Re: [PSUBS-MAILIST] Reserve buoyancy

["Alan James" <alanjames@xtra.co.nz>]

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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