Redundancy question

[john j]

Yes-if you cut a hose bad enough, you would probably not be able to use the rebreather at all and you might start having a bad day. I have hose protectors on my unit which are just ballistic grade nylon covers to help protect the hoses. The Halcyon rebreather as another example has some really tough material on it's hoses for this purpose, but I'm told that if it rubs on your ears it can actually scrape them so they bleed, ouch.

Sorry, I was a little vague in my description of where the gas is. Inside the shell of the rebreather I have a 25ft3 bottle of oxygen and a 25ft3 bottle of bottom mix. In rebreather jargon, we call these the "on-board" gasses meaning that they are mounted inside the rebreather. In addition to that, I would carry a 40-80ft3 bottle of bottom mix and a 40-80ft3 bottle of air, each side mounted using the standard d-rings and clips like everyone else does. All of the tanks I listed above, both the on-borad and side mount tanks have "whips" attatched. These whips are hoses of whatever length you want with a quick connect fitting that plugs into the counterlungs of the rebreather. I can plug in any two tanks I want to at any given time. Oxygen from the on-board cylinder is always plugged in on the right counterlung and the left counterlung will have either on-board diluent or diluent from a stage bottle plugged in (we would call that "off-board diluent". Some people dive with the on-board diluent plugged in and others dive with the off-board diluent plugged in. The advantage to running from the off-board diluent cylinder is that if you have to give it to your buddy, you can then plug in to your on-board diluent and you will have a full 25ft3 cylinder to use. All of my stage bottles have both standard OC regulators and whips on them so I can breathe OC off them or plug them into my rebreather. If I pass one of my stage bottles to my buddy, he can plug his rebreather into the whip or he can breathe off it using the OC regulator if he needs to. This system of whips is really flexible becasue we can all plug into each other's bottles, or into bottles that we have stashed along the route or we could even have whips hanging from a boat if we wanted to. Stage bottles can be mounted on any side you want or all on one side if that's your gig. I don't normally use a scooter so I mount one bottle on each side, which balances me out nicely.

For the Gunilda for example, we might each carry a 40ft3 bottle of bottom mix and one of air and have an 80ft3 bottle of oxygen on the line at 20ft. Could even bring an extra tank of bottm mix down and clip it to the line at the bottom and leave it there until the last divers come up. Lots of things you can do. Some people carry 2 different trimixes-one in the on-board tank and a different mix in the off-board tank. I was trained like that but don't see a strong advantage so I will be carrying the same mix in both tanks this year. Some people like to carry nitrox 36 or 50 in the other off board tank. Calculations I did convinced me that overall, the best way to go is air in that tank for dives in the 200-450ft range. You could probably recite specific reasons why it might be better to use EAN 36, or EAN 50 or something else but I'm saying that overall, when I considered everything, in my opinion air was the best compromise. Actually if you look at it, for wreck dives in general that I do (maybe not true for caves or long wreck penetrations) you don't need a huge amount of bottom mix bailout because the deep stops are pretty short and you will soon be at a depth where you can safely breathe air. Then of course your stops get progressively longer so the gas you need the most of is the air or EAN 36, EAN 50, whatever you choose to have in the other stage bottle, plus some oxygen too.

The total system failure is really what I am most concerned about. The other failures like electronics failures, cell failures, etc which people might initially think are really bad actually are not a major problem if you practice and follow your training. You would still abort the dive but unless you totally flood the unit, you have hours of gas available, even if you lose one or two tanks of gas for some reason.

How are you using team appraches to gas sharing in you diving?