100 or 120cf tanks in Coz?

[PaulVS]

100's work really well for me, But I'd really like to try a 120 at least once.

I'm not real suprised that my wife gets more time, she's roughly 52% of my weight and 85% of my height... I'd think that has something to do with it. I'm not worried about keeping up with the rest of the pack - just not cutting her dives as short.

 

[lowwall]

I like to blame it on the fact I have abnormally large lungs (x-ray techs have to do 2 separate chest x-rays, a top and a bottom) but the fact is I'm an air hog. Especially irritating is that I'm the natural "fish" and had to convince my wife to learn to scuba dive... yet she has half a tank left when I'm ready to ascend with an 80cf tank, so obviously her dive is cut short as well.

I always ask for 100's when setting up with the dive ops in the caribbean, but most of them act like I'm asking for my own private submarine, although I've found that if I press the issue I usually get set up. I haven't even tried asking for a 120, nor ever tried diving with one at all.

Trip to Cozumel in June and likely Bayahibe in the Dominican in September. Any tips on getting larger tanks or op's there that I could even get 120's with? Anything wrong with going with a 120? (I understand I'd use less lead)

I've dived with Aldora and used their 120s. I'm pretty good on air so it's almost a comical amount of gas. These are 70 minute dives and I don't think I ever got back on the boat with less than 1200psi and I'd do stuff like swim against the current just to see what progress I could make.

With my steel BP and no lead, I was a few pounds heavy at the beginning of the dive. But it was easy to swim up and I was neutral by the end of the dive. It also feels a little tippy at first, but I got used to it pretty quickly.

The one thing I always suggest for improving air consumption is to do long and slow exhales. Really just dribble the air out. Ultimately consumption is volume of the breath x the number of breaths you take. You don't want to cut down on the volume because you don't want CO2 to build up. But long exhales will cut down on the total number of breaths during a dive. You mentioned you were on your HS swim team. If you ever did long freestyle swims, you probably switched to inhaling every 3rd, 4th or 6th stroke and then exhaling in the water until the next breath. This is the same thing, except a much lower exertion rate and much higher 02 content (PP02) means you can take even longer between inhales.

 

[gmerick]

From a fellow air-hog. Go Sidemount. I've dived with at least a dozen operators in the Caribbean (LOB, Resort, 6-pack, and cattle-car). Every operator was quite willing to let me rent two tanks per dive. Most times it was two RH yoke valves, never rented a R-L pair. Upfront I said more air doesn't mean longer dive, I end when the group goes, or the planned time is up. And if you can hoover two 80s while your wife is still sipping on her single, ----

 

[lowwall]

A quick note on AL80 vs HP120. An AL80 at its working pressure of 3000psi actually contains 77.4 cu ft of gas. An HP120 contains 120.1 at its working pressure of 3442.

Anyway, assuming you want to have 500psi left at the end of the dive, the amount of gas available for the dive is 64.5 cu ft for the AL80 vs 102.7 for the HP120. That's just under 60% more.

And Aldora has traditionally filled these tanks well past 3442. This is from one of my dives in early 2020.

If they are still doing 3800psi fills, you get 113 cu ft with 500 psi remaining.

[edit: @inquisit's post Al 80 vs HP100 useable amount of air reminds us that all these numbers are a little high due to the difference between ideal gas laws and the compressibility of gases in the real world.]

 

[ChuckP]

Aluminum 100's are available here with very little issues other than high season. Of the two main filling stations that supply them, one is way better - you want tanks from AICO.

An aluminum 100 is only 100cf when it's filled to 3300 psi, when they are only filled to 2900, they are about 88cf - still more than an 80 but.........

Aldora, Living Underwater (he has switched tanks so I'm not 100% sure on them) and one other company use steel tanks here and have the 120's....

I personally think steel tanks are overrated for diving here for normal people, they are more of a crutch and diving them here does you no good when you go dive somewhere else - they are a band aide that follows you for life. My 14 year old overweight out of shape son learned how to do 70 minute very aggresive profiles, he's 16 now, had not dove in a year and on dive two back in the water, he was right back at great air consumption....

What's really the difference between a 60 minute and 70 minute dive? If we are going to do 90+ minute dives, then you really need nitrox and factor in the swim time when crossing over to the shallow reef to extend the dive....... It's all what flavor of cake you want!!!

 

[ChuckP]

A quick note on AL80 vs HP120. An AL80 at its working pressure of 3000psi actually contains 77.4 cu ft of gas. An HP120 contains 120.1 at its working pressure of 3442.

Anyway, assuming you want to have 500psi left at the end of the dive, the amount of gas available for the dive is 64.5 cu ft for the AL80 vs 102.7 for the HP120. That's just under 60% more.

And Aldora has traditionally filled these tanks well past 3442. This is from one of my dives in early 2020.

If they are still doing 3800psi fills, you get 113 cu ft with 500 psi remaining.

I dove with them for a year or more - never seen one filled that high unless it had been sitting in the sun - jump in the water and in 5 minutes you loose all that goody. Aldora and AICO have the most uniform fills on the island - 3400-3500 for steels and 3050-3150 for the aluminums.

 

[PaulVS]

For the record I'm 6'2", 230lbs. Last time Iin Cozumel with 100cf my best time was around 50 minutes with about 500-600 PSI left, which is acceptable to me, but would like to be able to stretch it to an hour consistently. (Obviously aware that depth, fighting against drift etc.need to be taken into account ) I typically carry about 12-14lbs of lead.

Years ago I also found I was getting kind of overheated (mostly on the boat) with a 1.5mm shorty, so I pretty much do a rash shirt and swim trunks now when possible, which seems to have helped somewhat.

 

[boulderjohn]

What is the recommendation for weighting when using steel 120s vs 100s?

The answer depends upon whether you are talking about steel or aluminum 100s.

 

[ChuckP]

Relaxing like your are laying on the couch and not moving your legs will get you the biggest gain. Good buoyancy, no, great buoyancy combined with patience gets you to the point where you don't use your legs, fin tips by moving your ankle but not your core or thigh muscles.

The worst air consumption I ever seen was this 6' body builder, dude was huge - he proabaly burned more O2 farting than I do walking a mile......... Muscle mass burns O2 and that makes you breathe....

 

[NovaCane]

The answer depends upon whether you are talking about steel or aluminum 100s.

Steel for both