RE: [PSUBS-MAILIST] Weighing

[Alec Smyth <Asmyth@changepoint.com>]

Hey, it worked! By the way, the data is out of date in the sense that much
of what is color-coded as "designed" is thankfully built by now.

Alec

-----Original Message-----
From: Alec Smyth [mailto:Asmyth@changepoint.com]
Sent: Monday, August 05, 2002 11:05 AM
To: 'personal_submersibles@psubs.org'
Subject: RE: [PSUBS-MAILIST] Weighing


I did just the same sort of spreadsheet, except as my design is laterally
symmetrical I only needed two dimensions. I'm not at all sure this will
work, but I just posted it to http://www.prismnet.com/~moki/subfiles.html. I
know its intended for images, so this might not be downloadable. But hey, it
might work.

Please disregard the actual data in the spreadsheet, which will not make any
for most designs. I am purposely trying to minimize my righting moment
because this particular design will be capable of inverted flight.


Alec

-----Original Message-----
From: Marco Zeeman [mailto:marco@zeeman.co.nz]
Sent: Sunday, August 04, 2002 9:12 PM
To: personal_submersibles@psubs.org
Subject: 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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> 
>