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Thread: Steel v Ali Bailout Buoyancy

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    RBW Member EvoMatt is an unknown quantity at this point EvoMatt's Avatar
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    Steel v Ali Bailout Buoyancy

    Hi,
    I currently use Luxfer Aluminium 7lt 232bar bailout. I've seen people using Faber Steel instead and am considering doing the same to cut weight (I'm a bit feeble), but even Fabers own database doesn't make clear what I want to know regarding in water buoyancy.

    The ali tanks are 9,8kg in air and the steel are 7.6kg in air.
    What are they in seawater?

    Ali are reported to be more buoyant, and to suffer a larger change in buoyancy when drained. It therefore seems that I'm carrying heavier tanks plus more lead to sink them.
    If I switch to steel they'd be lighter plus I might drop some lead?

    I know there are other considerations such as in-water trim etc, weight of regulator, gas pressure, but leaving those aside - can anyone confirm?

    Thanks,
    Matt

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    Re: Steel v Ali Bailout Buoyancy

    Quote Originally Posted by EvoMatt  View Original Post
    Hi,
    I currently use Luxfer Aluminium 7lt 232bar bailout. I've seen people using Faber Steel instead and am considering doing the same to cut weight (I'm a bit feeble), but even Fabers own database doesn't make clear what I want to know regarding in water buoyancy.

    The ali tanks are 9,8kg in air and the steel are 7.6kg in air.
    What are they in seawater?

    Ali are reported to be more buoyant, and to suffer a larger change in buoyancy when drained. It therefore seems that I'm carrying heavier tanks plus more lead to sink them.
    If I switch to steel they'd be lighter plus I might drop some lead?

    I know there are other considerations such as in-water trim etc, weight of regulator, gas pressure, but leaving those aside - can anyone confirm?

    Thanks,
    Matt
    Hi Matt,

    I don't have numbers, I'm afraid, but have made the switch in the other direction. I may well have been overweighted, but I didn't find that I needed to change my weighting after making the switch, so you may not save any lead.

    On the surface, I haven't noticed that difference in weight to be honest. It's certainly a difference I am willing to pay to have the much better behaviour of ali cylinders in the water.

    Sorry I don't have hard numbers for you, but if you do decide to change to steels, let me know. I'd be interested in at least one Ali 7 and I know a few others who'd happily buy any others from you.

    Cheers,

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    Re: Steel v Ali Bailout Buoyancy

    Quote Originally Posted by EvoMatt  View Original Post
    Ali are reported to be more buoyant, and to suffer a larger change in buoyancy when drained.
    The Faber low-pressure steel cylinders tend to be about neutral when empty, while the aluminum are slightly positive. The difference is on the order of a couple of pounds at most for the smaller cylinders.

    Be aware that the CHANGE in buoyancy from full to empty of any cylinder is ONLY a function of the amount of gas removed.

    --
    Art

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    Re: Steel v Ali Bailout Buoyancy

    Ali are usually less heavy underwater, and tend to be slightly buoyant when drained. However the change in buoyancy is the same for the same amount of same gas drained from them - after all the dimensions of the cyl don't change and you remove the same mass of gas from inside!
    You could carry a bit less lead with steels as they are still negatively buoyant when drained - BUT many people want to weight themselves to be correctly weighted even if you have passed off/dropped your stages. At least with a positively buoyant ali cyl you could clip it to a line and send it to the surface.

    Neil

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    Re: Steel v Ali Bailout Buoyancy

    Try an experiment before making the switch: Remove each type of tank and hold out as if passing to another diver. The steels, being more heavy, can have a significant effect in your trim/posture.

    Next, try trading with someone that uses the opposite type of tank. There will be a big buoyancy change.

    Now, consider all of the above in a situation with stress and a silty area.

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    Re: Steel v Ali Bailout Buoyancy

    Quote Originally Posted by ScubaDadMiami  View Original Post
    Try an experiment before making the switch: Remove each type of tank and hold out as if passing to another diver. The steels, being more heavy, can have a significant effect in your trim/posture.

    Next, try trading with someone that uses the opposite type of tank. There will be a big buoyancy change.

    Now, consider all of the above in a situation with stress and a silty area.
    Well put,
    I tried it and when I passed off the steel tank I started for the surface!

  7. #7
    RBW Member Mike R. is an unknown quantity at this point Mike R.'s Avatar
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    Re: Steel v Ali Bailout Buoyancy

    Hello, I was also thinking of switching to one of the small Faber pony bottles for bailout to save on carrying a couple pounds of lead weight and simply the robust nature of the tank itself. The downside is occasional tumbles to remove rust. In my KISS sport I typically carry a 19cuft aluminum bottle mounted laterally across the bottom to make my rig self contained. My brackett will fit a Faber 23 Hp or a slightly smaller LP tank. Using the tank for bailout only would mean the tank typically stays negative for the entire dive. I figure on reducing my weight by 4 lbs and depending on my drysuit to take up the slack if I ever had to bail out and use the gas to the point where the tank becomes neutral.

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    Re: Steel v Ali Bailout Buoyancy

    Quote Originally Posted by EvoMatt  View Original Post
    Hi,
    I currently use Luxfer Aluminium 7lt 232bar bailout. I've seen people using Faber Steel instead and am considering doing the same to cut weight (I'm a bit feeble), but even Fabers own database doesn't make clear what I want to know regarding in water buoyancy.

    The ali tanks are 9,8kg in air and the steel are 7.6kg in air.
    What are they in seawater?

    Ali are reported to be more buoyant, and to suffer a larger change in buoyancy when drained. It therefore seems that I'm carrying heavier tanks plus more lead to sink them.
    If I switch to steel they'd be lighter plus I might drop some lead?

    I know there are other considerations such as in-water trim etc, weight of regulator, gas pressure, but leaving those aside - can anyone confirm?

    Thanks,
    Matt


    Is this website any use to you:
    UK Scuba - Cylinder Buoyancy Calculation

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    Re: Steel v Ali Bailout Buoyancy

    Can I offer this for metric users?
    Diving Rant

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    Re: Steel v Ali Bailout Buoyancy

    Faber light weight steel float when empty. The steel 10ltr floats with 250bar of 18/45in and my Ali80 is neg with 230bar of 50% in.

    I se a stel 10 for mix and an Ali 80 for nitrox. Small tanks i use steel 7s as I can blow them to 250 with less of an issue than Alis and they trim out OK left right.

    10ltr floating arse up in fresh water with 250bar 18/45 Ali 80 has 505 in



    Steel 7 full on right with 100bar 32% on the left








    atb

    Mark

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