[PSUBS-MAILIST] Lurker finally surfacing!

Wed Aug 29 19:23:03 EDT 2018

Jon/Jim there is not enough info in the thread to do this ABS stress
calculation rigorously.  Not sure if the 12.5' length is overall or SS
(seam to seam).  Also we need details of stiffeners including dimensions of
the inner stiffeners and spacing.  The ABS spreadsheet is for stiffened
cylinders.  As you note, you can trick the spreadsheet by putting some
stiffeners in with 0.001 web and flange thickness.  If you do this, then
you need to ignore results (maximum allowable working pressures) associated
with stiffeners and just look at the depth associated with overall
buckling.  With this diameter of a hull, even with 0.625" wall it really
should have stiffeners to address the concern of overall buckling.   This
is what happens on an externally pressured unstiffened cylinder when
overall buckling occurs.

Cliff

On Wed, Aug 29, 2018 at 10:09 AM Jon Wallace via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> I'd like to see Cliff and Sean respond.
>
> The unstiffened cylinder calculator and Cliff's hull spreadsheet are
> pretty close, the former at 315 feet and latter at 308 feet.  Both are
> based upon ABS rules but Cliff's spreadsheet does consider some of the
> finer and nuanced points of failure.  There is one section of Cliff's
> spreadsheet calculator (inertia requirement) that shows a cause of concern
> but I think it is due to the fact that his spreadsheet requires stiffeners
> for this section to be calculated correctly and I assume Jim's cylinder has
> none.  The spreadsheet will not accept "0" for a stiffener dimension to
> simulate a cylinder with no stiffeners, so I usually enter ".01" as a value
> with the distance between stiffeners the overall length of the hull to
> represent an insignificant stiffener effect.  Using .01 for stiffener
> values, the "inertia requirement" section shows max depth of 5 feet.  Using
> K-boat stiffener values the same section shows max depth of 101 feet, and
> using more appropriate stiffener values for this hull of .625 thickness and
> 2 inch flange the same section shows max depth of 227 feet.  Now, I'm
> pretty sure...would bet money on it...that Jim's hull will easily survive 5
> foot of depth without collapsing so I don't know how to really interpret
> the inertia requirement section of the spreadsheet in this case.
>
> Sean's calculator doesn't seem to take into account cylinder length so I
> couldn't use it as a triple check on the other two calculators.
>
> At this point Jim, I would tread cautiously with max depth until you (or
> we) are comfortable with a figure.  Personally, I think your original max
> depth of 100 feet is reasonably appropriate.  An unmanned test dive when
> the sub is ready would be highly encouraged.
>
> Jon
>
>
> ------------------------------
> *From:* james hughes via Personal_Submersibles <
> personal_submersibles at psubs.org>
> *To:* Alan via Personal_Submersibles <personal_submersibles at psubs.org>
> *Sent:* Tuesday, August 28, 2018 9:24 PM
> *Subject:* Re: [PSUBS-MAILIST] Lurker finally surfacing!
>
> Thanks Allen for that hull calculation!  I hope you're right!  I thought
> it might be shallower than that without reinforcement.  I've tried to build
> a good safety margin in all the parts on the boat (using thicker steel in
> the conning tower, for example, than what the K250 plans called for).
> Still, this being my first boat I don't really want to go deeper than I
> could safely get up from on SCUBA (I've got a 2" flood valve if I ever need
> to get out while on the bottom).  Plus most of the sea life I'm hoping to
> see is usually in shallow water.  But you're right, little more investment
> now may make a difference if I decide to go deeper for some reason in the
> future.
> THANK YOU again and God bless, Jim
> On Monday, August 27, 2018, 2:51:34 PM PDT, Alan via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:
>
>
> Hi Jim,
> thanks for the introduction, and welcome along.
> Can't help you with the seals as my motors  are external.
> I have been making my own thrusters & have contacted seal reps &
> even emailed the manufacturer for advice on a non standard mounting
> method I was proposing. Normally seals are used on pumps to keep
> fluid that is under pressure in rather than out as in our case.
> I did a quick calculation on your pressure vessel & it came out as a 600ft
> crush depth. Don't take that as gospel, but it may be worth looking at it
> in depth if you haven't already. If the 600ft is right you could dive to
> 300ft
> with that hull! For all the work that goes in to building a submarine you
> may
> find that it is only a relatively small amount of extra effort & cost to
> give
> you an extra 200 ft of diving capability. I would think about this first
> before
> choosing a seal as the added pressure may have bearing on your choice.
> All the best,
> Alan (New Zealand)
>
>
>
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