Tank Position

[Puffer Fish]

I have had my tanks mounted low, for two reasons:

1. I use double hose regulators a lot, and the lower position improves their performance.

2. When the tank is lower, it is better for surface snorkeling with the scuba unit on. If it is mounted higher, then the diver's head is pushed underwater by the weight of the tank. Many compensate for this by inflating their BC, but I would rather not be BC dependent for maintaining my head in an optimum snorkeling position (and yes, I do wear a snorkel when scuba diving, and use it about every dive).

I started diving when there were no alternatives so far as BCs go to maintaining position on the surface. I also have made some pretty spactacular entries into the water; as a USAF Pararescueman, we would make parascuba jumps from 1250 feet in the air, and we did not want the scuba unit high enough to hit our heads during our exit of an aircraft. This carries over to my diving today (many years later) when I don't want to be banging my head against the tank during an entry off rocks, for instance, into a river.

I would add that in my years of diving, since 1959, I have never had reason to access the scuba valve in an emergency situation. The DIR folks preach the need to be able to touch and shut off the valve during a dive, but realize that they are diving extreme environments (wreck and cave diving), where any kind of emergency can be life-threatening.

Also, I dive my own version of a BC, and in that kind of emergency, I would simply remove the scuba unit (my BC is not part of the scuba, as we did years ago, and look at the valve. Modern BCs, which are integral with the scuba, limit the ability of the diver to cope by removing their scuba, as the BC/weight system is on the scuba, and separating one's self from the scuba could initiate a positive ascent.

SeaRat

Wow John Greetings from another world (NAUI #4186), nice to see you are still diving and have learned the ways of the Computer.

Your post versus DA's is a great example where different equipment requires a different setup. What you do, would not work for most BC'd divers, but it works for you.

By the way, you still using the old US Diver, or have you gotten a "new" double hose?

 

[John C. Ratliff]

Wow John Greetings from another world (NAUI #4186), nice to see you are still diving and have learned the ways of the Computer.

Your post versus DA's is a great example where different equipment requires a different setup. What you do, would not work for most BC'd divers, but it works for you.

By the way, you still using the old US Diver, or have you gotten a "new" double hose?

Hi Pufferfish,

In case you're interested, I'm NAUI #2710, currently retired from dive instruction. My double hose regulators that I use currently are the DA Aquamaster (no pun on DA's comment--this is an actual US Divers regulator for those who don't know), the AMF Voit Trieste II (my favorite), the Sportsways Hydro-Twin, the USD Mistral, and a Snark III. I have others, but those or my double hose regs currently.

I will probably be picking up the new Aqualung Mistral, because it fascinates me. It is made for single tank diving (it doesn't hook up well with double tank manifolds), but has a possibility I'd like to explore, which is front (chest) mounting it. This would make it independent of tank positioning, and allow other experiments on scuba configurations. I have heard that some have been returned to Aqualung for poor performance, when the issue was really that they were positioned too high on the diver for optimum performance. We have a good discussion of this on the Vintage Scuba website:

http://vintagescuba.proboards2.com/index.cgi?board=instruction&action=display&thread=1071971414

There are also diagrams there showing the effect of regulator placement on performance:

http://vintagescuba.proboards2.com/index.cgi?board=instruction&action=display&thread=1071253464

Concerning DA's comments, I'd like to say a few words. What the heck is a dive master doing turning off someone's air? That seems bizzare to me, and bordering on sabotage. Someone who does that should be canned (fired). On the ice diving, or extreme cold water, that is a valid arguement. But let me say that scuba manufacturers have not done a really good job in making their regulators overall free from icing problems. The new Mistral would be a regulator some should think about for this.

I've been using the computer quite a lot, and in fact work for a semiconductor manufacturing company, Applied Materials, as a Safety Engineer.

SeaRat

 

[John C. Ratliff]

Just to show some others one of the reasons I continue to wear my scuba low, here's a 1969 photo of one of our parascuba jumps, taken in Okinawa (what is now Japan). I've posted it elsewhere here, but these tend to get lost as new threads develop.

I've also enclosed a photo of my ParaSea BC concept, from the 1980s, which never quite got off the ground. It made for one of the most expensive BCs in the world, what with the patent and all, and I still dive it.

SeaRat

 

[Doc Harry]

Tank should be mounted so that you can reach the valves.

Don't mount the tank to adjust the trim, for if you are using an AL80 the trim will change as you consume the air. The AL80 is negatively buoyant when full, and positively buoyant when empty.

For instance: if you mount the tank high keep your trim head down, when the tank is near-empty it will actually start pulling your head up.

Tank should be mounted so that you can reach the valves, period.

 

[Diesel298]

Tanks should be in a postion where you can turn the air on/off.

on a single tank.
so you can adjust flow??

 

[bradshsi]

on a single tank.
so you can adjust flow??

From the same thread....

As indicated above, it does happen that a DM or boat crewman turns off a diver's air with the result that about 3 breaths later they suddenly get nothing - usually after just exhaling everything. Being able to reach the valve makes this a non-event. It's not just a skill needed only by tech divers.

As a cold water diver I also see recreational divers have their first stage freeze resulting in a free flow. This may happen from the diver temporarily breathing hard on the reg, inhaling and inflating the BC or dry suit simultaneously or perhaps after inflating a lift bag. If the diver has a pony bottle and can reach the valve on their primary tank, they can switch to the pony, shut off the freeflowing primary and after a couple minutes when the first stage thaws, turn the primary back on and continue the dive. If they can't reach the valve, the dive is over as the contents of the primary tank are goign to be completely lost.

In the event the diver does not have a pony, breathing off their buddy's octo works the same way. And being able to turn off the free flowing reg is still preferrable even if the divers elect to abort as the diver can switch back to his or her reg during the ascent or safety stop or both divers can switch to the first diver's now thawed reg in the event the second diver's reg freeflows.

Those reasons seem pretty good to me.


Oh and on an unrelated topic (since it's Xmas) shouldn't your signature quote be ?

"Fleshy-headed mutant. Are you friendly?
No way, eh? Ra-... radiation has made... me an enemy of civilization."

 

[Diesel298]

From the same thread....






Oh and on an unrelated topic (since it's Xmas) shouldn't your signature quote be ?

"Fleshy-headed mutant. Are you friendly?
No way, eh? Ra-... radiation has made... me an enemy of civilization."

actually i was thinking about changing it to " im getting whiplash from my burps"

 

[wcl]

Hi,

My two cents, as a simple recreational single-tank diver ...

In priority order:

1. Need to be able to reach first stage
2. Want to avoid banging head when bending neck back

The primary reason for #1 is to be able to execute the "follow the hose" regulator recovery manouver. Being able to use the valve is another important reason, but for simple single-tank recreational diving it is a little less important than for more demanding diving. Still important, though: simplifies fixing "air off" entry problem (though one should find that before descent); does mitigate "half-on" problems (hard breathing as you get deeper); and does allow for managing free-flows once an alternate air supply is obtained.

Note that using these or other practical tank positioning algorithms does mean the tank position will be different with different setups: my tank is in a different spot when diving the drysuit ...

Cheers,
W

 

[Puffer Fish]

Just to show some others one of the reasons I continue to wear my scuba low, here's a 1969 photo of one of our parascuba jumps, taken in Okinawa (what is now Japan). I've posted it elsewhere here, but these tend to get lost as new threads develop.

I've also enclosed a photo of my ParaSea BC concept, from the 1980s, which never quite got off the ground. It made for one of the most expensive BCs in the world, what with the patent and all, and I still dive it.

SeaRat

I happen to have been through paradiving school in Panama - understand.

Thanks for the information, by the way. Interesting.

In the "old" days, at the end of a class, we would show everyone how to do a high water entry (10 meter platform) and then let anyone that wanted to make a jump. Have the tank too high and one might need a surgery to remove it from the back of your head(if you did the entry wrong).

I would still go with - protect the head, and be able to reach the valve.

 

[String]

on a single tank.
so you can adjust flow??

Fairly useful even on a single tank setup. Uncontrolled freeflow, switch to buddys octo, turn tank off, stay on octo for a minute or so to allow first stage to thaw, turn main tank back on. Check air then decide whether to continue or abort.

Without reaching valve its abort immediately.