[PSUBS-MAILIST] Hull Calc: 78" spheres

[Sean T. Stevenson via Personal_Submersibles]

On 2015-01-11 11:09, David Colombo via Personal_Submersibles wrote:
> Hi Sean, Couple of questions. Is the net payload capacity in kg, the
> amount that would make the sphere neutral buoyant? what FOS is the rating?
>
> Best Regards,
> David Colombo

Exactly.  The payload capacity shows how much mass can be added inside
the sphere before it becomes neutral in (in this example) 1025 kg/m^3
seawater.

The software was written to use the equations prescribed in the "ABS
Rules for Building and Classing Underwater Vehicles, Systems and
Hyperbaric Facilities" (2014).  The factor of safety in that example is
given by the usage factor eta, prescribed by ABS as 0.67 for spherical
shells under external pressure (Section 6/23.3).  This means that the
maximum allowable working pressure is 0.67 times the critical or sphere
limit pressure.  While this is the absolute minimum factor of safety
acceptable by the rules, additional margin should probably be added by
the designer.

I should also add that the weight and buoyancy calculations in the
posted images make no accommodation for corrosion allowance (Section
6/13).  This is a change that I have made in the most recent revision of
the program, to add material to the outer diameter which is ignored by
the strength calcs but taken into consideration for the weight and
buoyancy numbers.

Sean