Anyone slinging/sidemounting ST72s?

mempilot

Anyone slinging/sidemounting steel 72s for bailout/OC deco?

How's the full negative bouyancy?

How's the empty bouyancy?

How do they ride?

How is the size/weight in your opinion to the AL80?

Thanks,

Eric

__________________
MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

gottrimix

I have tried aluminium 72's... just got back from CCR Cave crossover in High Springs....Wayne at Amigos Dive Shop had some aluminum 72's (not steel) . I sidemounted them as bailout and as stages on the Meg. Lighter and really are nice in the water. Seemed like less drag than 80's. Not sure about steel.

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Steve

www.lakemeadtechnicaldivers.com

mempilot

I'm interested in info on Faber steel 72's or OMS 66's.

__________________
MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

nigelh

That 9L in euros isn't it?

I sling a pair of steel Faber 7Ls from chest (outside of C/L) to waist on the YBOD and they hang down nicely, stay below so they don't get between me and the valves for those OMGIGTD moments and are well behaved to unclip and hand around in mid-water (although I've only done that on a course).

The valves sit just where I want them and the regs/whips are snoopied and I label them on the inside edge as that's the easiest one to see.

In fact I like the things in as much as I'd like anything that I hope is just along for the ride. They lie under me and point in the direction I'm going so that seems reasonably streamlined - although something with a chunky Apeks reg on the sharp end is hardly going to score low on that point.

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nigelh

mempilot

Nigel,

Thanks for the post. I have access to a stock of these tanks. I may buy one or two.

Eric

__________________
MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

netmage

Eric, you guys are killing me. Did none of my DIR mindset rub off over the last 2 years of diving w/ you guys....?

Steel tanks will permanently impact your weighting, especially if your going to be carrying for the duration of the dive, a la ocean diving... Unless your looking at ditching weight carried elsewhere, your going to be compounding the dynamic instability of your rig... At depth you'll be needing to compensate by inflating your wing furthur... According to the good folks over at Huron Scuba (who IMHO have one of the best cylinder spec charts), the faber 72 will swing from -8.5 -> -3.7, whereas the traditional AL80 swings from -1.4 to 4.4...

What about your AL40/80's are you not liking...?

Like I mentioned Sunday, I'll be shipping 2 or 3 from Cincy over the holidays... they might need a hydro and tumble, but I'll likely sell 2 and keep one as a large oxygen bottle for visits to the caves or as a booster supply for trips.

-Tim

Tom Mount

Why would any one wish to sling steel cyliners of any size

Al' are much better trim and do not weigh you down
my preference is Al 40 and Al 30's
Instead of a larger single cylinder work with multiple (when needed) al 30 or 40 this provides redundant regs and easy management- plus more flexiability if one must hand off
Tom

mempilot

First, I'm just collecting information and feedback, so let's not get all jumpy and assume I'm doing anything at this point other than that. We don't want to piss off the cave gods, even though this has nothing to do with caves.

Second, let's get the numbers straight. These figures are pulled from the tank chart Tim speaks of. At 5.8 lbs shift, the AL80 has the largest swing in bouyancy between all the mentioned tanks, and it goes from negative to positive in a big way.

Full / Empty / Swing
AL40 / -0.8 / 2.2 / 3.0
AL80 / -1.4 / 4.4 / 5.8
OMS66 / -5.15 / -1.67 / 3.48
Fabr72 / -8.45 / -3.7 / 4.75

Going from negative to positive bouyancy as the tank is drained creates a more dynamic situation, and is the reason I am collecting feedback on the OMS 66's and Faber 72's as an intermediate bailout/deco tank. There is a reason people 'float' them up the line when they are used up.

Short of offering a second regulator, pairing an AL30 and AL40, or even two AL40s, does not give any noticeable advantage to a single AL80; and therefore, the AL80 wins out. I started to look at an advantage of carrying two different mixes across the 30/40 or 40/40 combo, but at depth and stress, the diver would breath down a 40 in short order, so a single large source still gets my vote.

Full / Empty / Swing
AL30 / -1.0 / 1.2 / 2.2
AL40 / -0.8 / 2.2 / 3.0
30&40 / -1.8 / 3.4 / 5.2
AL80 / -1.4 / 4.4 / 5.8
OMS66 / -5.15 / -1.67 / 3.48
Fabr72 / -8.45 / -3.7 / 4.75


Here's the argument that I don't get. If a tank has the potential of being positively bouyant, then weight must be carried to offset that potential bouyancy. The AL80 goes positive in relative short order after consumption starts, so sending it up the line is not a solution for not carrying the weight. That added weight carried would need to be 4 to 5 lbs per AL80 being carried. That is the same amount of swing weight in the OMS66 or Faber72, both of which remain a little negative after usage. The amount of lift required is dang near the same. Duduction states that no extra weight needs to be carried with the steel tank, and in the event the tank is ditched, the diver is back to being basically neutral.

Since an AL80 really only holds 77.4 cf, the steels and the aluminums are very close in capacty at service pressure. The LP OMS 66 could easily be pressurized to 75 cf at 3000 psi.

The configuration I would propose using this in would be an intermediate depth where greater than 40 cf of deep bailout is required, but an AL80 would be overkill. Let's say that 50 cf of deep bailout is needed to ascend up to 70 fsw where a switch to an AL40 of ean50 would take place. An AL80 would be well into the postive bouyancy realm with only 30 cf left in the tank. A steel 66 (75 @ 3000) would still be negative by a couple of pounds.

At this point, I'm either carrying an extra 5 lbs to offset an empty AL80, which isn't empty, or I'm in harmonay without the added weights.

I'm not saying any is wrong. I'm just throwing out possible alternatives. If my reasoning is flawed, then point it out with fact and figures. I haven't made up my mind, and I'm open to suggestions and fact, not carpet statements.

__________________
MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

mempilot

Tom,

Are you using AL or ST for onboard? Is it the same on all the different you dive? AL and ST provide bouyancy characteristics that are not preferred in all situations. The swing between + and - on AL is higher than that with ST. I agree that when you don't need the gas, AL is better, but when you use it, the AL tanks have to be offset by some other weight, correct? What is the difference if that weight is the tank itself, or on the harness? Is it ditchable, yes. If you must ditch the AL tank while full, it sinks; while empty, it floats; but you still have the additional offset weight to dump to get neutral. With the steels, you just dump the tank and you are neutral, provided you dive a balanced rig to begin with. I do. I don't require any additonal weight to be neutral/slightly neg at 15 fsw. I'm lucky in that my AL backplate works perfect for diving wet, and my SS backplate gives me the four pounds I need to offset the drysuit.

__________________
MEM "Da Pilot"

Black holes are where God divided by zero.

"If at first you don't succeed, don't dive silent."

"Would you mind not shooting at the thermo-nuclear weapons." ~ Vic Deakins

"Donkey's kill more people annually than plane crashes."

netmage

If one didn't know we are friends, they might think we're sparring...

Throw in the 1.5-2lbs for the regulator, and that 4.4lbs shrinks....

From a practical standpoint, diving my AL80 doubles I am weighted perfectly... Carrying multiple aluminum deco bottles through the course of the dive has had negligible impact on my buoyancy.

Since we're talking a bailout scenario, you have two fundamental situations in front of you... your either on a fixed line attached to the wreck, to which you can hang on the line.... or your drifting under a bag on deco, drain the bottle and send it up....

The key item I think to drive home here is that these bottles are dynamic, they are not fixed to your rig, as such you need to be able to maintain buoyancy w/o them, should you need to ditch at some point.... The characteristics of steel impose a far greater dynamic shift than aluminum.

The swing from empty to full is really splitting hairs; gas under pressure weighs roughly the same per volume, i.e. 3-5lbs for the volumes we're talking