Hanging bottles underwater

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Thanshin

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Messages
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Location
Spain
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I feel this might be a really stupid question but, it's the basic questions so I'll do it anyway. :)

Why isn't it a standard safety measure to hang an air tank at 15ft under all diving boats while divers are under? It looks like an extremely low cost measure that might save someone from time to time.


[Edit: Yes, with "bottle" I meant "tank". Today I'm switching between French, Russian, Spanish and English and I mix things up from time to time. :) ]
 
What purpose would it serve? Seems it would only encourage divers to push their limits a bit farther than they normally would. The vast majority of recreational dives are within NDL's. So, in a near OOA situation there should be little risk with continuing on to the surface at a safe rate of ascent (IMO). Others might say they would try to do their full safety stop, right down to the last breath. Personally I'm not going there.
 
Rather than an air bottle how about some lead weights for those divers who have a problem staying down? Or maybe a sandwich.
 
I am sure I will be the first of many to say it is simply not practical in most cases to do so. Some boats that are doing stationary dives (hooked to a mooring line or anchored) may drop a tank or may even have a long hose with just the regulator and a little lead on it to keep it at depth below the boat. It is usually hanging next to a rope with a chain or bar to hang on while doing a safety stop.

In the many many dives I have seen done with a regulator hanging under the boat, I can't remember anyone ever saying "gee, I am glad there was more air there when I needed it"

The safety stop chain however almost always had a line behind it.
 
Or maybe a sandwich.

The bread will get all soggy and icky. There's a thread on here somewhere, but as I recall, chocolate covered Oreos were a good choice. The chocolate keeps the cookie from getting all mushy. Crunchy chocolatey goodness on your safety stop...
 
We use hang tanks as a standard practice for deep dives. I've seen similar procedures used in many dive ops around Thailand and the Philippines.

The issue with deep dives isn't 'just' running out of air... it's the risk of divers going into emergency deco and not having sufficient air to complete their stop. Accidental deco, when it happens, tends to be a double-edged sword, as not only do you encounter a 'ceiling', it usually combines (post deep/long dive) with being low-on-air.

It isn't used for shallow dives and there are occasions (drift diving, strong current etc) where it wouldn't be workable. But otherwise, it isn't too hard to drop a tank/reg down to 5m on the end of a nylon rope.

Normally hang a few spare weights from the cylinder also, as low-on-air divers can often find themselves under-weighted.

Never actually had it used by customers here in the Phils, but it seems like a prudent contingency to plan/prepare for.
 
A bottle hanging under the boat assumes that a diver in need would be coming up under the boat. In an OOA, the diver should make a direct ascent to the surface from wherever they run out of air.

Divers ... particularly newer ones ... need to understand that a safety stop is a precautionary measure, and should be skipped if the diver is OOA or LOA. For typical recreational dives, skipping the safety stop under those circumstances presents a lower risk than remaining below the surface searching for a hang tank.

The only time I've ever seen hang tanks used is on dives where people are going deep ... where a deco obligation might be incurred. In this case, it is there because a direct ascent may not be a viable option ...

... Bob (Grateful Diver)
 
This procedure is actually standard practice on many liveaboards. The tank and regulator is usually on a "trapeze" 15 to 20 feet (5 to 7 meters) below the surface. Because of the repetitive dives and substantial hours in the water each day on a liveaboard excursion, (and because many dives are deep) the spare tank is placed to insure everyone does a full and complete safety stop, and is also easy to access if someone has gone into deco and needs additional safety stops at greater depth. The buddy who is not in deco can retrieve the tank and take it to the diver in need. The hanging bottle is not "spare air" for out of air emergencies, it is a contigency resource for safety stops and unintended deco situations. In my experience, they are rarely accessed. That is as it should be. But when needed, it is good to have them there.
DivemasterDennis
 
Where I have been diving in north Cyprus this is standard practice for deep dives. A tank is dropped on a rope to 5m, for any dive into the 30m plus range. Phil
 
I always drop an oxygen hose over the bow with two second stages hanging at 20 feet.
 

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