From: "Steve Ewing" 

On Fri, 18 Feb 2005 19:31:31 -0500, Frank Haber  wrote:

> A landlubber asks
>
> 1. I presume a hatch trunk is the equivalent of an airlock on a space
> ship.

Yep.

> 2. and that both hatches open outwards, and have wheels to dog them down
> on the inside, and seal tighter with increasing depth.

Yep again.

> Does the hatch wheel actually and visibly show more stem as the sub
> dives?

The hatch has a rubber seal around it, and there are three (in our case)
dogs on the hatch, cranked shut with the handwheel.  The dogs clamp onto
the rim of the trunk, holding the hatch closed.  So, as the hatch is
pressed tighter by sea pressure, there is more room for the dogs to clamp
further, but the wheel itself isn't pushed in-- it's part of the hatch/dog
assembly on the inside of the hatch itself.  Undoing the dogs completely
allows the hatch to open, with the dogs/wheel going with it (and lurking to
bang the unwary as they climb out).

> And how can they risk the single point of failure by working in the
> trunk at depth with the inner hatch open?

There is a chain of authority to be followed when breaking "rig for
dive", up to and including the captain.  Since it would be impossible
to open the upper hatch even if completely undogged, this one is pretty
safe.  All the maintenance procedures are very thoroughly outlined: you
know that for every stupid, obvious, micro-managed instruction, someone
somewhere screwed it up once ("pick up the screwdriver by the handle
and insert the metal end into the slot" ).

In the grease fitting incident, I don't think rig for dive would be
involved.  Just not thinking.

> So how much does the diameter of a pressure hull shrink at 300m?  How
> much does the cover flex?  (I presume it's a nice, ribbed 3/4" or so of
> steel.)

I don't know the numbers, but the diving officer has to compensate by
pumping out some water as you go deeper: smaller hull==decrease in
buoyancy.  I'm sure there's a fancy calculation that they had to know for
the test, but all the dives I knew did it by rule-of-thumb or seat of the
pants.

On my first trip underway (post-overhaul sea trials on the USS Kamehameha
SSBN 642) all us nubs were alarmed at all the "hull-popping" as
we got deeper.  The decks were on rollers or slides, and as the hull
contracted the decks would pop-pop-pop.  One of the things the yardbirds
were checking was doors: would they jam?  some had to be tweaked-- and the
wall "paneling": if there were not enough clearance at the edges
it would bow out.  Interesting.  Newer subs, BTW, don't do the slides
anymore: too noisy.  They have other means to provide a "floating
deck".

--
Steve 
http://www.qmss.com/sewing

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