Steel 72 Doubles

[alwaingold]

here is the what gue says you need for tech 1

1. "Tanks/Cylinders: Students are required to use dual tanks/cylinders connected with a dual outlet isolator manifold, which allows the use of two first-stages. All dives must start with a minimum of 80 cubic feet/2250 liters of gas. Divers must also have access to one deco tank/cylinder of 50% Nitrox. "

I don't understand where in that quote it says you have to have tanks bigger than 72s. I am not advocating using 72s for Tech 1, I just don't see how you are taking that to mean you need bigger tanks. You have to start each dive with a minimum of 80cuft. A slightly more than half full set of 72s would do the trick there.

look at tanks that you can use on a 150 foot dive or look at what type of diving your going to be in the next 5 years and ask your self do i want to spend money on 72s when in a year or even less time youll be putting them aside and buying bigger tanks

First of all, not everyone has aspirations for Tech 1. People have different reasons to want to dive doubles, and it's not necessarily because they want to do 150' dives. I don't think the OP made his intent clear. Second, if you start buying the tanks you will need in 5 years, you might end up with a set of 130s for those far off Tech 2 dives you might someday do. Not necessarily the best choice if you are going to fill them with 32% for some shore dives in the meantime.

ps rainman_02 is very smart and knows alot about dir

Yes, David is quite the DIR stud. Maybe we can start a separate thread on "why I want to marry rainman_02"

 

[MattL]

yes he is maybe i just miss read that but to me it seem that you need 2 tanks with the mainfold and each tank being atleast 80 cuft. and true he may end up with a set of 130 as i have got a set for my self but you can do a t2 dive with 100s but i think its more about not buying a set of tanks that in 3 mouths your going dam i need biger tanks but in my frist post i say that my 130 are not for the beach diving im sure were can fight on tanks all day long but i think looking at a t1 dives even if you may think youll never go there is a good plan for a few resons ie you never take t1 class but you go on a dive trip for 3 dives and want to dive 32% and the bout only has air tanks for a t1 dive can give you nice dives and give you more Nitrox% then a singal or a smaller set of dubs and im sure there are a list of reson not to get 100s frist but i feel they are an allround tank having more then one use

 

[amascuba]

here is the what gue says you need for tech 1

1. "Tanks/Cylinders: Students are required to use dual tanks/cylinders connected with a dual outlet isolator manifold, which allows the use of two first-stages. All dives must start with a minimum of 80 cubic feet/2250 liters of gas. Divers must also have access to one deco tank/cylinder of 50% Nitrox. "

All that means is that you need 80cf of gas in your tanks to start the dive. LP72's hold 71.2cf of gas at their rated fill pressure. Double them up with an isolation manifold and that is 142.4cf of gas. That's more than enough gas for a recreational dive to moderate depths and still be within limits of rock bottom.

 

[rhlee]

...
ie you never take t1 class but you go on a dive trip for 3 dives and want to dive 32% and the bout only has air tanks for a t1 dive can give you nice dives and give you more Nitrox% then a singal or a smaller set of dubs

There are several ways to solve this problem, (3 single tanks, 3 sets of doubles for 2 divers with a transfill whip, 1 set of doubles + stage(s))... To me, a set of double 130's filled with 32% would be my last option. I'd almost pay for the helium at that point just to lighten the tanks. I'm not sure I buy that 260cf of 32% makes for a balanced rig....

 

[onfloat]

I happen to know one GUE instructor that teaches all of his Fundies classes and does his less than T1 dives in a set of medium pressure Dbl 72's. So the double 80's thing as a minimum is not true.

Plus, I love my dbl 72's for all my simple dives.

 

[MattL]

There are several ways to solve this problem, (3 single tanks, 3 sets of doubles for 2 divers with a transfill whip, 1 set of doubles + stage(s))... To me, a set of double 130's filled with 32% would be my last option. I'd almost pay for the helium at that point just to lighten the tanks. I'm not sure I buy that 260cf of 32% makes for a balanced rig....

i trim out great with my 130 with 32 in them not all bouts will let you take 3 sets of dubs are even 2 sets or stages ect.

 

[lamont]

There are several ways to solve this problem, (3 single tanks, 3 sets of doubles for 2 divers with a transfill whip, 1 set of doubles + stage(s))... To me, a set of double 130's filled with 32% would be my last option. I'd almost pay for the helium at that point just to lighten the tanks. I'm not sure I buy that 260cf of 32% makes for a balanced rig....

If you take double-130s into a tech1 course i strongly suggest underfilling them to 2600 or else your buoyancy doing 10 foot open water no reference skills will be interesting.

 

[BarryNL]

As to the DIR answer, it would be "balanced rig." In this particular case with steel doubles, that probably means "drysuit."

I think the whole "balanced rig" thing is a bit overdone. The (DIR) reasoning behind the balanced rig is that you can swim it up in the event of a buoyancy device failure. If you run the numbers (even using GUE's course material) you actually find that steel doubles are often a better choice with a wetsuit than aluminium doubles provided you can ditch about half your weight independently.

(And before anyone says this isn't a DIR answer this is exactly what we came up with on my DIR-F ).

 

[amascuba]

I think the whole "balanced rig" thing is a bit overdone. The (DIR) reasoning behind the balanced rig is that you can swim it up in the event of a buoyancy device failure. If you run the numbers (even using GUE's course material) you actually find that steel doubles are often a better choice with a wetsuit than aluminium doubles provided you can ditch about half your weight independently.

(And before anyone says this isn't a DIR answer this is exactly what we came up with on my DIR-F ).

If the average person can swim up about 10lbs of negative weight with no help from a buoyancy device, how do you figure that steel tanks are better in a wet suit?

The average steel tank is going to be about 3 - 5lbs negative when the tank is empty. If you are wearing doubles that's 6 - 10lbs total. Then you get to add the weight of your manifold, bands, regs, fins, backplate, and wetsuit compression at depth. Thicker wetsuits are going to be more negative at depth than a thinner wetsuit. That can be well over the 10lbs of negative weight. Hence the need for a drysuit for redundant buoyancy if your wing fails.

Luxfer AL80's are 4.4lbs positive when empty. How are you doing your math?

 

[BarryNL]

Luxfer AL80's are 4.4lbs positive when empty. How are you doing your math?

Actually, looking again at the material we were doing the calcs with single tanks, not doubles. Steel doubles is probably pushing it. Maybe with an aluminium backplate and no primary light it might be possible to get a sensible rig but otherwise difficult.