Hang tanks and floats

[2airishuman]

I'm putting together the support items I need for deep dives (60'-130'). Those of you who follow my posts already know that my diving is usually in freshwater, either from shore or (less often) from a small boat that I have borrowed or rented that isn't outfitted for diving. One of the things I want to have along is a float and hang tank that will stay at 15' as a safety item to mitigate emergencies involving either loss of gas or unplanned deco.

Here's what I've decided so far:

• It will be an LP72. (They sink, and I have lots.)
  
• Will be filled with EAN40. (Highest oxygen content without the expense of cleaning everything for oxygen service and getting an AN cert).
• Cylinder painted green with a full-size nitrox band to make it stand out from my other cylinders to avoid mixups with air or EAN32.
• Reflectors on cylinder to make it easy to find at night. (will also use a strobe)
  
• DIN reg with button gauge and one 2nd stage held in place by bungees and elastic bands.
• Large float incorporating storage, handholds for emergency buoyancy, and a dive flag.

A friend who is an instructor has a homemade float made from an old galvanized steel milk crate with a trailer tire inner tube wrapped around it, and a mast for the flag held on with zip ties, and this is the score to beat for the float. (I may substitute a 5 gallon bucket with some drain holes drilled in it for the milk crate) (or maybe an antique egg basket)

Some questions.

1. Chain, rope, or flat strap for the 15' line from the float to the cylinder?
2. How to fasten the line to the cylinder. Metal ring installed around the valve neck? Line tied in a knot? Stage rigging? Sewn strap? Sizes?
   
3. Any photos of your rig? Any commercial floats or ideas for building floats that make more sense than the milk crate?
4. Any other innovations you use?

 

[dumpsterDiver]

If you are going to need it for deco carry it with you.

If you want emergency deco gas, maybe just keep it inside a float on the surface. Going up, grabbing a bottle and descending in 20 seconds is probably not too bad.

I would prefer a bottle of 100 % you could have it in a raft with it tied off, so you surface , throw it over, swim done 20ft and use it. Also serves as emergency bottle on surface if you are bent.

Tie it off with cord to the valve.

I would not want to tow. A float and a suspended tank. Too much drag for the minor benefit of avoiding a quick trip to the surface.

Over all, an emergency deco bottle of 30 cuft which is carried as a stage bottle and a streamlined float and reel sound like a better option if you want to be extra cautious and not overly burdened. A 30 will give you a lot of hang time at 20 feet, enough for a pretty big screw up.

 

[archer1960]

That's similar to what my instructor built, except he uses a plastic milk crate. I'd go with the rope to hang the tank, so you can cut it if necessary.

 

[dumpsterDiver]

Another option is keeping the tank in a raft, buying a 25 ft hose and an inline shut off valve and then clipping the second stage to the float tether at 20 feet.

 

[2airishuman]

If you want emergency deco gas, maybe just keep it inside a float on the surface. Going up, grabbing a bottle and descending in 20 seconds is probably not too bad.

Even a short trip to the surface would lead to the formation of bubbles that would then take time to re-dissolve vs. keeping bubbles in solution during offgassing. Big difference

Tie it off with cord to the valve.

..nod...

I would not want to tow. A float and a suspended tank. Too much drag for the minor benefit of avoiding a quick trip to the surface.

For a shore dive, the tank stays in the float between the shore entry site and the actual dive site, then throw it down.

Over all, an emergency deco bottle of 30 cuft which is carried as a stage bottle and a streamlined float and reel sound like a better option if you want to be extra cautious and not overly burdened. A 30 will give you a lot of hang time at 20 feet, enough for a pretty big screw up.

Typically now I'm carrying a 40 cf pony and I doubt if I'll stop just because there's a hang tank. More gas, more better, use it for emergency deco, use it for emergencies at the surface, give it to any other divers who might be present whose gas planning skills prove to be weak. Big float provides something to hang onto in poor surface conditions or if unable to swim due to injury or whatever.

 

[Jim Lapenta]

In open water you carry your gas with you on deep dives.
Run out of air due to an o-ring extrusion on the neck or reg free flow you want the gas with you. Not 80-100 ft away requiring an emergency ascent to it.
Get a 30 or 40.
Fill it with bottom mix.
Hang a tank at 20 ft with 32% or whatever.
If you are not deco trained I'd keep air in it as well.
You don't go messing with switching gasses until you have some training with them.
If you put 40% in there for an emergency deco situation, what tables are you running to make sure you do the right amount of deco?
What tables are you using for an emergency deco on air?
More importantly, why did you choose those tables and what are you using as your PPo2 for the bottom and deco? Why?
What risk factors are you including in the calculations?
Realize that if you accidentally go into deco your plan and execution of it was a failure.
I would also not be setting up a bottle for use by others with anything other than air if they are not deco trained.
Though the odds of it happening are astronomical, what if that diver has been using nitrox and is near his CNS clock limit? He gets on your 40% and takes a hit, seizes, and drowns. You covered for that?
Why paint the tank green? Green is usually reserved for O2. Just put one of those goofy nitrox bands on if you must but proper procedure is a contents label near the neck with a large MOD sticker on the cylinder so it's easily Id'd.
What's your MOD for 40%?

 

[dumpsterDiver]

Not ascending to the surface is better, but I am not sure (as a practical matter) a 30 second excursion to the surface really is a "big deal" . I do deco dives and my plan C or d is to surface and yell for the boat to throw the emergency deco bottle. It's not happened yet, but I have thrown the bottle to a diver whose computer was beeping on the surface...with no ill effects.

 

[Killerflyingbugs]

Not ascending to the surface is better, but I am not sure (as a practical matter) a 30 second excursion to the surface really is a "big deal" .

SOP in the commercial world when doing Decompression dives you have 5 min to get from 10' in the water to 40' in the chamber, so a quick up and down won't kill you. It may not be the best thing but it happens all the time with little chance of DCS.

Back to the question I would hang it with some line and be sure the float can support the tank and you in full gear hanging under it, you don't want it to sink on you in case of BC failure.

 

[hroark2112]

Are you finding yourself in deco often? Instead of planning for unplanned deco, which sounds more like "I'm going to go into deco and I think this will help me get out", why not just get proper deco training and do it right?

 

[2airishuman]

Are you finding yourself in deco often?

Never have, probably never will.

Instead of planning for unplanned deco, which sounds more like "I'm going to go into deco and I think this will help me get out", why not just get proper deco training and do it right?

Because prudent contingency planning is not the same thing as pushing the limits or exceeding the scope of one's training.