The purpose is to burn in the difficulty of swimming up dead weight, and how surprisingly small that amount is. It is nice to have a number to compare with future fin changes/leg strength/etc.
It's true that there is some expansion of air in the wing as they ascend, but this is after we've put in some work to get them weighted correctly; they're in a pool, so the expansion amount isn't much, percentage-wise; and the amount in the wing is very small.
Most seem to have maybe a couple pounds of air in the wing, so they might gain at most a pound of lift as they ascend.
All the best, James
It's true that there is some expansion of air in the wing as they ascend, but this is after we've put in some work to get them weighted correctly; they're in a pool, so the expansion amount isn't much, percentage-wise; and the amount in the wing is very small.
Most seem to have maybe a couple pounds of air in the wing, so they might gain at most a pound of lift as they ascend.
All the best, James