Re: [PSUBS-MAILIST] end caps [was: what is the diference k250- k600]

["Captain Nemo" <vulcania@hawaii.rr.com>]

----- Original Message -----
From: "Ian Roxborough" <irox@ix.netcom.com>
> Very interesting, I've been thinking about using two end caps
> welded together as a two person pressure hull.    The end caps
> I had in mind was a six foot diameter 2:1 elliptical end cap
> made of 12.5mm thick steel.
>
> This doesn't seem like a good idea after reading that, since
> it's not easy to have the entry/exit hatch clear of the
> waterline and avoid having any welds in the weakest/most stressed
> area (where the big curve meets the little curve)...


Ian,

Any structure will fail at some point; that doesn't mean they're all bad.
It means they must remain within the envelope of their own particular design
limitations.  Yours is an experimental homebuilt; possibly built for
recreational enjoyment.  Operated as such it could be made to work,
depending on what you want the submarine to do.

Your design isn't an elliptical cap mated to a cylinder; it's two caps mated
together.  Strain patterns of those two structures aren't the same.

Variations in the relative strengths of the weld versus parent metal can be
reduced by annealing.

In the water, how the positioning of your submerged components (battery pod,
tanks, etc.) effects Longitudinal Hydrostatic Center of Gravity depends on
whether they are positively, neutrally, or negatively buoyant.  Consider
this when determining placement.  For example, if the battery pod is
negatively buoyant, it might work better in a framework directly below the
pressure hull.  While this may slightly change the shape of the outer hull
in that area,  it could also give you a flatter surface for the boat to rest
on when trailered; and that's good.

Am I correct in guessing that your diagram is a preliminary study?  If so,
you'll find opportunities to "tweak the design" when you start using scale
representations of the actual components, either on graph paper or in your
CAD program.

With the right configuration of components (top buoyant / bottom heavy),
your design could be comparatively stable because it's pressure hull is
"short and round".  History shows it's the long cylindrical boats that have
the greatest potential for pitch control problems.

Keep up the good work!

Pat