Alternative to doubles

[Queequeg]

Hey friends,

I'm taking the intro to tech course, advanced Nitrox and deco procedures. When considering gear configurations, my buddies are going doubles. One is doing back mounted HP 100's, the other is doing sidemount 119's. We are planning on OW dives, Northeast, Midatlantic, 100-150' range. No penetration, no caves.

I dive a Dive Rite Transplate with the venture wing and an hp120. I trim out nicely with this setup. I sling a 40 on occasion on deeper dives.

I'm thinking , rather than doubles, I can dive my hp120, and sling a 40 on each side? One forty for reserve, the other as a deco gas. That gives me 200 cu ft of air, just as much as my buddy diving double 100's, without the hassle.

Is this unconventional? Its not my idea, the owner of my LDS, who I dive with quite a bit, did this, until he went side mount. It seems to me such an easier and cost efficient way to go than back mounting doubles or buying a side mount rig. Especially when we are talking about dives in the 100-150' range...seems sufficient to me.

Please weigh in. Whats the disadvantage of this?

Thanks
:cool2:

 

[DevonDiver]

It depends on the agency - some dictate specific set-ups; normally isolated doubles or side-mount.

If you get used to that set-up, what will you do when you progress to using 2 deco stages? You'll have to re-learn. So why not start now and build experience in the ultimate configuration you'll be using?

 

[Jim Lapenta]

Where are you taking your intro course and from what agency? The instructor may also want to see you in a set up closer to what your buddies are using to start out. As Andy said the configuration you choose to start with should be as close to what you hope to end up in for most of your tech dives. The problem I see with slinging a pair of 40's is the gas planning and handling of them in the beginning. Especially if you are going into Adv Nitrox and Deco Proced and will be using a deco gas in one of them. Tech in the beginning is going to be pretty intense as far as task loading and equipment management. Going down this route is also no time to be trying to figure out the least expensive way to do it. You can use regs that are less expensive than some brands but will perform just as well but you will still need at a minimum 3 first stages and 3 second stages plus 2 spgs. You also do not have to start out with double HP 120's. Why not go with a set of double al80's or LP85's. I use LP 72's for dives in the range you are talking about and pumped up they give me 160-170 cu ft of gas and they are a very reasonable cost to set up.

Or you could sling an al80. The problem I see with what you all are doing is there will be some serious planning involved with the different gas amounts you all will be carrying. As long as you are ok with this and can stick to the plan it's fine. But a better choice is to just bite the bullet and get a set of doubles and if necessary postpone the AN an DP courses. Do the intro to get familiar with the gear configuration and then dive that. Once you have it down and are comfortable with it add the DP and AN courses. And if you are seriously going to be hitting the 130-150 range on a regular basis I'd consider getting a course that will allow you to put some helium in the mix. I did Intro and then NAUI helitrox. I hope to do AN and DP this season. Having some helium in the mix for those deeper dives in the Atlantic with what is involved will be a plus with your head nice and clear.

I'm good now to 160 and deco on back gas or 32-40% nitrox and fine with that. The AN DP will just allow me to speed up the deco a bit.

 

[Queequeg]

You bring up good points. I suppose if we are headed in that direction I may as well start learning to dive a configuration that I will probably end up in at some point down the road anyway, rather than relearning. I can appreciate that.

We are taking the courses through TDI.

 

[dumpsterDiver]

I don't have any training in tech diving and back when i wore doubles, there were no isolation manifolds, just a single outlet and single reg.

However 100-150 feet dives are not that big of a deal on a single tank. I often use a 149 cu-ft tank and a pony bottle for dives deeper than than 150.

At times, I contemplate getting a set of doubles and a "proper" manifold, but I find myself often thinking about the complexity of such a rig. I hear people talk about left and right posts, which reg is hooked to which, which side the inflator is hooked to, which side the pressure guage reads, how and when to operate the manifold, the potential strain and difficulty of having you life literally dependent on the ability to reach over your shoulder to effectively and quickly manipulate various valves (by touch).

If I bought such a rig, I would study on the internet and maybe get a text book and would learn to operate it. I know that it would take me a bunch of time to pound into my brain exactly which of the three valves to turn when I run through all the MANY potential failures scenarios that I might run in to. I know I could teach myself, but I also know it would take me a long time before I was confident to take that rig to 200 feet solo.


I find it intuitively obvious that operation of back mounted double manifold just has to be more complicated (to learn anway) than to figure out how to work a couple stage bottles that you can see and touch and very easily operate.

I taught myself how to use stage bottles (and accelerated deco), primarily by just reading the DIR stuff... The basics are pretty simple: mark the tank, secure the reg appropriately, clip the bottle off the right way (no metal to metal connection), and make damn sure you know what the hell you are breathing because the wrong gas will kill you.... Seems a lot simpler to learn than the standard doubles and a stage bottle routine.

In any regard, wearing a single and two 40's as stages, one for bailout and one for accelated deco for 100-150 feet dives seems like a viable means to dive from my perspective. It might be a lot safer to be handing up unclipped 40's in rough seas and wearing a single tank too. On the other hand, if you want to eventually progress to doing 240ft dives with trimix, then you might as well learn doubles now.

I myself am happy staying above 200 (or a little more if there is a really good reason).

Lastly, diving a big single MIGHT even be safer than diving 40 year old steel tanks that are pumped to a pressure that is over 25% higher than their rated pressure of 2250 psi...

 

[JahJahwarrior]

Also consider how that configuration could work in an OOA situation. Backmounted, manifolded doubles are very easy for OOA situations. If you have a deco mix on one side and a reserve (pony?) on the other, you've present choices to the OOA diver, and atleast some of your gas is not shareable: either you use it, or the OOA diver uses it, and if you hand it off, it's gone. That goes back to the topic of, "if there isn't enough gas for us both, who lives?"

Diving isn't a cheap sport, but manifolded doubles aren't confusing, and make this easy. Skip a few weekends on the boat, and you'll have plenty of money for a set of doubles, or to build a set with your current HP120. Look for used tanks, doubles sets typically go for $550 or less. At 80 for the boat plus a $20 tip plus $20 in car gas and $20 in tank gas and $20 out for lunch afterwards, should take 3 missed trips to buy a set of doubles.

Whatever you do, I'm sure our buddy Jim will be glad to hook you up with a great deal on HOG regs.

 

[waterpirate]

At a bare minimum that hp 120 should be an h valve or simmilar to meet standards and then I am not so sure. The point of doubles is to train for going forward. Depending on alot of variables that hp 120 is barely good for 150 for 30min and what about lost deco gas and deco on back gas contingencies?
Eric

 

[Colliam7]

I dive a Dive Rite Transplate with the venture wing and an hp120. I trim out nicely with this setup. I sling a 40 on occasion on deeper dives. I'm thinking , rather than doubles, I can dive my hp120, and sling a 40 on each side? One forty for reserve, the other as a deco gas. That gives me 200 cu ft of air, just as much as my buddy diving double 100's, without the hassle.

What is the 'hassle' of your buddy's rig, from your perspective? Not saying there is or isn't a hassle, just trying to understand what you see as the hassle.

Is this unconventional?

Yes. That doesn't make it a bad idea at all, just not common / conventional.

It seems to me such an easier and cost efficient way to go than back mounting doubles or buying a side mount rig.

I don't mean this as a criticism, only as a question. How is going with three tanks, including two 40s, instead of two (back-mounted or sidemounted) tanks going to be 'an easier and cost efficient way to go than back mounting doubles'? Perhaps, I am missing something.

Whats the disadvantage of this?

Potentially, the number of tanks, number of regs. There is nothing at all wrong with the approach. It just means you have to sling two bottles in addition to the one mounted on your back. Three tanks, three regs, SPGs, etc. If I was looking for a rig to go a bit deeper, but not into a deco situation, I would rather have two larger tanks than 3 smaller ones. If I am going deeper / longer, to the point that I would be in a deco situation, I would want more backgas, PLUS I would then want a deco gas bottle (I don't really care to deco on backgas - takes too long). At that point, I would rather have three tanks than 4.

If you are going to sling two 40s, I presume you have the BCD to do it. Why not sling two 120s, and omit the back tank? If the 'hassle' of backmount for you is the manifold, or the weight placement, OK. Go sidemount, either 'real' or just by slinging two bottles on your BCD. You still need two regs (but not three).

 

[dumpsterDiver]

.I don't mean this as a criticism, only as a question. How is going with three tanks, including two 40s, instead of two (back-mounted or sidemounted) tanks going to be 'an easier and cost efficient way to go than back mounting doubles'? ).

The assumption is that the dive would be with doubles and one sling bottle of deco mix right? I thought it was a comparison of 3 bottles versus 3 bottles?

 

[DevonDiver]

If the 'hassle' of backmount for you is the manifold, or the weight placement, OK. Go sidemount, either 'real' or just by slinging two bottles on your BCD. You still need two regs (but not three).

Sidemount is the obvious solution here. Much better than a back-mounted single and two slung baby tanks. If the OP's instructor didn't suggest this, then perhaps he's not qualified to teach in sidemount?

Backmounted/isolated doubles may well seem like a 'hassle' to the prospective tech student - but it's really the job of the course to transition them into that kit so that it isn't a hassle. Again, I am surprised that the OP's instructor didn't offer them more reassurance on the capability of their training to allow that transition.