Negatively buoyant divers vs. ditchable weights

[Gilldiver]

You may also need to get positive at the surface in order to help another diver. Having both the rescued and rescuer positive leads to better outcomes. It may also be pointed out that getting out of your equipment fast gets you positive with a lot more, and quicker, freedom of movement which makes you a better rescuer - most rescues occur at the waters surface, not at depth.

 

[Gilldiver]

In my opinion you need to do whatever it takes to at least be neutral at the surface with a full tank at the start of your dive. That could be a thicker suit or a non inflatable float of some sort attached to your rig. I did see a product that was meant to keep a tank afloat if you wanted to dive surface supplied and tow the tank behind you. That would probably be too much lift but it might be something you could modify and attach to your tank. You would be better off neutral with even a small amount of weight that could be dumped if needed so you have a fail proof way to stay afloat in an emergency. Another way to go would be with a composite tank system like the Interspiro Divator system that is buoyant even when filled to 4500psi.

It also helps if you have some extra air in a dry suit or a BC if you do a giant stride off of a boat - the higher the boat step off, the more air. When I was crew on a number of wreck boats we called heavy divers "Dirt Darts" as they had a tendency to go down far enough off a high giant stride to get 4 feet or so down, if there was no air in the BC or suit, or not enough, they just kept on going.

 

[boulderjohn]

I'm relatively new to diving, so perhaps it is my inexperience talking, but unless I was really far from a boat on rough seas with a busted BCD, I can't think of a reason why I would need to ditch my weights. It wasn't really covered in the e-learning or the classes.

I'm more than a little surprised that your e-learning modules and OW class sessions never discussed specific scenarios in which ditching weight was a good option. Perhaps something was skipped by you or omitted by PADI.

Assuming it was PADI, it is in the eLearning and on the final exam. Under water, it is the process used to perform a buoyant ascent, which was described as your last choice for low on air/out of air ascents. On the surface you were taught that the first step in assisting a diver is to establish buoyancy.

 

[windapp]

I knew that you needed to drop your weights if you couldn't get buoyant any other way. However, with a working BCD, I would think that this would be a non-issue, and dropping of weights would not be necessary. Now that I think about the rescue scenario, however, it would be a lot easier to remove someone from the water with their weights removed.

The buoyant emergency accent was really de-emphasized in the course I took, and I had forgotten that dropping your weights was recommended for this. So now I have another question. Why wouldn't you use your BCD for this? I would think you could control your accent a lot better using your BCD like an elevator (exactly the opposite of how it is normally supposed to be used) rather than by dropping your weights. Once your weights are dropped, your minimum accent rate is fixed. For my setup, in a 7mm two piece, that means dropping a minimum of ten pounds, giving me five to ten pounds of lift depending on how full my tank is.

 

[MauiScubaSteve]

Dropping weights to do Buoyant Emergency Ascent is theoretically performed just before you lose consciousness.

If you are controlling your emergency ascent speed by venting your BC and you lose consciouness, who's to say you don't spasm a little and vent your BC too much.

This would most likely be done when one is OOA/OOG. If you have air/gas then your emergency is failed BC, so you swim up, dry suit up, &/or marker buoy up and perhaps drop weights too, but again only as a last resort.

 

[Banyan]

I dive a compact AL80 with a 1 mil skin with no lead, and recently switched from my heavily padded vest BC to a Kydex plate rig that I've figured has removed a further 3-4 pounds of buoyancy. (On a recent trip to Hawaii I worked myself down to 4 pounds of lead wearing a beat up rental 5 mil and diving a neutral AL80.)

With all this talk about the awesomeness of ditchable weights, I think it's worth pointing out that weight systems are also a point of failure, if the weight pockets that I occasionally find on the ocean floor at dive sites are any indication, which I am cleverly avoiding by not using. And I never have to worry about moving weights around to establish proper trim. And my spine and leg muscles appreciate less weight when I'm doing a ten minute hike to the dive entry point.

Choice of tank, exposure protection, amount of weight, and how much of that weight should be ditchable are all factors which are considered in setting up a "balanced rig." I'm not a DIR diver, but the DIR crowd has put a lot of thought into this. There have also been many threads here on SB discussing this. Here's a link to one of them.

Per those links, a balanced rig can be swum up from depth with full tanks and all weights, if you use them. I have a balanced rig. If I ever move on to doubles, I likely would need to use aluminum tanks and weights to balance it, but we need to distinguish between the "negatively buoyant at the start of a dive and therefore balanced rig" and "uncontrolled descent to certain death rig" that would likely result if I lost my mind and used steel doubles on a stainless steel backplate.

In the event that my BC has failed on the surface AND I can't breath from my regs or snorkel AND swimming back to shore or treading water is not an option, I always carry a DSMB that I can inflate if I just need to bob along.

So I'm giving up the ability to do an emergency buoyant ascent though I can still establish significant positive buoyancy and upward momentum by filling my lungs, assuming that both my regs haven't failed instantly, preventing me from taking the final big breath. On balance, I'm willing to accept the risk. If ever both me and my buddy both go OOG and I can't do an emergency swimming ascent, then I expect all you guys to tsk tsk at the report on A&I.

 

[TSandM]

Ditching weights at the surface is a good idea whenever it may not be possible to count on the diver to do what he needs to do to remain buoyant. This includes panicked divers, divers with nonfunctional BCs, and anyone who is injured or ill. People who remain at the surface have a MUCH better chance of rescue than those who sink, and we've all read stories of folks who were seen by the boat, only to submerge again and be lost.

If I were negative with an empty tank and my preferred exposure protection, I would rethink my gear to see if there were any way to fix that. Failing that, I'd make sure I had an easily accessible and adequate source of additional buoyancy. Even if you are a good swimmer and good at treading water, you will fatigue if you have to wait a half hour or so for the boat to arrive.

Luckily, complete BC failures are rare. But especially with the pull dump kind, the plastic can fatigue where the corrugated hose meets the bladder, or the corrugated hose can come off. This is a failure that causes the BC to hold no air at all, with the diver in an upright position, and it is not fixable in the water. For this reason, I don't like pull dumps, and I think people who are diving a negative rig should think hard about whether that's fixable.

 

[Dack]

There's another scenario for ditchable weights that can occur with NO equipment failures, just a simple mistake. Imagine before the dive you turn on your air, then for some reason turn it off again. You gear up and check your pressure and it's good, and even a breath from a reg works. You jump in, deflate your BC and start descending. After a few breaths you discover:

- You are out of air
- Your BC is completely empty
- You are negatively buoyant and descending


If you aren't significantly overweighted you might be able to kick to the surface... If you are negatively buoyant with NO ditchable weight, what are your options?

- Dack

 

[fjpatrum]

In my case I will sink without some sort of exposure suit on, period. If I need buoyancy to counteract my 6 pound plate and my BC fails for whatever reason (it has happened to me) then I'll swim higher in the column or I'll cut the damn thing off in an emergency. If I'm incapable of that, my buddies always know where my sheers are and that I want the thing cut off me if I need to get up/stay up and can't do it on my own.

Alternatively I have started carrying a 6' SMB that can act as an alternate source of about 35 pounds of lift, or so.

 

[DevonDiver]

I can't think of a reason why I would need to ditch my weights.

BCD malfunction. You tread water. You get cramp.

Ended.