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Re: [boatdesign] 2. 16' hard-top trailer sailer design project (16HT-CTS)

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  • Robert Gainer
    Lew said, ... Why is that? The easier to capsize part. All the best, Robert Gainer _________________________________________________________________ On the
    Message 1 of 6 , Sep 1, 2004
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      Lew said,
      >The wider the boat gets, the more stable it will be
      >initially, but the easier it will be to capsize.


      Why is that? The easier to capsize part.
      All the best,
      Robert Gainer

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    • Lew Clayman
      ... It s a general statement, many other thing (ballast, form, etc etc, influence these thing. But focussing for the moment on just the one factor... A wide
      Message 2 of 6 , Sep 1, 2004
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        --- Robert Gainer <robert_gainer_2@...> wrote:

        > >The wider the boat gets, the more stable it will be
        > >initially, but the easier it will be to capsize.

        > Why is that? The easier to capsize part.

        It's a general statement, many other thing (ballast,
        form, etc etc, influence these thing. But focussing
        for the moment on just the one factor...

        A wide boat is initially stable, in port-starboard
        listing (leaning) terms. It takes a great deal to
        submerge the part way out on the "low" side, and a
        great deal to lift the part way out on the high side.
        Think of levers. However, once a wide boat gets to
        around 90 degrees, over it goes, flop. Way before
        this, comes the point where you submerge the sheerline
        on the low side and start to take on water - bad news.

        A narrower boat will be less stiff initially (shorter
        levers) but will usually "flop" a lot later. Also it
        can tip to a larger angle of list before submerging
        the rail and "drinking the ocean."

        Like I say, these are general tendencies and many
        other factors come into it. But for initial design
        purposes, I am of the opinion that keeping basic ideas
        pretty conservative allows two things: (1) Fewer
        forced radical compensations elsewhere in the design
        (like extreme ballast, say) and (2) Greater "elbow
        room" to incorporate more unforced (desired,
        specialist) "extreme" or "radical" elements later.

        In other words, if you start off plain vanilla, you
        are unlikely to be forced into oddball features yet at
        the same time, desireable oddball features are more
        readil accomodated.

        Start off radical and you have to work a lot harder,
        in my experience - though of course, if your initial
        concept is radical, there's noplace better to start
        from!!

        In this case, a 16' daysailer/hard-top microcruiser
        that rows and sails well and motors a little bit too
        does not sound outrageously radical. It'll have
        tradeoffs, but not (I'm guessing) anything too
        wildass.

        -Lew, who doesn't mind a wildass boat design in the
        least, but didn't think one was being discussed in
        this case.




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      • nutty_boats
        ... It has to do with wave action. Without waves, that would not be true. For example, the racing boats on Minnisota lakes, where there are no waves to speak
        Message 3 of 6 , Sep 2, 2004
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          --- In boatdesign@yahoogroups.com, "Robert Gainer"
          <robert_gainer_2@h...> wrote:
          > Lew said,
          > >The wider the boat gets, the more stable it will be
          > >initially, but the easier it will be to capsize.
          >
          >
          > Why is that? The easier to capsize part.
          > All the best,
          > Robert Gainer

          It has to do with wave action.

          Without waves, that would not be true. For example, the racing boats
          on Minnisota lakes, where there are no waves to speak of, tend to be
          wide and flat. Those boats do not capsize easily. In fact, the wider
          it is, the more stable it is.

          But in bays and on the ocean, there are waves. It's the lever action,
          the wider the boat, the more effect a wave has in tipping it over. If
          the wave is high enough, the boat can tumble. Interestingly, a wide
          boat is also more prone to pitch poling. The Colin Archer
          redningsskøyter had a wide beam, but they tamed the tendency to
          capsize by having a large keel as roll damping and heavy weight to
          increase inertia.

          On a very narrow boat, there is a different problem again connected
          with waves: unless it is very heavy, waves can lift up the bow and
          stern enough to lift up the center of the boat as to reduce or
          eliminate resistance to rolling enough to cause capsize. This is why
          on many kayaks the ability to do an eskimo roll is so important.

          The length six times the beam compromise seems to give maximum
          seaworthiness in waves.

          The more roll damping a boat has, the more it resists wave induced
          roll. The cross section shape that gives the greatest roll damping is
          a flat bottom box shape. That's why the traditional sharpie, with its
          L/B of 6 and box shape had such a good reputation for seaworthiness.
          But they had so much cross chine water flow induced drag that they did
          not have a reputation as easy rowing boats.

          Getting back to the question of the row/sail beach camper, will it
          have to deal with waves? Even an occasional wave, such as thrown up by
          a ferry or cabin cruiser can knock a wide boat over if it is already
          heeling under sail. Other than that, the main considerations will be
          interior space and ease of rowing.

          T. Lee.
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