Aluminum 80s versus larger steel tanks

[Dave Dillehay]

Dear Christi,

For the life of me, I just cannot understand how you get more bottom {or dive time} with LESS air molecules. That just makes no sense at all unless you BC was loose, currents bad, or who knows what. Physics is Physics!

Dave Dillehay
Aldora Divers

 

[cvchief]

CVChief is quite a bit larger than I am (I'm 5'0" and a pretty normal weight)

So you are saying I am taller?

 

[Ron Lee]

Take a random set of 475 divers with 120 cu ft tanks. Dump another random set of 475 divers in at the same place. They all dive the same initial profile until they need to ascend. The chi squared three sigma median standard deviation will clearly show that the group using 120 cu ft tanks have significantly longer dive times than the 80 cu ft group.

It is not physics....it is physiology or more air is better than less air.

 

[nodakdive]

Take a random set of 475 divers with 120 cu ft tanks. Dump another random set of 475 divers in at the same place. They all dive the same initial profile until they need to ascend. The chi squared three sigma median standard deviation will clearly show that the group using 120 cu ft tanks have significantly longer dive times than the 80 cu ft group.

It is not physics....it is physiology or more air is better than less air.

What if the profile is 60 feet for 60 minutes? Do the AL80 people still need to ascend first?

 

[Ron Lee]

What if the profile is 60 feet for 60 minutes? Do the AL80 people still need to ascend first?

We can make it a multi-level dive to avoid deco issues.

 

[Dirty-Dog]

CVChief is quite a bit larger than I am (I'm 5'0" and a pretty normal weight) and he uses way less air than me- probably got 15-20 minutes more in most cases, diving about the about the same profile (he did tend to go deeper than I did, and probably used more energy taking photos, which would lead to him using more air, not less).
Out breathing a divemaster with thousands of dives is going to be tough- but size is really not the only factor. We had a DM in our OW class who was a BIG guy- clearly overweight, big guy. He said he had better air management than the other DM, who was a very fit guy with similar experience level.

Christi wasn't just saying SHE gets 70-90 minutes, but that her customers do. (90 does seem long to me for a 'typical' dive; but what is 'typical'? I'm guessing that 90 minutes is a shallow dive, but shallow dives like Columbia Shallows, Paradise Reef, or similar aren't uncommon for second dives, so that could be typical.)

Of course there are multiple factors. The point was that you don't "manage" your air, really. You use what your body needs. And more air available means a longer dive is possible.


Sent from an old fashioned 300 baud acoustic modem by whistling into the handset. Really.

 

[Gdog]

Because they are an awesome option! I wish they were an option in more places, as I always check where ever I'm diving and unfortunately the old aluminum 80 rules the diving world in almost every location. Going to Cozumel AND having the option of steel 120s is awesome.

Would so love to get ahold of 120s in Bonaire. It's not unusual to do a 80-90 minute dive there on an al 80, with a steel 120, I'd need people to bring food to me on my dives, I'd be a wrinkled prune by the end of the week.

+1 on that. I mean if you enjoy 60 minutes give or take on an AL80, why wouldnt you enjoy a little more back gas to sip, use less weight on your belt, and stay down longer??! We do it all the time up here in the Cozy Pacific Northwest.

 

[Skittl1321]

So you are saying I am taller?

Well, you are. (Unless you are 4'11" and were on stilts when I met you.)

---------- Post added May 15th, 2014 at 07:12 AM ----------

+1 on that. I mean if you enjoy 60 minutes give or take on an AL80, why wouldnt you enjoy a little more back gas to sip, use less weight on your belt, and stay down longer??! We do it all the time up here in the Cozy Pacific Northwest.

Because the extra air isn't free. If I were to dive with Aldora, I could only get 3.6 days of diving for the same price I paid for 5 days. Living Underwater, 3.2 days of diving. (And if you were someone who usually uses Dive with Martin for multiple day packages- those ratios get even worse; but my op charged more than them, so I used MY costs to compare for me.)

Me, I'd rather dive 5 days at 10 sites than 4 days (at a slightly higher cost) at 8 sites, even if I spend the same, or a bit less, total amount of time underwater. I like the variety more than I like the idea of extended dives.

If you were going to give me the extra air for free, I wouldn't turn it down. But it isn't something I value as an 'extra'. Just like I have no interest in a beach surface interval. (Why would you want to be on a beach when you can be on a boat out on the water? Unless you are on an uncomfortable boat, which I wasn't.)

 

[Mike]

+1 on that. I mean if you enjoy 60 minutes give or take on an AL80, why wouldnt you enjoy a little more back gas to sip, use less weight on your belt, and stay down longer??! We do it all the time up here in the Cozy Pacific Northwest.

Makes sense to me.

Well,
Because the extra air isn't free. If you were going to give me the extra air for free, I wouldn't turn it down.

Exactly. This was the 2nd point I made long ago as to the generic question for the real reason 'why wouldn't you want more air? As I said, if you had the choice between the two tanks with no additional costs the Al 80 would go extinct. Almost 200 posts later everybody is slowly coming around and saying exactly what I said a week ago.

 

[Lorenzoid]

I wouldn't turn down the "extra air" if it were free, either, but the point is I believe I don't truly NEED the extra air for the kind of diving I want to do in Cozumel. As I said many posts above, after an hour in the water my wife and I are more than ready to get out and into some sunshine, sip some water, etc. There is always another dive. This is our vacation, not a dive marathon. And the need for an air reserve for contingencies seems marginal to me in drift diving.

Also--and I suspect this has been discussed--isn't a steel 120 generally a few pounds heavier topside than an aluminum 80? I realize the weight-in-air difference is small and that the characteristics we logically should find important relate to buoyancy in water (in which a steel tank excels), but some petite types may prefer to deal with the familiar, easy-to-handle aluminum 80. As I recall someone commenting, if more is better, then why not then push doubles on everyone? One answer is that out of water they are difficult on one's back, especially for people of slighter build or with back problems. Many of us visit Cozumel to enjoy relaxed, tropical vacation diving, not to do the kind of diving they do in, say, the Pacific Northwest. Heck, I can imagine feeling too lazy in Cozumel to even want to adjust my cam bands to accommodate a different sized tank.