Twin 72’s vs HP133

[Eric Sedletzky]

My urchin team and I are always looking for ways to stay down longer and clear more urchins. Nothing worse than filling a bag or two then running out of air when there’s work to still be done. We’re finding that smaller tanks just don’t cut it. We work hard and blow through a LOT of air sometimes, so we’re always on a quest for more air.
So, my idea was to put together a set of double 72’s instead of looking into something like an HP133. One reason is because I already have the 72’s and the manifold.
I’ve used those massive single tanks before but my experience was that after a certain point in size and diameter they become kind of unwieldy and have a tendency to turtle you. Is there such a thing as a single tank that is too big?
With twin LP 72’s, even at 2250 psi that would still be like having a 130, and upwards from there at 2475 I’d have a 144.
Steel 72’s end up about neutral. I don’t know what a 133 ends up at.
Solid bar center outlet manifolds are not that bulky and I’d be using a thin yoke Conshelf XI on it which are small and light.
It seems like 72’s would balance a little better in the water being two smaller lower profile tanks on each side.
My only concern is how heavy they would be doing beach entry/exits? How much heavier would they be than a single HP133 on land?
I suppose it also matters what brand of 133 and how thick the steel is.
I need to be careful with my hip.

 

[Tanks A Lot]

As you point, this will depend a little on the manufacturer of the cylinders. The below data excludes the valves or manifolds.

Faber:

Water Capacity (L)	Estimated US Designation	Diameter (mm)	Length (mm)	Working Pressure (Bar)	Empty Weight (Kg)	Empty Buoyancy Seawater (Kg)	Full Buoyancy Seawater (Kg)	Real Weight Seawater (Kg)	Empty Buoyancy Freshwater (Kg)	Full Buoyancy Freshwater (Kg)	Real Weight Freshwater (Kg)
11.1	LP 71	183.90	569.98	188.23	14.11	-0.82	-3.51	13.29	-1.20	-3.90	12.90
12.6	LP 72	203.71	525.02	165.47	14.79	0.12	-2.57	14.91	-0.31	-3.00	14.47
17.0	HP 133	203	680	237	19.4	0.66	-4.02	20.06	0.07	-4.6	19.47

Worthington:

Name	Water Capacity (L)	Gas Type	Working Pressure (Bar)	Diameter (mm)	Length (mm)	Empty Weight (Kg)	REE (cc)	Buoyancy Full (Kg)	Buoyancy Empty (Kg)
X8-130	16.7		237.32	203	648	19.5	100	-5.3	-0.9

PST:

Part #	Specification	Pressure (Bar)	Volume (L)	Diameter (mm)	Length (mm)	Weight (Kg)	Buoyancy Empty (Kg)	Buoyancy Full (Kg)
E8-130	E-9791	237	16.2	203	649	19.1	-0.82	-5.2

I guess all in all, your twinset will be around 10Kg (22lbs) heavier on land then the single big cylinder will be.

 

[USdiver1]

You would be hard pressed to find a more trim friendly setup than twin 72s. I love mine and prefer diving them to all other setups.

 

[Jim Lapenta]

Before I went sidemount, I had a set of 72 doubles. I called them my baby doubles. Light, easy to handle, and filling them myself to 2800 PSI, I had 150 cu ft of gas available. I used to use them in OW checkouts, so I didn't have to swap cylinders. Could get at least (2) one hour plus dives out of them.
I also used them for deep dives to 120 ft with a little deco obligation and had plenty of gas.
Much easier to move around than my LP85's. They even felt better trim and stability-wise than a single LP95 or 120.

 

[Eric Sedletzky]

Before I went sidemount, I had a set of 72 doubles. I called them my baby doubles. Light, easy to handle, and filling them myself to 2800 PSI, I had 150 cu ft of gas available. I used to use them in OW checkouts, so I didn't have to swap cylinders. Could get at least (2) one hour plus dives out of them.
I also used them for deep dives to 120 ft with a little deco obligation and had plenty of gas.
Much easier to move around than my LP85's. They even felt better trim and stability-wise than a single LP95 or 120.

Stability is what I’m really looking for (and a lot of air!). We’re working in close right now, 10’ to 25’ so NDL is zero concern. The surge can be a real whipper that close in. Having a big heavy single on your back and getting thrown around is where the turtling effect comes in. I’m using an HP 120 right now, and it does the job, but I want more. I also submerge right off the beach and cruise out underwater. I do this to scan for pockets of urchins close in. I’ll continue heading out, cleaning out urchin pockets as I come across them and when I reach the bigger densities I’ll really bag up. Then when the urchin bags are full I send them up on a lift bag with a 50’ tow line clipped off to the floating bags, I take a compass reading and head into shore towing the bags underwater. So a lot of times I never go to the surface, I’m underwater the entire time. Plus it’s just plain hard work! We burn through a LOT of air.
I’m hoping to get two hours with the doubles. With the 120 I can get about 1-1/2 to 1-3/4 hours.

 

[Eric Sedletzky]

The only other solution that I can think of besides doubles is a surface supplied hookah setup. But that would require a topside platform like a boat and more crap. So no.

 

[tbone1004]

if you want stability then double 72's are the way to go IMO. Shore diving with doubles isn't that bad and since you'll be taking lead off your net weight won't really change vs. the heavy tanks

 

[happy-diver]

Tell you what numbers on a sheet isn't two tanks on your back and walking out standing up forget it
Surge and swell, I'd rather be thrown around and be able to recover easily under there, with a single

This is why they invented double discs, if you feel it or not, having a breather between tanks is good