Larger Tanks for deep dives (100ft)

[zaberman1]

It was certainly my mistake, I misread the deep course and interpreted it as deep and wreck course. Consequently, my post about 1/3 and 1/6 is misplaced. However, the OP should still consider SAC rates, conversion factors, and multiplying by x (how much reserve he wants to maintain in the cylinder).

To answer those that commented on it, yes 1/6 gives you the usable supply in one cylinder and is meant to add an additional barrier to penetration until further training is sought. You would obviously use that number in the above equation instead of thirds to find out total gas supply needed plus reserve.

EDIT: Using 1/6th for a recreational wreck dive penetration on doubles is just as prudent as using 1/6th penetration for cavern and intro. It also gives us the opportunity to do multiple dives

 

[Web Monkey]

HI,

Planning a few deeper wreck dives this summer.
Would like to have a single tank that can have
superior bottom time over what I have now. using a HP steel
100. I am thinking of the Faber 118 blue steel. Any thoughts..
I am 250 pounds and consume air very fast at depth, but it has gotten
much better in the past year or so. Still would like the safety of extra air.

Sorry to be a wet blanket, but "extra air" doesn't actually provide safety, in fact, by allowing you to extend your dive, it could make your dive more dangerous by allowing you enough bottom time to incur a significant deco obligation if you're not paying attention to depth and time. And while a lot of people will say "Deco is no big deal", what it does is completely invalidate nearly all the emergency procedures you learned in OW class, since surfacing with a deco obligation is not an option (you could be injured or killed).

And in fact, even with a SAC rate of 1.0, your current 100 CuFt tank is already enough to let you rack up a 10 minute deco obligation on a 100' dive if you're using air.

If you're looking for safety, I'd suggest finding a good buddy and working on gas planning.

If you really need more time than you have, I'd suggest doubles and Advanced Nitrox/Deco training as well as the above buddy and gas planning.

Terry

 

[elan]

When I switched to double tanks I was wondering why the hell I was wasting my time with pony setups. Cumbersome ,heavy and I need to carry 3 tanks for 2 rec dives. Switched to double HP100 and I was able to do 3 rec dives and still have gas, no crap hanging in front of me no rolling under the weight of the pony and hoses are nice and clean routed and redundancy is there. IMHO either dive singles with good buddy and no pony (or very small pony) or just get the doubles in places that requires redundancy like very cold water. YMMV

 

[DaleC]

use the hp 100, sling an al80

Just curious, but why do you suggest this?

Just call it a stage. Start the dive on the 80, breath it down to 1500psi and then switch to back gas. Now call it a pony and you have aprox. 40cuft. of gas in it. This also allows aprox.140cuft of gas for the dive (100+40). Of course, this presumes one is comfortable doing bottle name switches while under water.

However, unless one is comfortable diving a non conventional system I would personally recommend a single HP130 + good buddy skills or double whatevers and proper training.

 

[Rhone Man]

Sorry to be a wet blanket, but "extra air" doesn't actually provide safety, in fact, by allowing you to extend your dive, it could make your dive more dangerous by allowing you enough bottom time to incur a significant deco obligation if you're not paying attention to depth and time.

Not sure I follow the logic of that. "Extra air" has sure as hell got to be safer than "insufficient air". Yes, more air would, theoretically, allow a careless diver to rack up a deco obligation before they ran out of gas. But surely the assumption must be the trained diver will monitor depth and time, and not just their SPG? A good diver can get into deco at 60 feet with an aluminum 80 - it doesn't follow that people should wear smaller tanks just to force them back to the surface earlier.

My own view is that it will be a rare thing that too much gas constitutes a safety problem.

 

[UCFKnightDiver]

Delete

 

[izibo]

My own view is that it will be a rare thing that too much gas constitutes a safety problem.

I would go one step further and say it NEVER constitutes a safety problem.

 

[TSandM]

As a very wise instructor of mine once said, "You can fix bent; you can't fix drowned." I'll take extra gas, any day. In fact, I routinely dive with a lot more tank and a lot more gas than I need for any given dive. It gives me a warm, fuzzy feeling. (It's one place where I'm not into minimalism!)

 

[Puffer Fish]

How did we get into talking about penetration and diving thirds? The OP just said he was going to do some deeper wreck dives -- he didn't say he was doing any penetration. There is generally no need to dive thirds on exterior surveys, unless it is imperative to return to the upline.

As far as a pony bottle size, it isn't dependent on what size tank you use. You're carrying a pony as insurance against a catastrophic gas loss from your primary supply, so the pony bottle needs to have enough gas in it to get you, in a safe and controlled fashion, to the surface from the deepest part of your proposed dive. To calculate this requirement, you need to know what your typical gas consumption rate is, and then make an adjustment for stress (typically doubled). Then you need to look at the ascent profile you would like to do in such a situation.

We use 20 cubic feet per diver as a reserve from 100 feet. If your gas consumption is typically significantly higher than .5 cfm, you might need more.

What She said.

 

[Sas]

What is "recreational penetration"? You mean not going past the light zone? Sorry, I just haven't heard that term before.

Also I am interested to hear how often 1/6ths is taught. I have always been taught rule of thirds, in wreck + cavern training and have not heard (other than posts here) of people being taught to dive 1/6ths. I'm a recreational diver too.