OP
don't ever look at the Navy Tables. I think they go down to 240 feet on air. so you would then need to dive 241
Deep Diving
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Braunbehrens
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I have a question for the guys who are talking about 400 ft dives (or even 300 ft dives).
How much bottom gas are you taking along?
What is your bottom time?
Are you diving 3rds and taking away rock bottom or just winging it?
The reason I ask...is that on double 104's (even overfilled) it seems to me you don't have more than 10 minutes on the bottom, if you follow those rules. 10 minutes isn't a lot of time.
If it's just about going deep...ok, but I hear there's a girl who does the same thing holding her breath, so don't pound your chest too much....
How much bottom gas are you taking along?
What is your bottom time?
Are you diving 3rds and taking away rock bottom or just winging it?
The reason I ask...is that on double 104's (even overfilled) it seems to me you don't have more than 10 minutes on the bottom, if you follow those rules. 10 minutes isn't a lot of time.
If it's just about going deep...ok, but I hear there's a girl who does the same thing holding her breath, so don't pound your chest too much....
OP
based upon your last paragraph it appears that this may just be a troll looking to get something going.
giving you the benifit of the doubt.
I will keep it simple..
when i am deep diving i use 2/3rds of my bottom gas for the dive and 1/3 for reserve. bottom gas is figured to the first gas switch.
if deco gas or travel gas is lost there are other methods available.
bottom times deeper than 350 feet are generaly very short, 5 - 15 minutes..the deeper the less time spent there.
I don't totaly understand the term rock bottom as that is a GUE term and I am not GUE trained.
It is not just about going deep, the depth is just the destination, it is more about the road to get there and back that is the appeal.
I can't hold my breath for more than 2 minutes so freediving to that depth is not an opption, however i do act as a freediver's saftey diver for the Canadian National freediving team, so sitting at 300 + feet while judging or video taping or both i have certainly gained a lot of respect for those who can hold their breath long enought ot do that sort of diving.
I don't know anything I want to do much deeper than 300.. but when I choose so its usually up to a 30 minute dive because the decos get crazy beyond this and the bailout gas(on a rebreather) is a problem..
My limit is set by TTS which I limit to about 180 minutes..
Braunbehrens
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I was asking about the guys doing OC. Rebreathers are a different story, I wouldn't touch one with a 10 ft pole unless you put a gun to my head.
Your loss... did the open circuit thing for many years.. I'll never go back willingly..
OP
Just spent 10 days diving my new Insperation in Scapa Flow.
OC will be a thing oof the past soon
OC will be a thing oof the past soon
welcome to the club.. are you going to do zero-g at Sunset house this summer??
Braunbehrens
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This sport is all about managing risk. IMO the risk of diving a rebreather is too high. Especially an inspiration, but any rebreather really.
The risk depends on the type of diving.. An OC diver doing a 300ft dive IMO has a higher risk than someone on a rebreather..
Doing a deep dive inside of a wreck.. I'll take a RB anyday.. God forbid your guideline gets severed and viz is poor.. Gas supply is not a concern for the RB diver.. You have as long as it takes to get out.. You may have to be treated in a chamber but you most likely will live.. Deep dives on OC leave very little room for error..
Now do a 30 foot dive on OC and the same on a rebreather.. The RB risk is higher... The most dangerous place for a RB is shallow..
lets assume I am at 300 ft approx 10 ATA, if my setpoint was 1.3 and my approximate loop volume is 6 liters displacement(kinda low) that means I have approximately 8 liters of oxygen in the loop, assumming I can't inject oxygen and I am staying at the same depth, after 6 minutes my loop PO2 shoud be around .37), losing 6 liters(my choice just a coincedence to loop displacement volume, if I chose 7 liters my PO2 would be about .30) of o2 should only drop the overall displacement by 10%.. This gives me a fair amount of time to come up with a solution.
If you were on OC and had an RMV of .7 (reasonable for a tech diver) and assumming you are staying very calm thats 7 cu ft of gas per minute, or 42 cu ft of gas for this time( mor likely you will start to breather faster..I'd bet anywhere from 50%-100% more gas per minute)..
If the RB diver has a buddy or offboard slings and the bailout gas/or buddy gas is appropriate for depth, a simple loop flush at 300 fsw takes about 2 cuft and will give another 6 minutes while allowing the po2 to drop to .37, longer if you allower a lower po2.
Given the same situation who is more likely to survive a problem at depth.
also remember your deco obligation is piling up very quickly, on OC if you get out your mostlikely heading for the surface and explosive decompressin.. on the RB its just going to be alot of work to the surface, but again no rush..
I would run it as a combination of both using diluent flushes and my 50% deco gas.. that means I am getting at least a 20 to 1 extension on my bottom gas and if I try and maintain the same setpoint at least a 3 to 1 extension on my deco gas
a 30 min dive @ 300 has approx 3 hours of deco (depending on the model). I know in an emergency I can push my scrubber well past it official limits, and running the unit with flushes will also help to extend the duration.
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