Question about “balanced rigs” and having all ballast unditchable

[Akimbo]

I just thought of a some other pointers when performing this buoyancy experiment:

• We didn't have BCs when I did these experiments. Be certain that all the air is out of your BC so your buoyancy doesn't dramatically increase beyond suit expansion.
• Stay close to the line (rope) tied to your weight belt so you can snatch it if you are ascending uncomfortably fast.
• Do these drills in 20-30'/6-10 M of water and at the beginning of your day of diving so residual Nitrogen is minimal.
• Your computer may whine a bit about ascent rates and safety stops.

 

[ams511]

My apologies, all the above is assuming nothing thicker than 5mm when deeper than 100’. If you have a 7mm on then the principle does still apply but the amount you have to swim up increases. At some point it may not be possible to swim it up then you need to accept an uncontrolled ascent at some point in the dive.

If I dived like that I would obviously change the amount of ditchable weight I had. I would also ensure I had redundant buoyancy.

There is no need to apologize, I just wanted clarification. I used to dive a 2 piece 7 mil in cold water. I don't think I would do that again. I think I would go with a 1 piece semi-dry instead. I know it is not ideal, but it should be better than a 2 piece farmer john.

 

[Eric Sedletzky]

What about a complete drysuit flood (catastrophic failure, major cut or tear, blown out seal or shattered valve), a total BC wing catastrophic failure (plastic elbow breaks off) and you have no ditchable lead, and all this happens at depth, what’s the plan for survival?

 

[Akimbo]

What about a complete drysuit flood...

In theory, you can inflate you BC or increase the backpressure in your drysuit to compensate -- as long as you don't have a problem on the gas supply feeding them. That would be fine except that divers rarely die from a single failure. It is often a cascade of three or more failures and/or oversiights.

That argues in favor of dropping lead because it is independent of any supporting technology, other than planning ahead enough to require carrying it.

 

[Centrals]

I have been using ditchable weight since day 1 and yet to find a reason NOT to use it. 2-3kg round my waist never caused any inconvenience. All dive operators in SE Asia will provide belt and weight as part of the package and yet to come across who act otherwise.

 

[CT-Rich]

What about a complete drysuit flood (catastrophic failure, major cut or tear, blown out seal or shattered valve), a total BC wing catastrophic failure (plastic elbow breaks off) and you have no ditchable lead, and all this happens at depth, what’s the plan for survival?

It depends on whether the shark bit off the top half of you or the bottom half...

In the early day of diving such catastrophic failures were surprisingly common... here is a promotional video from the Bermuda Department of Tourism. Ca you identify the causes involved in catastrophic BCD failure?

 

[ams511]

What about a complete drysuit flood (catastrophic failure, major cut or tear, blown out seal or shattered valve), a total BC wing catastrophic failure (plastic elbow breaks off) and you have no ditchable lead, and all this happens at depth, what’s the plan for survival?

Eric, as you pointed out we are in basic scuba discussions. Why are you talking about torn dry suits and broken elbows? These things are far more likely to happen to technical divers than recreational divers. What is more likely to happen to recreational divers is jumping in without the gas turned on or a regulator problem. Either of these things cause the same problem the diver being too heavy and not able to fill the bc. Either you kick like hell and exhale into the BC or you need to dump the whole rig if you have no ditchable weight.

I am puzzled as to your fixation about divers that don't want ditchable weight. I don't know of any and most (if not all) of the posters use ditchable weight. The people that post that they don't have ditchable weight are tropical divers that only need a few pounds anyway because their only wearing a skin or a thin wetsuit. They should be able to kick that up.

 

[ams511]

It depends on whether the shark bit off the top half of you or the bottom half...

In the early day of diving such catastrophic failures were surprisingly common... here is a promotional video from the Bermuda Department of Tourism. Ca you identify the causes involved in catastrophic BCD failure?

First, no one has a BC. Second, Bond seems to have the same type of device that Obi Wan had in "Attack of the Clones". Third, it seems that the villains all use double hoses while the good guys use single hoses. We need to ask Bryan from VDH about that . Forth and most importantly, it seems both sides are using Freedom Plates. I am shocked that Eric would sell them to SPECTRE.

 

[MichaelMc]

Eric, as you pointed out we are in basic scuba discussions. Why are you talking about torn dry suits and broken elbows? These things are far more likely to happen to technical divers than recreational divers. What is more likely to happen to recreational divers is jumping in without the gas turned on or a regulator problem. Either of these things cause the same problem the diver being too heavy and not able to fill the bc. Either you kick like hell and exhale into the BC or you need to dump the whole rig if you have no ditchable weight.

I am puzzled as to your fixation about divers that don't want ditchable weight. I don't know of any and most (if not all) of the posters use ditchable weight. The people that post that they don't have ditchable weight are tropical divers that only need a few pounds anyway because their only wearing a skin or a thin wetsuit. They should be able to kick that up.

I'm fairly sure the discussion of torn drysuits came from: cold climate people still learn (thus basic) in wetsuits -> loss of wetsuit buoyancy at depth -> replace wetsuits with dry if deep, very thick suits, and negative steel tanks... yeah, but dry suits are not trouble free (leaks/catastrophic failure) and wetsuits are really robust (no leaks/failure catastrophic or otherwise).

It was not about trying to venture outside of basic, for the northern latitudes some learn in. It might have been not keeping things simple and sticking to their main concern, but it was still basic for some. Short of the compound failures we've gotten into which might not be rec. scuba much less basic rec. scuba. Maybe in thick suits just stay away from deep and really negative steels, then you can stay in a simple-ish basic world.

Well really the deep part is AOW, not OW, so the thick wetsuits deep concern does not exist much, yet, in basic. Depending on the limits of basic.

 

[Jay]

I did some experimenting several years after I started diving to figure out how much weight I could drop and reasonably control my ascent rate. Keep in mind that the maximum ascent rate was 60' or 18M per minute then. I tied about 50'/15M of line from my weight belt to a surface float.

I was using a pretty heavy wetsuit with 3 layers that required about 25 Lbs/7.6 Kg to reach neutral at 10'/3M. I transferred about half the weight to a second belt that I didn't drop and started testing. I moved about 2 Lbs/1Kg to the belt I dropped for each test. I found I could drop 22 Lbs/10 Kg before I got uncomfortable controlling the ascent. YMMV.

I just thought of a some other pointers when performing this buoyancy experiment:

• We didn't have BCs when I did these experiments. Be certain that all the air is out of your BC so your buoyancy doesn't dramatically increase beyond suit expansion.
• Stay close to the line (rope) tied to your weight belt so you can snatch it if you are ascending uncomfortably fast.
• Do these drills in 20-30'/6-10 M of water and at the beginning of your day of diving so residual Nitrogen is minimal.
• Your computer may whine a bit about ascent rates and safety stops.

Thank you @Akimbo for these posts and it's a great skill to add to my practice list. I have a few questions:

[I think there's a typo of the first weight in kg. 25#=11.3kg.]

Big picture; you managed to drop most 22/25# (88%) of your weight with a very bulky wetsuit and using the techniques described to maintain a reasonably controlled ascent (checking I've read it correctly?).

Would you happen to be able to roughly recall what your max ascent rate was in the test you did from 50'?

I guess in your setup, theoretically, if you tried it from double the depth then you would only be able to ditch ~half* of the previously ditched amount to have the same max ascent rate? (Don't worry, I'm not trying it, I'll start the exercise at 5m!, but more curious re a what-if scenario) [*'m assuming that wetsuit compression would be less from 50-100ft versus 0-50ft, offset against a longer ascent acceleration build-up].