#AskMark: Cylinder Storage, Aluminium vs Steel Tanks & Hooded Vests in Cold Water

@tomczega

#AskMark: Can I store tanks horizontally, or do they need to be vertical? Also, can I leave them in a car for a few nights when the temperature is sub 0°C?

Ideally, cylinders should be stored upright for longer periods, anything longer than a few days. Mois-ture and contaminants inside will settle and collect at the lowest point and can cause corrosion. The bottom of your cylinder is the strongest point, and if you’re going to have corrosion anywhere, the bottom is the best place. It is fine to leave your cylinders horizontally for short periods though, it re-duces the chances of them falling over but, anything longer than a week or so, I secure them in an up-right position.

Freezing temperatures can cause flash rust when moisture in the air condenses on the cold metal. There are also reports of cylinders draining due to contracting O-rings in cold climates. While rare, and many divers store their cylinders in cold temperatures, it is a possibility you should be aware of and try to avoid if possible by keeping your cylinders in a warmer spot if available.

@TheClownMaster

#AskMark: What are the pros/cons between aluminium and steel cylinders?

The advantages of steel cylinders are that they’re strong and will last for decades if you look after them, they’re always negatively buoyant, making weighting easy to calculate, and you can take some weight off your weightbelt. Steel cylinders are popular in colder climates and for backmount. They can rust if you don’t look after them, and the additional weight can make them harder to transport.

Aluminium cylinders have many advantages. They’re lighter to carry, they cannot rust, they often have flat bottoms so they can stand without a boot, and they’re more neutrally buoyant in the water. How-ever, aluminium is a softer metal, which makes them larger in size, a bit more fragile, and reduces their lifespan. At a certain gas pressure, some aluminium cylinders become positively buoyant, requiring more lead to stay underwater. See what local divers use where you plan to go diving and that should help you decide which is better for you.

@hanna565

#AskMark: I want to start diving in colder water. Should I wear a hooded vest under or over my wetsuit?

It depends on the design of the hooded vest and how much space you have underneath your wetsuit. If your wetsuit is already tight around your chest, then there won’t be enough for a 5mm underneath. The benefit of a hooded vest is that there is no break between the hood and the vest for water to flow through, and many divers find that wearing it on the outside is warmer.

If there is some space under your wetsuit, it may be worth filling that space with neoprene anyway because a baggy wetsuit will allow cold water to flush around your suit. On some hooded vests you’ll notice a smooth section of neoprene around the neck where the neck seal of your wetsuit can seal against it to slow water ingress. Chances are your wetsuit already fits well, so I would be looking for a hooded vest to go over the top.