Aluminum 80s versus larger steel tanks

[nodakdive]

Dave,
I'm not knocking big tanks. It just seems to me that the main advantage is longer dives and I'm ready to get out in an hour. I suppose there is a safety margin in certain circumstances but as nimoh mentioned, if the AL80 has enough gas for the dive, and I'm diving safely, it shouldn't be a huge safety advantage. Otherwise, steel 120s should be mandatory, and then where do you draw the line? Dual 120s would be even safer yet.

The buoyancy characteristics might have some appeal to me but I haven't tried it yet so I don't know. I'm kind of an odd duck there anyhow. My BCs are weight integrated, but I dive a belt for several reasons. For instance, when I'm upside down, the weight belt stays at my waist and the bc pulls away from my neck, toward the surface. With weights in the pouches, the bc has a tendency to feel like it's pushing down around my neck. There are tradeoffs.

Again, not knocking big tanks, though I may be defending my desire to dive an AL80 without feeling like I don't get it. LOL. I can see the advantage of a longer dive and the ability to profile deeper and longer, NDLs notwithstanding. If that's what I want, I'd seek it out.

I can see the advantages and draw of the way a dive day lays out too. For some doing two long dives with a long SI between is appealing. There are a lot of things that sound a lot worse, for sure and I can see why there are those that really like having big tanks. They're not crazy or wrong and though for heavy breathers it's a great boon, it's not a crutch. There's a purpose for it.

-Blair

 

[chillyinCanada]

My first question was what profiles are you people doing in order to get→ 90 ← minute dives. Profiles provided had total depths of 70-75.

Second question was average depth instead of "profile". You seem to have plenty of time to write insults and attempts at condescension but not the answer I've asked for. So be it. I shall draw my own conclusions in that regard.

As it happens, I dive with a computer, the vast majority of my dives are multi-level, and while I'm familiar with Cozumel diving it has been years since I've been there.

If you are only speaking to regulars that dive in Cozumel, so be it.

Let's say I didn't bother to ask in the first place, shall we. I'd prefer not to play your childish game any further.

 

[DjDiverDan]

This should really not be that difficult. Divers come in different sizes, shapes, conditions, and levels of experience, and they have different needs and desires. What's great for some might not work at all for others. I like the heavier weight of the HP Steel tanks, because I need a lot of weight to descend in any event - putting on 16 lbs of lead with a Steel 120 is, IMO, more comfortable than strapping on 21lbs or more with an AL 80. And, as an infrequent diver whose SAC rate is NOT what it ought to be, I really like the extra time, and extra peace of mind, that all that extra air brings me. BUT, if you are one of those divers who need little or no weight to descend, the HP Steel tanks, whether the 100 or the 120, are likely to make you overweighted, requiring you to use up some of the extra air to fill your BC, and requiring to constantly adjust the air in your BC as you go through a multilevel dive. And if you dive regularly, unlike me, you are probably much more relaxed in the water and have a much better SAC rate, so the extra air is unnecessary - you are going to approach the NDL on the air in an AL 80.

BUT, how many of you have ever bitched about being on a dive that had to be cut short because there was one, maybe two, real airhogs in the group that blew through the air in the AL 80 in 40 minutes? Wouldn't it be nice if that never happened? Wouldn't you like to know that those air hogs weren't going to cut your dive short because THEY had the extra air in a Steel 120?

 

[Skittl1321]

BUT, how many of you have ever bitched about being on a dive that had to be cut short because there was one, maybe two, real airhogs in the group that blew through the air in the AL 80 in 40 minutes? Wouldn't it be nice if that never happened? Wouldn't you like to know that those air hogs weren't going to cut your dive short because THEY had the extra air in a Steel 120?

I think this is why a lot of divers favor dive ops that send people up individually (or my preference- as buddy pairs). I complained about my buddy being out of air before me (though it was my choice to go up with him, as I think that is important), but I didn't have to complain about the people who went up 10 minutes before him, and the people who went up quite awhile after us weren't inconvenienced either.

Besides- won't an air hog in a steel 120 STILL cut the dive short for everyone else with their steel 120? They are still going to go through whatever air is available faster than the other people in the group. The problem is only solved when the air hog gets MORE air than everyone else (and possibly A LOT more air... as I experienced on one dive, where we did give one diver more air than everyone else, some people really suck that stuff down. Thankfully for that particular experience, it didn't wreck everyone else's dive)

 

[DjDiverDan]

Besides- won't an air hog in a steel 120 STILL cut the dive short for everyone else with their steel 120? They are still going to go through whatever air is available faster than the other people in the group. The problem is only solved when the air hog gets MORE air than everyone else (and possibly A LOT more air... as I experienced on one dive, where we did give one diver more air than everyone else, some people really suck that stuff down. Thankfully for that particular experience, it didn't wreck everyone else's dive)

Not if everyone in the group is diving on the tank best suited for them - the air hogs with steel 120s, the divers with great SAC rates on AL80s, people in the middle on AL or Steel 100s.

 

[Zman96]

Christi, thanks for going to the trouble of posting those profiles but somehow I doubt that square profiles are getting those times. Ergo, I'm assuming they were multi-level dives (just as I did in the first place). Therefore, I ask, what are the profiles of these multi-level dives? What times at what depths? How long at total depth, at 50; at 30; at 20; 10? Is a 90 minute dive spent noodling around at 15'?

I have made more than 100 dives with Christi's op and the dives that are regularly over 70 minutes are not spent noodling around at 15'. You start deep and slowly make your way shallower as the dive progresses just like any other op on the island. My computer doesn't give me a minute by minute dive profile but I find my time at max depth is more than sufficient before slowly moving shallower and I always finish with a 5 minute stop at 15-20 feet.

 

[Skittl1321]

Not if everyone in the group is diving on the tank best suited for them - the air hogs with steel 120s, the divers with great SAC rates on AL80s, people in the middle on AL or Steel 100s.

So the ops that give steel 120s to customers stick their best (in terms of SAC) divers in AL80s? I've never seen that mentioned.

It has been implied that the ops that use steel tanks give them to everyone. And that women get steel 100s, regardless of their SAC (which is NOT always better than men.)

 

[nimoh]

The problem with giving the gas hog a bigger tank is that it complicates gas planning. If your plan is to start ascent at 700psi and you give the gas hog a big enough tank such that you both reach 700psi at the same time then you are carrying much less reserve gas and possibly not enough to share with the gas hog if necessary.

 

[diver 85]

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A ScubaBoard Staff Message...

this thread has been split from another which is located here: http://www.scubaboard.com/forums/cozumel/482254-dive-operator-suggestions.html
marg, sb senior moderator

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i don't really understand the hype with the whole 120cf tanks, to me they are a crutch for inexperienced divers in a place where 80cf tanks will give you 70min bottom times. Just my .02

........lol......

 

[nodakdive]

As Skittl suggested, many ops don't bring the whole group up when one is low on air except in certain situations, for instance, diving up north or crazy currents.

So, I haven't had that DjDiverDan, but I sure have had the "....oh, right here at the end is a big ole loggerhead and I have a little NDL left but not enough air to really hang out...". That's not loads of fun. On the other hand, sometimes the loggerhead is at the beginning. You never know what you might see or when you might see it.

As to profiles, lots of people do long dives on 80s here. I've personally witnessed, meaning start and end pressures, a DM do a second tank and only use 500 lbs of air. I've been on boats many times where others are profiling just as I do and they're shooting pictures and they get 15 minutes more than I do, and they come up with more than 500 lbs. Them getting more doesn't mean I didn't get enough in my book.

-Blair