Switching to doubles - Am I in a rush?

[TSandM]

How charters respond to divers in doubles depends, I think. Some boats simply aren't set up to accommodate them well at all. Others require only a simple adjustment. Still others do just as well with doubles and single tanks. When we dive off the Peace in Southern California, for example, the people diving doubles like having a piece of lumber in the "well" where the tanks sit, to raise them so that they don't have to lift them up so much to get them out after they've gotten into their rigs. The Sea Dragon in Nanaimo does something similar, to keep the tanks out of their wells. Our local charter just bungies them in like they bungie in the single tanks.

When we took a group to God's Pocket a couple of years ago, the owner was very apprehensive about all the folks with doubles . . . and then realized it was much easier on his compressor to fill LP doubles than it was the HP130s that those of us single-tanking it were using!

As far as doing two dives off a set of doubles -- if you plan your diving according to the expected profiles, you'll plan adequate gas and reserve for the second dive. Then, when you don't have an emergency on the first one, you do the second dive with the reserve you planned for that dive AND the gas you didn't use on the first one . . . so you may actually end up with more usable gas than the person who dives two single tanks of the same size.

It is sometimes very nice not to have to switch tanks out between dives, especially if the boat is pitching.

And as far as the argument about getting into decompression trouble with doubles . . . I can get into just about as much trouble on a single 130 Any diver, whether using a single tank or double tanks, should be monitoring his decompression status, and shaping the dive to keep that status where he wants it, whether that's out of deco, or a planned amount of deco. If someone is sufficiently careless that they swim along until they're at 100 feet and suddenly out of no-deco time, they're going to get into trouble with a big single tank, too.

 

[spc751]

PADI needs to develop a doubles certification course. There's money to made!

\

I like side mount for two tank diving.

PADI Sidemount Diver Course | Ocean Quest Dive Centre - Scuba Diving Vancouver, BC - Experts in Scuba Training

 

[doctormike]

Assuming one is diving from a dive op's charter boat, how do dive ops generally feel about people using doubles on no-deco dives, and how do the mechanics of stowing the rig, switching tanks, etc. typically work on board? I can imagine that some boats in the Northeast and other wreck diving locations routinely have people diving doubles and make accommodations for them with appropriate tank holders and sufficient space between seats/holders. ...

As for the mechanics of handling doubles on a boat, are two standard single-tank holders typically spaced apart by the same width as two tanks rigged as doubles? Or does the diver with doubles necessarily take up extra spaces on the boat that would otherwise be used by single-tank divers? If so, I'm sure the dive ops just love that.

Every northeast dive boat that I have been on has the doubles standing on the deck, secured to a rail with bungees. Same goes for warm water boats doing tech diving. You couldn't really have tank holders given the variation in rigs, it's not something that is typically done for boats that cater to people who dive doubles. People diving single tanks on these boats also just put them on the deck and bungee them to the rail. Some people who dive steel doubles don't like to use tank boots (because they trap water and cause corrosion, or because they are cave divers who don't want them to catch in restrictions), so they don't stand on their own due to round bottoms, but those usually are OK strapped to the rail or occasionally flat on the deck.

If one is doing a 2-dive (no-deco) charter, is it typical to switch out tanks between dives? It occurs to me that unless the diver switches out tanks, he is starting the second dive without the ample reserve that presumably prompted him to use doubles in the first place. Switching out tanks on a doubles rig is obviously not a quick thing to do like it is with a single tank. I imagine it requires tools.

Divers on big excursions, where they might do two dives requiring all of the gas in a set of doubles before being able to top off, generally have two sets of doubles. No tools necessary, about as quick as changing a single tank. You just would move your regulators from one set to the other, and move your backplate and wing from one set to the other (both of these involve a hand tightened thread assembly). When I dive my doubles, where I do two non-deco dives with a surface interval, I just use half of the gas for the first dive and the other half for the second. Same amount of gas used on each dive as if I was just diving the two tanks as singles on two dives. Although I do have a lot of extra gas on the first dive, but that's not part of my planning since I'm not going to be able to use that much and stay out of deco. As mentioned above, unless you are doing deco you really aren't using the doubles to give yourself more gas, it's more for redundancy.

---------- Post added February 7th, 2013 at 09:57 PM ----------

IMHO (and it really is humble), a dive computer is generally not a planing device

Dunno about that. I'm on my fourth Suunto, they have all had planning modes.

 

[rlynch]

i took a class on doubles when i started - i would recommend it. Biggest things you need to keep in mind are 1) you need to be able to manipulate your valves i.e. turn all 3 on and off if needed 2) become comfortable in doubles which most like better than singles actually.

My question is Why switch before your trained in at least Nitrox and deco procedures. If you plan to exceed the NDL limits you should know what the risks are and how to plan those dives. Its not as simple as hitting 100' go into Deco and wait on the hang line till it clears. Deco accumulation is not a linear thing, and frankly not something that should be done lightly.
The other thing to consider is the type of dives you will be doing, and as others have said from what - if your on a 2 tank trip and you hit 1000 psi on dive one, your done for the day i would hope. You need to be able to plan your dive and gas consumption in order to ensure you have enough to accomplish what you want (2 dives, etc). If your plan exceeds that you need for the dives(s) then plan to add extra gas (bigger tanks, or a stage). So the gear and complexity mounts. Its all pretty simple initially, but if something happens during your dive or you surface in 4 chop, things get interesting in bad way quick.
don't get me wrong i dive doubles almost exclusively and love them, just look at the pro's and Con's.

 

[p1p]

Why limit yourself to doubles. With a KISS GEM, single tank, you'll outlast the mightiest bubble blower, carry less weight, save your back, and get other benefits underwater (warmer diving, easier creature hunting for example).

 

[Danseur]

Hi Kyle,

This is the Justin Bates that TraceMalin mentioned.

Perhaps we could have a chat?

I'm a Sidemount instructor as well if you have any interest. I can loan you a set of super easy to use LP50s, more suitable AL80s, HuP100, LP108, or LP120s. They all ride differently, but we can play in the pool or in the Sound.

I started in doubles on my 9th dive and never looked back.

Many points were raised about Deco etc, but if you're not certified in Deco diving, be aware and stay out of deco. (Duh)

Doubles let you get into more trouble, but nobody EVER died from having too much gas.

The rest is probably best said offline. Drop me a line if you want to chat about it!

Oh, Bob and Trace were/are mentors, and Wayne 100% solid. ALL GREAT INSTRUCTORS!

 

[AfterDark]

Why limit yourself to doubles. With a KISS GEM, single tank, you'll outlast the mightiest bubble blower, carry less weight, save your back, and get other benefits underwater (warmer diving, easier creature hunting for example).

The best part is if your 02 goes too low you'l never know it or care.

OP you also have the option of independent doubles.

 

[kylehorn]

My question is Why switch before your trained in at least Nitrox and deco procedures. If you plan to exceed the NDL limits you should know what the risks are and how to plan those dives.

I'm certified for Nitrox and I don't plan to exceed NDL limits. I plan to use doubles to extend my bottom time on deeper wrecks that I will dive like the San Diego. At 120 feet I'm likely going to hoover a single tank before I get close to my NDL on N02. With doubles, I can get more out of my dive. But you're right, in the future I would definitely like to take Adv. Nitrox/Deco Procedures and other tech courses so that I can plan dives in which I'll exceed my NDL. I understand it's not as simple as splashing, waiting too long and then hanging - I'm not interested in playing around underwater; just because I have more gas to breath doesn't mean I'm going to abandon the things I've learned - that would be just plain stupid.

 

[Sevenrider860]

"

At 120 feet I'm likely going to hoover a single tank before I get close to my NDL on N02."​

At 120 feet, you will be no richer than EANx30 and lower would be better. 30% gives you an EAD of 103 feet. Based on your OW training you will round 103 to 110. The PADI Tables give you a 15 minute NDL, many computers would be less than that. A single tank will let you get close to that and even exceed it. Doubles give air reserve, your NDL's don't change and the need for selecting the correct O2 mix for the depth does not change either.

 

[p1p]

The best part is if your 02 goes too low you'l never know it or care.

OP you also have the option of independent doubles.

If your O2 goes low, you arent monitoring it and you are diving shallow without monitoring.(less than 20ft). Either indicates poor training and usage.

---------- Post added February 8th, 2013 at 07:43 AM ----------

BTW, you can sling a 40 with a single tank, get redundant air, as well as get practice with bottles. If you're heading towards tech land, you'll need to get used to bottles anyways