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

[Doug Niessen <dniessen@pacbell.net>]

Ed,

If I remember correctly from sub school (1964), doesn't the center of
buoyancy move up and down the vertical axis of the boat as the ballast
tanks are blown or flooded? Seems that in the Trigger trainer they
stressed the point of quickly and completely blowing the ballast tanks
during surfacing. There is a point when the center of buoyancy and CG
cross during diving and surfacing and at that point a big wave broadside
to the sail could capsize the boat.

This may not be a problem for small subs if the ballast tanks don't
encompass the hull.

Or..... I may be making all this up and am completely wrong.

We have done the same thing, moving ten or fifteen guys for to aft to
play with a fresh diving officer. The giveaway is these guys streaming
through control like a line of ants.

Cheers,
Doug,   K6STS
ex-STS2 (SS)  

Ed Greany wrote:
> 
> Lew,
> 
> You said:
> "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. The center
> of gravity is useful when determining where to weld the hook to raise
> the craft in the middle by a winch or crane so it balances fore and aft.
> Trim, on the other hand which I believe what you are referring to is the
> movement of ballast (water or weights) to level the sub both on the
> surface and submerged. Yes, it is most important in a very small craft.
> 
> 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!
> 
> Ed
>