Is there anyone diving tiny doubles? Need some input.

[Cyborg Pirate]

i posted this in the tiny bubbles thread but it’s an older thread. Hopefully I can get some input here.

I currently have a set of HP 120's I dive with. Since moving to doubles I really enjoy them and prefer the redundancy. I only dive singles now when we have students. As many have stated they can be quite cumbersome however for short shallow dives. Shallow meaning non tech dives. I spend a lot of time diving around 100-110 ft on solo dives. I am seriously considering a set of the Faber LP 50's. I do have some questions though if anyone is up for answering them. I work for a dive shop, as an DM/AI and boat captain. I do my own fills and VIP's so that is not an issue. what I do want to know is has anyone tried to transfill from AL80's? when we load the boat (no compressor on board) its no biggie for me to load the same two 80's I would be diving with for the day, but use them as a transfill from 1st to 2nd dive. I realize 1 80 would not give me a complete fill but would topping off from a 2nd 80 get me pretty close? Also diving a single AL80 with an AL backplate I need 16lbs, in a drysuit. with the 50's by just doing the math I am figuring I need 14lbs. I have 2 Al backplates. Both Mares XR. 1 is set up for singles, the other set up for mydouble 120's. I intend to just move the doubles wing and BP back and forth between the 120's and the 50's. That being said.... the doubleswing I have is the Mares XR 52#. I certainlydon't need that much lift for the 50's but, isthat going to be too big and create more dragand a taco effect, or will it be fine until I pick up the smaller 44# from Mares? Long post I know just looking for some insight before I pull the trigger.

 

[tbone1004]

to start this off, I have a set of 50's, granted they are on my rebreather rack, but I have dove them as baby doubles, in a cave. My primary set of doubles are HP120's, so I have a bit of direct experience.

low pressure steel tanks are VERY inefficient when it comes to weight:gas volume if you fill to working pressure. So assuming you fill to working pressure, you have 100cf in a rig that weighs 50lbs. A single HP 100 weighs 42lbs, al80 is 38lbs+6lbs to get it same buoyancy as a 100. Your double 120's should weight around 100lbs full for funsies.
If you have 16lbs on a single 80, you should be able to knock off 6lbs for the first 50, 1.5 for the second, 4lbs for the bands and crossbar, and 2lbs for the second regulator should put you 2-4lbs of lead required. *note that their negative buoyancy should be essentially identical as your HP120's

for transfilling, you won't get very far with AL80's, but then you're still humping a pair of 80's on top of the 50's.

Now, couple questions.
Why are you diving with aluminum backplates if you are in a drysuit? With the rough math up top, the 2-4lbs you need in doubles would make a SS plate OK, and the 16lbs in a single 80 certainly does.
Are double 50's plus a pair of 80's really easier than just carrying the 120's around? With that, you won't have to carry a transfill whip, won't have to take off one of the regulators to transfill, won't have to carry all the extra tanks to begin with, and won't have to buy a set of 50's.
Why are you diving singles vs. doubles when teaching? In a pool I use singles because I just use the same equipment as the students and that's easier. In open water though, doubles all the way. Don't have to switch tanks, have the redundancy so I shouldn't ever have to call a dive if a reg fails, have oodles of gas in case something happens underwater, etc etc. The students should be diving "on their own", so having similar equipment to them is good to minimize questions and distractions, but going to doubles isn't an issue.

I'll be honest, when I saw "short shallow dives" for 50's, I was thinking 30-50ft dives, not 100-110ft dives. If you're going that deep, I'd really just stay with the 120's unless you can't deal with the extra 50lbs. I don't believe in going deeper in ft than what you have in cf on your back. So 50's at working pressure are just barely cutting it for that dive, and you won't transfill them up to service pressure. On the 120's, you can easily get 2 out of there with no extra work

 

[Cyborg Pirate]

Thank you for the response. Couple answers. I have a couple of aluminum BP’s that are not in use. That’s why I would be using them. I dive a SS BP in the drysuit (my 120’s do have an AL BP attaches to them however, obviously no addl weighting needed even will all my gear on and tanks at 200 psi.) As far as diving singles with students. 2 reasons, 1 the lead instructors want us diving the same configurations as the students. As to avoid distraction and confusion. Also the singles vs doubles. Moving through the water quickly to grab a student that panics or tries to rocket to the surface, being able to get to them quickly and safely is more feasible in the single 80 vs double 120’s.

I am really just toying with the idea and that’s why I am trying to get some real answers from those that have them already. That’s a big sticker price to pay to find out I made a mistake. I really like redundancy of doubles and that is what started this whole train of thought. Your insight has been very helpful. Thank you

 

[Cyborg Pirate]

If I am able to find a set that someone is wanting to part with for a low price I would still do it. But not gonna invest a lot in them for a novelty.

 

[tbone1004]

@Cyborg Pirate the 50's shouldn't have any change to your rig from the 120's. Same wing, same plate, same regs, etc etc. they should just do a straight swap over with no changes because the buoyancy characteristics are about the same.

 

[Gareth J]

Most places other than the USA cylinder sizes are in litres, which is the 'water capacity' (empty cylinder volume). The majority of the cylinders would also be considered high pressure (232bar - 3400psi). I struggle with american dive cylinders and volumes, so I always work with what I know.

A number of the women in my club have dived either 7litre twins or 10litre twins. Which they find more comfortable in terms of weight, especially those of a more slight build.

A set of 7 litre twins have a capacity of 2 x 7litre x 232 bar = 3250 litres of gas.
Take off the 50 bar reserve gives 2600 litres of 'dive' gas.
At 30 meters (90feet) breathing a heavy 20litres/min gives approximately 30 minutes of dive time.

You can only really only do one dive on a set of 7's, in truth even a set of 10's can prove challenging if you want to do a second dive. Most of our group bring either a second twinset, or a cylinder to decant from.

Gareth

 

[tbone1004]

@Gareth J

lp50's= Faber 8L filled to 180bar
HP120's=Faber 15.3L filled to 237 bar *same diameter as an AL80, so the long skinny ones*

Doesn't directly equate to any of your tanks, but that's about what they are

 

[211ratsbud]

Old l.p. 72 's offer a compelling advantage imho , 50% increase in volume (approx). Building a set now

 

[Chris H]

I have double 50s and I love them. I usually dive them with a Drysuit, a SS backplate and a 40lb wing. They are a nice break from CCR, bailout bottles, and whatever else. The only setup I might like more is sidemout LP85s. YMMV.

 

[Cyborg Pirate]

I have double 50s and I love them. I usually dive them with a Drysuit, a SS backplate and a 40lb wing. They are a nice break from CCR, bailout bottles, and whatever else. The only setup I might like more is sidemout LP85s. YMMV.

I ended up with a set of the 50’s. How much lead are you using with your set up like this Chris?