I dont really understand what you mean?
Im sorry im a beginner haha.
Do you mean how heavy my tank is when full or empty?
Cylinder buoyancy is a measure of how negative or positive a cylinder will be *in the water* The dry weight, i.e. in the the parking lot on the way to the water matters to who ever has to carry them, but it is not the number we need for wing selection.
It is most helpful to have these numbers for full and empty, but if we have one or the other and the working pressure of the tank the 2nd number can be calculated.
The european method of listing tanks by the internal volume of the tank, and not by the equivalent volume of gas they contain at their working pressure has some advantages for gas planning, but it complicates buoyancy calculations.
For example in the US a typical cylinder would be referred to as an "HP100" That means at it's working pressure, usually 3442 psi or 237 bar this tank will contain the equivalent of 100 cubic feet of gas at in atmosphere. Because the mass of a air is known, ~ 8 lbs / 100 cu ft one can easily determine the change in mass of this tank from full to empty.
With Euro tanks it is the internal volume of the tank that is specified. A "12 L" tank would hold 12 liters of water. What is the weight of the gas? To determine that we need to know the working pressure. A 12 L tank at 237 bar holds less gas than a 12 L tank at 300 bar.
Unfortunately the Huron Scuba site does not provide tank info for "euro" designated cylinders.
You might have to dig a little. Look at the websites for the tank manufacturer. If we have the dry, empty weight of the tank, it's internal volume and the working pressure the magic of math will yield the buoyancy numbers.
Steel is ~495 lbs / cu ft. If we start with the empty weight of the tank we can calculate the volume of steel. Add that to the claimed internal volume and you have the total volume. Add the mass of the steel to the mass of the gas and you have the total mass. Mass / volume yields density. Comparing this density to the density of water and get the buoyancy.
A bit of work, but remember everything you get into the water with that does not float is part of your ballast, and your cylinder can be a huge chunk of that.
Alternatively you could directly test the buoyancy of your suit.
To test a wetsuit simply roll it up, making sure not to trap a huge bubble, throw it in the water and add lead until it just sinks, then weigh the lead. Typically you can start by wrapping a weight belt around the suit, and then tucking extra lead under the belt.
With a drysuit you need to put on your undergarment, the ones you plan to actually dive, and the suit. No other gear.
Jump into neck deep water holding a bag of lead. It's easier to start with more lead in the bag than you think you need.
Vent the suit.
Pick up your feet. If you sink remove some lead from the bag. Stop when you just barely sink.
Weigh the lead. This represents the buoyancy of your drysuit with minimum gas in it, assuming a reasonably fit diver.
This is directly the number you need to be able to compensate for if you suffered a total failure of your suit.
Knowing the actual buoyancy of your exposure suits not only allows you to select wing, it's a huge help in getting properly weighted.
Good luck,
Tobin
