Which tanks in cold water?

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BlueOcean2015

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Which tanks should I use in Cold Water and dry suit diving side Mount? Aluminium or steel and why?


Edit: I changed steal to steel :blinking:
 
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hopefully you aren't stealing tanks, but read the how to choose the right tank threads

no reason to use aluminum if steel is available to you. Lighter weight on land per gas volume, and less lead required in the water is a winning combo. In sidemount especially it is hard to pack weight onto the systems so whatever you need to sink your drysuit and rig, plus the 10lbs required to sink a pair of AL80's, and you're going to have trouble finding room to put that much lead. With heavy steel tanks, LP104's, HP80's, Worthington HP100's, you can take 8lbs of lead off, per tank, compared to an AL80. So you buy Worthington HP100's, and take 16lbs of lead off of your rig which is pretty significant....
 
I can have 9 kg on my back so I think it should be fine... According to something I read, you should not use the weights of the tanks for buoyancy they should be neutral. Otherwise they would be too heavy to moved, and they would be below you while diving...?
 
so using your reasoning above, then you shouldn't be looking at steel tanks because almost all of them are neutral or sink, especially with large gas volumes. If you believe in that system, then you have no choice but to dive AL tanks. In the US and for cave diving, that is impossible to adhere to, so we tend to prefer steels.

In the US my favorite example is this.
AL80 without valve is 26" tall x7.25" diameter and weighs 32lbs, plus it requires almost 5lbs to make it neutral for a total full weight of somewhere around 45lbs for 77.4cf of gas.
LP72 without valve, is 25" tall x 6.9" diameter and weighs 26lbs, requires no lead to make it neutral, for a total full weight of somewhere around 34lbs, and carries 71.9cf of gas.

The LP72 holds about the same amount of gas, is smaller in both height and diameter, but saves the diver from having to carry an extra 10lbs for no reason. The LP72's aren't around anymore, but the Faber FX71's which are 9l's hold the same math except are 21" tall.

In cave country, we need gas volume, so I can use a 19l tank, which holds twice the gas of an AL80. So my option is to carry a pair of 19l's, or 4 al80's to get the same amount of gas. The 19l is much more efficient, so we don't dive AL as primary bottles.

The tanks will only be below you if they aren't rigged properly, the only reason to dive AL bottles is if they aren't available to you, or you believe in handing off your primary bottles with your buddy in an OOA scenario.
 
Unless you're diving the ali cylinders that go positive when breathed down, why not use the weight of the cylinder your weighting? Just offset the weight of gas breathed down...
 
Tanks are tools, the best one depends on the type of diving your doing. I've done Hp100 's, al80, and now lp50's. Which pair I use depends on the dive. So what type of dives are you doing? That will help narrow down the choices.
 
According to something I read, you should not use the weights of the tanks for buoyancy they should be neutral. Otherwise they would be too heavy to moved, and they would be below you while diving...?

This is not true.

Someone who lives somewhere knows that a aluminum tanks are the best option for some sort of diving, which is true :)

I dive regularly in cold water using steel tanks (both Eurocylinder 7 litre and 12 litre 232 bar steel cylinders). With those, I only need 16-18 vs. 8-10 pounds of lead - and I can still drop one tank if I need to. These tanks are really comfortable. The smaller ones are small and comfortable but may be bottom light when breathed down. The larger ones trim nicely and need no repositioning either during the dive - if properly adjusted in the first place (which of course requires some care). One would generally not like to remove steel tanks (at least not both) under water but side mount diving and no mount diving are two different things.
 
This is not true.

Someone who lives somewhere knows that a aluminum tanks are the best option for some sort of diving, which is true :)

I dive regularly in cold water using steel tanks (both Eurocylinder 7 litre and 12 litre 232 bar steel cylinders). With those, I only need 16-18 vs. 8-10 pounds of lead - and I can still drop one tank if I need to. These tanks are really comfortable. The smaller ones are small and comfortable but may be bottom light when breathed down. The larger ones trim nicely and need no repositioning either during the dive - if properly adjusted in the first place (which of course requires some care). One would generally not like to remove steel tanks (at least not both) under water but side mount diving and no mount diving are two different things.


;-) so you would always use alu for SM?
 
;-) so you would always use alu for SM?

Only if you buy me a wetsuit and turn the local ice water into a balmy paradise...

____
230 bar steel cylinders are nice (but the 300 bar ones are too heavy). Things change if you need to remove the cylinders... You will want near neutral cylinders then.
 
I'd say it's less about the water temp you're in and entirely about your expectations. If you want to be able to detach and bring forward one of, or both of the cylinders, then you're going to need something that is neutral to slightly positive, and therefore need Aluminium cylinders.... the trade off being the extra wieight you'll need to carry to offset the cylinder characteristics.If however you're happy leaving the cylinders attached to your sides where they should be, then there is no advantage to Aluminium, so stick with Steel cylinders and enjoy the benefit of less personal weight needed.The only caveat to this of course is you need to remember your weight is all non-dumpable (in most cases) so if you're wetsuit diving, and therefore don't have a secondary source of buoyancy, you need to consider the fact that with Steel cylinders you'll be quite overweighted, especially in the first portion of the dive. So if you have a wing/bladder failure, you'll need to think about how you'll achieve positive buoyancy should you need to! Personally if i'm wetsuit diving, I like to stick with Ali80's, if i'm Drysuit diving, then i have a choice based on my requirement to remove the cylinders underwater.
 
https://www.shearwater.com/products/swift/

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