Let's talk about balanced rigs

[rstofer]

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.

I was going to make this point yesterday but the thread soon ran beyond my comfort level. For an absolute certainty, a tank with 8# of air and a loss of buoyancy in the wetsuit of, say, 20# leaves the diver 28# negative at depth. I KNOW I can't swim that much off the bottom.

I can open my weight pockets and dump weight in 5# blocks. Leaving 10# behind early in the dive wouldn't be a problem. I still have the majority of 8# of air. The net effect is I am 2# more buoyant at the surface but my wetsuit won't decompress that fast anyway. I shouldn't rocket.

I MIGHT be able to swim 18# off the bottom. I only need to go up a short way before the wetsuit becomes more buoyant. Maybe not what it was on the way down but more than it was at depth. Besides, I am consuming the air.

When I reach the surface, I will probably still be negative because a) there is still a lot of air in the tank and b) the wetsuit hasn't decompressed. Now is the time to ditch the rest of the weight.

I think the wing failure is survivable. At the moment, I am diving with my grandson and we are limiting the depth to 30' or so. That's fine with me! I've been down there and I have the pictures. I'm in no hurry to go back.

All of the above based on single tank recreational dives with a 7/8mm wetsuit and an HP100 tank.

Richard

 

[Diver0001]

There is a thread raging that involves a diver who dropped to the bottom after the failure of a BC hose. Since he chose to drop some weight to make an ascent he is immediately pronounced over weighted. Nowhere in the posts is it said what he was wearing for a suit. The message is that any diver should be able to swim up from the bottom.

((I'll read the rest of the posts in a minute. Please forgive me if I'm repeating))

Well, actually I'm going to get picky with you but first I'd like to thank you for starting this thread. This is bound to be a good one.

In the other thread he said he was wearing a 5mm wetsuit with a HP100 steel tank and 24lbs of weight. He also said that he was unable to swim it up from depth and decided to dump his weights because of that. He also seemed to indicate that he did not make an uncontrolled buoyant ascent after he dumped his weights so that lead a lot of people, including myself, to doubt if he needed the 24lbs he had. Please review the thread. These are the facts.

...snip...

So with the compression of cold water exposure protection at what point will the balanced rig directive break? I'm looking for the input of cold water divers who have been down this road.

Pete

I'm a cold water diver with experience in wetsuits (100 dives), crushed neoprene drysuits (700 dives) and trilam drysuits (700 dives----give or take). In my experience, a 7mm or 7/5 wetsuit or a neoprene drysuit, will start to feel heavy at depths 20metres or deeper with the drysuits being the worst of the two. At 40-odd metres, a crushed neoprene drysuit is very negative and (according to a friend of mine who has actually tried this... I haven't) at least one brand of crushed neoprene drysuit "suddenly" collapses and loses several kg of buoyancy at about 70-75 metres.

Trilam suits have none of these issues.

But here's a question for clarification. *What* is actually meant by "balanced rig"? Are we all talking about the same thing? What do you mean by that?

R..

P.S.
The exchange between Doc I and Jeff is one of the best I've read in months! Jeff, it's nice to see you posting something worth reading! I was really starting to think that you had been reduced to lobbing sarcasm grenades instead of contibuting content. I hope to see more of this.

R..

 

[rstofer]

Another idea for the wetsuit divers: Tobin at Deep Sea Supply suggests a different scheme for setting initial buoyancy. Start at the surface with a FULL tank. an empty wing and adjust the weights to be eyeball level.

By definition, you just removed 8# of lead because you no longer account for 8# of air in the HP 100.

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.

There is also the problem that you have to swim down the first several feet. One approach is to kick UP and try to bounce down.

Since you started out 8# more positive at the surface (compared to traditional weighting), you are 8# less negative at depth. Still, at the beginning of the dive the wetsuit could lose 20# of buoyancy but that's better than 28# when we have to include the air.

Richard

 

[JeffG]

Another idea for the wetsuit divers: Tobin at Deep Sea Supply suggests a different scheme for setting initial buoyancy. Start at the surface with a FULL tank. an empty wing and adjust the weights to be eyeball level.

By definition, you just removed 8# of lead because you no longer account for 8# of air in the HP 100.

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.

There is also the problem that you have to swim down the first several feet. One approach is to kick UP and try to bounce down.

Since you started out 8# more positive at the surface (compared to traditional weighting), you are 8# less negative at depth. Still, at the beginning of the dive the wetsuit could lose 20# of buoyancy but that's better than 28# when we have to include the air.

Richard

I would consider that bad advice.

at the end of a dive (when you have the most nitrogen saturation), is when I want the most control, not the least.

 

[JeffG]

The exchange between Doc I and Jeff is one of the best I've read in months! Jeff, it's nice to see you posting something worth reading! I was really starting to think that you had been reduced to lobbing sarcasm grenades instead of contibuting content. I hope to see more of this.

R..

The sarcasm grenades are easier to type and funnier to read though.

 

[Cave Diver]

The sarcasm grenades are easier to type and funnier to read though.

 

[Bismark]

I would consider that bad advice.

at the end of a dive (when you have the most nitrogen saturation), is when I want the most control, not the least.

Ditto.

Even worse in a dive where you have upwards of 30 minutes of 02 deco left.........

Hope your boat has DAN on Speed dial.

 

[Diver0001]

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..

 

[maged_mmh]

.....
In answer to the original question -- steel tanks and thick wetsuits can make a pernicious combination...

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

me ain't skierd

 

[Bismark]

My setup is close to yours.

Here are the differences.

I did the dive with an al40 of 50%

My Backplate is an Al plate with a tail weight and a 6lb belt.

So, I am not as heavy due to the minor change in the 50% bottle and I have 6lbs of low cost ditchable weight.

So I would drop my belt as a first resort. If I couldn't cheat my drysuit into carrying the load (which would be approx 16-20lbs using your numbers) I would start handing my bottles to my buddy...until I could (carry the load).

Yep, Works for me. We do the same thing sometimes, especially if the environment makes it more likely we might have some issues. 6lb plate and a 6lb belt. We normally do the 200' stuff with AL 40 also, unless we just need more gas. I watched someone hand a AL 80 stage with reg to the RIB dude in the Red Sea. As Maxwell Smart would say "Missed it by that much"...............over about 400' of water at that point. Bye bye stage bottle......