Re: [PSUBS-MAILIST] Weighing

[Doc <doc@bionicdolphin.com>]

Thanks Gary,

I understand now. I'm still flashing back and forth between
Center of Buoyancy and Center of Lift, and Center of Mass
and Center of Balance.

Sorry William, I turned off the vcf but forgot to restart the application,
my bad.

Doc

"Gary R. Boucher" wrote:

> Doc,
>      All of the calculations are for the sub outside of the water.  The
> Center of Mass is independent of being inside or outside of the
> medium.  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.
>      Also, remember that nothing inside the hull contributes to the
> CB.  The Hull itself is the largest component effecting buoyancy.  Thought,
> only things that go into the water can generate buoyancy.
>      Payload in many airplanes is a large percent of the aircraft's
> weight.  Moderate payloads in a sub are usually a much smaller ratio to the
> weight of the sub.
>      Remember that the CM will always swing down to be located below the
> CB.  If you add payload and the CM changes by going forward, that new CM
> will rotate the sub bow downward until the CM is directly below the CB.  In
> Most subs the CB much higher than their CM.  Therefore a small longitudinal
> change in CM will cause only a small rotation.  In my sub the CB is very
> close to the CM.  Therefore if I change my CM by just an inch or so I have
> a very noticeable angle up or down as a result.
>
> G Boucher