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Re: Physics?

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  • Ernie Murphy
    a boat would behave the same whether ballasted with 500 lbs. of water, or 500 lbs of lead Well, not true, let me see if I can give you a feel for this. I
    Message 1 of 37 , Nov 2, 2000
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      "a boat would behave the same whether ballasted with 500 lbs. of
      water, or 500 lbs of lead"

      Well, not true, let me see if I can give you a feel for this. I
      concidered this while imagineering a catfish, which has a water-
      filled keel.

      Imagine you have any boat, and start filling baloons with water,
      knotting the end and tying off with string. Weigh each baloon, then
      dump it overboard. Tie the string to the gunnel and do another. How
      many baloons will it take to sink your boat?

      Well, not *quite* an infinite ammount. After all, the string and
      even the baloon itself have some weight. But close.

      Now start doing the same with fishing sinkers that have the same
      weight as a water filled baloon. As long as the weights stay off the
      bottom they will start to pull your boat down as soon as you add the
      first one.

      Sure, 500 pounds of water and 500 pounds of lead both weigh 500
      pounds *in air*. Put em underwater and the water weighs.... zero,
      nada, nothing. Just remember: all boats float cause they weigh
      nothing.

      It's displacement you see. A 500 pound boat displaces an volumn of
      water that if you could scoop out and take out on land and weigh it
      would weigh... exactly 500 pounds. If the weight of water your boat
      displaced weighed any less, your boat would be sinking.

      (Water inside the boat isn't displaced. It may be out of place, but
      thats something different.)

      The lead will have weight underwater, as it is denser then the
      water. A thing is good for balast under water as long as it is denser
      then water, but only by the difference in it's weight and the weight
      of water it displaces.

      For my 'water keel' catfish, the water filling the keel still does
      a few useful things: It still has mass, hence it will help damp out
      movement (it will take more time for it to heel all the way over wet
      over dry), and also help carry it thru tacks. But, since underwater
      water "don't weigh nothing," it will not add to the righting moment
      till the boat heels to it's side and the keel comes out dry. And once
      outside it gets heavy FAST, helping to stop a rollover when it's
      getting disasterous.

      -Ernie


      --- In bolger@egroups.com, "Bill Jochems" <wjochems@s...> wrote:
      > Estimado grupo Bolger
      > I have a question about something which is related, I think, to
      David
      > Ryan's question about 100 lbs. centered vs. 50 lbs. on each side.
      Bolger
      > has written that water ballast is of no effect until it has been
      lifted
      > above the water line. I don't understand this. It seems to me
      that weight
      > is weight, be it water, concrete or lead; and that a boat would
      behave the
      > same whether ballasted with 500 lbs. of water, or 500 lbs of lead,
      if the
      > centers of gravity of each were the same.
      > Bill Jochems
      > -----Original Message-----
      > From: David Ryan <david@c...>
      > To: bolger@egroups.com <bolger@egroups.com>
      > Date: Monday, October 30, 2000 10:17 AM
      > Subject: Re: [bolger] Physics?
      >
      >
      > >Hooray! Dr. Wah would be proud, even if he never did understand
      what
      > >I was doing in his class.
      > >
      > >Moving on.
      > >
      > >In a flat bottomed boat, is there a difference between putting 100#
      > >dead in the center of the center, or putting 50# on each chine?
      > >
      > >YIBB,
      > >
      > >David
      > >
      > >
      > >
      > >>That's about right. Let the weight of your 900# beam act in the
      middle;
      > the
      > >>lever arm is from fulcrum is then (15-3)=12', so the moment is
      > 12*900=10800
      > >>ft-lb. To balance the beam, you need to apply 10800/3 = 3600# on
      the
      > short
      > >>end (i.e. 3*3600=10800 => equilibrium).
      > >>
      > >>(To figure it much, much more simply, convert your units to SI
      metric,
      > >>divide by 1000 and then once again by .001 ;-)
      > >>
      > >>Gregg Carlson
      > >>
      > >>At 09:58 AM 10/30/2000 -0500, you wrote:
      > >>>FBBB --
      > >>>
      > >>>It's been 12 years since I cracked a physical text book (my
      degree is
      > >>>in fine art, go figure.)
      > >>>
      > >>>Anyone care to check me on this:
      > >>>
      > >>>A 30 foot beam that weighs 30 pounds per foot is balanced on a
      > >>>fulcrum 3 feet from one end (and 27 feet from the other.)
      > >>>
      > >>>By my (suspect) calculations, there is a torque of 10935 foot-
      pounds
      > >>>on one side, and 135 foot-pounds on the other.
      > >>>
      > >>>Further (dubious) arithmetic says that if I apply 3600 pounds of
      > >>>force directly on the end of the short side, the beam will be
      > >>>balanced.
      > >>>
      > >>>Anyone wanna check my math?
      > >>>
      > >>>YIBB,
      > >>>
      > >>>David
      > >>>
      > >>>
      > >>>CRUMBLING EMPIRE PRODUCTIONS
      > >>>134 W.26th St. 12th Floor
      > >>>New York, NY 10001
      > >>>(212) 243-1636
      > >>>
      > >>>
      > >>>Bolger rules!!!
      > >>>- no cursing
      > >>>- stay on topic
      > >>>- use punctuation
      > >>>- add your comments at the TOP and SIGN your posts
      > >>>- add some content: send "thanks!" and "ditto!" posts off-list.
      > >>>
      > >>>
      > >>
      > >>
      > >>
      > >>Bolger rules!!!
      > >>- no cursing
      > >>- stay on topic
      > >>- use punctuation
      > >>- add your comments at the TOP and SIGN your posts
      > >>- add some content: send "thanks!" and "ditto!" posts off-list.
      > >
      > >
      > >CRUMBLING EMPIRE PRODUCTIONS
      > >134 W.26th St. 12th Floor
      > >New York, NY 10001
      > >(212) 243-1636
      > >
      > >
      > >Bolger rules!!!
      > >- no cursing
      > >- stay on topic
      > >- use punctuation
      > >- add your comments at the TOP and SIGN your posts
      > >- add some content: send "thanks!" and "ditto!" posts off-list.
      > >
      > >
    • Jeff Gilbert
      Bravo Jim Pope. My vote for the worlds best sub 40ft cruising monohull, the Roger Martin designed Grey Wolf, holds a ton of water in a tank just under the
      Message 37 of 37 , Nov 4, 2000
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        Bravo Jim Pope.
        My vote for the worlds best sub 40ft cruising monohull,
        the Roger Martin designed Grey Wolf, holds a ton of water
        in a tank just under the side-deck. Pumps it across to
        a mirror tank when tacking. Sails flatter, and if racing the football
        team on the rail can go below or home.This arrangement does take
        72 cubic feet out of the boat, but the football teams bigger!
        And half is a bouyancy tank
        Jeff Gilbert.


        ----- Original Message -----
        From: Jim Pope <jpope@...>
        To: <bolger@egroups.com>
        Sent: Tuesday, October 31, 2000 3:23 PM
        Subject: Re: [bolger] Physics?


        No soy estimado, I'm approximato
        Pero for my two cents----
        As long as the water filled compartment is submerged, its only effect is to
        reduce the vessel's buoyancy. After all, it weighs the same as the rest of
        the
        water all around the boat. When, however, you lift that filled ballast tank
        above the ocean's (or lake's, or river's) surface it weighs much more than
        the
        air and generates a gravity vector downward from its center of mass. If that
        center is out on an arm from the boat's center of buoyancy, the water
        ballast
        adds to the total righting moment acting on the boat.

        Bolger's boxes enjoy a huge movement of the center of buoyancy towards their
        top deck as they heel over and submerge more and more of their square
        topside
        shape. That allows water ballast boxes located out towards the chine to
        gain
        effectiveness,
        an advantage that low sided hulls, such as the traditional sharpie, can't
        offer. To be self righting that type of boat needs to employ different
        strategies such as lots of ballast. Traditional sharpies didn't, by the way,
        and were not self righting.

        Jim

        Bill Jochems wrote:

        > Estimado grupo Bolger
        > I have a question about something which is related, I think, to David
        > Ryan's question about 100 lbs. centered vs. 50 lbs. on each side. Bolger
        > has written that water ballast is of no effect until it has been lifted
        > above the water line. I don't understand this. It seems to me that
        weight
        > is weight, be it water, concrete or lead; and that a boat would behave the
        > same whether ballasted with 500 lbs. of water, or 500 lbs of lead, if the
        > centers of gravity of each were the same.
        > Bill Jochems
        > -----Original Message-----
        > From: David Ryan <david@...>
        > To: bolger@egroups.com <bolger@egroups.com>
        > Date: Monday, October 30, 2000 10:17 AM
        > Subject: Re: [bolger] Physics?
        >
        > >Hooray! Dr. Wah would be proud, even if he never did understand what
        > >I was doing in his class.
        > >
        > >Moving on.
        > >
        > >In a flat bottomed boat, is there a difference between putting 100#
        > >dead in the center of the center, or putting 50# on each chine?
        > >
        > >YIBB,
        > >
        > >David
        > >
        > >
        > >
        > >>That's about right. Let the weight of your 900# beam act in the middle;
        > the
        > >>lever arm is from fulcrum is then (15-3)=12', so the moment is
        > 12*900=10800
        > >>ft-lb. To balance the beam, you need to apply 10800/3 = 3600# on the
        > short
        > >>end (i.e. 3*3600=10800 => equilibrium).
        > >>
        > >>(To figure it much, much more simply, convert your units to SI metric,
        > >>divide by 1000 and then once again by .001 ;-)
        > >>
        > >>Gregg Carlson
        > >>
        > >>At 09:58 AM 10/30/2000 -0500, you wrote:
        > >>>FBBB --
        > >>>
        > >>>It's been 12 years since I cracked a physical text book (my degree is
        > >>>in fine art, go figure.)
        > >>>
        > >>>Anyone care to check me on this:
        > >>>
        > >>>A 30 foot beam that weighs 30 pounds per foot is balanced on a
        > >>>fulcrum 3 feet from one end (and 27 feet from the other.)
        > >>>
        > >>>By my (suspect) calculations, there is a torque of 10935 foot-pounds
        > >>>on one side, and 135 foot-pounds on the other.
        > >>>
        > >>>Further (dubious) arithmetic says that if I apply 3600 pounds of
        > >>>force directly on the end of the short side, the beam will be
        > >>>balanced.
        > >>>
        > >>>Anyone wanna check my math?
        > >>>
        > >>>YIBB,
        > >>>
        > >>>David
        > >>>
        > >>>
        > >>>CRUMBLING EMPIRE PRODUCTIONS
        > >>>134 W.26th St. 12th Floor
        > >>>New York, NY 10001
        > >>>(212) 243-1636
        > >>>
        > >>>
        > >>>Bolger rules!!!
        > >>>- no cursing
        > >>>- stay on topic
        > >>>- use punctuation
        > >>>- add your comments at the TOP and SIGN your posts
        > >>>- add some content: send "thanks!" and "ditto!" posts off-list.
        > >>>
        > >>>
        > >>
        > >>
        > >>
        > >>Bolger rules!!!
        > >>- no cursing
        > >>- stay on topic
        > >>- use punctuation
        > >>- add your comments at the TOP and SIGN your posts
        > >>- add some content: send "thanks!" and "ditto!" posts off-list.
        > >
        > >
        > >CRUMBLING EMPIRE PRODUCTIONS
        > >134 W.26th St. 12th Floor
        > >New York, NY 10001
        > >(212) 243-1636
        > >
        > >
        > >Bolger rules!!!
        > >- no cursing
        > >- stay on topic
        > >- use punctuation
        > >- add your comments at the TOP and SIGN your posts
        > >- add some content: send "thanks!" and "ditto!" posts off-list.
        > >
        > >
        >
        >
        > Bolger rules!!!
        > - no cursing
        > - stay on topic
        > - use punctuation
        > - add your comments at the TOP and SIGN your posts
        > - add some content: send "thanks!" and "ditto!" posts off-list.



        Bolger rules!!!
        - no cursing
        - stay on topic
        - use punctuation
        - add your comments at the TOP and SIGN your posts
        - add some content: send "thanks!" and "ditto!" posts off-list.
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