Question BCD size for cold-water diving & steel tanks

[Nic2750]

Hi All,
I've been diving for a couple of years, and switched to sidemount about 100 dives ago. As I've only dived in nice, warm water, I normally dive in t-shirt and shorts with AL-80s, deco bladder, and 3kg of weights.

In May, I'll be going to New Zealand for a month or so. To avoid freezing (given that I'm used to warm water), I'm planning to do a drysuit course, then some diving. Apparently the local dive shop normally uses 12L steel tanks. So, given the steel tanks, will the deco bladder provide sufficient buoyancy? If not, can anyone recommend a particular type/size to use instead?

Also, will I need to tweak my rig for cold water in any other ways that I might not anticipate?

Thanks in advance

 

[Valeriy Vakshul]

Cargo pockets on waist belt
Cargo pockets on the waist belt, horizontal.

 

[Nic2750]

Cargo pockets on waist belt
Cargo pockets on the waist belt, horizontal.

Thank you. Why do you prefer that over using a pouch in cold water?

 

[BoltSnap]

deco bladder

What's a "deco bladder"? You mean BC bladder?

 

[Nic2750]

What's a "deco bladder"? You mean BC bladder?

Sorry, it's one of these: DECO Sidemount Bladder 22# with Hose, Inflator and Dump Valve.

 

[BoltSnap]

Sorry, it's one of these: DECO Sidemount Bladder 22# with Hose, Inflator and Dump Valve.

I see, they sell the harness and wing separately for their SM kit.

 

[inquis]

A 22 lb / 10 kg wing is borderline but probably doable. Most people don't need the larger tech-oriented SM wings.

The gas weight swing for 2x D12s is 14 lb. Imperfect weighting conceivably gives you a margin of only 6 lbs. That won't compensate for much of a suit flood, so you'll need a strategy for that possibility (e.g., ditchable weight, DSMB).

ETA: for reference, the AL80 gas weight swing is about 11 lbs, so not much difference there. The steel tanks will want to make you more foot heavy (with no changes from your AL80 setup).

One issue with cold water diving is where to put all the additional lead without it screwing up your trim. The Highland weight plates (or just a bungee loop) may be useful:

 

[Jai Bar]

Bear in mind that steel tanks can vary considerally in weight, even from the same manufacturer- depending on working pressure, year etc. Some can even be slightly positive when empty. The empty weight is stamped, but not always readable..

I always carry a couple of weight plates, bungee and small cam band pockets just for these discrepancies- they are not heavy nor take space when traveling.

 

[grantmac]

My Xdeep Classic is JUST able to manage heavy steel D12s (-3kg empty) using thick undergarments and 6kg of weight on the rig.
I'm still tweaking that weight requirement but the wing is very full at the beginning of the dive and empty at the end. It has 16kg of lift.

 

[grantctobin]

My Xdeep Classic is JUST able to manage heavy steel D12s (-3kg empty) using thick undergarments and 6kg of weight on the rig.
I'm still tweaking that weight requirement but the wing is very full at the beginning of the dive and empty at the end. It has 16kg of lift.

It might advertise as 16kg, but that assumes it is not wrapped around you. 12L*230bar*1.23g=3.38kg each = 6.76kg of weight shift as Inquis described above. If it is “full” and then is totally empty as your describe, the wing is holding about half of advertised once it conforms to you. Iirc, the DECO bladder is measured the same way and 12s would be…uncomfortably snug.