When to ditch weight?

[Don Quixote]

During our OW, we were taught how to ditch weight. After learning how to dive and completing so many dives, the more I am lost about when or what situation warrants ditching one's weight. For example, I will be scared about ditching my weight while underwater. So, can anyone explain what situations call for ditching the weight?

One situation I can think is jumping into the water with the tank close. However, this has happened to me before and it was easy to kick to the surface, blow air into the BCD with the mouthpiece and take time to open the tank. Even with no air in the BCD, one just does not sink quickly downward.

 

[DevonDiver]

1. If underwater and you feel that you may pass unconscious in the immediate future.
2. At the surface, if in distress.

When weighting, consider a balance between ditchable and non-ditchable weight. You only need to jettison sufficient weight to guarantee positive buoyancy. That doesn't need to be your total weight. Ditching ballast underwater is a lot less scary in concept if you won't be heading to the surface like a ballistic missile...

You are most negative on reaching maximum depth at the start of the dive. That factors for the heaviest weight of gas in your cylinder, coupled with the most compression (loss of buoyancy) from your exposure protection (wetsuit compression, or no gas available/puncture to inflate your drysuit).

At that point, you should be able to ditch enough weight to attain slight positive buoyancy. That means you will float up... gently and controlled. Any necessary weight beyond that amount, can be integrated directly onto your rig (doesn't need capacity to be jettisoned).

 

[stuartv]

At that point, you should be able to ditch enough weight to attain slight positive buoyancy.

First, I would suggest to only ever ditch weight when you're under water as an absolute last resort.

Second, if you're on the bottom and you decide you do need to ditch weight, I would not suggest to ditch enough to become slightly positive. I would suggest that your goal be to ditch just enough that you can swim up against however negative you still are.

Here's a bad-but-not-worst-case scenario. You're diving a tank with 120 cu-ft of air and wearing a 7mm wet suit. The gas in your tank weighs roughly 9 - 10 pounds. Let's say 10 to make it easy.

Imagine that you've dived to 130' and your 7mm wetsuit was providing 20 # of buoyancy at the surface, but has now compressed enough to lose 75% of its buoyancy. So, you've lost 15# of buoyancy when you get to the bottom.

When you first arrive on the bottom and your tank is full, that means you have -10# for your gas and -15# for your suit loss, so you are 25# negative.

If you can swim up 25#, then you wouldn't need to ditch any weight, even if your BCD lost 100% of its lift capacity - or you jumped in with an empty BCD and a closed tank valve. But, if you jumped in with a closed valve, you should realize that right away, which is long before you've lost hardly any lift from suit compression. So, you're only 10# negative. As you said, you ought to be able to fin yourself up to the surface against 10# negative buoyancy from your tank.

If you get to the bottom and you pull your corrugated hose off your BCD and lose all capacity, you're 25# negative. That might be too much to swim up. But, rather than ditch 26# (which you're probably not carrying anyway), you only NEED to ditch enough that you can swim up. If you can swim up 10#, then you only need to ditch 15. As you swim up, your suit will uncompress and it will get easier and easier. If you ditched 15#, in this scenario, you'll arrive at the surface 5# positive

For carrying less gas (i.e. an 80 or 100) and using a thinner wet suit, your max amount your would be negative at the start, on the bottom, gets less and less.. An 80 only has 6 # of gas. A 3mm suit might only lose 3 - 5 # of buoyancy. So, the most you should ever be negative would be around 10#, total. And that's only at the very beginning of the dive, and only at recreational limits for depth.

That is all assuming you are properly weighted. If you are carrying more lead than you need, then every extra pound you are carrying is another pound you might want to be able to ditch.

 

[tbone1004]

so your first scenario isn't one that should ever happen with a properly adjusted rig. You should have no problem reaching your tank valve to turn the tank on. Most instructors/agencies teach a tank position that is far too low and that is dangerous in my not so humble opinion.

Andy mentions the two scenarios that I ever see as a possibility. You're going to pass out, for whatever reason, and possibility of getting bent is better than death, though shallow water blackout is real bad. This should never really happen btw. The other being distressed at the surface, which is a very real possibility but this can also be compounded by a wing failure at the surface and you have to be at the surface for some period of time or kick somewhere.

If you have to kick up in one of Stuarts scenarios which is you can't kick up the rig without ditching weight, then you are diving an unsafe rig and should re-evaluate some combination of lead, tanks, and exposure protection to make it so you don't have this problem. With fins on, swimming up roughly 20lbs should be a non issue. It is a regular requirement to retrieve a 10lb diving brick from the bottom of the pool and if you can do that with no fins on, then this shouldn't be a problem with fins on.

 

[boulderjohn]

I imagine someone will eventually bring up statistics on the percentage of dive fatalities in which the diver did not ditch weights, implying that failing to ditch the weights was the reason that the divers died. This is not a logical assumption. If you read through the descriptions of dive accidents, such as those found at the end of the DAN reports, you will see that in probably about 90% of these fatalities, the diver either could not have ditched weights or ditching the weights would have provided no benefit. The largest category of such fatalities involve cardiac events, and a person who has a heart attack and passes out suddenly will not be able to drop weights. The largest percentage of deaths that would be prevented by training involves divers who, often because they went out of air without a buddy nearby, sprinted to the surface while holding their breath, thus suffering an embolism. In these cases, the weights were not an issue--the diver did reach the surface and suffered a fatal injury as a result of that ascent. Other events (like a rare entanglement) are also often unrelated to dropping weights.

The advice given to you previously is good. You want to be sure you can make it to the surface in case you think a normal swimming ascent is not going to work, and you may need to be able to ensure buoyancy once you are on the surface. The biggest reason you would want to drop weights on the surface is if you are out of air, have forgotten how to inflate the BCD orally, and are overweighted to the degree that you cannot stay on the surface with an empty tank.

 

[Bob DBF]

Ditching ballast underwater is a lot less scary in concept if you won't be heading to the surface like a ballistic missile...

The ballistic missile surface will involve a BC / drysuit that is not vented, rather than the dropping of weight. They may come together in a panicked diver, however I found that in a 7mm farmer John with an empty BC dropping a belt in 50' of water dropping a belt did nothing. Kicking up and then having the wetsuit increase buoyancy brought me up faster than I like in the last 20', but after spreading out flat to increase drag it probably wasn't any faster than the old ascent rate of 60'/min.

I agree there is little to no purpose to dropping your belt at depth unless you are trying to assist your recovery team postmortem, but it is not the death sentence some seem to imply as long as you keep your head.


Bob

 

[KevinNM]

If something bad is happening and the thought occurs to you "should I drop my weights" I would argue the answer is pretty much always yes, you should.

In the same way, if the question occurs to you "should I call the dive" the answer is pretty much always yes, you should.

 

[stuartv]

If something bad is happening and the thought occurs to you "should I drop my weights" I would argue the answer is pretty much always yes, you should.

"OMG! I'm running out of air. I need to get to the surface! Should I drop my weights?"

And you think the answer is always yes?

 

[Corleone]

as far as I remember, I once came across a site that details diving accidents, like, what was the cause, paramedic/recovery report, sometimes even dive buddy side of story. I traced dive accident up until the 90s. all in all, no one talked about ditchable weight as a factor to survivability nor a contributor to a disaster !!

I do belive its one of those skill that you need to learn but might never ever use!! just like when you practice remove and replace scuba unit underwater!!

 

[John C. Ratliff]

Dropping weights at depth is more probable when breath hold diving than when scuba diving. During breath hold diving, there is the potential for shallow water blackout. Years ago, when I was spearfishing while breath hold diving, we taught a technique of taking our weight belt off and holding it in our hand until we successfully gained the surface without blacking out. I remember actually doing this as a teenager on dives off Thetis Island, Vancouver B.C. when I was somewhere around 60 feet and had over-extended the dive. I made it to the surface, but just barely. The idea is that if we did blackout, we would automatically drop the weight belt.

In my 50+ years of diving, I have dropped my weights only once, and that was on the surface. My buddy and I were diving off the north Oregon coast in December, had vstarted a dive in marginal conditions (5-7 foot waves), felt huge waves start when we were underwater, surfaced and started swimming toward shore when we were rolled by a 15-20 foot wave (it seems to get bigger as I get older). My buddy dropped his while we were being rolled by this wave, and I dropped mine shortly after we had recovered on the surface and knew we would be out a long time. It took our girl friends time to call the Coast Guard, and time for them to get to us. It was nearly nightfall before the sighted us, and we got picked up. Luckily, I was wearing a kayaking helmet, which is what they saw (red helmet with white stripes). They were happy, as they got a "live" pickup, and we were pretty happy too.

One one other I had a Pararescue team in training for entry and exit on a rocky shore (coincidentally the same place as above), when two divers came into view who did not know how to exit not a rocky shoreline in waves, and needed help. This was at Rocky Creek State Park on the Oregon Coast. I removed their weight belts and swam those belt ashore myself while we helped them to exit.

John