Have you ever had to dump your weights?
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Is that with 1 mil wet suits? I dive steels but with 3, 5, and 7 mm wet suits and need a bit more weight evem with the 3 in fresh. Not much but a bit.
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An empty LP108 is negative 1 lbs. If you can't maintain positive buoyancy from the negative force of 1 pound, you shouldn't be diving. Your head is probably more negative.
#1 and #2: Let's say you knew absolutely nothing about diving, and a diver said to you, "It is important that I have ditchable weight, because when I dive, I am always grossly overweighted." Could you come up with a different piece of advice for that diver? Think hard.
#3: If the diver had another tank he or she was planning to ascend with, that tank would be negatively buoyant and would not be bringing them to the surface. If it is pulling them to the surface, then it is empty or nearly empty, and the effect is only a couple pounds at most.
#4: Never use a BCD as a lifting device for more than a couple of pounds.
What if...
You were injured, or incapacitated, and unable to swim your way to the surface? Or were attempting to assist another diver in that circumstance? Dropping a weight pocket gets you moving in the right direction, while still allowing some control by deflating BC
You were injured, or incapacitated, and unable to swim your way to the surface? Or were attempting to assist another diver in that circumstance? Dropping a weight pocket gets you moving in the right direction, while still allowing some control by deflating BC
Okay. Let's decide where we're starting from. Since this is the Basic Discussions forum, let's assume we're in a wetsuit, not a drysuit. Let's assume we are diving single tank, not doubles.
So the only two options left are bathing suit or wetsuit.
If you are neutrally buoyant (remember the buoyancy check from OW class? Normal breath, BCD empty, float at eye level with a near-empty tank) then when you exhale you will descend, and if you fill your lungs to full capacity you will ascend.
Bathing Suit
As you descend, only your air spaces get compressed by ambient pressure. But the only significant source of buoyancy is your lungs, and they are kept from compressing by the increasing pressure of your inhaled air, courtesy of your first stage. So your buoyancy will not change no matter what depth you are at. You may or may not be carrying lead to compensate for body fat or the buoyancy of an empty Aluminum tank. In this case, the ONLY thing making you negative is the weight of air you are carrying for your dive. If you get into trouble at the beginning of your dive, you are 5 lb heavy with an AL80 tank. Any diver can swim up 5 lb. But if you couldn't, for some reason, ditching 5 lb would make you neutrally buoyant at the beginning of the dive, both at depth and at the surface, with the amount you could shed decreasing as the dive progressed as you used up air.
In this case, you could ditch from 0-5 lb without risking a runaway ascent.
Wetsuit
Once again, let's assume you have made yourself neutrally buoyant with a near-empty tank check and are carrying the correct amount of weight. Now, you carry compressible neoprene that is less buoyant at 80 feet than it was at the surface. Perhaps 60% less buoyant! So if your 5-mil suit provided 16 lb of buoyancy at the surface, it might only provide 6 lb of buoyancy at 80 feet. Lets assume you were carrying 16 lb of lead along with 4 lb of regulator and miscellaneous equipment weight, to compensate for the 4 lb buoyancy of an empty AL80, your wetsuit's buoyancy and your intrinsic buoyancy in sea water. You are neutral at the surface with an empty tank. However, you are 5 lb negative at the start of the dive due to carried air.
Assume you have an emergency at 80 feet, at the start of the dive. Your bcd bladder just tore. At 80 feet, your wetsuit is providing you 10 lb less buoyancy, and you are carrying 5 lb of air. At this point, with a non-functional BCD and no ability to orally inflate, you will have to start swimming up 10+5 lb of absent buoyancy. If you dump your 16 lb of weight, you will be 1 lb positive and start ascending.
HOWEVER, as you ascend, your wetsuit regains its buoyancy as the neoprene cells expand, and you finish your ascent with 10 lb more buoyancy than you had when you dumped your weights. That's a runaway ascent, and a prescription for disaster. If it's getting bent or dying, dumping your weight might be a choice, but that'd be about the only reason to go that way.
Instead, how about you swim up with the aid of your buddy? You start 15 lb negative and need some help, but hit the surface only 5 lb negative - an easy swim. AT THAT POINT, no-one will argue with dumping your weight to stay buoyant at the surface.
If you take both these scenarios at the end of a dive (almost out of air???) then you're five pounds lighter and the swim up is much easier. With a bathing suit you hit the surface neutral, and with the 5-mil, you hit the surface neutral, WITHOUT dropping weight.
All of this is dependent upon being PROPERLY weighted.
You don't need a 500psi tank to do a buoyancy check. Take your full tank and add weight to an empty bcd until you float at eye level. Then, realizing that you're carrying 5 lb of air that you'll breathe off during the dive with your AL80, just add 5 lb more to be neutrally buoyant at the END of the dive.
Folks that dive grossly overweighted use more air, have less buoyancy control, and are at risk for needing to ditch weight and then maybe suffer a runaway ascent as they near the surface. Don't be that diver.
As with any discussion, there are exceptions. But flooded drysuits and doubles diving and other scenarios don't seem to apply to the original post. And if you cannot get neutral with zero added weight, but still sink, you should be carrying redundant buoyancy, in my opinion. Hence, the comments about 1 mil suits and steel tanks, perhaps. But my steel 100 cu ft is 0 lb heavy when empty, and my 1 mil (if I had one) could support 3 lb. to include my regulator weight. Not much of a burden.
Dive safely! Cheers!
So the only two options left are bathing suit or wetsuit.
If you are neutrally buoyant (remember the buoyancy check from OW class? Normal breath, BCD empty, float at eye level with a near-empty tank) then when you exhale you will descend, and if you fill your lungs to full capacity you will ascend.
Bathing Suit
As you descend, only your air spaces get compressed by ambient pressure. But the only significant source of buoyancy is your lungs, and they are kept from compressing by the increasing pressure of your inhaled air, courtesy of your first stage. So your buoyancy will not change no matter what depth you are at. You may or may not be carrying lead to compensate for body fat or the buoyancy of an empty Aluminum tank. In this case, the ONLY thing making you negative is the weight of air you are carrying for your dive. If you get into trouble at the beginning of your dive, you are 5 lb heavy with an AL80 tank. Any diver can swim up 5 lb. But if you couldn't, for some reason, ditching 5 lb would make you neutrally buoyant at the beginning of the dive, both at depth and at the surface, with the amount you could shed decreasing as the dive progressed as you used up air.
In this case, you could ditch from 0-5 lb without risking a runaway ascent.
Wetsuit
Once again, let's assume you have made yourself neutrally buoyant with a near-empty tank check and are carrying the correct amount of weight. Now, you carry compressible neoprene that is less buoyant at 80 feet than it was at the surface. Perhaps 60% less buoyant! So if your 5-mil suit provided 16 lb of buoyancy at the surface, it might only provide 6 lb of buoyancy at 80 feet. Lets assume you were carrying 16 lb of lead along with 4 lb of regulator and miscellaneous equipment weight, to compensate for the 4 lb buoyancy of an empty AL80, your wetsuit's buoyancy and your intrinsic buoyancy in sea water. You are neutral at the surface with an empty tank. However, you are 5 lb negative at the start of the dive due to carried air.
Assume you have an emergency at 80 feet, at the start of the dive. Your bcd bladder just tore. At 80 feet, your wetsuit is providing you 10 lb less buoyancy, and you are carrying 5 lb of air. At this point, with a non-functional BCD and no ability to orally inflate, you will have to start swimming up 10+5 lb of absent buoyancy. If you dump your 16 lb of weight, you will be 1 lb positive and start ascending.
HOWEVER, as you ascend, your wetsuit regains its buoyancy as the neoprene cells expand, and you finish your ascent with 10 lb more buoyancy than you had when you dumped your weights. That's a runaway ascent, and a prescription for disaster. If it's getting bent or dying, dumping your weight might be a choice, but that'd be about the only reason to go that way.
Instead, how about you swim up with the aid of your buddy? You start 15 lb negative and need some help, but hit the surface only 5 lb negative - an easy swim. AT THAT POINT, no-one will argue with dumping your weight to stay buoyant at the surface.
If you take both these scenarios at the end of a dive (almost out of air???) then you're five pounds lighter and the swim up is much easier. With a bathing suit you hit the surface neutral, and with the 5-mil, you hit the surface neutral, WITHOUT dropping weight.
All of this is dependent upon being PROPERLY weighted.
You don't need a 500psi tank to do a buoyancy check. Take your full tank and add weight to an empty bcd until you float at eye level. Then, realizing that you're carrying 5 lb of air that you'll breathe off during the dive with your AL80, just add 5 lb more to be neutrally buoyant at the END of the dive.
Folks that dive grossly overweighted use more air, have less buoyancy control, and are at risk for needing to ditch weight and then maybe suffer a runaway ascent as they near the surface. Don't be that diver.
As with any discussion, there are exceptions. But flooded drysuits and doubles diving and other scenarios don't seem to apply to the original post. And if you cannot get neutral with zero added weight, but still sink, you should be carrying redundant buoyancy, in my opinion. Hence, the comments about 1 mil suits and steel tanks, perhaps. But my steel 100 cu ft is 0 lb heavy when empty, and my 1 mil (if I had one) could support 3 lb. to include my regulator weight. Not much of a burden.
Dive safely! Cheers!
If you were diving neutral at the moment you ran out of air, as you always should be for a calm, enjoyable dive, then your bcd has air in it at depth. That air aids your emergency ascent, and helps you as it expands. In fact you'll need to vent on the way up. It is your flotation once you finally surface. Your reg has another half breath in the hoses as you ascend and the gas expands. Don't dump your rig.
However, if you are suggesting 1) a torn useless bcd, AND 2) out of air, AND 3) no nearby buddy, I guess Darwin has it in for you. Yeah, dump your rig.
AfterDark
Contributor
Dropped weight once back in the 1980's. Putting my fins on sitting on a rock with a 15 FSW drop off. I slipped of the rock and sank to the bottom. On the way down I tried to inflate the borrowed BC I was using but it was very slow and my descent was not slowing. I then tried to find my 2nd stage as I hit the bottom, couldn't find it. I was wearing 2 full AL80 the thought kept running though my head, " I'll be damned if I'm going to drown wearing 2 full tanks"! I released my weights and ascended, after breaking the surface I sheepishly asked my buddy if he could get my weight belt please. These are how lessons are sometimes learned.
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IncreaseMyT
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