center of gravity (CG), the center of buoyancy (CB) and the shape of the hull (chined vs, non-chined). In a powerboat, the location, weight and distribution of engines, tanks and furniture form the ballast structure which greatly influences the CG. The lower in the hull these items can be located, the lower the CG is. Lower CG means greater righting moment. There is a lot more to designing in the CG of a vessel but that is essentially the basics.

    In reference to the hull form of the 3870: The 3870 should have good initial stability and righting moment because it has wide beam, hard chines, twin engines mounted low in the hull and multiple well distributed tanks. Even though it has a flybridge, the superstructure is not so high or weighty as to cause the CG or the CB to be raised significantly. Higher CG's and CB's tend to increase roll which degrades a vessels' stability.

    Steep beam seas are the biggest enemy of powerboats so most mariners try to avoid them.

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      #3
      Sound like you are in engineering or something else technical. (Me, too)

      Scientifically, it's called "GzMo". However, as a licensed master, and 26 year vetran of the CG Auxiliary, instead of worrying about calculating something in a world of independant variables all working (or not) together, I would concentrate on handling the boat to minimize the need for knowing the GTzMo, and/or testing it.

      If I am coming on a bit strong, this is coming from someone who spent many days (and nights) looking for the aftermath of a boater who did a major no-no. Some we did not find.

      Some hints, when the going gets rough:

      Only one person on the flybridge. ALL others as low in the boat as possible.

      Avoid at all costs, heavy seas on the beam. Zig zag ot tack thru the seas for a more favorable motion.

      Keep the bilges dry; water in motion is deadly

      Speed does not count, handling does

      Probably, when the boat was in the design stage, Bayliner did some tests by the CG for the GzMo, However, in this ligitous society we live in, they will deny it, and/or refuse to disclose the results.

      besides that, we boaters do not operate in a test lab like where the data was taken. They do this in calm water, and use sandbags to simulate passengers. Real world, passengers move around, usually the wrong way when the boat heels.
      Captharv 2001 2452
      "When the draft of your boat exceeds the depth of water, you are aground"

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