Not enough buoyancy

[Dnaber]

There's a conversation in the Advanced section about Aluminum or Steel double 80's, and in there were several comments about the ability to surface with a tank strapped the your back with no weights. This got me thinking..... I been diving the fresh water springs here in N. Florida and I wear a 2.5 MM wetsuit with a Faber 117HP tank. With that combination I only need about 4lbs (2lbs in the trim and 2lbs in the ditch pockets) to achieve neutral buoyancy. My concern is if I had a ruptured bladder emergency and had to surface would dumping my 2lb weight pocket be enough to get me to the surface. Made me think...... What do you folks think?

 

[KevinNM]

I don't know. You might try swimming your rig up from the bottom at the start of your next dive (so you have the weight of the air in the tank) and see.

 

[Steve_C]

Good to check but If you have a full tank of air and your bladder blows and you have a hard bottom at a recreational depth in a fresh water spring then I do not see where it is an immediate emergency. You can always shed a few more pounds by taking your tank down to 1000 psi. You can also dump the weights in the trim pockets given time. You could also put all 4 pounds in your weight pockets to start with if worried.

 

[Akimbo]

In an ideal world, I like to be able to drop at least 10 Lbs/5 Kg of lead. That provides a reasonable balance between the added weight of full cylinders and loss of displacement at depth due to compression for a ~3mm suit. It also provides a lot of buoyancy during an emergency on the surface.

As an absolute minimum, I would shoot for being about 2 Lbs/1Kg positive at depth with full cylinders and max suit compression. On the other end of the spectrum, I like to limit my weightbelt to 22 Lbs/10 Kg because that is about the max weight I can drop and maintain a proven safe ascent rate… which I consider 60'/minute in an emergency.

As a matter of principal, I try to find a balance where losing a BC is a minor inconvenience.

 

[Doppler]

You can and should certainly conduct a test to check for too much ballast; but you might also conduct a straw poll asking how many instances of "ruptured bladder emergency" have been recorded... and better yet, how to avoid them.

I'll get you started.

I have several thousand dives logged... my peer group have several more dives logged. Among us, we have zero ruptured bladder emergencies. Perhaps we have been lucky, and perhaps our luck has been reinforced by pre-dive gear checks.

Something I would suggest... a drill... practice disconnecting your LP inflator then control your buoyancy going deeper and shallower for a full dive using oral inflation. Simulates a realistic kit failure.

 

[Akimbo]

Doppler makes some good points. Maybe I am biased but never felt comfortable betting my life on a plastic bag with a corrugated hose attached. Part of that bias probably comes from learning to dive before BCs or horsecollars that could be inflated at depth. The other part comes from using a wing for years that was protected by nothing but a thin elastic cover over the clear bladder. I always just assumed it would fail from a puncture wound.

On the other hand, Archimedes principle and bits of lead on a belt have never failed me.

 

[TSandM]

The couple of catastrophic BC failures I've seen reported have been the same failure -- corrugated hose pulls off the connection to the air bladder, and all of those were BCs with pull dumps.

I didn't, in a quick search, find the buoyancy characteristics for a Faber HP117, but some of the Faber tanks can be 7 pounds or so negative when empty, or about 15 pounds negative for your tank when full. You will lose very little buoyancy from wetsuit compression with a 2 mil shortie, so I think 20 lbs is probably a liberal estimate of how negative you could be, at the beginning of your dive, should your hose pull off. I know I can swim up 10 lbs without too much stress; I've seen video of a friend swimming 25 pounds off the bottom of the pool. It's a chore, honestly, and maintaining your buoyancy at the surface would be very fatiguing. If I were you (and assuming these are the very negative Faber tanks) I'd consider something else for diving wet.

 

[nimoh]

The couple of catastrophic BC failures I've seen reported have been the same failure -- corrugated hose pulls off the connection to the air bladder, and all of those were BCs with pull dumps.

I didn't, in a quick search, find the buoyancy characteristics for a Faber HP117, but some of the Faber tanks can be 7 pounds or so negative when empty, or about 15 pounds negative for your tank when full. You will lose very little buoyancy from wetsuit compression with a 2 mil shortie, so I think 20 lbs is probably a liberal estimate of how negative you could be, at the beginning of your dive, should your hose pull off. I know I can swim up 10 lbs without too much stress; I've seen video of a friend swimming 25 pounds off the bottom of the pool. It's a chore, honestly, and maintaining your buoyancy at the surface would be very fatiguing. If I were you (and assuming these are the very negative Faber tanks) I'd consider something else for diving wet.

I agree with that...mostly. I don't think it is a good reason to go out and buy new gear. After swimming the heavy gear to the surface, it could be ditched and the wetsuit would provide enough buoyancy....then go out and buy new gear

 

[RJP]

Good to check but If you have a full tank of air and your bladder blows and you have a hard bottom at a recreational depth in a fresh water spring then I do not see where it is an immediate emergency. You can always crawl out of the water [-]shed a few more pounds by taking your tank down to 1000 psi. You can also dump the weights in the trim pockets given time. You could also put all 4 pounds in your weight pockets to start with if worried.[/-]

Fixed it for you.

 

[LeadTurn_SD]

Lightning sometimes does strike.

My wife and I both had the welded seams on the bladders of our 32lb wings fail... discovered during the same pre-dive inspection (the evening before the dive) while orally inflating the wings. Not catastrophic, but in both case about a 1-2" section of seam "let go" and the wings would not hold air.

These were NOT pinch flats, just a bad quality inspection day at the factory I guess, the wings were several years old; both bladders were replaced under warranty without any fuss with "improved" bladders, and we are still happily diving those two wings.

In our case it would not have been an "emergency" in any event since we dive Al80 tanks and we can easily swim up to the surface from depth even with an empty wing, and can then if necessary drop out weight belts at the surface to get "neutral" or slightly "positive"...

Just wanted to chime in that although extremely rare, failures of wings and jacket BC's CAN occur, so you should have a "plan" in place for dealing with this type of failure at the surface or at depth.

Best wishes.