Tech Wreck - Opinions on staging your deco tanks for penetration?

[boulderjohn]

Having moved to sidemount, the issue of passing restrictions becomes a lot more flexible. This increased capacity to venture into smaller areas is one of the reasons why I am re-visiting my own perspectives on the staging of deco tanks. I now have the option to move more freely around inside a wreck - and carrying more than 2 cylinders during that phase of the dive would somewhat defeat the goals I am attempting to achieve.
John, what do you identify as the big risk inherent with removing/replacing equipment in order to pass through a restriction? Obviously, the description of John's penetration in Shadow Divers is pretty extreme..mainly because of the visibility issue on return through the restriction. Increased risk of entanglement, sounds the worse issue to me.

Have been looking at options for this - including the use of micro-sidemount or no-mount single cylinder, in addition to back-mounted doubles.... as a solution to pre-determined goals on a planned and rehearsed dive. The concept of a rig-under-a-rig... lightweight harness (little/no buoyancy), with a suitably sized cylinder/s worn underneath the primary rig. Reach the restriction, remove the primary rig.. continue onwards with the 'secondary' rig. Deco cylinders left at the primary tie-off. Basically, peeling away layers of an onion through progressive stages of penetration - and re-donning those layers upon egress. Obviously, this relies upon returning upon the inwards route (same risk as cave diving) and involves complicated gas management/planning issues. Crazy talk?

All hypothetical at this point - because sidemount config has answered most questions, and has opened up sufficient options for access in all cases thus far. At most, I might remove a single sidemount cylinder and progress with one only... my body size being the main restrain on the spaces I could pass through. Removing the sidemount rig itself and going onto a 'no-mount' with smaller cylinder (i.e. 'British style cave mounting olde style') would only gain me an 1" or so...

Here you go beyond my training and experience, and I cannot make a meaningful response.

 

[waterpirate]

Sorry I bugged out yesterday, I had to do yardwork PT. Once the distinction has been made of a " tech only trip" the rules change a little bit, and when you get to "exploration/expedition level diving" all bets are off.

Here there are no guided dives, period. So the al80 crowd is left to their own devices and it makes for some bad desicion makeing on their part.
Eric

 

[Dive Bug Bit Me]

Sorry for disappearing last night as well. Wanted to watch the Chelsea / Bayern game. Anyway, I've had a day to process my thoughts. While I've set out what I prefer to do, the reality is that each situation is different. Most times, I do X but sometimes Y.

I guess that the most important tech diving equipment is your brain. All that knowledge can do is show you the advantages and disadvantages to a specific approach. It's for the diver to reason out the situation he is faced with.

 

[TSandM]

Although it doesn't directly relate to the original question, I'm surprised at the negativity here to running external lines. For our wreck dives in Lake Washington, we drop a shot, and try NOT to hit the wreck (they're airplanes, and fragile). The viz in the lake is often so bad that, if the line is two feet off the wreck, you won't see it, so we not infrequently run search patterns with a spool or reel, and leave it tied off to the wreck, so we can get back to the shot line. I don't understand what is undesirable about that.

 

[DevonDiver]

Although it doesn't directly relate to the original question, I'm surprised at the negativity here to running external lines. For our wreck dives in Lake Washington, we drop a shot, and try NOT to hit the wreck (they're airplanes, and fragile). The viz in the lake is often so bad that, if the line is two feet off the wreck, you won't see it, so we not infrequently run search patterns with a spool or reel, and leave it tied off to the wreck, so we can get back to the shot line. I don't understand what is undesirable about that.

That use of a guideline (between shot and wreck) must be pretty common?

As in...



What I've not heard used is a guideline running 'over' the wreck - to link potential entry/exit points and the shot-line. It could also be the baseline from which individual penetration lines are run... and where deco stages are stowed for penetration.

(thinking specifically of the 'Rouse Scenario' here).

 

[waterpirate]

I think in the absence of helium no little string would have changed anything, but that is only a guess. The report was that they both were so overdue that they were in flight mode, and potentially swam right over their stages. That is conjecture. What was said is that they blew past other divers on the line that could have rendered aid.
It was tragic, but I think that the lack of helium continued the cascade of failures including poor decision makeing, while potentially still impaired and in full flight mode.


I do not think that anything negative has been said about exterior line running, and I feel as tough Lynns example is beyond the al80 crowd based on low to no vis, ergo only people willing to dive in those conditions are on the dive, and running line certainly seems prudent.

I love to tell the story of my brail dive on the northern pacific in 140fsw. I attempted to count the links in the tie in chain beyond the first clevice and ran face first into the wreck.lol Not enjoying that sort of fun I quickly returned and the pool was open for cave certed people only, who also did abreviated bottom times as well.

Up here being capable of natural navigation is a prerequsite and a skill taught in AOW for anyone diving local.
Eric

 

[DevonDiver]

Up here being capable of natural navigation is a prerequsite and a skill taught in AOW for anyone diving local.

That seems at odds with the reluctance of many experienced divers in this thread/poll, who wouldn't stage deco tanks, for fear of being unable to return to them.

Assuming that we're talking about staging tanks externally on the wreck (at primary tie-off or at the shot line), and assuming no interference with those tanks... then the primary fear seems to be an issue of navigational confidence, when balanced against the severe repercussions of not recovering deco tanks for ascent.

An AOW diver may be 'confident' in their nav... but they're not placing the same level of life-preserving dependence on their nav skills as a technical wreck diver would.

 

[boulderjohn]

Assuming that we're talking about staging tanks externally on the wreck (at primary tie-off or at the shot line), and assuming no interference with those tanks... then the primary fear seems to be an issue of navigational confidence, when balanced against the severe repercussions of not recovering deco tanks for ascent.

I don't think the reluctance has anything to do with navigational confidence. I think it has everything to do with a recognition that something can happen during a dive that can prevent you from returning to your starting point. If something like that happens and you have to ascend away from your planned ascent point, it is nice to have your gas with you.

 

[BabyDuck]

this is theoretical on my part and i totally admit that & might change my mind if i get more 'real' wreck experience.

but my thought about keeping my gas isn't really because of fear of navigational shakiness. it's more that i might choose to come out another hole instead of doing an out and back. planning an out & back with a tech-only boat? i'd be much more likely to leave the gas.

 

[DevonDiver]

this is theoretical on my part and i totally admit that & might change my mind if i get more 'real' wreck experience.

but my thought about keeping my gas isn't really because of fear of navigational shakiness. it's more that i might choose to come out another hole instead of doing an out and back. planning an out & back with a tech-only boat? i'd be much more likely to leave the gas.

Let's assume nothing else goes wrong, except a deviation to exit from the wreck (not out-and-back/linear penetration). What stops the diver returning to their original entry point and collected the staged tanks from there?

1. Gas. We gas plan for such contingencies, so that shouldn't be the issue, except in the most dire of scenarios.

2. Bottom Time. In this case, the rational (tech) diver makes a decision between retrieving their deco tanks (and potentially over-staying at depth) or immediately ascending without deco. Again, any prudent technical (wreck) diver will have (I hope) balanced that contingency before entering the water. Quite often, the decision to exit via an alternative route may be quicker than returning via the original (no line recovery needed, for a start). So, what were really talking about here isn't a deviation to exit, but rather a delay - that pushes the diver beyond their turn-point. Again, we plan for such contingencies... and adopt turn-points to help mitigate against them.

If the diver/s cannot exit the wreck - all discussion is moot.
If the diver/s are delayed and/or deviated exiting the wreck - their staged deco is still available and may still be the best option, regardless of the time taken to retrieve it.
If the deviation means the diver/team don't have sufficient gas to return to the staged cylinders then, again, something went drastically wrong.

Should the 'scale' of dive and penetration present such risks at an unacceptable level (anything more than a freak chance) - then alternative options (support divers/back-up deco staged on the line etc etc) are perhaps the obvious solution.

What size of wreck...and what length of penetration... would need to be attempted to make returning from an alternative exit point such a drama?

So, what else 'stops' a diver retrieving their deco? Navigation? Strong currents?