Let's talk about balanced rigs

[Bismark]

I know that this thread started out with some less than 200' tech dive questions, however, the principles are essentially the same. If we can work out and understand how a fully bombed out tech diver can accomplish this, then it becomes easier to understand it on a more simple gear configuration. The very fact that we at least talk about this and work it out puts us in the less than 1% minority.............

Interesting thread.

 

[Cave Diver]

LOL

It's sad to see people writing Jeff off though. He's an awful lot smarter than some of his posts make him look.

R..

If only his power could be harnessed for good instead of evil!

This has been a pretty good discussion and I think it's cleared a lot of things up for some people.

 

[JeffG]

I like that.

 

[Gombessa]

You will be positive at the end of the dive (if you consumed the air) and making the safety stop is based on the idea that a wetsuit doesn't decompress very quickly. You are counting on the difference in wetsuit buoyancy to overcome the change in tank buoyancy and allow a safety stop.

I think more pertinent is the fact that at 15ft depth, you're at roughly 1.5x the pressure at the surface, so your wetsuit won't fully decompressed at all, regardless of the speed at which it recovers buoyancy. In a thick suit, that can easily account for most of the weight of the expended air in an 80-100cf tank (I don't think I'd want to do this for a much larger tank though). Add to that the fact that most people can control ~6lb of lift though lung volume, and you should be able to hold 15ft even if the wetsuit decompresses to ambient instantaneously.

 

[rstofer]

I think more pertinent is the fact that at 15ft depth, you're at roughly 1.5x the pressure at the surface, so your wetsuit won't fully decompressed at all, regardless of the speed at which it recovers buoyancy. In a thick suit, that can easily account for most of the weight of the expended air in an 80-100cf tank (I don't think I'd want to do this for a much larger tank though). Add to that the fact that most people can control ~6lb of lift though lung volume, and you should be able to hold 15ft even if the wetsuit decompresses to ambient instantaneously.

That's the theory as it was explained to me. I'm pretty sure it will work but I haven't tried it yet. As I pointed out, I am staying pretty shallow for the foreseeable future.

I have tried removing 4# by using a 2# SS travel plate in lieu of a 6# DSS plate and I did have to swim down a ways but my wetsuit compressed in a very few feet so I'm pretty sure the scheme works as described.

Richard

 

[denniscloutier]

It fascinates me how this thread has morphed from a question that arose from a recreational, single tank dive, into what one does with scooters and multiple deco bottles.

In answer to the original question -- steel tanks and thick wetsuits can make a pernicious combination. This was one of the examples we worked through in Fundies, that made me look at the instructor and think, "Wow, these guys have really thought things through." What works at the surface is a whole different animal at 100 feet, where a thick wetsuit can lose a large percentage of its original buoyancy. Then you are at depth with a large, negative tank, and you're 20 lbs more negative than you were at the surface, due to neoprene compression. At that point, you either need some kind of redundant buoyancy (and a 6 lb SMB may not be enough) or you need weight you can jettison (recognizing that discarding it may make it quite difficult to control the later portions of your ascent).

This is why the DIR recommendation is not to dive deep in cold water in a wetsuit. It's hard to make it work.

But, if your drysuit is punctured, then you instantly lose whatever buoyancy it provides. So, how is a drysuit better than a wetsuit? By the way, this is an honest question. I consider myself a newbie, so I'm finding this a very interesting thread.

 

[Slonda828]

I think more pertinent is the fact that at 15ft depth, you're at roughly 1.5x the pressure at the surface, so your wetsuit won't fully decompressed at all, regardless of the speed at which it recovers buoyancy. In a thick suit, that can easily account for most of the weight of the expended air in an 80-100cf tank (I don't think I'd want to do this for a much larger tank though). Add to that the fact that most people can control ~6lb of lift though lung volume, and you should be able to hold 15ft even if the wetsuit decompresses to ambient instantaneously.

I know some of you may not like this, but that's mostly how I dive wet as well. I usually dive an al80, and many of my dives are in full vintage gear (no BC). I just do my buoyancy check with a full tank and use my wetsuit compression to offset for the gas consumed.

A couple of points on this:

-I know it's not DIR, and I'm not saying it should be. You boys and girls have your SOPs, and I respect that.

-I wouldn't do it with a steel tank. I do it with a 3mm and a AL80. I can lung over 4 lbs anyway so it's a non-issue for me.

-I'm not saying this approach works for everyone. I've been diving vintage gear long enough that I really know how to weight myself. It is not for everyone.

-I only dive NDL dive in this fashion. I wouldn't do it if coming up meant calling DAN.

 

[Cave Diver]

But, if your drysuit is punctured, then you instantly lose whatever buoyancy it provides. So, how is a drysuit better than a wetsuit? By the way, this is an honest question. I consider myself a newbie, so I'm finding this a very interesting thread.

A drysuit is a huge bag full of air. Due to the size of it, there would be plenty of places to move air to where it could be trapped to provide lift.

 

[Gombessa]

I know some of you may not like this, but that's mostly how I dive wet as well. I usually dive an al80, and many of my dives are in full vintage gear (no BC). I just do my buoyancy check with a full tank and use my wetsuit compression to offset for the gas consumed.

A couple of points on this:

-I know it's not DIR, and I'm not saying it should be. You boys and girls have your SOPs, and I respect that.

-I wouldn't do it with a steel tank. I do it with a 3mm and a AL80. I can lung over 4 lbs anyway so it's a non-issue for me.

I'm not sure I understand what you're saying. Vintage gear or not, if you're properly weighted, you're properly weighted. What's not DIR about being neutral at the safety stop at the end of your dive?

Also, plenty of DIR divers will monkey dive without a BC in tropical waters. UTD also teaches a no-BC "zero buoyancy" class (Zero Buoyancy Diving - Unified Team Diving).

I think you're reading something into DIR that doesn't actually apply.

 

[Gombessa]

But, if your drysuit is punctured, then you instantly lose whatever buoyancy it provides. So, how is a drysuit better than a wetsuit? By the way, this is an honest question. I consider myself a newbie, so I'm finding this a very interesting thread.

First off, it takes quite a long time to completely flood a suit. I bet most drysuits have some kind of puncture in them. Even small tears don't immediately flood the entire suit, though it will certainly feel like it. A complete and catastrophic failure which eliminates all the buoyancy of a drysuit is pretty rare. But let's assume that happens.

The point then is "redundancy." Wing + drysuit gives you an extra source of buoyancy in the event of failure in one. If your drysuit fails, you can still inflate your wing. If your wing fails, you can still inflate your drysuit.

With a wetsuit, all you have is a wing (unless you go with two wings, a double-bladder wing, a big smb/lift bag, etc., but that's a different thread). You lose the wing at depth (to that same puncture you described for a drysuit) and you're very negative with nothing but ditchable weight and your leg muscles to help you out.