Doubles etc.

[AndrewJD]

NJScubaDoc,

Since the cost of setting up independent or manifolded doubles is approximately the same. Why do you want to go with independents vs. a manifold?

Jonathan

 

[JimC]

Independents let you use the same tanks on singles dives when you don't need to haul around 100 pounds of crap on your back. Contrary to the prevailing opinion there is nothing wrong with indy's and the extra 'task loading' is trivial. The ability to switch back to a single very nice.

 

[in_cavediver]

Independents let you use the same tanks on singles dives when you don't need to haul around 100 pounds of crap on your back. Contrary to the prevailing opinion there is nothing wrong with indy's and the extra 'task loading' is trivial. The ability to switch back to a single very nice.

While I agree there is nothing wrong with indepenendent doubles, there is quite a bit more to using them safely than manifolded doubles. You have to revisit your gas planning, hose routing, air share procedures and task loading.

I personally think a diver going from singles to doubles would be better served to start with a manifolded set to eliminate some of the new tasks and overall tasks needed to dive them. Independents to me fall under the too much too soon arguement for most divers. (at least to do right). Once a bit of expierence is built up with doubles, going to independents is much less of an issue.

To the OP, before making a decision on either option, perhaps rent a set of each for a weekend to try for yourself?

 

[AndrewJD]

I'd like NJScubaDoc to answer the question. He should be able to artigulate why he feels independent doubles are better then a manifold. I am unsure what his objective function is (min cost, max NDL, do three dives on a boat, min wasted gas, max ease of switching the same tanks from singles to doubles, etc.) and would really like to hear his reasoning.

A technical quesiton for anybody. With independent doubles, how do you attach the tanks to your backplate? Is a set of bands or some sort of cam straps? I don't know.

Jonathan

 

[AndrewJD]

Another question for NJScubaDoc.

Are you diving a drysuit or wetsuit? Will double 95s (independent or manifold) be a balanced or unbalanced rig?

 

[UP4AIR]

To answer a recent poster's question, I think the discussion the OP is looking for is probably NOT sarcastic discussion!

So, here's my shot. NJScubaDoc, I'd ask that you think about this line from your previous post:

Does this mean you would be using one set of doubles for two dives? If this is the case, it means that on the second dive, you have no real "gas advantage" compared to the first. It also means that if you are diving paired singles, you would need to use a thirds planning rule (or something similar) on each tank to manage your gas, meaning a "switch" partway through each dive. Again, no gas advantage on the second dive. Alternatively, if you’re planning to use 2 sets of doubles for 2 dives, then what I said is not an issue.

I’d also suggest you ask the question "am I in good enough shape to use doubles when boat diving?" Doubles TAKE strength AND endurance. Both the weight of the kit and the increased profile create issues both in and out of the water. Sure, putting them on at the car then walking 30 yards to a beach might be OK, but try climbing a steep ladder on a dive boat in 6 FT seas after making a 100 FT surface swim back to the boat because you missed the tag line in the current. It becomes difficult.

Your information also indicated you were using LP steels. That's good, because LP steels when jam filled can give you a bunch more gas. Assuming your 10% overfill is 2640 PSI, a fill to 3200 will give you 115 CFT of gas. That gives you almost 80 CFT of useable gas following a simple rule of thirds with no other adjustments. For most experienced divers, I'd say such an amount of gas should get you "in the ballpark" for a turn pressure near the EAN NDL down to about 140 FT assuming an EAN mix between 28% and 32%. Doubles might be “sexier” for the type diving you are doing, but ask yourself, “do I REALLY need them?”

OK, so you want to do deco too. For depth ranges to around 140 FT (with planned BTs beyond EAN NDLs), I'd recommend switching to "H" valves on your 95s and using a 40 CFT 50/50 mix stage. Sling the stage. It's small, fairly unobtrusive, and easy to dive with. The "H" valve provides you with good redundancy for your bottom gas in the event of regulator failure, assuming you can cut off quickly. Personally, I'd always use an "H" if I did the type of diving you described earlier. Using the 50/50 mix for deco really decreases hang time, so even if you do EAN BTs close to 60 minutes for 100+ FT dives, deco stops are often short, generally 20 minutes or less. From a safety standpoint, the "goal" of this type diving is to minimize nitrogen exposure, stay below a 1.4 PO2 "ceiling" and minimize deco hang time. For beginning deep diving, in my opinion, this is exactly where you need to be going. Save the higher exposures and more complicated stuff for trimix, if you ever want to do it. Save the doubles for below 140 FT, or use them on specific dives where LONG BT on the first dive (or only ONE dive) is important to you.

Finally, and needless to say, get some training! Learning gas management, deco theory and the other stuff often isn't the hard part. Instead, handling the equipment while underwater, especially if you get stressed, is the challenge. Learning gas switching on a computer AND knowing how to use back-up tables while underwater takes some getting used to. Getting the "feel" of stage bottles, understanding how to handle "emergencies" with other divers, overcoming equipment problems and getting used to hanging on a line while bouncing up and down in rough water while doing nothing for 20 minutes are all part of the process. Hooking up with a GOOD mentor and "seeing" how it's done completes the training process.

Good Luck!

The best advice in the entire thread thus far!

The only thing I would add is that doubles are sometimes the red glowing eyes in the dark forest...if you get my drift.
Set your mind to mastering the skills to dive doubles...and DO IT!

I switched to doubles because I too wanted more bottom time. A 2 hour boat ride through 6ft seas to a submarine off the Carolina coast only to have 15min on the bottom is crap! A set of doubles and a slung 40cu/ft with some high content O2 makes it all worth it.

 

[mwhities]

The best advice in the entire thread thus far!

The only thing I would add is that doubles are sometimes the red glowing eyes in the dark forest...if you get my drift.
Set your mind to mastering the skills to dive doubles...and DO IT!

I switched to doubles because I too wanted more bottom time. A 2 hour boat ride through 6ft seas to a submarine off the Carolina coast only to have 15min on the bottom is crap! A set of doubles and a slung 40cu/ft with some high content O2 makes it all worth it.

What tanks and what was the bottom time? I may have a set of Faber 133's (doubled) near the end of May/first of June.

Michael

 

[UP4AIR]

Double 100's with 28% and a 40 cu/ft w/80%. Bottom time of 30min and deco of 17

 

[mwhities]

Nice. I have a set of 100's (Catalinas/Not doubled). I am; however, looking at a set of Faber 133's doubled up. I think that would be nice to have on a deep dive. I could use my two c100s as deco tanks.

Michael

EDIT: Don't you love it when someone repeats themselves?

 

[NJScubaDoc]

My reason for independents vs. manifolded doubles....

With the independent doubles I'd be able to get maximum gas volume out of 4 tanks to do 3 dives in relatively shallow (<100fsw) to get as close to my NDLs as possible. I refer to my gas management post a few pages ago for extended explination.

I dive a dry suit, and would route the wing and the dry suit off different tanks. Not sure what you mean by balanced, please clarify.

To attach manifolded doubles to your back plate you use SS straps around the tanks that attach via screws and nuts. Independents use cam bands with metal clasps and attach in the same was as manifolded doubles.