Some Thoughts on Independent Doubles

[AfterDark]

@Gareth J @MichaelMc +1

Independent Doubles (ID’s) have been my choice for double tank configuration for 3 decades. At the time I began diving ID’s I had been using what was common then, non-isolation manifolds. Given the 2 choices at the time ID’s IMO were the better choice. Two BM SCUBA tanks each with a regulator was more redundant and gave “reserve” air even if the supply of air was reduced by 50% overall. Always leaving me with the air I needed to safely surface in the event of a problem that required the dive be aborted.
The likelihood of 2 SCUBA setups failing on the same dive where pretty low then, and have only gotten lower with the advancements in material and manufacturing of equipment.

Manifold tanks are dedicated as doubles, and the manifold increases the total weight.

The ID setup allows flexibility of use.
The tanks used as ID’s can also be used as single tanks, and handled as single tanks until such time as they are mounted on the BCD.

 

[AfterDark]

The main reason divers should be able to reach their valves- doubles, single, side mount, rebreather or any other configuration is in case they jump into deep water with them accidentally turned off.

Like the doctor said don't do that. I can't reach behind me to turn valves in any configuration, so I don't jump into deep water with my air off. In fact 98.9% of my diving is walking into the water shore diving. I've done some yak diving but I don't hit the water negative, I can't remember the last hot drop I did, for me that kind of diving is over. Seniors need to change their diving MO for many reasons the hard part is accepting.

There was a time many years ago (1980's) after falling off a rock while trying to put my fins on, I found myself in 15FSW with full double 80's, a BC that wasn't inflating fast enough, a 2nd stage I couldn't find and wearing a 30lb weight belt. I couldn't bear the thought of drowning with that much air on my back, so I ditched the belt and shot to the surface. That is the closest I've came to jumping into the water with my air "off".

 

[rx7diver]

The main reason divers should be able to reach their valves- doubles, single, side mount, rebreather or any other configuration is in case they jump into deep water with them accidentally turned off.

Either turned off, or not turned fully on. But, also to close off the valve in the case of a free-flow. And also as a last option if you need to feather the valve in the case of a free flow.

Something to think about: What happens if one of your tanks drains empty when your valve is open and you are at depth?

rx7diver

 

[AfterDark]

Either turned off, or not turned fully on. But, also to close off the valve in the case of a free-flow. And also as a last option if you need to feather the valve in the case of a free flow.

Something to think about: What happens if one of your tanks drains empty when your valve is open and you are at depth?

rx7diver

I come up using the other one. Since I only dive NDL shouldn't be a problem.

 

[2airishuman]

Interesting thread.

A question to consider is what advantages/disadvantages your BM ID configuration of choice provides over an equivalent amount of air split between a BM single and a suitably sized slung pony.

 

[rx7diver]

Interesting thread.

A question to consider is what advantages/disadvantages your BM ID configuration of choice provides over an equivalent amount of air split between a BM single and a suitably sized slung pony.

For me, an immediate advantage was/is not having to reconfigure the regs I used for my manifolded BM doubles--except for adding a SPG. I already owned the manifolded doubles and hardware, etc., so all I needed to do was remove the isolator part.

Another advantage is, rec diving BM doubles (either manifolded or independent) keeps your front torso clear of clutter.

rx7diver

 

[AfterDark]

Interesting thread.

A question to consider is what advantages/disadvantages your BM ID configuration of choice provides over an equivalent amount of air split between a BM single and a suitably sized slung pony.

Doesn't matter to me I don't sling tank(s). I've got a 19cuft pony bottle, used it 3 times, nothing but a PITA so now I use it for regulator service.

 

[SoloMonkey]

One of the great joys of Indy Doubles, or Twindies as I like to call them is that both are simply standard bottles put together by the diver themselves. Avoids the need to supply a pony for soloing and that in itself saves a load of hassle coming from the UK to go anywhere on an airline.

So two regs, a set of blue flexi pylons from AP and a Dive Rite with 4 x cam bands through her. Et voila.
Easily dismisses the "We don't rent out ponies" argument. Err. I'll rent two singles then!

When the shop owner sees you put together your twindy, they then know you are not to be messed with either.

PGB

 

[MichaelMc]

True ID for rentable quick make-your-own doubles is a great setup. There is also a soft version of that with tanks at the sides, or one at the side and one in hand walking to the water.

 

[Akimbo]

Another variation on this discussion is progressive equalization. This is where the isolation manifold valve is normally closed and it is only opened periodically to equalize the tanks. These "equalizing events" can be integrated to your dive plan.

Depending on the dive profile the first equalization can mean leave bottom, turn around, or move to a shallower area. I first learned the technique from ex-Royal Navy divers in the 1970s. It works well in demanding conditions where the distraction level is high or you can't read a pressure gauge. I built some protectors so the doubles can be worn valve-down.