Re: formulas

[Ray Keefer <ray.keefer@eng.Sun.COM>]

Hi David,

> I've been reading some very old (try March) p-subs messages, and came
> across a couple discussing how to figure displacement -- and from there,
> how much the thing has to weigh to sink. I'm wondering how fussy you people
> (those of you who have done this; those who have something to sink) got
> with this: what about all the various junk inside, which takes up volume
> and weighs more than air? What about gizmos which protrude on the inside?
> Do you stick them in a carefully-calibrated bucket of water and measure the
> water level rise? Do you weigh every little thing before installing it? Or
> do you just figure ballpark: the volume of this cylinder plus this cylinder
> plus these hemispheres -- and then allow for heavy enough trim weights or
> big enough trim tanks to compensate for the little stuff?

To get really acurate you have to take in accout all the above. As you build
you have to weigh everything, including your welding rods!

Also keep in mind that the stuff external to the hull, like planes or soft
ballast tank structures, also displace water. So they are actually lighter in
water the in air.

Still you will not account for every static weight so you design light
and put in hard ballast. 

For the variable weights, to account for air usage (air has weight), depth
compression on hull, temperature, salinity of the water, cargo (people and
their stuff) you will need a VBT. How big despends on how much of a variance
in the variable weights you design for.

Regards,
Ray