120 with pony VS Dual alum 80's

I am looking to get some longer bottom time and want to know the pros/cons of going with a HP steel 120 with 30 pony VS going to doublel alum 80’s. As far a price goes they will be close. I don’t want to go as far as getting a new BC or Back plate wing. I want to try and do it with mostly the gear that I have. I dive in a tropical climate and wear a 2mm sortie wet suit or a 3/2 mm full and 90% of my dives are from the shore so weight matters. I have two BC’s a Tusa Imprex Pro 3D and an older Sherwood Outback, The Outback can be set up for duel tanks with out any modifications. I have three sets of regs so there are no problems there. Except they are all yoke and at least one will need to be converted to DIN. So what the would be the big differences between the two I will be running 150 to 160 CF both ways and can ad a extra pony to either one for a deco bottle.

Thanks in advance
Derrick

Is your intent to use the pony to extend bottom time or just as a safety in case you have problems with your main tank? In any case, I don't think I'd try doubles in anything other than a backplate, though I have heard of people doing it.

What kind of tank do you have now, what kinds of bottom times are you seeing, and what kinds of depths are we talking about here. 150-160cuft is a LOT of gas for a shallow tropical dive.

If you are diving deep enough to put yourself into mandatory decompression, I'd do doubles for sure.

If you choose the hp and the pony, breath the pony down first then switch to the 120.

The 80s are a much nicer rig (I dive a set) however, it sounds like you want to stick with the gear you have (rec/jacket bc) etc.

A 120 is a big tank for someone in a thin wetsuit.. may or may not be too much non-ditchable weight.

A 100 may be preferable... a 100 has about 30% more gas than an Al80.

Personally I love double 80s in a wetsuit, but they're good for two short dives or one longish dive.... a pair of steel 100s would get you a lot more mileage.

I notice that you don't have an awful lot of dives, and what I'm reading makes me a little uneasy.

I think you might be better served by just diving more, working on your relaxation in the water, and exercising more to get the SAC down. Going to a steel 100 or 120 is fine... but using a giant steel tank PLUS a pony bottle because you simply need all that gas for rec dives is a little too far IMO.

DTB1981:

I am looking to get some longer bottom time and want to know the pros/cons of going with a HP steel 120 with 30 pony VS going to doublel alum 80’s. As far a price goes they will be close. I don’t want to go as far as getting a new BC or Back plate wing. I want to try and do it with mostly the gear that I have. I dive in a tropical climate and wear a 2mm sortie wet suit or a 3/2 mm full and 90% of my dives are from the shore so weight matters. I have two BC’s a Tusa Imprex Pro 3D and an older Sherwood Outback, The Outback can be set up for duel tanks with out any modifications. I have three sets of regs so there are no problems there. Except they are all yoke and at least one will need to be converted to DIN. So what the would be the big differences between the two I will be running 150 to 160 CF both ways and can ad a extra pony to either one for a deco bottle.

Thanks in advance
Derrick

Click to expand...

The extra tanks are going to add weight (even alums when full and you have to carry weight to offset buoyant effects at the end of the dive) so you really should be considering a wing for the extra lift, I'm not sure what the Outback will lift though. The twins will be a lot more stable in the water but I would have to suggest extra training before you take them out and to do a recognised course you may well find that the wing is required.

With what you have the 120 and pony is probably do-able and if you are nitrox certified you could start using different mixes. Again, that would require training and if you are planning on using either rig to run deco dives.... you need training!
Decide how far you want to go with this gear and you may find that now is the time to invest in gear that you will be able to use with more technical setups. Don't just buy what you think you need now because you will probably be selling it in a year's time.

The short answer is; if you want to stay within recreational limits the 120 and pony. No special training and total redundancy.

DTB1981:

I am looking to get some longer bottom time...

Except they are all yoke and at least one will need to be converted to DIN...

So what the would be the big differences between the two?

Click to expand...

As the others have noted, longer bottom time...to do what? If you are essentially a macro photographer, and you want to be able to spend an hour working on photos at 35' or so on a warm reef, thats one thing. If you're going to spend that same hour on a wreck in 90', thats another.

In the case of the former, the single tank is much more convenient. In the case of the latter, I'd opt for the doubles.

Doubles may be set up with a manifold that will accept yoke regulators, using small inserts that screw into the DIN port. You need not (necessarily) convert your regulators to DIN

In terms of big differences between the two, I can think of several. Double 80s balance nicely. They are not severely negative. They provide (with appropriate training) redundancy and enough gas (as Jonny noted) to do either two NDL dives to around 70'-80' or so, or one longer dive with rock bottom backed out. OTOH, annually you must break apart your set of doubles and VIP two tanks, O2 clean two tanks if you're partial pressure blending your nitrox, and then reassemble the doubles - which isn't difficult, but its time consuming and more expensive than VIPing/O2 cleaning one steel tank. Ergo, the PITA-factor is a difference worth considering.

If you do carry a "pony bottle", or bail-out bottle, it is designed NOT to be used (or calculated into your gas plan), but to be held in reserve in case some catastrophic failure were to occur on your primary gas source. If you breath it first, simply to extend your bottom time, you're using it as a stage. This is one thing in doubles, where the doubles themselves provide some redundancy, but another in a single tank, where the practice leaves you without redundancy. If you're using a single tank, it would be unwise to breath off your bail-out bottle first, then switch to your backgas. The double 80s would be a much better option than that scenario.

FWIW. YMMV.

Doc

PerroneFord:

What kind of tank do you have now, what kinds of bottom times are you seeing, and what kinds of depths are we talking about here. 150-160cuft is a LOT of gas for a shallow tropical dive.

Click to expand...

I have 4 Alum 80's now for tanks, I am geting about 70 min bottom time at an average depth of 45ft. and about 32min with an average depth of 69 ft. and a max of 118.
Depending on the dive site the end of the reef is between 135 and 84 ft. I was planning on getting all the tanks ready for Nitrox, And have the pony filled with EAN 40 to use during the safty stop, My computer will do gas switching so It will save me some time on the surface.

Doc Intrepid:

As the others have noted, longer bottom time...to do what? If you are essentially a macro photographer, and you want to be able to spend an hour working on photos at 35' or so on a warm reef, thats one thing. If you're going to spend that same hour on a wreck in 90', thats another.

Doubles may be set up with a manifold that will accept yoke regulators, using small inserts that screw into the DIN port. You need not (necessarily) convert your regulators to DIN

Doc

Click to expand...

I am doing some shell diving, most of it is between 70 and 100 ft. depending on the location.

I have found a Pro valve manifold that will accept yoke or DIN regs so I can hold off on geting my regs converted.

I was also think I want to go to a bp wing In a while but dont have the money to do it all at once, If I get one of my back infalte BC's set up for doubles it would be one less thing I have to get when I go over to the BP wing, I will already have the tanks and regs set up for it.

DTB1981:

Depending on the dive site the end of the reef is between 135 and 84 ft. I was planning on getting all the tanks ready for Nitrox, And have the pony filled with EAN 40 to use during the safty stop, My computer will do gas switching so It will save me some time on the surface.

Click to expand...

So if you are at a depth of 135', and your primary gas supply fails due to O-ring failure, LP hose failure, 1st or 2nd stage failure, etc, what do you intend to breath then?