Diving Dry? Balance your Rig!

[PfcAJ]

http://archive.rubicon-foundation.org/xmlui/handle/123456789/7962

Abstract for the interested reader. Turns out the manikins were submerged.

 

[RJP]

never mind......

too late...

:d

 

[trpplp]

These things are in the course curriculum so it's safe to bet that with the exception of instructors who are cutting corners, it is taught. There seems to be a glaring issue, though that even though people are made aware of this, taught the skills to do proper weighting and told why it's important, it often doesn't translate into doing it (very well) in practice.

Is that because the risks involved in not doing it aren't stressed enough (too much emphasis on "diving is fun") or is there some other reason like divers not taking it seriously?

R..[/QUOTE]


I am not a tec diver, and I think some of this thread went over my head for that reason. But just a little in-put from a more newbie stand point. I was originally trained during college (what an awesome P.E. elective!!) I love diving!! But I had a whole semester of the basics over and over and over again. We were taken out to the lake and told to make an emergency ascent from 30ft, of course after much practice in the pool. This was a huge eye opener for me. In a 12 ft pool an emergency ascent on one breath is easy, however, it is a lot different from 30ft on one breath (not dumping weight and was achieved). Of course we talked, and practiced in the pool, dumping weight in an emergency. If it's my life or the weight, the weight is going.

I think, and I am definitely not an expert, that a lot of problems are from panic and not recalling what to do. I recently took another certification class with my husband (as a refresher for me but his first experience to diving). Sure they went over the basics in the pool 1 day, and yes there were a lot of things discussed in class, but when you look at the risks and lack of repeated exposure to the basics of what to do in an emergency it was scary. Not to mention how much information they through at you in a couple days and expect you to remember. I agree I think too much emphasis is placed on fun and not on the basics. I am a very busy person and I don't know if I would have the time to take an extend certification class now like I had in college, but I wonder if being able to get certified in a weekend, or a week is really making safe divers. Maybe we should be talking about taking a little more time to train. Even with a semester to work on B.C. I wonder sometimes how to get even better at when my diving comes from the couple major trips we take a year. I will definitely get this book y'all have been talking about! Thanks!!

 

[TSandM]

I think people don't think about this stuff for several reasons. One is that they aren't given a good analytical framework for thinking about their equipment to begin with. Scuba is largely rote teaching . . . we stuff people into gear and don't talk about how it works or what it does very much at all, or about failure modes. Then we teach them a whole roster of behaviors, often without going very much into WHY those behaviors might be necessary to a diver. The end product is not a "thinking diver" but more along the lines of a trained monkey -- as long as the situational problem lies within what someone has been trained to do, they will manage; if it falls outside, they may have significant difficulty.

Proper weighting is mentioned, and we do do weight checks in class. But we don't ask people why proper weighting is important, and we don't give them thought problems as to how improper weighting or BC/suit failures might impact them, and how they might think them through. For one thing, there isn't time, and for another, I'm sad to say that I think a lot of divers really aren't interested in "thought problems". They just want to learn how to "do" this. Unfortunately, particularly with pull dumps on inflator hoses, a complete BC failure is actually a relatively conceivable underwater problem, and really ought to be mentioned and worked through even in beginner classes. It starts with a rig where you can either swim up with no wing air (I can swim up my double 85s when full of Nitrox, so almost anybody ought to be able to swim up a single tank, IF they were weighted right to begin with) or you have weight you can ditch to ensure you get to the surface, even though getting there may not be able to be controlled. You can fix bent, but drowning is harder.

Then you have to think through how you STAY on the surface when you get there. That's where ditching weight is wonderful, because it has no downside other than financial loss.

A flooded dry suit (well and truly flooded) is a bad thing at the surface. My experience with it was that underwater, it was annoying, because my legs sloshed -- but it wasn't until I tried to keep my head out of the water that it got kind of scary. I had lost a good part of 25 pounds or so of lift, and my 32 pound wing was struggling to keep me up. But it managed -- I just wasn't able to float as high as I normally do. I had 20 pounds or so of ditchable weight, if I had needed to let it go, so there was not going to be a drowning (so long as I thought to do it, and it was so long ago, I can't remember if I did).

 

[stevensamler]

A balanced rig is one that, when empty is a near neutral as possible, and when full you can swim to the surface.

We need to be able to swim a FULL rig to the surface without any air in the BC.....at 15ft there should be little to no air in the BC. (ie being properly weighted)

BTW, there has been plenty of talk about ditching weights and why it isn't stressed more......well lets go to this. Why isn't proper weighting taught.....and why aren't people taught that they need to change their weighting in different environments, gear, etc.

I've seen sooooooo many new divers over-weighted its ridiculous.....and no need for it.......that seems like a good starting point for me.


So lets take this one step further.

A 7mm wetsuit will lose about 10lbs of buoyancy in around 70-80ft of water. That is now 10lbs of just dead weight you need to be able to swim up which can be very difficult if you had a complete wing failure at the beginning of a dive......now if you ditch that weight, as you come to the surface, your wetsuit will expand and gain back those lbs of buoyancy essentially turning you into a meat missile as you get close to the surface. Not a desirable situation. A drysuit, IMO is better in this scenario.

If you look at dives where a thinner wetsuit can be used, doesn't compress as much at depth so you don't lose that buoyancy like in the 7mm because you didnt have it in the first place. So if you wear an alu tank that is positively buoyant at the end of the dive, you need a few lbs to offset that. If you dive steel that ends negatively buoyant, you may not need any weight. So now here comes the important part....with the alu, at the very beginning of the dive, if you have an issue, you can drop a weight and away you go....if you have steel then you have no ditchable weight then you MUST be able to swim the entire rig up. In this case, Alu tank may be a better choice unless you have the ability to swim the steel to the surface with no air in the BC.


At the end of the day, if you can swim your rig to the surface with full tanks and all the weight still on you, then your rig is balanced. If its too heavy, you better have enough ditchable weight to make it swimmable to the surface.


For what its worth, I have no ditchable weight on my sidemount rig. I wear a drysuit with undies, and 2 hp100 tanks. I can swim this rig from 100ft to the surface with an empty wing and squeezed drysuit.

If I am diving it in a thin wetsuit, I use only alu tanks....so again, I can swim it to the surface with an empty wing.

I have had wing failures where I needed to be able to do this.




In a drysuit, you should be wearing enough lead that you can descend with an empty suit. Ergo, your net buoyancy should be near 0 (ie drysuit with undies is +7, lead is -7)

Then comes the rig, enough lead, that with a near empty tank, and empty wing, it is neutral.

At this point, you are weighted properly and all the BC needs to do is be able to compensate for the change in buoyancy of gas in the tank from the first of the dive to the end of the dive, and the change in buoyancy of your exposure protection.


If you did all this, you should never have a bc so full that you also need the DS to have air in to to compensate for all weight you have on you. if you do, you are grossly overweighted.

I dive a Scubapro Evertec Trilaminate ds in so cal waters with a lp 95 steel tank it is negative 10 lbs when full and negative 3.5 lbs empty. With undergarments I use 20 lbs of lead , 16lbs are ditchable and to descend I have to empty bc , ds, and exhale until I,m about 5' underwater then use lung volume to control descent. At this point I can add air to ds to offset squeeze, at the end of the dive I can hover in comfort at the safety stop and then use lung volume to slowly surface.

 

[Nwcid]

Ok I will try to give a couple examples (assume a wing failure)
Diving a dry suit with AL80 full of Nitrox and 3 stages full of the same nitrox. Perfectly weighted without stages I will be overweight by the weight of gas - about 10-12 lbs , with the stages it will be another 15 lb of gas. And will be another 12-15 lb negative so in total it is about 25-27 lb negative and there is no way I can swim it up. Does it mean Im not balanced? No Im balanced because I can ditch the stages and swim 10-12 lb to the surface. ( I tested this)

Now another example is diving a set of HP130 full of Nitrox with no ditchable weight would be unbalanced as it will be about 20lb of gas in them and it is hard to swim that up unless you are an athlete. Now if the configuration of you rig is that it allows you to have some of uour weight ditchable while being properly weighted, say 8 lb, you can ditch those 6 lb an that will make it more managable.

Or if you dive the same HP130 set with 18/45 in them instead of nitrox plus 5 stages and deco tanks it will also be balanced because the gas in doubles will weight around the same 12 lb and you can ditch the stages and deco bottles.


Of cause we then come to a question about whether we have any deco obligations and such but then you have to an further and prioritize. Carry backup lift bag etc.
Of cause you can remove the whole rig always but I do not think it is a good idea if you dive dry an do it at 150 ft.

I guess I am confused. How do you have an AL80 that is -10-12lbs? All the charts I have seen the average AL-80 is only -1.8lb when full. According to this chart, Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan there is on as heavy as -5.9lbs.

Even my HP-130's are only -10.5lb.

In a pool when we are doing some of our training dives I am only wearing shorts. I will either be using my HP-130 single, or my LP-72 doubles (about -5.4lb each full) with a steel back plate (-6) and I sink like a rock. Again no problem swimming either up and I am far from and athlete.

 

[gcarter]

I guess I am confused. How do you have an AL80 that is -10-12lbs? All the charts I have seen the average AL-80 is only -1.8lb when full. According to this chart, Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan there is on as heavy as -5.9lbs.

Even my HP-130's are only -10.5lb.

In a pool when we are doing some of our training dives I am only wearing shorts. I will either be using my HP-130 single, or my LP-72 doubles (about -5.4lb each full) with a steel back plate (-6) and I sink like a rock. Again no problem swimming either up and I am far from and athlete.

I think you are mis-reading what he wrote. I read it as that is the weight of the gas in his bottles. That is independent of the type of bottle used or its own inherent buoyancy characteristics.

 

[Nwcid]

I think you are mis-reading what he wrote. I read it as that is the weight of the gas in his bottles. That is independent of the type of bottle used or its own inherent buoyancy characteristics.

But he is still using that amount of weight to say he is -25-27lb in the water. No matter the weight of the gas or the gear what matters is buoyancy. An aircraft carrier weighs 100,000 tons and it is still positively buoyant.

 

[gcarter]

But he is still using that amount of weight to say he is -25-27lb in the water. No matter the weight of the gas or the gear what matters is buoyancy. An aircraft carrier weighs 100,000 tons and it is still positively buoyant.

Because the gas is used in the course of the dive, you need to carry weight to compensate for its loss by the end of the dive in order to avoid being underweighted and risk an uncontrolled ascent. You SHOULD be overweight by the weight of your gas at the start of the dive, and you need buoyancy capacity to allow for this. That is what he is talking about, and what he would need to deal with if he lost buoyancy.

The larger number included stage bottles (10-12 back gas + 15 in stages). Again, though, it has nothing to do with the type of bottle used.

 

[Nwcid]

Because the gas is used in the course of the dive, you need to carry weight to compensate for its loss by the end of the dive in order to avoid being underweighted and risk an uncontrolled ascent. You SHOULD be overweight by the weight of your gas at the start of the dive, and you need buoyancy capacity to allow for this. That is what he is talking about, and what he would need to deal with if he lost buoyancy.

The larger number included stage bottles (10-12 back gas + 15 in stages). Again, though, it has nothing to do with the type of bottle used.

Correct, but it is still NOT the weight that matters. It is the buoyancy. Again take the standard AL-80 it is -1.8lb when full, and +4lb, in buoyancy when at 500 psi. That is a total swing just under 6lbs. On this site, http://www.instructables.com/answers/how-much-does-air-weigh/ air weighs 0.085lb/cf. So 80cf (I know it is really 77) x 0.0855 = 6.84lbs of air, NOT 10-12lb still. My HP-130 = 11.11lbs of air.

So in the OP's example at the start of the dive, IF he is using a standard AL-80 he should be "overweight by his gas" as you state by 4lbs to make up for change in BUOYANCY. The AL80 even empty still weighs about 34lb with valve. So it has EVERYTHING to do with the type of tanks used because you need to know the buoyancy swing.

I understand the weight swing, the numbers he gave just do not make sense.