BC Lift Question

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Bubbletrubble

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4) It's nice to be able to come up under a panicing diver and give them some altitude while you figure out and deal with whatever their problem is. Getting a diver's head significantly out of the water calms them down quickly.
I would hardly consider this the "go to" method for dealing with a panicked diver at the surface, though, since there are other methods to help the panicked diver establish positive buoyancy without exposing the rescuer to excessive risk -- and these other options should be considered prior to acting. Coming up under a panicky diver and inflating one's BCD can lead to a good outcome if the panicked diver is a small person/child and the rescuer is a larger person. If the panicked diver is a large man, however, the rescuer exposes himself to the risk of getting punched in the face, i.e., physically overwhelmed by the victim. Moreover, I suspect there are many slight-of-build folks out there who can be extra-feisty under the right circumstances. Suffice it to say, I wouldn't recommend over-sizing BCD lift for the sole purpose of being able to pull off this maneuver.

flots am understands this risk, so his decision is more of an "informed" one. I just wanted to make this point so that newbies reading this thread don't automatically assume that this is always the most desirable way to deal with a panicked diver at the surface.
 

ScubaSteve

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2) you are diving in conditions that can present strong downward current and you want the lift for emergency response if needed

is this seriously how you would tell someone to get out of a downcurrent? Go overboard on your BCD and Lay on the inflator until positively buoyant enough to compensate? Very dangerous. What happened to swimming away from the wall? Climbing across and up using the wall? My understanding is these will typically present themselves down a wall (but I am sure not every single time) so these are valid. Laying on your inflator is just plain dangerous
 

flots am

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Coming up under a panicky diver and inflating one's BCD can lead to a good outcome if the panicked diver is a small person/child and the rescuer is a larger person.

Actually, it's from under/behind and I've never met anybody who could reach back far enough to do any damage when I have their tank valve.

flots.
 

DTm

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Interestingly I have searched a couple different times and as a whole I have not found any stated lift ratios for jacket style BCDs. Some do say they have I high lift. It could be that I am just not looking in the right place. Wings almost always states, their lift rating.
Now, as some have alluded to 101 in dry suit diving is you use 1 device to control your buoyancy and that is your dry suit.
But in 201 dry suit diving moving into tech you end up with much more equipment. If you used only the dry-suit you would look like the stay-puff marshmallow. So you end up using the wing.
I am not really buying the whole you need more lift if you have a dry-suit failure to cover the additional weight needed. The weight of water in water is zero -- If you are putting on that match weight to get down in the first place – in the advent that your primary Buoyancy device fails in 101 the dry suit and the secondary device, THE BCD, does not have enough lift – Just drop weight till you are neutral and terminate the dive.
I do not know, part of me would like to see this to be tested on myth busters – there is a post on their forums with a like question. Maybe I will see if my LDS will loan me a few different types and a lot of weight; go to the pool and test it;
Another part thinks there is a little bit of an exaggeration, to justify the purchase to our spouse’s just so we can have what all the cool kids have.
Now I do think, that BP/W’s are more configurable and when you get in to tech diving needing more equipment and more redundancy (like a double or backup bladder). The BP/W does offer more options.
 

Bob DBF

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Interestingly I have searched a couple different times and as a whole I have not found any stated lift ratios for jacket style BCDs. Some do say they have I high lift. It could be that I am just not looking in the right place. Wings almost always states, their lift rating.

When I was changing to a BP/W from a jacket I wanted to know the lift of the jacket since it had worked well for me. I e-mailed the manufacturer of the BC and gave them the model and size and the next day I had an answer. An XL Genesis Cayman is 40# of lift.



Bob
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I may be old, but I’m not dead yet.
 
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I did not read all the answers but there are different reasons you want to have a big volume bcd.
- If you are diving a dry suit and it foods you need a lot of lift to come back up to the surface.
- If your dive buddy looses buoyancy because of a malfunction of his bcd a lot of volume in your bcd helps as well.
-Technical divers are so heavy with all the gear and tanks that they don't need no weight to descent. So they need enough lift to be neutrally buoyant during the dive and to surface at the end of the dive.
 

danvolker

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I did not read all the answers but there are different reasons you want to have a big volume bcd.
- If you are diving a dry suit and it foods you need a lot of lift to come back up to the surface.
- If your dive buddy looses buoyancy because of a malfunction of his bcd a lot of volume in your bcd helps as well.
-Technical divers are so heavy with all the gear and tanks that they don't need no weight to descent. So they need enough lift to be neutrally buoyant during the dive and to surface at the end of the dive.

Maybe you should have :D....Divers should not be making themselves so heavy that it takes massive lift to get them up. We deal with this issue by choosing the right gear--gear that does not make you too negative.
If I just use a steel hp 100 tank, I don't need to use a weightbelt with my tls 350 drysuit and 5th dimension insulation optimal for 55 to 70 degree water. I have had a full flood from a seal being pulled open, and I was only about 10 pounds negative, which is nothing to swim up, even if the BC failed at the same time as the seal opened.
Tech divers with doubles need to choose tanks that are not too negative, and can't mix heavy tanks with a thick wetsuit ( which will lose all its bouyancy at depth).

The real issue on this thread, is what kind of lift will a recreational diver need, and by far, many more accidents have occurred to divers using BC's with far too much lift.
Most divers will never have experienced a diver in their group having a failure that required assistance to get positive ( help from other divers or an additional lift device they carried) ----however, large numbers of divers will have been in a group where a diver with a high lift BC, had some type of gear failure or issue which led to the BC inflating at depth, and the diver taking a rocket ride to the surface.....
The more lift the BC has, the less time you will have to fix the problem, if the BC begins to self inflate from a failure. If you wear a BC with only 15 or 20 pounds of lift beyond what you need to be neutral, the upward speed is slow enough to give you time to think and solve things, or to fight the upward movement....A BC with 50 to 75 pounds of extra lift, will be impossible for any diver to fight, the immediacy of the rocket ride upward leaving little time to fix anything, and the game then will be about how fast the diver can exhale.
The real danger is a BC with too much lift.
 

ADimitris

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In reading a number of posts, I see people talking about switching from a jacket to a BP/W to get more lift because they are going from wet to dry and need to add more weight, or changing the wing for one with greater lift.

They may also be switching b/c they can't use their traditional BCD with double tanks.

Don't feel embarrassed by your questions. The answers are complicated and you are not the only one who doesn't understand this perfectly!
 

ADimitris

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In reading a number of posts, I see people talking about switching from a jacket to a BP/W to get more lift because they are going from wet to dry and need to add more weight, or changing the wing for one with greater lift.

They may also be switching b/c they can't use their traditional BCD with double tanks.

Don't feel embarrassed by your questions. The answers are complicated and you are not the only one who doesn't understand this perfectly!
 

Sigma13

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I enjoy a lot of what is on this post and lean towards a smaller wing. I was in that line of thinking but the lds and one of the wing manufacures are steering me to a larger wing (60#). I am contemplating double 130 on a ss plate. 22 neg on tanks full, 8 lbs gear, 6 lbs plate only gets me 36 negative. Adding 26 lbs posative from the drysuit implies i am 10 neg and only need 10 lbs of extra lift to start. By the end of the dive i would shed 20lbs of air so i would need an extra 10 to start. That would still only imply I need 20 lbs of lift.

Do you agree with this math? Also if the suit fails I loose the 26 lift at the beginning or end of the dive when tanks are 22neg and 2 neg, respectively I would 36 neg and 16 neg, respectively. Seems like a smaller wing could swing that espc as one could ditch the 10 lbs of lead. what am I missing.

FYI. I'm not entirely sold on diving the 130s but was using them to do the math as I had the nbrs handy.
 
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