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#769
Advice on diving Aluminum 80’s vs. Steel 120’s
scubagreg - 10/17/2012 6:38 PM
Category: Equipment
Replies: 7

I need some advice. I’m used to diving Aluminum 80’s and have never dove anything else. My newly found dive buddy has offered to share her steel 120’s of which she has four so we are planning to dive this Sunday. We are diving in Ohio so I’ll be in a 7 mil. farmer john. I usually dive 28 lbs. of lead, 10 lbs per ditchable pouch and 4 lbs. per non-releasable pocket. I sometimes have trouble staying down when I am shallow after my tank starts to empty. For the most part we will be around 40 to 50 feet for both dives. I’m usually good for aroung an hour of bottom time on an Aluminum 80. Can I expect to cut my lead that I’m wearing and will I have a significant increase in bottom time diving her steel 120’s. I hope the answer is yes to both questions as I would love to kick up my bottom time on our Sunday dives at Gilboa. Any advice would be appreciated!
#358
pphan13 - 10/17/2012 8:31 PM
I’ve never gone diving with steel tanks but am min the process of doing some research to get some. From what I’ve gathered they are negatively buoyant towards the end of the dive so you shouldn’t have any issues with staying down. You should also theoretically be able to take off some weight as well. Are they high pressure tanks or low pressure tanks by the way? Here’s a good article on tanks.

http://www.scubagearreports.com/index.php/how-to-gear-buying/50-scuba-tanks.html

I’m sure others on here can give you better input from experience though.
#4236
tazzer9797 - 10/17/2012 8:56 PM
As a diver that has more than 500 dives on steel 130’s heres a few tips I can pass along... FIRST OFF..you will loose some of that 28lbs but only you can tell how much by getting in the water with them and do a check of your own. Remember one thing , the weight difference with a full and almost empty tank are very different. you may want to do a bouyancy check at about 1300psi for a high pressure and 800psi for a low pressure(in a pool or very close to shore for these tests is safest)...SECOND..The tanks weight alot more than an aluminun tank so be careful with lifting and it takes more energy to get around on a rocking boat with a steel strapped on.... all in all I love the extra air and after a bunch of dives you wont want aluminum 80’s unless you need stage botles... hope it helps... by the way I now dive 130 steel doubles and love them... 3 dives a day and still air left... i usually get cold before I run out of air...lol.....STAY SAFE
#28736
RAWalker - 10/18/2012 1:43 AM
I just started diving a low pressure 108 and removed 9 lbs between changing to my aluminum backplate and reduce my belt to just 2 lbs. I was wearing a 3mm full wetsuit and probably could have gone without the belt completely. I did feel the buoyancy swing as I used the air supply but was able to stay submerged for a 3 minute safety stop at 15’. The best time to do a buoyancy check would be at 500 psi regardless of the tank size and pressure rating.
#20384
LatitudeAdjustment - 10/18/2012 5:49 AM
I hope you are tall, when carrying 80’s my arms are almost straight. With 120’s I’m doing curls from the car/shop to the boat!

For me the lead difference between AL80’s and my ST72’s is 6 pounds less. Going from AL80’s to ST120’s you’ll need to do some testing with almost empty tanks.
#538
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jshoemaker_1 - 10/18/2012 6:35 AM
The answer to your questions is absolutely yes.


I just made the switch recently so my experience is limited but here is what I noticed. Since weight makes a difference, I weigh about 225lbs. In a 7 mil suit diving AL80’s I would dive with 22 lbs. Which is most likely two or more LBS. over what I needed but its what i felt comfortable with. With a Steel 120 I was able to shave off 6 lbs and most likely could have gotten away with 8.


As far as bottom time think about it in cubic ft. A 120 is exactly 1.5 times the cubic ft of an 80. I could be wrong but my guess would be that steel 120s are High Pressure. Since more pressure means more air you will have slightly more than 1.5 times the amount of air you would have when diving an 80 filled to 3000psi.


Good luck, dive safe,
#5471
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DiveBuddyChgo - 10/18/2012 2:24 PM
At 50ft what is the max. bottom time on air ? I you can stay down for an hour anyways with the alum. 80 so why bother with a 120 ? At 50ft. in a quary you’ll be to cold in a wetsuit to stay an hour down anyways. You’ll have more fun with the gear that you are familiar with. Have a great dive.
#152
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Pauldoucette - 9/22/2016 5:31 PM
Do divers no longer use dive tables. A dive to 50 ft would give you a no decompression limit of 80 min pressure group X. Divers should not be asking these types of questions. Please refresh yourself on your dive tables and stay safe