We are not talking about weighting for the dive, but rather the lift needed. In order to be neutral with an empty tank at the end of the dive, at a depth of 1 foot, the diver will need to carry extra ballast to offset the weight of the air used. If he does not, then he will float up. Proper (or minimum) weighting will make him neutral with an MT BC, and an MT tank at the surface.
So, this means that when he starts his dive, with a full tank and at a depth of zero he MUST be over-weighted by an amount exacty equal to the weight of the air in the tank.
Total nonsense.
Wetsuits and drysuit undies both compress. The majority of the compression happens shallow *where the % change in ATA's are the highest.*
A diver in a thick suit diving a normal capacity single cylinder (no 149's or Heiser 190's) can effortlessly hold a 15 ft safety stop if they start the dive weighted so they are eye level with no gas in their wing and a
full tank.
Their suit will compress enough from the surface to 15 ft (1.5 ata) to offset the gas in a typical single cylinder. 5-7 lbs for most tanks.
Most divers do not end their dives with empty tanks, and if that day comes they still have lung capacity to deal with small amounts of positive buoyancy.
In addition neoprene doesn't rebound instantly. That allows for easy, slow ascents from 15 ft to the surface.
Anybody that doubts a 7mm suit can lose 5-6-7 lbs from the surface to 15 ft needs to swim down to 15 ft with out adding any gas to their bc as see what happens.
The obsession among some to use their BC and not their lungs to control buoyancy shallow is not without risk.
I recommend (and have recommended for years over 100's of posts) divers in thick suits using typical single cylinders adjust their initial ballast so they are
eye level at the surface with no gas in their wing and a full tank .
As long as the wing has been sized to 1) Be able to float the rig, with a full cylinder if the diver ditches it, and 2) So it provides at least as much lift as the exposure can possible loose there is no need for a larger wing.
Weighted as I describe
1) Provides the diver with 100% of the wings capacity for comfort at the surface, Only a puff is needed, but 100% is available
2) Provides 100% of the wing's capacity to assist another diver at the surface if needed.
3) Makes a total wing failure fairly trivial, remember the diver is weighted so they are
eye level at the surface with no gas in their wing and a full tank. Dropping a few lbs, or using a few lbs of gas and the diver is positive at the surface even if they or their rescuer can operate the wing or the wing has failed. Contrast that with those that advocate being over weighted with larger wings. The consequences of a wing failure is hugely magnified.
Weighted as I advocate a diver that makes back to the surface can stay there with little effort even if they fail to drop ballast or add gas to their BC. Any review of recreational dive deaths will reveal that many recreational divers panic, kick to the surface, fail to drop ballast or inflate their BC, eventually tire and are found on the bottom with their weight belt on and gas in their cylinder.
Of course I fully expect that we will all now be treated to a list of tortured ( and largely false) scenarios involving rescues of grossly overweighted divers and recoveries of long lost bells from notable wrecks
..
It's so utterly predictable on Scuba Board
.Tobin
,, what will be his buoyancy situation? The answer is ... he will be negative by an amount exactly equal to the suit compression AND the weight of air in his tank(s). So in order to establish neutral condition - the wing MUST have the capacity to offset the negative force generated by suit compression AND the weight of the gas in the tank(s).
