Question Do you ever practice dropping weights and handling the unexpected ascent?

[RobPNW]

 

[happy-diver]

Wearing a fabric sack over sleeping bag soaked in your own sweat and gruel with a condom glued to your bits

Ha ha ha ha ha let's go drysuit diving because the drysuit divers said so

Let us not go diving at all!

 

[dmaziuk]

A 100 cuft tank is only gonna have another pound of air in it - compared to an 80. Not seeing continuity in your logic?

What, next you'll tell us a pound of lead is not heavier than a pound of feathers? It's lead, FFS!

 

[eightytwenty]

A 100 cuft tank is only gonna have another pound of air in it - compared to an 80. Not seeing continuity in your logic?

Buoyancy swings positive on an AL80, compared to a 100. -1.7 to +3.4 compared to -8.8 to -0.7. So to answer your first question, yes. Diving an AL80 can allow for more ditchable ballast in a thick wetsuit. From what I can remember, it is possible to balance a rig in a wetsuit with a single heavy steel cylinder, but it's not suggested.

 

[boulderjohn]

Buoyancy swings positive on an AL80, compared to a 100. -1.7 to +3.4 compared to -8.8 to -0.7. So to answer your first question, yes. Diving an AL80 can allow for more ditchable ballast in a thick wetsuit. From what I can remember, it is possible to balance a rig in a wetsuit with a single heavy steel cylinder, but it's not suggested.

The buoyancy swing in an AL 80 that uses up 5 pounds of air is identical to the buoyancy swing of an HP 100 that loses 5 pounds of air. They are both 5 pounds more buoyant than they were before.

For your buoyancy, what matters is your total volume and weight (you and all your gear), not each part of that total volume and weight. If your total volume remains the same throughout a dive, the only difference in buoyancy will be the loss of air.

Since a steel tank is considerably less buoyant than an aluminum tank, if all else is the same, the diver with the aluminum tank needs to make up for lesser tank weight by carrying more lead weight, but that extra weight is carried from the beginning of the dive to the end, regardless of any "swing" in tank buoyancy. If that extra weight is carried in a way that is ditchable, then, yes, using an aluminum tank does mean that you can have more ditchable weight than you would using a steel tank.

 

[Celt]

I was on a dive recently with a rental BCD which had all my weight in the two drop pockets. Not how I usually dive but it's what they had for me. We descended somewhat quickly to the bottom at 30 feet due to wanting to get under the moderate current.

Right when I stopped by descent at the bottom, I felt both pockets slip right out! I spotted them on the bottom under me and realized I was headed right back up to the surface. I dumped by BCD's air and kicked downward to slow my ascent, and was able to make a fairly safe return to the surface. Thankfully I was only under for about 2 minutes total and did not suffer any decompression symptoms.

This got me thinking though: While I've been taught theoretically about how to drop weights and ascend, I realized I have never actually practiced it and was not very well prepared for the situation. So I'm curious fellow divers:, do you ever take time to go to a pool or maybe 20ft deep open water area and just practice dropping your weights and handling the quick decisions required to keep the situation safe?

I wouldn’t bother practicing buoyant assents, things are happening very fast. A much better idea is to practice swimming up the weight without the aid of a drysuit or bcd. The reason we use heavy neoprene drysuits or high density wetsuits (7mm+7mm)is you can swim them up, you can’t swim up a flooded bag suit.

 

[rsingler]

I already pointed out in an earlier comment, if your wetsuit is thick enough to cause a problem getting up with a failed wing then the correct solution is to use a proper shell drysuit rather than carrying extra ditchable weight. This is part of having a balanced rig.

Ah, well. I won't reopen the perennial argument about a proper balanced rig. Instead, I'll merely point out, as I did many years ago, that not everyone has the experience or the luxury of "doing things properly", and extra ditchable weight is a safe solution.
Example? The thousands of OW student divers at San Carlos Beach in Monterey who don't know they'll eventually spend another thou' or three on a drysuit for the area's 52° water, and choose a 7 mil for their training, which is conducted with a steel tank.

-6# of gas,
-2# tank,
-2# of regs and fittings, and
-19# of suit compression at 60 feet
means they can't dive balanced. A bcd tear on a rock at depth at the beginning of the dive cannot be swum up from 60 feet by half of divers who are now 17# negatively buoyant. But as the Optimal Buoyancy Computer points out, if you ditch half of the weight you are carrying, your negative buoyancy is something you can handle, and your buoyancy improves as your suit expands. You have self-rescued, and are now neutral at 20 feet. There you can rest, and then prepare for a mildly buoyant final ascent which you can slow with exhalation and a flare.

I'm not saying it's "best technique". I'm saying it's a life saving and DCS-avoidant solution for a HUGE population of divers who don't yet know what "balanced" even means.

And if you DO want to dive balanced? The OBC is a nice tool to fine tune your rig with whatever drysuit and liner you choose.

 

[WillieJustice]

Dumb question, maybe. I just dove in cenotes with a 3 mil and no ditchable weight. Is this bad? Good? It just is?

It is perhaps a little off topic, but having read this thread, it seems more or less relevant since cenotes are often 130 or more feet deep.

 

[rsingler]

Dumb question, maybe. I just dove in cenotes with a 3 mil and no ditchable weight. Is this bad? Good? It just is?

It is perhaps a little off topic, but having read this thread, it seems more or less relevant since cenotes are often 130 or more feet deep.

Buoyancy loss of a 3 mil at 130' is about 10 lb. Unless you were overweighted with fixed weight at the start, you should easily be able to swim that up in the event of a TOTAL bcd failure. And as you ascend, your buoyancy improves with suit re-expansion.

 

[inquis]

I just dove in cenotes with a 3 mil and no ditchable weight. Is this bad?

If properly weighted, not an issue. You'd lose about 5 lb of wetsuit buoyancy (relative to safety stop depth) and at the beginning of the dive you would have 5 lbs of air that you'll breath later. On the plus side, you should be able to compensate for at least 5 lbs with lungs alone, so you'd need to swim up about 5 lbs initially. (The wetsuit expands/helps as you make progress.)

OTOH, if you use bad advice for weight (e.g., 10% of your body weight), you could have a problem.

Take it on yourself to empty your wing at max depth and see how hard it is to make progress. (Be careful not to stir up the bottom, though!)