Rental-Steel 120 vs? ??-Educate Me Please

[scubafanatic]

Now you have me scared. Is the weight of the tank too much? Too much air? Please elaborate. Thanks.

...Aldora also offers 100 and 80 cu. ft. steel tanks...you might be more comfortable, both topside and underwater, with one of those, especially if you're an inexperienced diver...the 100 cu. ft. tank might be a good compromise choice for you.

 

[JBRES1]

If you get to dive a 120 rather than an 80, thats a good thing.
The added weight of the 120 isn't too bad, its about 6 to 8 #'s , and you will be diving with about 4 to 6#'s less lead, so its a wash +/-.
Are you Nitrox certified ?
I ask because if you are diving steel 120's and going down to lets say 90 ft. you may run out of no NDL time before you run out of gas.
If you were diving on Nitrox at the same depth you would be just fine with the NDL.
A nitrox class is a non dive required class, and would cost about $150.00 total.
Enjoy the trip.
Jim Breslin

 

[scubafanatic]

.....the HP 120 tank will be a bit heavier, but a possible bigger issue for you will be the tank's length...ah HP 120 is a 'tall' tank and you will not be happy with it if you're 'shorter' in stature. I've got 2 HP 100's and 4 HP 120's, so I'm VERY familiar with how they dive...I've used them locally, as well as having dove with Liquid Blue Divers of Cozumel....the ladies used HP 100's, the guys used HP 120's...although they will let you request/use whatever tank you prefer.

 

[halocline]

I have done about 20 dives over the last 10 years-almost exclusively Hawaii or Caribbean, with a dive operator supplying the tanks.

I just recently booked a dive with an operator in Cozumel. They say they are giving me 120 steel tanks. Can you kind people explain what that means?

It sounds like you are an occasional diver; 20 dives over 10 years is not much. You might want to try to do some sort of dive before your Cozumel trip if you can, even if it just means a pool trip. Another option would be to try to do some sort of shore dive as soon as you get there. The reason for this is that Cozumel dives tend to be fairly deep and often have a fairly strong current. Despite the fact that Cozumel is a really popular destination for new divers, the conditions are not really beginner-level on many of the dives. There are also very easy, relatively shallow dives in Cozumel, and I'm sure you'll do those as well. But, often, the first dive of the day is deep, with a current, on a wall, and if that happens your first day, and you're not used to the bigger heavier tank, and you only have a handful of dives over the past several years, it might not be such a good situation. It's easy to deal with, just get in the water before that in some way to refresh.

As far as the difference between AL80 and steel 120 tanks, there's a lot. The reason you're getting that big tank is because competition among Cozumel dive ops is brutal, and Aldora is offering something that allows them to compete better. That something is extended bottom time; and it's especially attractive in Cozumel because you have so many novice divers (read high air consumption) diving in fairly deep conditions where air consumption is increased. With the currents the way they are, it's usually better to keep the whole group together, which means that if one diver blows through his air, the whole boat is surfacing early.

There are a couple of problems with this. One has been already discussed; extended bottom time at depth means more N2 loading and a theoretically greater risk of DCS. Given your slim dive history, I would strongly encourage you to use a computer and pay close attention to your NDL. Another really simple strategy is to simply extend your safety stop. Spending an extra few minutes at 10-15 ft is pretty efficient at lowering N2 levels on NDL dives.

The other problem is buoyancy. A HP steel 120 is 11 lbs negative when full. A luxfer AL80 is 1.4 negative. This means you need to potentially adjust your weighting quite a bit to avoid being overweighted at the beginning of the dive. The empty weights are -2 for the HP120 and +4 for the AL80. This means that the HP120 swings 9 lbs instead of 6 for the AL80. Since you do your weighting for an empty tank, you'll need to theoretically subtract 6 lbs of weight from your typical AL80 weighting, but since the gas weighs 3 lbs more, you'll be 3 lbs overweighted at the beginning of the dive. No big deal, just make sure your BC has the lift you need (it almost certainly will) and it actually makes it easier to get down. But, you will be diving with more air in your BC, especially at the beginning of the dive. That's because you're compensating for the increased weight of the air. This makes buoyancy control a bit trickier, especially for someone who has little dive experience and none with a high capacity tank.

Personally I'm not a fan of wholesale use of the HP120 in Cozumel, because I've seen the dive behavior of so many divers there. I think that one reason there are relatively few cases of DCS in Cozumel is the fact that the AL80 is a low enough capacity tank to match well with NDL diving at typical recreational depths. And it's often the people who's skills and air consumption are poor who need the higher capacity tanks to stay with the dive, and these are exactly the people who are probably less likely to be aware and in control of their N2 loading. I hope I'm wrong, but I wouldn't be surprised to find that if many dive ops switch to the larger tanks, DCS incidence in Coz will increase over time.

 

[Bratface]

Ooohhhhh, steel tanks! How nice. Steel is heavier so you can drop weight from your bc, they are great tanks and are not negatively buoyant at the end of the dive. I dive with a steel 80 which is the same size as an aluminum 64 and holds 3400 psi. It's just the right size for me--a smaller female. You might want an 80 or 100 like others have said in this post.

 

[Jim Baldwin]

I have done about 20 dives over the last 10 years-almost exclusively Hawaii or Caribbean, with a dive operator supplying the tanks. They have always been silver, but it I never took note of what size they were. I was only concerned that they looked ok, were functional (valve opened and closed), and BC, regulator and pressure gauge (with decent PSI) were able to get air from the tank.

I just recently booked a dive with an operator in Cozumel. They say they are giving me 120 steel tanks. Can you kind people explain what that means? What type of tanks have I probably been given in the past? Will I get significant more air, and more dive time. I am kind of an air hog.

Thanks in advance for helping the ignorant.

I have been in Cozumel for a number of years and have dove with Aldora, Liquid Blue and Living Underwater. All three use High Pressure or Low Pressure Steel tanks in 95, 100 or 120 cubic feet.

For the past eight years I have used Living Underwater almost exclusively. Jeremy Anschel uses low pressure steel tanks. Steel 120's are about 10 pounds heavier than AL 80's. With a steel 120 you get about 50 percent more air than a standard AL 80.

The advantages are clear. You will wear less weight on your belt, you can do a deeper profile and doing a multilevel computer profile can give you hour plus dives. Remember that you never get penalized for carrying more air than you need.

The disadvantages are that you are slightly more negative at the beginning of the dive and this does take a little getting used to. If you make longer and or deeper dives you need to watch your computer times closer. And plan on making a nice long safety stop of about 5 to 10 minutes and good surface intervals between dives which all three of these opeators do. These things will all be discussed with you prior to your diving.

Divers with smaller frames, such as women, children or divers with excellent air consumption use the LP 95's or HP 100's.

 

[Night Vision]

In warm water (T-stirt diving) it appears that a steel tank could could have you wearing no weights at all and still be negative at the end of the dive. Do I have the right?

I'm looking at steel tanks also. I've never needed to ditch weights, but it's nice to know that it has been an option. Do you carry a small lift bag as an alternative? (no, I'm not leaving my gear!

 

[Clammy]

If you get to dive a 120 rather than an 80, thats a good thing.
The added weight of the 120 isn't too bad, its about 6 to 8 #'s , and you will be diving with about 4 to 6#'s less lead, so its a wash +/-.
Are you Nitrox certified ?
I ask because if you are diving steel 120's and going down to lets say 90 ft. you may run out of no NDL time before you run out of gas.
If you were diving on Nitrox at the same depth you would be just fine with the NDL.
A nitrox class is a non dive required class, and would cost about $150.00 total.
Enjoy the trip.
Jim Breslin

The 4# is in buoyancy. In actual weight out of water, there is a bigger difference sometimes. The worthington HP 120s are only 6-8# heavier than AL80s but the Faber 3180 +10% tanks are like 50lbs (15-20lbs heavier than an AL80.) They are also -7lbs empty as opposed to just -2lbs. So it's not a wash on total weight carried by a diver. If you want to compare Al80s to Steel HP80s, then the HP80s are actually a little lighter in total weight AND you get to still drop 4lbs or so! If they are LP120s, then they are REALLY heavy out of water!

 

[Jim Baldwin]

In warm water (T-stirt diving) it appears that a steel tank could could have you wearing no weights at all and still be negative at the end of the dive. Do I have the right?

I'm looking at steel tanks also. I've never needed to ditch weights, but it's nice to know that it has been an option. Do you carry a small lift bag as an alternative? (no, I'm not leaving my gear!

When I use my PST HP 100's or Faber or Worthington LP 95's in Cozumel I wear a full 3 mm wetsuit and don't require any additional weight. At the end of the dive I can hang at 15-20 feet with no air in my BCD so no weight belt. I always carry a lift bag or SMB and reel wherever I dive.

At the start of my dive which is when I'm the heaviest I can swim my rig to the surface with no air in my BCD so I don't carry any ditchable weight.