Diving doubles recreationally

[eelnoraa]

Someone mentioned GUE, if you go by the GUE min gas requirement, dive 32% for rec depth, you will ALWAYS be gas limited with single tank even you dive at square profile to 100ft with HP130. This maybe a good excuse for doubles.

"I am sure I would need to spend a little (maybe a little more)". This is a huge understatement. You are looking at 2 matching tanks, manifold, bands, double wing, 2 matching regs, maybe a backplate of lighter weight. This can easily run you into $1000 range even if you buy them all used.

 

[Rainer]

Someone mentioned GUE, if you go by the GUE min gas requirement, dive 32% for rec depth, you will ALWAYS be gas limited with single tank even you dive at square profile to 100ft with HP130. This maybe a good excuse for doubles.

Nope. We do this quite often. Math:

100' dive, let's call min gas (conservatively) 40cf. That leaves 90cf usable. MDL at 100' is 30 minutes on 32%. Assuming a rather *terrible* SCR of 0.75 cf/min/ata that gives: 90/(4*.75) = 30 minutes. For any SCR better than 0.75 (i.e. everyone I know), you're MDL-limited, not gas-limited for a 100' dive with a HP130 with 32%.

It's really only for *aggressively* multi-leveled recreational dives that I need to break out the doubles. HP130s rock for 90%+ of the MDL dives I do. In fact, they are usually overkill and we'll bring smaller singles.

 

[TSandM]

Someone mentioned GUE, if you go by the GUE min gas requirement, dive 32% for rec depth, you will ALWAYS be gas limited with single tank even you dive at square profile to 100ft with HP130.

Uhhh . . . speak for your own gas consumption, please!

I dive doubles for recreational dives. For me, LP85s will give me enough gas to do two nice terrain-based dives, or multi-level wall dives, and maintain gas reserves. On 72s, it was more difficult, and I was sometimes gas limited on the second dive. There are a couple of solutions: Take two sets of doubles (a pain, and removing one of the redeeming factors of doubles, which is not having to switch out tanks). Take bigger doubles (downsides being expense, and difficulty climbing ladders). Take a stage (need some coaching and experience in carrying additional tanks, and there are safety considerations). Or bring along a big HP tank to transfill, which is what we usually do.

How much doubles will cost you depends on whether you intend to dive them exclusively, and what you can buy used. I bought my 72s for $400 and my 85s were $500 and $450. That's actually probably close to your cost for a set of bands, manifold and new valves for your existing tanks, if you buy everything new. If you intend to dive doubles exclusively, you will only have to buy one more first stage and some hoses, which is not bad; if you have to buy a whole new set of doubles regs, that's more, although again, I bought my doubles regs used for $600 all set up with hoses and gauges, and you can get HOG regs, I think, for just about that brand new.

Doubles make tricky shore entries trickier, and boat reboarding a lot more work. They cost more to fill in a lot of places, and if you use them recreationally, you have the annoyance of using 1000 psi out of your tanks and then paying for a full double fill. (We avoid that by having a yearly membership at our shop, so we don't pay by the fill at all.) They do, once you have learned how to manage the manifold, offer more possibilities for self-rescue, and I like that when diving deep or diving with people who are new to me.

 

[cool_hardware52]

I dive doubles 95%+ of the time. Shore dives + deco bottles and scooter, Boat dives, etc.

I have a range of sets of doubles LP45's, LP72's, Al80's, LP85's, LP120's, HP130's

Pick the ones that fit the need. By far the LP 72's get the most use, and if I had to downsize I'd keep just the 72's and 85's

I prefer having the same reg sets fit and I've grown pretty accustomed to having two fully redundant gas sources. Singles just feel a little odd.

Besides doubles don't roll around in the back of my pick up truck

Tobin

 

[waterpirate]

I train how I fight and dive doubles only. I have 3 sets all different sizes. I use the ones that fir the dive or have the right gas in them for the dive. Only singles I have are stage rigged. The cheapest way to get good sets of doubles is to find people moving from oc to ccr and buy their doubles all ready banded and manifolded and ready to go.
Eric

 

[Scarborough Diver]

I dive doubles 100% of the time. I enjoy the redundancy, they trim out better IMHO than single tank, and especially for multiple dive days saves time and are more efficient on air because you can breathe down what would be considered the redundant air supply from your first dive.

Cost-wise I found it didn't get too pricy since I sold my recreational gear to put towards my doubles upgrade. bands and manifold and doubles wing cost me about 400 dollars used. Then I had to add another first stage and was golden. Not a huge expense and I'd do it a hundred times over.

 

[eelnoraa]

100' dive, let's call min gas (conservatively) 40cf. That leaves 90cf usable. MDL at 100' is 30 minutes on 32%. Assuming a rather *terrible* SCR of 0.75 cf/min/ata that gives: 90/(4*.75) = 30 minutes. For any SCR better than 0.75 (i.e. everyone I know), you're MDL-limited, not gas-limited for a 100' dive with a HP130 with 32%.

It's really only for *aggressively* multi-leveled recreational dives that I need to break out the doubles. HP130s rock for 90%+ of the MDL dives I do. In fact, they are usually overkill and we'll bring smaller singles.

My min gas is a little more conservative than yours. I assume 2 minutes at bottom to take care of air sharing. SCR under stress for both diver is 1. Min gas = 46cf.

But even with your math, it just shows that HP130 is just about balancing NDL and min gas requirement for rec dive. If you take smaller tank, say HP100 or LP85, you are definitely gas limited.

Now, you mentioned 0.75 is terrible SCR. I actually don't know exactly what mine is. I assume it is 0.75. I will need to start keep track of that.

 

[eelnoraa]

For me, LP85s will give me enough gas to do two nice terrain-based dives, or multi-level wall dives, and maintain gas reserves.

I am sure you can. In fact, most people I know do 2 nice recreation dives with a set of double. The question is at the end of the 2nd dive, are you coming up because of NDL or gas. I bet with LP85s, it will be gas.

 

[ScubaFeenD]

Doubles are totally awesome for recreational dives, and I use them for all recreational dives. BUT, singles tanks are great too, I just dont own any "single" tanks (all mine are in doubles or configured as stages, which I dont like to assemble and disassemble just for some recreational dives)I actually spent a lot of time in a single tank setup before going to doubles .

You might consider, if you are so disposed, to get a "light" set of Al80 doubles for recreational dives, because they arent that much heavier (in total while full) than an HP130 and they allow for redundancy, etc, blah blah blah. There is minimal training you should recieve on them before diving them, but it doesnt require a GUE instructor (although they would be a very good resource ).

 

[Jax]

If you search really,really hard you might even find non GUE divers that dive doubles!

That may work too if you carefully avoid those who move the tank bands for trim and then adjust the harness to be able to reach the valves and then have to add ankle weights and dive like a seahorse...

*cough* *cough* sidemount *cough*