"Safe" weight distribution? Weight ditching question.

[boulderjohn]

know it's not a high-probability scenario, but what if the drysuit floods?

The first time I ever did a hot drop on a wreck, I realized I had left a tiny gap at the end of the zipper of my dry suit. (On a hot drop, the boat calculates the current, positions itself, and tells you to begin your dive. If you swim downward at full speed, you should hit the target. There is no time to stop on the surface and make a suit adjustment.) I did the dive, deco and all, water slowly entering the suit the whole time. It warmed up enough during the dive for me to be reasonably comfortable. When I got onto the boat, my legs looked like elephant legs. I had no trouble maintaining buoyancy throughout the dive.

 

[rick00001967]

Not being able to swim to the surface without dropping weights in case of loss of buoyancy means you are overweighted

example:
lets say you were diving a tank holding aprox 6lbs of gas weight. if you are weighted to be neutral with low or empty tanks, this means you should be aprox 6 lbs "over weighted" at the start of the dive.
lets also say that you are in a 7mm wet suit. perhaps even a double layer 7mm suit with hood and gloves. i dont pretend to know exact numbers but would it be safe to assume you could easily loose 10 to 15 lbs of buoyancy at maybe 100 to 130 feet from the compression of the neoprene ? i have been told you can loose up to 25 lbs depending on the actual total thickness of the suit worn and the actual depth of the dive.
but if we use 10 to 15 lbs as an example, that means combined with you being 6 lbs "overweighted" at the start of the dive, you will be at least 16 to 21 lbs "over weighted" at the bottom.
now what if your wing fails ? can you swim to the surface, while exhaling, from 100 to 130 feet, without passing out, and can you stay afloat once you get there ?

we know most people will now say.......thats why you use a drysuit, thats why you have a wing with a redundant bladder, thats why you carry a lift bag etc etc all valid points. but my example simply illustrates that in some cases, your statement may not be completely true. an average recreational sport diver is probably not aware of this info.

i agree with many of points made about balanced rigs, proper weighting, the different considerations if deco diving etc. but if we are talking about the vast majority of people who dive only for fun,not on a regular basis, and may not be in peak physical condition, would it not be better for them to have the option to, and be taught how to get rid of at least some of their lead either at depth or at the surface if that truly was what they consider to be their last resort??

 

[The Chairman]

The thing is that I use a back inflate bc and in order for it to be properly adjusted to allow me to float vertically at the surface

You don't distribute your weight to be "vertical" on the surface. You distribute weight to be horizontal at depth. If you're being pushed forward on the surface, then you're simply inflating your BC too much. How much lift does your back inflate BC have? This is especially true with a steel tank, which is easier to float on your back with.

 

[tursiops]

but if we use 10 to 15 lbs as an example, that means combined with you being 6 lbs "overweighted" at the start of the dive, you will be at least 16 to 21 lbs "over weighted" at the bottom.
now what if your wing fails ? can you swim to the surface, while exhaling, from 100 to 130 feet, without passing out, and can you stay afloat once you get there ?

It's not quite as bad as you make it out to be. When you get to the surface your suit has expanded again, and that helps you all the way up, too.

 

[dmaziuk]

...in some cases, your statement may not be completely true. an average recreational sport diver is probably not aware of this info.

Then it's a dive that average diver is not qualified/trained to do.
Nobody can stop someone from darwinating themselves if they're dead set on doing that. This does tie in very nicely into the threads about requiring "Advanced" certs and medical clearances and all, but at the end of the day you can't overcome stupid.

 

[Mustard Dave]

I am a firm advocate of non-ditchable weight, however, it is essential that your weighting is perfect before adopting this configuration.

 

[boulderjohn]

A lot of people ara overweighted because they truly do not understand weighting and buoyancy, and they consequently make bad decisions about their weights. I am specifically referring to people who have successfully descended and then find that during the dive they they keep tending to go toward the surface. They end up dumping air to get back down, swimming, rising up, dumping air to get down, rising up, etc. They draw the conclusion that they need more weight. They dive again and the problem is even worse, so they add even more weight. Their strategy of adding weight is exactly wrong.

If they have enough weight to descend and dive, then they have enough weight for the dive, at least at that point. Every pound of lead they add beyond the bare minimum needed requires about 15 fluid ounces (nearly a pint) of air volume to compensate. Many divers are at least 12 pounds overweighted. That means they must have the equivalent of 6 quarts of air in the BCD to become neutrally buoyant. All of that excess air reacts to even minor changes in depth by expanding or contracting. It makes maintaining buoyancy, especially in shallow water, a real problem. Adding more weight makes it even worse.

Even people who should know better are fooled by this. You will see DMs hand more lead to people who are already overweighted and struggling with buoyancy as a result. In a very famous case of (going from memory here) coast guard divers diving during a rest break in dry suits, the senior diver had had the problem I just described on an earlier dive, and so she wore an ungodly amount of weight, and she told the less experienced divers to do the same thing. None of them survived.

 

[Professor Nemo]

You don't distribute your weight to be "vertical" on the surface. You distribute weight to be horizontal at depth. If you're being pushed forward on the surface, then you're simply inflating your BC too much. How much lift does your back inflate BC have? This is especially true with a steel tank, which is easier to float on your back with.

My lift is rated a 50lbs. However, I do not enter the water with but fully inflated.

 

[Rred]

John-
I don't think our doff-n-don was aimed at encouraging penetration diving. But as you may remember, before 1990(?) a wreck was a wreck, not a curated underwater theme park. If you went in through a perfectly wide space, you couldn't be certain that the fire doors or hatches had been welded open (you knew they hadn't been) and you couldn't be sure something might collapse, obstructing your exit.
So learning how to doff and don was just aimed at "How the **** am I going to get out of here?" more than anything else.

In today's curated wrecks it could just as easily be that someone finned up a dirtstorm, created zero vis, and someone else wound up someplace else and in need of a different way up and out. How to "get unstuck" and back to the surface should still be part of the normal training for independent divers. Especially since ditching gear can be so useful in varying situations.

 

[Cr.padlo]

Whatever configuration works for you. I personally prefer to have some ditch able weight just for the sake of an emergency where dropping weight might be useful. One of my buddies dives a backplate and has half of her weight on the plate and several pounds centered in a weight belt in the small of her back. Its entirely up to you on whats confortable and how important it is to you to be able to ditch weights if needed.