Doubles advice

[RAL]

you really are saying the same thing both for and against."you can save money..," "you can get a 1st rate side mount...for the same money," "...you can get a set up a little cheaper back mount these days..." So he can go back mount cheaper. Right?

False economy. You can find used back mount gear cheap.......but where are the savings once you realize that you will be better off using side mount and you want to buy ANOTHER set up? Granted some still use back mount but many hardcore " I'll never dive sidemount" divers are finally changing over. Why because it is a more versatile, balanced system that has the added benefit of being a lot easier on the Ol back.

RAL

[a64pilot]

1/3 of a single is as good as or better than 1/6 of doubles.

I don't understand that comment, can you explain it?

[DA Aquamaster]

It is perfectly possible to cave dive in a backmounted single. Your range will be short, but at the intro level your range should be short. 1/3 of a single is as good as or better than 1/6 of doubles. When I was an intro cave diver, I dived a single backmounted 130 with a Cochrane Y valve. The 130 fitted nicely onto my Beuchat jacket-type BC. This rig was a little tippy, but I mastered it just before I got into doubles in my apprentice course.

I don't understand that comment, can you explain it?

Me too, because I just don't see it.

Assuming the tank sizes are the same (one 130 versus double 130s for example) the penetration gas provided by 1/3rd of a 130 is the same as 1/6th of a set of double 130s and the penetration distance is very close - although maybe slightly farther with the single tank (less drag).

There are two major differences between singles and doubles.

The first the difference is the reserve gas available to deal with a problem. In this case, at max penetration/turn pressure if diving to thirds with a single 130 you've got 86 cu ft remaining - 43 for exit and 43 in reserve. In contrast, in double 130s, you'll use the same 43 cu ft for penetration with 1/6ths, but then have 216 cu ft at the turn - 43 for exit and 173 cu ft in reserve.

43 cubic feet does not equal 173 cu ft, and if a problem arises, it's an easy guess which reserve you want, especially as an intro level diver.

The second difference is that even with a Y valve, you don't have full redundancy as a blown burst disc or a fails neck o-ring will dump all of your gas, leaving you totally dependent on that same very small reserve your buddy is carrying. And in this case, if you're at max P, you're screwed as you'll burn gas working the problem, then breathing off your buddy's long hose, possibly starting in a silt out caused by the rapid gas loss, you'll almost certainly exit slower than you entered and need more gas to exit than you have. At the very best, there is zero margin for error in a 2 person team with 1/3rd of single tank gas planning/management if you have a problem at or near your turn pressure.

In contrast with doubles and 1/6ths management, even if you are painfully slow isolating, you've got half of 216 cu ft to work with at max P, and you'll only need to save maybe 50 cu ft of it, so the margin for error is large.

Personally, if I were king of my own cert agency, I would not allow single tanks beyond the cavern zone, and personally, I've never taken a single tank past the cavern zone for the reasons stated above.

[Sludge]

where are the savings once you realize that you will be better off using side mount and you want to buy ANOTHER set up?

What about those that get a sidemount setup and realize backmount works better for what they do?

The best advice would be to buy used. If it doesn't work out for you, you'll probably be able to get your money out of it, as long as it's in the same shape you bought it in. And assuming you didn't pay too much in the first place.

[DA Aquamaster]

What about those that get a sidemount setup and realize backmount works better for what they do?

The best advice would be to buy used. If it doesn't work out for you, you'll probably be able to get your money out of it, as long as it's in the same shape you bought it in. And assuming you didn't pay too much in the first place.

I buy cars the same way - I'd rather buy a 3 year old low mileage vehicle still under warranty, rather than a new one, as it lets the previous owner eat the major chunk of depreciation.

Buying used scuba gear is generally what we've done as well, more or less. We either buy used gear in near new condition, or in rare cases we buy new equipment at a killer out the door price equal to the near used gear price, or we buy new gear with a key man discount.

In that regard, it's about a toss up. Back mount gear is available used for comparatively great prices as so many people are defecting to sidemount. On the other hand, lots of people buy a sidemount system that does not meet their needs and sell it for something else, so prices on used SM gear are not bad either.

[Shocky]

If you choose doubles, I recommend Highland bands. Good alloy, seam welded, wider, heavy duty hardware.
John

[LCF]

I think they should rename this forum "SidemountBoard".

Funny, I was just floating around in the pool (tune-up for my upcoming MX cave trip) in my doubles, and thinking I really ought to dive them more often than I do, because they dive so WELL . . .

[Puttzer]

I can't say I've ever seen a "single tank" past the cavern zone. I'm sure it happens, but it's not common.

Regardless, if that's how you're comfortable, go for it.

My wife ALWAYS dives past the cavern zone with a single tank.

[allen]

I am sorry that my original post was not clear. The heaviest set of doubles I can carry is a pair of 100's. 1/6 of 208 cu.ft. is 34.3cu.ft. I can, however, carry a 130 cu.ft. single which gives me 1/3 of 130 cu.ft. which is 43.3 cu.ft. Thus as an Intro Cave Diver I could get farther in a single than in doubles without breaking the rules. This ignored the safety and balance advantages of doubles. A blown burst disc on a single tank is a disaster for a solo diver in any event. It is fatal in a cave and may be fatal on a deep wreck. (On a deep wreck I carry a pony bottle. I intended to do so in caves when I bought my 130.) This is the reason for Alex Brylske's rule, "Solo dive only to twice the depth or distance you could free dive." An intro cave diver certainly should not be cave diving solo.

[DA Aquamaster]

I don't think that rule originated with him, it was a very old rule when I got certified in 1985 - but he's certainly a promoter of that rule.

Your example is an excellent one, and one that makes me shake my head about some agencies allowing thirds of a single tank in a cave, and at the same time being restrictive about Intro level divers using doubles in caves.

As you point out that allows a diver to use a full third of a 130 and have 9 more cubic feet of gas for penetration than the same diver using double 100s to sixths.

The general idea is to limit penetration at the intro level, but assuming a 60 feet average depth, a SAC of .6 cubic feet per minute and a swimming speed of 50 feet per minute, that 9 cu ft difference will get the 130 diver 250 ft farther into the cave than the diver with double 100s. Unfortunately, that also means that if a serious problem occurs at max penetration, the single tank diver has very little margin to work with (only a 43 cu ft reserve) even with a buddy present, where the double 100s diver would still have 156 cu feet in reserve, even if he busted his sixths and used the same 43 cu ft of penetration gas. Getting farther on a single than you could in smaller doubles, just highlights some of the flaws in the single tank is ok concept.