Tank Position

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DavidHickey

Contributor
Messages
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Location
Kingsman, Ohio. Near Wilmington and Waynesville
# of dives
50 - 99
Now that I've been to a few dive parks and have observed other divers set ups I've been curious on if there is a correct way to mount your tank to your bcd??? I've noticed divers with there tanks mounted to were it looks as though the valve is half way down their back with the bottom of the tank is past their butts. The way they showed us in class was to keep the top of the bcd about even with the top of the valve. And if it worked out right you can put your BCD handle around the valve to hold it in place. Anywaze what are the advantages and disadvatages of the placement? Just seemed as thought there was no rhyme or reason to it.

David
 
the tank will affect your head-down feet-up trim (and vice-versa)

the higher your tank is (i.e. the lower on the tank your BC strap is) the more
it will push your head down

the lower the tank is (i.e. the higher on the tank the BC strap is) the more
it will push your feet down.

aluminum tanks tend to get "head heavy" when near empty, so ideally, you
should trim your tank so that at the beginning of the dive it is slightly
foot heavy and by the end of the dive is only slightly head heavy.

other considerations are whether the valves will hit your head, whether you
can reach the valve in an emergency, and wether the tank can be held securely
by the strap to the tank without falling off.
 
Tanks should be in a postion where you can turn the air on/off.
 
As a rule I just like to be sure I can grab my first stage easily.
 
Some people like it mounted high, others are into buttbumping. Everyone else falls somewhere in there. After a few dives, you'll have a pretty good idea about where the tank sits best for you.
 
While buoyancy is certainly a concern, the main one, IMO, is this:
ShakaZulu:
Tanks should be in a postion where you can turn the air on/off.
or reach the reg's 1st stage.

It's important to notice that the final position of the tank's valve (relative to your head) not only depends on "how high" you mount the tank relative to the BCD, but also on how the BCD fits your body.

DavidHickey:
The way they showed us in class was to keep the top of the bcd about even with the top of the valve. And if it worked out right you can put your BCD handle around the valve to hold it in place.
This is true, but is one-half of the picture. The final position of the tank will be different if YOU use a BCD that's too big (or too small) FOR YOU, as the whole back of the BCD, tank included, will tend to slip if it's too big. (I've noticed that the variation exists also among models of BCDs).

So mount your tank and see if you can reach the reg's 1st stage, if you can, see if you're comfortable with the buoyancy, and correct it as adequate (you can even correct it UW; I hope you were trained for that, weren't you?)

Happy bubbles,
Gio.
 
DavidHickey:
Now that I've been to a few dive parks and have observed other divers set ups I've been curious on if there is a correct way to mount your tank to your bcd??? I've noticed divers with there tanks mounted to were it looks as though the valve is half way down their back with the bottom of the tank is past their butts. The way they showed us in class was to keep the top of the bcd about even with the top of the valve. And if it worked out right you can put your BCD handle around the valve to hold it in place. Anywaze what are the advantages and disadvatages of the placement? Just seemed as thought there was no rhyme or reason to it.

David

Assuming a standard BCD, the top of the plastic backpack should be at about the same height as the point where the tank and the tank-valve meet.

Adjusting trim is a matter of placement of weights. For example, under the shoulders of your BCD, on the cam-band, on the tank neck, attached to an apart cam-band low on the tank etc etc.

Don't confuse wearing the tank around your ankles with proper trim. Moving the tank up and down for trim is millimetre work. Achieving proper trim often takes a little more.

To check tank position, it shouldn't hit your head if you look up and you should be able to easily reach the valve with one hand while pushing the tank up a bit from the bottom with the other.

R..
 
I agree completely with PavoDive. The most important thing is to be able to reach your valve. Find that range, and adjust within it untill you have the best trim posible.

Most of the people with tanks around there asses are asking for trouble -when- the DM turns off there tank and they jump in. Been there done that. I could reach my valve and didn't drown. After that experince no one but me touches my valve(s) and I pratice valve drills so its second nature.
 
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
 
With a double hose reg the body of the regulator needed to be down between your shoulder blades for maximum breathing performance.

However with modern equipment I agree the valve should be reachable by the diver if at all possible. As long as your head does not contact it when you look up while swimming, it isn't too high.

Having the tank smack you in the head is a valid concern, but one that is better addressed with a properly fitting BC than by moving the tank lower. Also, if you look down at about a 45 degree angle during the giant stride entry you not only ensure you can see where you are going and can time the kick properly, but you also ensure the back of your head is out of the potential path of the tank. Plus you further ensure that, if anything, you are angled slightly forward rather than slightly backward which again tend to prevent the tank from smacking you in the head.

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.
 

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