This brings to mind WHOI's simple operational rules for Alvin, quite obviously designed to keep it out of trouble to start with. That failing, onboard mechanisms, such as breakaway manipulators and crew sphere release, to make up for the rest...except of course, hull breach.
I wonder also, where the line is for a reasonable free ascent? To my thinking, once my little PSUB would pass normal safe SCUBA depths 130' or so, well then...I might as well be in the Abyss for all the difference it would make.
So pre-determined operational guidelines, is a must.
Outstanding post, will file this permanently...thanks Jay!
Joe
From: "Jay K. Jeffries" <bottomgun@mindspring.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
CC: "'Jay K. Jeffries'" <bottomgun@mindspring.com>
Subject: RE: [PSUBS-MAILIST] on-board air.
Date: Sun, 25 Feb 2007 16:34:00 -0500
Frank,
Your concern over the issue of entanglement is VERY valid but should be easy to minimize with a little forethought. Fiberglass shrouds over exterior protuberances blending external gear into the hull should alleviate most of the snags and make the sub look more professional. Joe has started this with the Alvin Jr. and we have discussed further covers for the battery pods and external gas tanks.
You are going to find in most PSUBs that there is little room to carry a bunch of tools and room to shift around to reach things in the hull difficult due to the already cramped space. 99.9% of the emergency repairs will occur on the surface and as for the other 0.1%, ever effort should be made to engineer the issue away prior to a potential failure. By keeping the sub?s system as simple as possible the opportunity for failure is minimized. As complexity increases the opportunities for failure do not increase linearly but in an exponential mode. Fire and flooding are the two major causalities that ever submariner should fear and the immediate action should be an emergency surfacing.
With a simple PSUB, there are few subsystems that are critical that could potentially be worked on within the sub (all other systems or components are non-critical):
- Hull integrity
- MBT blow
- MBT vent
- Electrical propulsion
- Life support
- Drop weight retaining mechanism
- Steering (while often thought of as critical, is not needed in most emergencies other then entanglement).
Let us consider each of these for contingencies and reparability underwater:
- Hull Integrity ? minor leak around a packing or shaft gland (few drips per minute) should be able to be resolved with tightening the gland night with an adjustable wrench, if not abort the dive. If it is a mechanical seal, there should be no leakage and this is a portent of things getting worse so immediate dive abortion should occur. Small main hatch leak should abate with depth due to increased pressure on the hatch, if not abort. This should have been found as part of the pre-dive checks by partially flooding down, increasing cabin pressure slightly over ambient, and observing for any escaping bubbles. Any major leak should be cause for immediate abortment of the dive. If the hull rapidly floods, the immediate response should be to go to an emergency swimming free ascent
- MBT Blow ? if the tanks are inside, there initially appears to be options for repair but is balanced by the loss of internal space and the possibility of a catastrophic HP air accident (loss of valve to tank neck seal or more likely a blowout disk failure). With two tanks and two regulators you have the opportunity to recover from the loss of a regulator or hose by cross connecting (or just running off of one tank). With the tanks outside of the hull increased internal space is available, a catastrophic HP air failure will not result in immediate personal injury, and with the addition of a remotely operated valve (with valve stem or valve stem extension protruding into the hull) the loss of a regulator or failed piping can be mitigated.
- MBT Vent Valve ? a failure here can not be worked on within the hull without causing massive flooding. Mitigation for this causality ? motor to the surface and blow what ballast you can. To reduce the magnitude of the causality, increase reserve buoyancy so that there are 3 MBTs instead of two thus if one is loss, the other two will bring the sail far enough above water to allow the operator to exit the boat without it scuttling. See Joe?s Alvin Jr?s saddle tank amidships. This is a departure from the standard K-boat design but 30% reserve buoyancy should be the minimum acceptable design.
- Electrical Propulsion ? Loss of power should be immediate cause for aborting the dive. Loss of the main thruster (in a K-boat styled design) would allow continuance of the dive under reduced propulsion of the thrusters. Loss of a thruster would only potentially cause steering issues. Any motor lost due to flooding should be removable from the electrical bus by unbolting the power leads from the buss bar with an adjustable wrench or a closed-end wrench to mitigate a short. Better would be a Guest-styled battery switch capable of isolating a defective motor. If the insulation is smoking due to a short, this is cause for immediate dive termination. With internal batteries you potentially have the capability of removing a faulty battery from the battery bank with a wrench (pre-dive checks should have found this issue). Internal batteries have the hazard of forming chlorine gas and releasing acid with a severe flooding incident. The chlorine will burn the skin and damage the eyes and lung lining (just had to deal with a gaseous chlorine incident Friday, fortunately not in a sub?NOT FUN!).
- Life Support ? A 72 hr. emergency life support capacity is the goal but 48 hrs. is probably the norm for those PSUB operators that are cautious. This means sufficient oxygen, scrubber material (usually slaked calcium carbonate), and dedicated scrubber fan batteries to keep the number of occupants alive for 48 hrs. with minimal movement. Often not considered s the need for thermal insulation for the occupants in the majority of operational areas for PSUBs (even Florida). Carrying O2 inside the hull should not be an option for two reasons related to tank failure: the rapid pressure spike could be injurious and O2 at higher partial pressures resulting from a leak can be very poisonous. If the scrubber is properly designed and there is a failure of the atmosphere-driving fan, you should be able to switch to lung-powered mode. The fan should be powered by a small independent, dedicated battery system sized to meet the duration of your scrubber. If the scrubber becomes wet due to a flooding incident, the scrubber material will become ineffective and even caustic. Not much here that can be fixed underwater.
- Drop Weight Retaining Mechanism ? Simple 90 degree twist handle or a threaded rod that will take multiple turns for emergency release of the drop weights. Not much that can go wrong here other than a hang of the external weight holding tray. Should be regularly lubricated and tested. Other than whacking the release mechanism inside with a small sledge (or one of your lead trim weights) to try to dislodge a hung tray, there is not anything repairable here.
- Steering ? Loss of steering can be mitigated with using the thrusters under proportional control. If a mechanical steering mechanism is frozen, slightly loosening of the packing gland nut with an adjustable wrench might free it. This issue should have been found on pre-dive checks. If the steering is fouled outside, there isn?t much the operator can do.
I am also a side-of-the-rode mechanic; unfortunately the motorcycle analogy doesn?t work very well with PSUBs. The safest option is to abort the dive and return to the surface. This response to emergencies has been well tested in the technical diving world which shares many similar hazards to those encountered in PSUBs?if the dive is not going to plan, TERMINATE! (I have to admit to taking apart a regulator underwater and performing a quick repair inside the Control Room of the USS Bass SS-164 in 165 fsw).
My analysis is not definitive and I would appreciate comments of others. Contingency planning is something that should be given more thought to in the PSUB community.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
It is the mark of an educated mind to be able to entertain a thought without accepting it.
- Aristotle
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of ShellyDalg@aol.com
Sent: Sunday, February 25, 2007 2:38 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] on-board air.
Vance and all.... I see the subs with batteries, tanks, and all the rest, bolted to the outside of the pressure hull, but what do you do if something goes wrong?
Maybe you get slammed against a rock outcropping, or maybe snagged on a submerged cable, or maybe a tank line or fitting fails. If the problem is outside.....How can I fix it?
I like the idea of having all my stuff inside.
With a set of tools onboard, I can re-route air lines, re-do electrical connections, jury rig something so I can get to the surface, save my self and passenger, and maybe even the sub.
Another point is entanglement.
I would like to keep my hull as smooth as possible. No hooks, corners, or snag points.
I ride a dinosaur motorcycle, and I carry tools. That baby always gets me home. It's the chrome bikes that go in the truck.
I can re-build damn near everything on the side of the road, and I expect the same sort of problems with my sub.
Shit happens, and you can't anticipate everything, but you can be prepared to improvise.
Frank D.
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