Re: [PSUBS-MAILIST] Center of gravity Vs. Center of Bouyancy

[Lew Clayman <lew_clayman@yahoo.com>]

--- Ed Greany <crest25@attglobal.net> wrote:
> "For small surface vessels, and I suppose for small subs, crew weight is
> an important and moveable component of overall weight, so CG moves every
> time the people move."
> and
> "movement is so much more constrained than on a surface vessel, this is
> less important and CG is more reliably fixed at or near the nominal
> design location."
> 
> I suppose your point refers to a very small sub - perhaps one person -
> but on an overall scale and especially larger boats, the center of
> gravity or "Trim" for a better word to use is very important. 

Yes, I was thinking psubs and perhaps slightly larger, where crew mainly stays in their seats.  

It is common on similar sized surface boats that crew weight is over 50% of the total.  Must be
less on a psub, but still significant.

Not to get too pedantic here, but if you move weights so as to to change trim, have you not in
effect changed CG?  And if you move other weight (water, below) to compensate, haven't you changed
it back?  Or do I still not get it?

> I recall on the big boats, when we wanted to "get back at" the Diving
> Officer (submerged) we would gather all the crew we could aft in the
> engine room. Then, we would all race to the forward torpedo room. When
> you have all this weight moving 400 feet all at once, it will require
> moving some water (aft). So the command to trim from forward to aft is
> given. About the time the boat is trimmed again, all the guys would race
> aft again and the cycle starts over. Pretty soon, the OOD senses what
> his Diving Officer doesn't and makes the announcement over the 1MC
> intercom system. The gigs up and every scats. Who me? Naw, never!

Love it!

I had forgotten about trim tanks, shows I'm a newbie.  Eases design when you have a mechanism to
correct things.  Duh.  Never realized it could be a toy, too.

Thanks for the lesson.

-Lew



=====
"Yo no soy marinero / Soy capitan"
          - Traditional Mexican Lyric (La Bamba)
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