Not enough buoyancy

[Doppler]

I wear a 2.5 MM wetsuit with a Faber 117HP tank.

Sorry, I missed the bit about diving in a wetsuit. The backup for a buoyancy cell is either a drysuit or a reel and DSMB with some floatation to it.

For the record, a Faber 117 has an inwater weight of more than four and a half kilos when filled... and barely weighs 500 grams when empty... lots of gas. Not a huge fan of dumping ballast as the end result is often a ballistic or at best an uncontrolled ascent.

Do the math, do some in-water research and act accordingly... and as already stated, inspect your gear.

 

[boulderjohn]

Just in general, I would say that if you NEED a certain amount of weight while diving in order to descend and stay beneath the water, then removing that weight would allow you to ascend without a lot of effort. Anyway, that seems logical to me.

Of course, if you NEED that weight, the point at which you need it is at the end of the dive, when you are trying to hold a stop with a nearly empty tank. You need to have just enough weight to do that. If you are concerned about the need to ditch enough weight to get to the surface easily when the tank is full, then you will want to have an additional amount of ditchable weight equal to the weight of the air in the tank.

Think about the classic weight check. If you are properly weighted, you should float effortlessly at eye level on the surface while holding a normal breath with no air in the BCD.

---------- Post added March 24th, 2015 at 02:40 PM ----------

A couple of years ago I was diving caves in Mexico with double AL 80s and my 58 # lift doubles wing. It was not the greatest because the wing was too big for those tankks, and someone loaned me a very well used smaller wing. (Did I mention it was very well used?) As I was getting near the end of a dive and getting shallower as we neared the opening, I reached back to dump air via the rear dump. The entire dump came out when I pulled the string. The plastic threaded area just broke off completely. No problem. All I had to do was go out of trim a little and I had plenty of air trapped in the shoulder of the wing.

 

[Akimbo]

... Not a huge fan of dumping ballast as the end result is often a ballistic or at best an uncontrolled ascent...

I did some experiments dropping weight in 60'/18M. I started around 5-8 Lbs/2-4 Kg and worked my way up to 22 Lbs/10 Kg before deciding that dropping more would be too hard to control a 60'/minute ascent. Even dropping 10Kg is far from ballistic.

Caution: Sea Story
I accidently did ballistic once and was incredibly lucky to be exhaling at that moment… 34'/10M to the surface in a little under one exhalation cycle. A bolt failed when filling an open-bottom steel can with air. The can was 3' in diameter and 3½' tall. Guys onboard a small support boat nearby said the can nearly cleared the water with me inside. Positive buoyancy was probably around 400 Lbs/180 Kg when it broke free and about 1200 Lbs/545 Kg when it broke the surface. I had no clue until noticing the can was moving in the swell and the water level was down to the bottom. It could have easily smashed that small boat into splinters. A lucky day all around.

I became much more interested in learning proper rigging after that… in addition to keeping my airway open when filling lift bags.

 

[dumpsterDiver]

Sorry, I missed the bit about diving in a wetsuit. The backup for a buoyancy cell is either a drysuit or a reel and DSMB with some floatation to it.

For the record, a Faber 117 has an inwater weight of more than four and a half kilos when filled... and barely weighs 500 grams when empty... lots of gas. Not a huge fan of dumping ballast as the end result is often a ballistic or at best an uncontrolled ascent.

Do the math, do some in-water research and act accordingly... and as already stated, inspect your gear.

I find a few of your comments on this thread- hard to reconcile- with my experience. You seem to indicate that BC failure is very rare, because you have not had one. Have you run out of air at depth? If not, then does that mean it is "nothing to worry about" either?

Failure of a BC can be a significant concern and I have seen several failures. One manufacturer even had a big recall - Dive Right with defective OP springs.. one spring fails and the BC will not hold air. On other BC's a fitting comes lose and no air. On some BC's a zip tie fails.. same result. A hose rips, another failure. Of course we should check our gear, but failures will occur. I have had two total failures at depth, one on a solo dive in 180 feet with no ditchable lead..

I think people should be very concerned about how they will deal with a total BC failure.

Your other comment about ballistic ascents if lead is dropped are even more off target. Dropping 6-8 or 10 lb of lead is not going to send anyone shooting to the surface, unless they fail to control their BC and their body position in the water. You are WRONG that dropping lead will cause an uncontrolled ascent. In all your experience, you have never dropped a weight belt and ascended without one to see what happens? I make my kids do it on their 2nd or third openwater training dive!

 

[DogDiver]

When diving dry, my dry suit is my redundant buoyancy. When diving wet I use a duel bladder Dive Rite Nomad.
When Cave diving with close to 180 pounds of gear on every dive, I haven't used a weight belt in over 10 years.
Be sure you always have enough buoyancy to get yourself out of a situation.


Sent from my iPhone using Tapatalk

 

[NAM001]

I have had 2 bladder ruptures. one with doubles lp85's on and another with single lp95. The doubles was not pretty. Had I followed the general rule of doubles = dry suit, all would have been well. Took my buddy to get me up the wall to he shallows. a similar thing with the single95 but I could swim it up after venting air. The real issue was why the bladders blew. It was mis-handling. I had my rig set up in the back of a suv with others rigs stacked on top of it. pinched the wing and cut the bladder. Both times same reason. I don't have that problem any more now I know the cause.

 

[Steve_C]

crawl out of the water Fixed it for you.

Actually on most of my saltwater dives there is an anchor line and that is an option. Use the anchor line and help pull up (if you need it).

Couple of times when bringing up some one else's weights I did that. Did not want to use my BCD in case I dropped the weight and did not want to work hard during the assent if I could avoid it.

 

[Altamira]

Gee, I wonder how any of us survived, or were even worried about swimming up our weights before the introduction of bcds or horse collars? We swam them up on every dive.

 

[Akimbo]

Gee, I wonder how any of us survived, or were even worried about swimming up our weights before the introduction of bcds or horse collars? We swam them up on every dive.

This observation reminds me of a speech by Scott McNealy of Sun Microsystems describing Internet security. It went something like: People worry about their document transmitted over the Internet that is split into packets traveling by different routes at the speed of light but trust dropping that document in a metal box on the street wrapped in paper and sealed with spit.

Compare that to betting your life on a plastic bag with a corrugated hose held on with zip-ties but you can’t depend on Archimedes principal in an emergency or just your fins normally… Connect the dots folks.

 

[cool_hardware52]

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.

Most of the seriously negative steels are "medium" pressure 3180+ or 3000+ tanks.

Very few (maybe none) 3442 tanks are more than -1 to -2lbs. empty.

Tobin