Hi Mark,
Re the large ballast tanks, another thought is that the larger they are
the more drag, & inertia due to them being filled with water while
submerged. I'm not sure how much of a problem or extra drain on the
batteries this would be. Someone with experience might like to comment
on that.
Alan
----- Original Message ----- From: "F. Marc de Piolenc"
<piolenc@archivale.com>
To: "Personal Submersibles" <personal_submersibles@psubs.org>
Sent: Thursday, December 03, 2009 7:00 PM
Subject: [PSUBS-MAILIST] Reserve buoyancy
I've been silently following the tender/reserve buoyancy discussion.
As my primary interest is in salvage rather than sightseeing, I have
assumed from the beginning that any sub that I build or am involved
in building will follow safety criteria more like those of cruising
Naval submarines than research subs. But now, reading the report of
the salvage of the Alvin by the US Navy, I see that the allowances
for research subs are inadequate.
Aluminaut was selected for the salvage op because she was the most
autonomous and robust of the submersibles available. After her first
dive, when she spent several hours trying to insert the lifting
toggle in Alvin's hatch, she surfaced with her batteries exhausted.
It proved to be impossible to recharge her at sea, because the main
hatch had to be kept open to allow hydrogen to escape, and when it
was left open she shipped water! She had to be towed to sheltered
water for repairs and a recharge. This is all the more remarkable
because Aluminaut is the most seamanlike of all the research
submersibles that I've actually seen.
Battery vented into the crew space? No means of airing the boat
without leaving the hatch open? I can understand not providing a
separate snorkel or air-induction trunk - this is a deep diver, and
every pressure-hull penetration is a potential failure point - but in
that case the saddle tanks should have been made larger and some
means of fitting a funnel over the main hatch to prevent water
ingress should have been provided. And as for venting the battery
into the crew compartment, ANY arrangement is preferable to one that
exposes the crew to hydrogen, or worse - chlorine!
http://www.archive.org/details/recoveryofdeepre00unit
I assume that reluctance to add saddle tank volume in a personal sub
is due to the need to trailer it home. If it exceeds maximum highway
specs it must obtain a special movement permit every time it hits the
road.
Best,
Marc
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