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[ucfdiver]

When I see incorrect ramblings like this, it makes me miss Lamont

In a DIR context, the above statement is incorrect. Here's why.

the issue is serious for any diving below about 30ft because of the amount of buoyancy the wetsuit loses, has absolutely nothing to do with warmth in a DIR context. You try to dive a balanced rig, you choose to dive wet which is a problem with steel bottles because it is difficult to get to a balanced rig with said bottles because now none of you weight is ditchable in the event of a wing failure and you have the potential to be very negative at the bottom to the point that you can't kick the rig to the surface. This is bad.

In a DIR context, if you're diving big steel doubles you NEED to have redundant buoyancy, whether from a drysuit, or lift bag. I'm not familiar enough with euro style cylinders, but your twinset is already offsetting about 9kg/19lbs of lead with them empty. This is not factoring in the bands, manifold, first stages, which are easily another 3kg, so you're really at 12kg/26lbs. This is with empty tanks. You mention 2kg are on drop weights, so if you feel that you can kick 10kg/22lbs of weight up from the bottom when your wing fails, then fine. I can barely do it, and it requires a LOT of effort including continuous effort at the surface. If you feel that you can safely do that, then fine. This is not including air in the cylinders, which is going to be another 7kg/16lbs if they are twin 100's which are about as small as bottles realistically get. So now you have a worst case scenario of a wing failure at depth, you ditch your drop weights, and have to swim 17kg/38lbs up to the surface. I don't know a single person that can do that and I've worked with Navy EOD divers and SEAL's, and USCG Rescue Swimmers. I don't know a single one of them that can maintain 38lbs of thrust out of their legs, some can give it in a burst, but not maintain it.

Situation above is your situation, this scenario if you choose to dive wet will require a 25kg/50lb lift bag minimum to be safe *this is not "DIR" because it still points to an unbalanced rig*. If you dive dry, you have constant buoyancy, so at depth in a suit failure you'd still have the wing, though for a drysuit to hold 0 air is quite difficult, and in a wing failure, you would at least have the drysuit offsetting a significant amount of weight with the ability to realistically take on the rest of the weight from the wing in an emergency. It will be unwieldy, but you'll get to the surface. Now, if you were diving aluminums in this case, you'd have a total of 7kg/15lbs required of extra ditchable weight from your current scenario, less the 3kg from your bottles, so net extra 4kg. So now you're at 16kg total ballast, but 9kg of it is ditchable, so now instead of having to swim up to the 12kg best case scenario, you now only have to swim up 7kg/15lbs. Many agencies require students in a bathing suit to acquire a 10lb diving brick and keep it at the surface, so 15lbs with fins is easy. This is why to dive steel bottles you need redundant buoyancy, easiest form is a drysuit. Sometimes you have to work around if you're diving in warm water, drysuits aren't accessible for whatever reason but you need the gas volume, in that case you have to carry a lift bag if you're adamant about using a wetsuit with those tanks.

 

[TSandM]

The numbers seem a little suspect (19 pounds negative for two empty tanks?) but the principles are sound DIR ideas, no?

 

[tbone1004]

The 19lbs was based off of the numbers the OP quoted.

I screwed up on the redundant buoyancy vs balanced rig, but the underlying reason of balanced rig with al80's vs the drysuit maintaining buoyancy regardless of depth is the reason the recommendation is there. Surprised you flipped out on the mention of redundant buoyancy vs the first post advocating it based on thermal comfort.... I edited it. That said, there is conflicting information from Halcyon and GUE which was cause for my confusion.

from gue equipment configuration page
21. Alternate Lift Device: Lift bag, diver alert marker, or surface life raft, for open water diving. Halcyon's MC system allows for storage in backplate pack for increased streamlining.

From Halcyons website
Halcyon Closed-Circuit lift bags provide the most reliable source of redundant buoyancy at depth or on the surface;

 

[PfcAJ]

Halcyon is a gear company and not a training agency.

Pls go take a class.

 

[TSandM]

When I took Fundies, a bag was discussed as an option for redundant buoyancy if diving wet. However, the conclusion was that, in general, steels don't go with wetsuits, and deep diving doesn't go with wetsuits, either. But if you are going to dive wet with doubles, you should have ditchable weight or be able to swim up the rig. Most people don't test it.

I think most people recognize that, if you had a total wing failure with full tanks, trying to get a bag out and shoot it while you are plummeting to depth is not a very good answer. It was, however, discussed in my class, so, even if the teaching has changed (and I don't remember going over balanced rigs when I just redid Fundies) it was at least at one time part of the curriculum.

 

[PfcAJ]

There's tons of potential discussion points in class. Discussing it and advocating it are different things. DIR is a framework, and lift bags for redundant buoyancy aren't part of that framework.

We we discussed lean left and rich right in my tech 2 class briefly. It's still not an option for dir diving.

 

[ucfdiver]

The 19lbs was based off of the numbers the OP quoted.

I screwed up on the redundant buoyancy vs balanced rig, but the underlying reason of balanced rig with al80's vs the drysuit maintaining buoyancy regardless of depth is the reason the recommendation is there. Surprised you flipped out on the mention of redundant buoyancy vs the first post advocating it based on thermal comfort.... I edited it. That said, there is conflicting information from Halcyon and GUE which was cause for my confusion.

from gue equipment configuration page
21. Alternate Lift Device: Lift bag, diver alert marker, or surface life raft, for open water diving. Halcyon's MC system allows for storage in backplate pack for increased streamlining.

From Halcyons website
Halcyon Closed-Circuit lift bags provide the most reliable source of redundant buoyancy at depth or on the surface;

Halcyon sold CCR wings years before GUE considered it.

Using a lift bag for secondary lift was never once mentioned as a DIR solution in my Fundies class.

 

[MXGratefulDiver]

Using a lift bag for secondary lift was never once mentioned as a DIR solution in my Fundies class.

It was in mine ... but that was 10 years ago ...

... Bob (Grateful Diver)

 

[LiteHedded]

It was in mine ... but that was 10 years ago ...

... Bob (Grateful Diver)

showing up to fundies or tech 1 with wetsuit and steel doubles and a liftbag will result in an interesting chat I'm sure.
might be worth doing for a giggle

 

[danvolker]

When I took Fundies, a bag was discussed as an option for redundant buoyancy if diving wet. However, the conclusion was that, in general, steels don't go with wetsuits, and deep diving doesn't go with wetsuits, either. But if you are going to dive wet with doubles, you should have ditchable weight or be able to swim up the rig. Most people don't test it.

I think most people recognize that, if you had a total wing failure with full tanks, trying to get a bag out and shoot it while you are plummeting to depth is not a very good answer. It was, however, discussed in my class, so, even if the teaching has changed (and I don't remember going over balanced rigs when I just redid Fundies) it was at least at one time part of the curriculum.

Lynne, I think this is a huge point the "redundant lift crowd" dont really consider.
If they actually needed 40 or more pounds of lift to be neutral, and suddenly lost the lift of the wing --they would in all liklihood fail to even slow their descent if not ALREADY standing on the bottom. If plummeting, they would have huge task loading issues for the deployment of a lift bag, and may even experience ear clearing pain and damage , which would serve to even worsen the task loading of the deployment. And then there is the risk of the lift bag getting away from them after it becomes positive and begins heading upward---they lose the bag, if they can't hang on to it....how many have the bag clipped to them so that if they let go of it, it could not escape them?

At least with wetsuit and double 80's, you can easily swim the rig to the surface with no wing whatsoever. There can be no uncontrollable plummeting.

I dont know why some divers have such a desire to use heavy steel tanks....when the 80 al works so much better, and is so inexpensive.