Negatively buoyant divers vs. ditchable weights

[aquaregia]

As I added to my previous post, it only takes half a turn of the valve before the problem is over.

Your post seems to suggest there is no hope and this will happen. It is an accident that is easily prevented. It is also not too hard to solve for an experienced diver, but I can see where a new diver might be in trouble.

It it very common for divers to be unable to reach their valves, or in some cases where they could, be of the opinion that a diver cannot reach his or her own valves, and will not try. Add a buddy separation, and that's enough. This isn't like skinning your knee skateboarding.

 

[rx7diver]

I have a real life example of why taking the time to get you and your rig balanced for neutral bouancy is important and the value of having ditchable weights. Last week my wife, daughter and one of my daughter's diving friends were down in Grand Cayman for sunning, snorkling and scuba. My wife had hurt her ear snorkling the previous couple of days so she was not diving the day they went out to scuba. My wife is well connected in Cayman so they were on a small boat with just the three of them, a dive master and the boat handler. The girls hadn't been diving for quite awhile so the dive master took the time to have them do a proper bouyancy check. They jumped in with empty BCs and no weights. He got them neutral on the surface then added just enough weight to counter balance their AL 80s when empty. They then proceeded to do their dive.

They surfaced right behind the boat after their safety stop. At that point my daughter grabbed her inflater to pump some air into her vest before taking her fins off. She couldn't get the vest to inflate! The inflator was working but no air was going into the vest. There was no problem, she just grabbed the ladder, doffed her fins and climbed up on the boat. Her buddy and the DM were right there the whole time so she was never in any real peril.

However, under different circumstances the situation could have been very hazardous. If she had been overweighted instead of neutral at the surface. Less confident in the water and farther away from the boat and or her buddy.

When they got home she showed me the inflator and hose (now broken completely off the vest). Boy, that made my heart skip a beat! I asked her "didn't they notice the hose leaking during their dive?" She said no, she only put a tiny puff of air in when they first got to the bottom (she's like her dad, only dives in a short sleeve rash guard) and then never touched it again until they were behind the boat. I asked her if she thought about ditching her weights when she discovered her vest wasn't working. She said yes, but because she wasn't having any problem staying on the surface and they were right by the boat she decided it wasn't necessary. She added if they had been a long way from the boat she would have dropped them for sure. She only has 50-60 dives but she is a pretty squared away recreational diver!

By the way the vest was an old ScubaPro with the plastic (fake corrogated) hose that used to belong to her mother. Its in the trash now. We also had some discussion about doing a more thorough equipment check before diving, especially when the gear hasn't been used for awhile (goes for Dad too, seeing as how he was the one who packed the gear for their trip!).

Alls well that ends well....and some lessons learned to boot!

jimthediver

Jimthediver,

First of all, kudos to the dive master for insisting (?) your daughter and her friend do a proper weight check prior to their dive, and to your daughter for keeping her head when she realized her BC wouldn't inflate.

I agree, a proper/thorough gear check before the dive, as the divers were gearing up, probably could have caught the broken BC inflator hose. Maybe a trial run in the swimming pool before all of you left for Grand Cayman would have caught the problem even earlier.

Now, about that Scubapro BC: Go pull it out of the trash, and take it to your local Scubapro dealer to have it serviced. Those things are practically indestructible, provided they are properly cared for and serviced. I still dive mine which was purchased new c. 1994. And a good friend, an instructor, just returned from an open water checkout this weekend during which she wore her early-1980's-era Scubapro BC which she purchased new after she had just OW-certified.

BTW, I've never had mine serviced. Well, more precisely, I've always "serviced" mine myself. It's pictured here: http://www.scubaboard.com/forums/ba...83464-streamlining-my-gear-4.html#post5909041.

Safe Diving,

Ronald

 

[matt_w]

It it very common for divers to be unable to reach their valves, or in some cases where they could, be of the opinion that a diver cannot reach his or her own valves, and will not try. Add a buddy separation, and that's enough. This isn't like skinning your knee skateboarding.

So now we have the following scenario?

Diver makes very negative descent
Air is turned off
Can not reach valves
Is separated from their buddy
Unable to swim to the surface

I am a huge advocate of people being properly weighted. I am also a huge fan of discussing things within the framework of a likely reality.

Why do all the divers in this thread dump all of their air to descend. Nearly everyone diving an al80 will need to be a few pounds negative at the start of a dive. They should only be dumping air till they are neutral or maybe very slightly negative.

 

[AbyssalPlains]

This is NOT
Personally I am a sinker with a standard BC + single steel tank in fresh water. So far I've only dived cold waters so it's not an issue. Yet...

- Dack

Your answer is right there. The reason you don't see this issue addressed very much is because it really is not an issue. Since our bodies consist mostly of saltwater, our buoyancy is pretty much neutral. So if you dive in warm water with an aluminum 80 tank, which is about 2Lbs negative when full and 4Lbs positive when empty, there is not a whole lot of extra weight and you don't need a flotation device, at least not in theory. In practice, most people wear at least a thin wetsuit or a small BCD, so they can get positively very easily. It kills me to see divers putting weights into their BC even when diving without an exposure suit. Makes no sense at all.

It all boils down to the idea that you don't want to put a lot of weight on yourself that is not ditchable. You will find different opinions on this, but in general, most people would agree that it's not a good idea to dive steel tanks in a wetsuit, for example, and certainly not without a suit at all, because only a drysuit gives you redundant buyouancy in case your BC fails.

The only cases where you may find yourself very negative with no ditchable weight would be in decompression diving, where losing weight may be more dangerous than being too heavy. In those cases, you will either use redundant buoyancy like a drysuit and a BC, or a BC with a double-bladder with two separate inflator systems. Some people even promote surface marker buoys shot from depth as a redundant buoyancy device, but I don't. I stick to the rule of wetsuit=aluminum tanks and drysuit=steel tanks.

Bottomline: A situation in which you are seriously negative under water and don't have redundant buoyancy should not occur. IF you find yourself in that situation, you didn't configure your gear right.

 

[AbyssalPlains]

So now we have the following scenario?

Diver makes very negative descent
Air is turned off
Can not reach valves
Is separated from their buddy
Unable to swim to the surface

This situation should not occur. I say "Should" because of course I know it does. Heck, i recently did a giant stride with my air turned off. However, if you sink like a rock at the surface only because there is no air in your BC, you're overweighted. Period. In my book, a diver should only be slightly negative on the surface, just enough to balance out the empty tank at the end of the dive. So let's say, four pounds negative. If your air is turned off, you can very easily swim to the surface. Someone who can't swim up ten pounds shouldn't dive in my opinion. And if all fails, ditching weights is always the last option.

So, in summary, the above situation should be a non-issue. At least when things are done right.

 

[Dack]

Yes "should" not occur, but we're talking subtleties here. Fresh water, aluminum backplate, no wetsuit, no weights = I sink slowly. Seems like the practical answers are:

- Switch to aluminum tanks so that I can add ditchable weight.
- If steels are all that's available, actually add bouyancy so that I can add ditchable weight


Again all this is hypothetical...I'm kindof a wimp for the cold so a wetsuit is always there and adds buoyancy nicely. I just like thinking about all the hypothetical cases, it helps me learn. Thanks!

- Dack

 

[smokn']

Your answer is right there. The reason you don't see this issue addressed very much is because it really is not an issue. Since our bodies consist mostly of saltwater, our buoyancy is pretty much neutral.

Some of us are naturally pretty negatively buoyant. I recently discovered that when in a pool and with 3/4 full lungs, I sink to the bottom like a rock. Given, I have 5% body fat, but our strange species do exist.

I'm relatively new to diving and I'm still getting the kinks worked out of with my weighting, but I recently noticed that when diving a lake with aluminum bp/w, aluminum 80, 5 mil all around and 6 lbs of weight (for some reason, I thought this was the right weight for me), I dropped to the bottom, even with a bit of air in my bc. I'm beginning to think I may not need any weight in fresh water with an exposure suit on. In any event, I'm going to spend a few pool dives figuring these things out before my next dive excursion.

But I'm really glad this point is being brought up, I was beginning to think I was alone in the world of negative buoyancy.

 

[elan]

Was it in the beginning of the dive ? If yes that should be happening as you are about 5 pounds overweight by the gas

 

[smokn']

Was it in the beginning of the dive ? If yes that should be happening as you are about 5 pounds overweight by the gas

It was, but I still think it may have been a bit too much weight. I had to inflate my bc a good bit.

 

[elan]

It was, but I still think it may have been a bit too much weight. I had to inflate my bc a good bit.

Just do a proper weight check