Doubles - a change in thought -

[Daylonious]

For a long time, I was thinking about getting a set of steel doubles for use in tech / deco dives - (like a set of HP 120's) but today I had a thought -

Since 99% of the time I'm traveling to the place I'm going to be diving via flying - I know I'm not going to be shipping a set of steel doubles to wherever I'm going - being in the middle of Texas, it's the rare dive trip to the gulf that I'd be able to drive / bring my tanks to.

Wouldn't it make more sense to buy and use a set of al80's as your double rig, since more than likely that's what's going to be available at the vast majority of divesites? Plus, if you're on a boat you're never going to get more than about 3000 pounds in your tank anyway....so those HP tanks would be underfilled a bit...

Just makes more sense to train with what you're more than likely going to be using on site...

I could be waaaay off base here, since I've never booked a "tech only" dive trip, but this made sense to me -

Now if I lived on the coast, or someplace easily driven to I'd probably go the larger capacity steel route, but here in the middle of Texas......


D.

 

[Ironman]

For a long time, I was thinking about getting a set of steel doubles for use in tech / deco dives - (like a set of HP 120's) but today I had a thought - Since 99% of the time I'm traveling to the place I'm going to be diving via flying - I know I'm not going to be shipping a set of steel doubles to wherever I'm going - being in the middle of Texas, it's the rare dive trip to the gulf that I'd be able to drive / bring my tanks to. Wouldn't it make more sense to buy and use a set of al80's as your double rig, since more than likely that's what's going to be available at the vast majority of divesites?

Interesting thoughts. A few comments:
1. Double 80s are fun to dive. I have several sets, find them very comfortable. You only have 160cf of gas, not a lot more than a single HP 130. So, you can use them for a lot of tech / deco dives, but you may not be going real deep, or staying very long. Nonetheless, for some mid-Atlantic coastal wreck dives in the 100-140' range, for example, they are great. Also, your backgas is not necessarily just what is on your back. You can also sling, along with a couple of deco cylinders, an additional 40 or 80 filled with the backgas, whatever it is, to augment your doubles.
2. One advantage of training with them is that you might find yourself using double 80s when you travel, because you can actually set them up, as INDEPENDENT doubles, yourself. If you are flying somewhere to dive tech, you are already taking your regs and gear anyway, the extra weight of taking a set of tank bands is minimal. (This opens up a separate discussion, of manifolded vs independent doubles, which others may want to pursue - I don't.)
3. If you travel to a destination for a 'tech-only' charter, the operator may or may not have doubles available. If they do, the likelihood they will have double 80s is not necessarily high. You will end up deciding before you go whether to drive yourself (even considering fuel prices) or not, in order to take the gear you want. It costs money to drive to FL from MD, but I prefer to do so in order to take my double steels. I have driven to Pensacola to do the 'O' with my own gear. So buying / setting up some double 120s or 130s IN ADDITION to 80s, is not a bad idea.

 

[dannobee]

Rig the AL80 like a stage bottle with something like this:

https://www.deepseasupply.com/index.php?product=1309

Bring your deco/stage reg with you, then it doesn't matter if the boat only has AL80's.

Just remember to tell the captain you wouldn't mind being one of the first off the boat and you might be down a little longer.

 

[Spectre]

Wouldn't it make more sense to buy and use a set of al80's as your double rig, since more than likely that's what's going to be available at the vast majority of divesites? Plus, if you're on a boat you're never going to get more than about 3000 pounds in your tank anyway....so those HP tanks would be underfilled a bit...

Once you become proficient with the doubles, switching between won't be that much of an issue. HP-120 doubles, however, are fairly bulky and awkward tanks... I would be sure to be very familiar with the tank before you think about doubling them up.

80s are very nice simple light doubles. You most likely won't be comfortable with the same wing for both sets. 120s would be most comfortable with a longer wing like the Apeks one or something like that; where 80s would be happier with a 45lb halcyon, an agir or something to that effect.

A different option would be to look at something like LP95s (or E8-119s). They are virtually the same internal size (e.g. capacity), but they are definitely more friendly via external size and they will go nice with the same wing you'd want for an AL80.

On a side note, you might want to look at picking up a set of bands and a manifold for AL80s. That way you never have to worry about actually arranging for doubles on vacation; you just take your bands and manifolds, and double up a couple rental tanks.

 

[Daylonious]

Thanks for the tip - that's a good price for a complete sling harness - I went ahead and ordered one right now (have a 40cf I just bought)

D.

Rig the AL80 like a stage bottle with something like this:

https://www.deepseasupply.com/index.php?product=1309

Bring your deco/stage reg with you, then it doesn't matter if the boat only has AL80's.

Just remember to tell the captain you wouldn't mind being one of the first off the boat and you might be down a little longer.

 

[peterbj7]

IMO the difference between diving aluminum 80's manifolded and any normal steels manifolded is trivial. You may need to adjust your weight and trim, but that's the case whenever you dive in water of different salinity anyway.

Far more interesting, and significant from a training perspective, is whether your two tanks are manifolded or independent. If you're travelling you're most unlikely to find manifolded doubles (though I have 15 or 16 sets) and you may not be permitted to replace the valves with a manifold even if you want to. So you need to work with independent doubles and understand all the issues that arise with them. Completely different from using a manifold in many ways.

 

[sporket]

Good thoughts and information. I'm also considering setting up a set. What type of bands and manifold do you suggest?

 

[Daylonious]

I'm no expert - but it's my understanding that if you're going to go the doubles route, DIN valves are better, and you want something that's at least rated to 300 bar pressure.

I'd say dont skimp on the manifold, after all, it's what's keeping you alive - buy the highest quality you can find.


That being said, there's not much variety in bands - you basically have highland mills (rare), OMS, Diverite and Xs -

They're all roughly 150 bucks or so - you just have to look at the thickness and steel quality and make your decision. Just make sure the diameter is right for your tanks (either 7.25 or 8 inch) -

That's pretty much all I know about it -

Good thoughts and information. I'm also considering setting up a set. What type of bands and manifold do you suggest?

 

[TSandM]

There are significant differences in manifolds. This ranges from the ease of moving the valves, to the number of turns between open and closed, to the nature of the knobs (rubber versus plastic), to the way the burst discs are installed (recessed or not). There are also differences in the way the crossbar is fitted into the valves, so that some crossbars can be moved under pressure and some cannot.

I have Thermo manifolds on my doubles, because they were locally available, they have rubber knobs, the crossbar is movable under pressure, and the burst discs are protected by a ring of metal, so they can't be damaged if the manifold takes an impact. (Not important in OW diving, but in wreck penetration or cave diving, it is.)

I'd also offer my opinion, for whatever it's worth, that 300 bar manifolds are a PITA. For the minimal improvement in safety (if any) you trade a lot of convenience and flexibility.

 

[DA Aquamaster]

I agree with the sentiment that 300 bar valves are a PITA. The 200(232) bar variety DIN/K valves are more than strong enough and are in any event rated for 3442 psi applications. Another 58 psi in a 3500 psi application is not going to kill them.

The 300 bar valve is very long and is more damage prone if the tank is dropped or falls over. You cannot dive with an oval shaped DIN fitting. The shorter 232 bar valve is less prone to damage and is almost bullet proof if the insert is left in.

There are not that many brands but there are even fewer manufacturers. Most brands are either identical or differ in very small details - such as whether there is a raised ring around the burst disc.

I have manfolds with and without the raised ring around the disc assembly. it is a nice addition, but I am not a believer that it makes any significant difference. The disc resides under the screw at least 1/4" below the surface of the manifold and you could hit the manifold hard enough to shear the exposed head off the screw and not have a significant effect on the burst disc. The "exposed" burst disc assembly on the non ringed manifolds also is located just above the flange for the tank neck, so it would take a very precise nearly million to one wack to do any damage to it inside a wreck. There are a lot more things that will get damaged long before the burst disc. If a burst disc goes under impact, it is because it was corroded or fatigued and should have been replaced anyway and whether the head of the screw was recessed or not makes no difference.

Some valves turn off very quickly in under 2 turns while others may take 3, 4 or even 5 turns. For an O2 bottle slow is better but for back gas the fewer turns the better.

Rubber knobs are more prone to roll off in overhead environments such as caves and wrecks, but are much less likely to get broken. In any event, it is easy to change a plastic knob to a rubber one so one or the other is not a deal breaker.