You MUST do your own weight check. It's for you, not a beauty contest with other divers.
I will submerge in 1.5m/4ft of water, get into flat trim and see how much gas I need to hover 15cm/6" of the bottom. With a full cylinder/tank, I MUST have added some air to the BCD/drysuit as there's 2kg of air in the compressed cylinder (assuming a single tank).
For the first dive I'll be very sensitive to weighting at the end of the dive to ensure there's enough weight to hold the safety/deco stop at 4.5m/15ft. May adjust the weighting accordingly.
I need for:
- Carribean OC sea diving: hot water (30C/85F), single cylinder ali80, rash vest, budgie smugglers: 2kg/4lbs weight
- Warm water OC sea diving (20C/70F), single cylinder steel 12 litre, drysuit, thin underclothes: 8kg/18lbs
- Cold FRESH water OC diving (7C/45F to to 12C/53F for 1h 15m), drysuit, thick undersuit + extra layer, sidemount with 2x steel 8.5 litre cylinders: about 8kg/18lbs
- Cold FRESH water CCR diving (7C/45F to 12C/53F for 2+ hours), drysuit, thick undersuit + extra layer, Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali7 litre bailouts, drysuit heater battery): about 3kg/6.6lbs
- Cold sea water CCR diving (7C/45F to 12C/53F for 2+ hours), drysuit, thick undersuit + extra layer, Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali80 bailouts, drysuit heater battery): about 4.5kg/10lbs
- UK south summer sea water CCR diving (15C/60F to 18C/65F for 2+ hours), drysuit, thick undersuit (no extra layers), Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali7 bailouts, no heater battery): about 3kg/6.6lbs
But if diving somewhere new with any significant kit changes, will always do a weight check.
Kit that affects buoyancy
during the dive, i.e. changes your weighting during the dive:
- Gas you are breathing. Rough weighting is 2kg/4.4lbs per full-size cylinder.
- Twinset/doubles which contain twice as much as a single and will be consumed during the dive (4kg/9lbs)
- Decompression/bailout stages where the gas will be consumed; must add weight to offset the gas volumes -- an empty ali80 gets very floaty!
- Heavy SMB reels (Kent Tooling - 1.5kg/4lbs) which will be detached from you in use
- Other cylinders that may be dropped off en-route or handed off to other divers
- Always consider an urgency scenario where you've had to use more gas than normal -- overstaying your dive time, helping other people, etc. -- empty tanks get very floaty!
Bottom line: always be aware of being too light at the end of the dive, this is extremely dangerous because you cannot hold your decompression/safety stop.