Aluminum 80s versus larger steel tanks

[Sue Sue]

Skittl..in time I would put bets that you will see your bottom time exceed your 51 min average. Once you conquer your "Freak out" , get more experience with buoyancy, and become more comfortable with the general routine you could very well see those 70 min. dives. Most importantly, Do Not take to heart what others are doing. Take your time, relax your breathing and get your weights right. Overall, experience is the best way to improve your bottom time.

 

[yardpro]

in every hobby or interest i have ever been involved in there are always those that are one uppers...
I followed the grateful dead (yes i was a deadhead)... I saw about 150 shows in 7 years. My friends and i would just look at each other whenever we met someone that was trying to out "head" us.... we could care less...

I raced motocross and qualified for loretta lynns (the pinnacle of amateur motocross)... when we were at tracks there was always that guy that tried to me more into motocross than us..

when i surfed, i was mediocre at best, but there were always those posers that would go on about how good they were...

golf...
frisbee golf in college
autocross,
bmx

it is always the same....



Who cares what size tank you use. I have a pretty good SAC. i am usually one of the last ones low on air... I also never get these times... 50-60 min is about it.

Why would you NOT want more air....

all the guys slinging pony's and using an 80 then getting uppity about me and my 120... WTF.....we have the same volume of air.....

personally i like to breathe, why in the world would i EVER want to in any way want to have LESS air....

that analogy is EXACTY the same as someone saying....
" you guys with 80's ust be air hogs... i only need a pony"

why would you ever want the MINIMUM air you need?

 

[drrich2]

An interesting question to ask is, if technology afforded us tanks similar to current options in size & weight but with, oh, say, 500 cf of air so most people would come up for other reasons besides low gas, how long of dives would most people wish for? If you could stay down as long as you wanted, how long would that be?

On another matter -

For the record, they cost me three times as much as aluminum tanks would and we have to be much more careful with them.

Much more careful how & why? Just curious.

Richard.

 

[pjhansman]

 

[Darol]

Doesn't really matter, I just want to dive Cozumel......... Longer BT = Longer Deco...... I'm just sayin......

 

[gopbroek]

Well under, just under, a little, a lot, short of, less than... substitute whichever description you would like, don't stress over it.

---------- Post added May 9th, 2014 at 02:14 PM ----------



just rare? quite rare, really rare, rarely rare, sometimes rare, a little rare, majorly rare, somewhat rare, medium rare....

I have to go with the plus 60 minutes on a standard drift dive with a an AL80 in Cozumel, excluding of course the 5000+ hour DM’s and the dive diva’s like Fishi, who I suspect has gills, they come up at 80-90 minutes with a 1000+ still in the AL80 tank. For the average diver with average skills the times that I see run to 60-70 minutes on average for a basic multi-level dive. That time will drop rapidly with improper buoyancy or extra task loading (like getting frustrated when you blow a shot at a Lion fish). What impresses me is watch Big Mike Buscher doing 70-80 minute multi-level dives on lion fish hunts. While large in stature he is trimed and wastes no movements and uses the current to his advantsage.

 

[Midge907]

There isn't anybody in Cozumel routinely doing 90 minute dives with AL 80's on a typical Cozumel dive site & profile, period. Nada. The average dive in Cozumel is well under 60 minutes.

And the major resistance to extending dive times is right here:

I will agree to a certain point that a good number of people come up in less the :60 minutes in Cozumel, however I know their are plenty of others that come up after that mark on average. I had a average dive time of :71 minutes with a average depth of 72ft when I was there in January. my longest dive was :82min where I still came up with nearly 1k psi on a night dive at Paradise. I did mess up my average and had a :43 minute dive, however it included a max depth of 118ft, and was deeper then 100ft for 20 minutes of it. If I was diving a 120 I still would of ended up with a short dive or gone into deco otherwise.

 

[KenGordon]

An interesting question to ask is, if technology afforded us tanks similar to current options in size & weight but with, oh, say, 500 cf of air so most people would come up for other reasons besides low gas, how long of dives would most people wish for?.

We have, it is called a rebreather. You get about a minute per litre of free O2. So a 3l (25 ft maybe) contains 3*200 = 600l or 10 hours. The scrubber limits the actual time to less than that.

Here in the UK we typically use 15l (approx HP 120 cu ft) for a first dive and 12l (approx HP 100 cu ft) for a second. Smaller people might use a 12 and a 10 (HP80).

Typically these will be rectangular profile dives so a 30m (100ft) dive is limited to a bottom time of about 25 minutes by the gas available. At a uk SAC of 20l/min that uses 2400l of the 3600l.

I am coming to Cozumel later in the year with a mixed group, some feel has worse air consumption than others.

So I'd be interested to see some actual profiles. Somebody posted a shot of a bunch of logs. Could you post some profiles? Are cozumel 100 ft dives a rush to depth, quickly coming up shallower and then a bimble on the top?

Using the kind of SAC I see quoted on here (15l/min) a 30m dive on a 15 (hp120) might stretch to 35m of bottom time but would incur 14 minutes of stops (on 32%). On air an entertaining 59 minutes of stops, surfacing with maybe 300psi.

The old timers round here have a saying "you can't get bent on a 12". Maybe given the perceived skill levels of their customers that is a reason for dive ops to use small cylinders.

I will have to do a weight check in the pool with my AL80 (a deco cylinder) to work out how much lead I will need. I expect the lead to be more than the difference in dry weight of the cylinders. For anyone not negatively buoyant naturally I'd expect the HP steels to be beneficial. Having said that I see that initially the turning effect of a heavy thing behind you can be a problem.

Ken


Sent from my iPhone using Tapatalk

 

[Ron Lee]

An interesting question to ask is, if technology afforded us tanks similar to current options in size & weight but with, oh, say, 500 cf of air so most people would come up for other reasons besides low gas, how long of dives would most people wish for? If you could stay down as long as you wanted, how long would that be?

On another matter -



Much more careful how & why? Just curious.

Richard.

Perhaps it is because steel rusts. You have to keep salt water out of them.

 

[DjDiverDan]

Perhaps it is because steel rusts. You have to keep salt water out of them.

Technichally, Aluminum rusts as well - or rather, it oxidizes, forming Al2O3, or corundum, the base crystaline structure in rubies, sapphires, and emeralds. The difference is that Aluminum Oxide is both very hard (9.0 on the Mohs scale) and very dense, and effectively forms a protective seal on the surface of the aluminum so that the oxidation never (on its own) proceeds beyond the surface. It needs cracks and fissures formed from external sources, like bending, twisting, or fracture from abuse, to corrode internally. Iron Oxide, on the other hand, is very brittle, and forms no seal at all, and Iron Oxide will, on its own and over time without help from any external sources, invade into the metal, exposing more and more of the interior to oxidation, eventually completely destroying the integrity. Certain Steel alloys have more resistance to corrosion - both Chromium and Zinc will retard oxidation, but they don't stop it completely. And adding too much of these components changes other characteristics of the Steel, like hardness and malleability. TMI?