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Re: [PSUBS-MAILIST] Weighing
Mike,
I developed that spread sheet years ago with some ancient software. I
don't think I can even call it up anymore. But, what you need to do is
simple. Create two spread sheets, or you can do it in one if you
want. You need one for weights and the other for buoyancies. You will have
the following columns:
Name of Component
X-position
Y-Position
Z-Position (optional)
Weight (buoyancy for second sheet)
X moment
Y moment
Z moment
The direct center of the hull is usually X=Y=Z=0
The X,Y,Z positions are the distances in inches from the direct center to
each component in their respective directions.
To get the X moment for a part you multiply the X position of that part
times the weight of that part.
The Y's and Z's are done the same way.
If the component is behind the direct center, it has a negative X value, if
below a negative Y, if to the left a negative Z.
Add up all the X moments with respect to sign. Do the same with the Y and
Z moments to yield three sums.
By dividing each sum by the total weight of the boat you will get the
location of the CM or what some call the center of gravity.
Lets say you have one simple submarine weighing 4000 pounds including all
components. You have a hull that is cylindrical, a 200-pound motor located
at X = -60 inches and a 300-pound battery in the forward end of the boat at
X = +50 inches. Lets see where the CM is.
X moment for Hull = (weight of hull) x (position) = (4000)(0) = 0
X moment for Motor = ( weight of motor) x (position) = (200)(-60) = -12,000
X moment for Battery = (weight of Batt) x (position) = (300)(+50) = +15,000
Sum of the moments = 0 - 12,000 + 15,000 = 3,000
Position of CM in the X direction = (total moment for X) / weight = +3,000
/ 4000 = .75 inch forward of center
Does this help your understanding?
G. Boucher
At 04:04 PM 8/4/2002, you wrote:
>On Sun, 04 Aug 2002 11:23:32 -0700 "Gary R. Boucher" writes:
>
> > The Center of Buoyancy is different. The CB is usually
> >calculated. I had a spread sheet that I used where I listed EVERYTHING
> >that went into the water. For example; even a steel bar used for
> >support had it's volume calculated. It was given an X, and Y position.
>Each
> >volume multiplied by the weight density of water gave a small upward
> >force. Each force was summed as a torque about the X=0 and Y=0 axis
> >of my sub. The result is the CB. The CB MUST be located above the CM
>or
> >the sub will roll inverted. This is good for excitement, but not good
>for the
> >crew that has to right the mistake.
>
>Can we see the spreadsheet? Is it on line?
>
>
>
>
>Mike H.
>
>
>
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