Next step for longer bottom times on deep dives?

[Blackfrogfeet]

I think if you can easily do the same dive on OC a rebreather is not the right tool for the job. It’s a lot harder to get hypoxic, hyperoxic, or hypercapnic on OC than it is on CCR.

Also, at those depths CCR and OC will have very similar decompression obligations,

I see guys say that a lot but isn't that mentality a little bit of a hold over from the days where CCRs were a lot less reliable, a lot higher risk, and the only people using them were doing exploration dives?

In my neck of the woods, I see CCR guys doing rec profiles and basic tec profiles (40-50m with 30-40min deco) all the time. Of course those dives could be done on OC very easily. I see guys diving CCRs on 15m/60 minute rec dives a lot, but they need to be doing those dives with their CCR so they can maintain proficiency so that when they go do a 75m dive, their skills are sharp.

I'm going CCR very soon, and the primary driver for that is Helium, but I fully intend to dive my rebreather on most of my rec dives as well to get hours on the unit, and avoid maintaining unnecessary sets of doubles and regs that I won't need because I'll have a CCR. And even on rec dives, 5lb of sorb is cheaper than a doubles nitrox fill ($35) so it will save me a lot in the long run.

 

[ginti]

One thing I have learned in my own professional training is to respect experts and listen to their recommendations. When it comes to decompression science, I absolutely will follow whatever @Dr Simon Mitchell recommends.

Like it or not, the more "scientific" approach is not to follow one person's recommendations. Instead, follow the entire scientific community. A single individual, even if very knowledgeable, can make mistakes. The entire community too, but it's more unlikely.

Should be a regular occurrence but when we hear of them it's normally unhealthy, overweight, inexperienced AND unlucky divers that have isses. Gas choice is rarely if ever mentioned unless its an idiot doing a 300' dive on an Al80 of air.

The fact that it is not mentioned doesn't mean that it didn't play a role. Maybe all of these people would be alive if they were breathing trimix; who knows? The only thing that we know for sure is that the scientific community recommends avoiding narcosis. And scientists of today know more than you, more than me, and more than the people who made reports on the deaths you mentioned.

In this case though, since the far majority of the dives we're discussing are done on air or nitrox and historically have been, the " deviants " are those who seem to lack the intellectual abilities at depth to dive like the rest of the world and need helium to do so. No shame but I certainly would be thumping my chest about this inability.

Did you ever think that these dives have been historically done in air/nitrox just because 20-30-40 years ago scientists knew less than today, and were giving recommendations according to their more limited knowledge? And that limited technology also played a role in those choices?

 

[Wibble]

Good evening gang.
Im researching the idea of stepping up into the tech world. Ive done several deep wrecks over the years, and I'm often wishing I had more bottom time 90-130 ft range eats up NDL even on Nitrox.
what would be a good starting point to get more bottom time out of this dive range? I often dive the Spiegel grove and the Duane down in the keys, and I want to get into the North Carolina wrecks, but id love to figure out what step I need to have better bottom time. I have good air consumption, but still can't win that fight against NDL, even on Nitrox.
Id love to be able to truly explore, staying down 45+ on these dives at this range. I see several options for classes that are 'tech', but not sure where to start. PADI certified, but TDI or other outfits are just as open to me.

any thoughts?

Rebreather.

Large entry cost in terms of finance and commitment -- think motorcycle. Once over that, it's amazing, cheap to run and flexible.

Failing that it's a twinset, stages and learning decompression procedures.

Other agencies factor in your future, not PADI.

 

[happy-diver]

Id still like to stay 'longer' in that 90-100 range than the EAN 30-32 allows.

Well, dive 36

 

[Wibble]

Well, dive 36

Or take a stage of 80% and stay as long as you like.

 

[Marie13]

Or take a stage of 80% and stay as long as you like.

OP would still need to get minimum Adv Nitrox cert to have access to 80%. As far as I can tell, no way around getting an advanced cert or two.

 

[doctormike]

Rebreather.

Large entry cost in terms of finance and commitment -- think motorcycle. Once over that, it's amazing, cheap to run and flexible.

Failing that it's a twinset, stages and learning decompression procedures.

Other agencies factor in your future, not PADI.

I love my CCR, has really revitalized my interest in diving. I use it for pretty much every dive other than very shallow shore dives where I don't feel like setting it all up for macro work in 5 feet of water.

But you have to be doing a good bit of OC trimix before buying a rebreather saves you money. Just considering consumables alone (sorb, cells and maintenance), it's really not cheaper for the vast majority of divers.

Yes, there are big deco advantages, but for the kind of diving the OP is doing, that would be primarily in shallower dives where a fixed PPO2 of 1.3 will give you a lot longer NDL than any reasonable OC mix. For example, if you are doing a dive to 60 feet (2.8 ATA), you would have to be diving EAN 46 to get the same NDL as a CCR. With the OP diving a relatively square profile to 100 feet (4 ATA) on EAN 32, they would have similar NDLs on OC.

For what the OP posted, I don't see why anyone would be suggesting a CCR. I think that they are great, and while they add risks they also remove other risks, and that's a whole different argument. But given the limits of what they are asking, OC tech training seems to be a better use of time, money and resources for this particular situation.

 

[doctormike]

OP would still need to get minimum Adv Nitrox cert to have access to 80%. As far as I can tell, no way around getting an advanced cert or two.

Not just access to the gas.

If you are taking 80% to extend your bottom time, that's not a "stage", that's a deco bottle for accelerated decompression. And of course, if you are planning to "stay as long as you like", you had better have enough back gas to complete your lost gas plan if for whatever reason you lose access to that deco bottle.

 

[flymolo]

I see guys say that a lot but isn't that mentality a little bit of a hold over from the days where CCRs were a lot less reliable, a lot higher risk, and the only people using them were doing exploration dives?

In my neck of the woods, I see CCR guys doing rec profiles and basic tec profiles (40-50m with 30-40min deco) all the time. Of course those dives could be done on OC very easily. I see guys diving CCRs on 15m/60 minute rec dives a lot, but they need to be doing those dives with their CCR so they can maintain proficiency so that when they go do a 75m dive, their skills are sharp.

I'm going CCR very soon, and the primary driver for that is Helium, but I fully intend to dive my rebreather on most of my rec dives as well to get hours on the unit, and avoid maintaining unnecessary sets of doubles and regs that I won't need because I'll have a CCR. And even on rec dives, 5lb of sorb is cheaper than a doubles nitrox fill ($35) so it will save me a lot in the long run.

I think it's useful to rack up hours on ccr initially, but there comes a point where it becomes unnecessary to take the ccr on every dive, especially when oc will work just fine. There are other considerations too, like keeping your oc skills sharp, or avoiding "mixed-team" diving. Plus, sometimes it can be refreshing to just screw some regulators onto some tanks and go open circuit diving, without the need to perform a whole ccr build/teardown procedure.

Also, again, even the "safest ccr" still presents risks not present on oc.

 

[doctormike]

I see guys say that a lot but isn't that mentality a little bit of a hold over from the days where CCRs were a lot less reliable, a lot higher risk, and the only people using them were doing exploration dives?

In my neck of the woods, I see CCR guys doing rec profiles and basic tec profiles (40-50m with 30-40min deco) all the time. Of course those dives could be done on OC very easily. I see guys diving CCRs on 15m/60 minute rec dives a lot, but they need to be doing those dives with their CCR so they can maintain proficiency so that when they go do a 75m dive, their skills are sharp.

I'm going CCR very soon, and the primary driver for that is Helium, but I fully intend to dive my rebreather on most of my rec dives as well to get hours on the unit, and avoid maintaining unnecessary sets of doubles and regs that I won't need because I'll have a CCR. And even on rec dives, 5lb of sorb is cheaper than a doubles nitrox fill ($35) so it will save me a lot in the long run.

5 lbs is the low end of scrubber size - but figure about $20 for that sorb. Plus you will need 100% O2 fills, and $300 a year for sensors. Unless you are doing a lot of OC trimix, it will take you a long time to get your money back!

But congratulations on going to CCR... and I would say that you should dive it on every dive (OK, maybe not a quick last minute shore dive to 10 feet). Racking up hours is really important, and even experienced CCR divers should keep their skills up. I really prefer not going back and forth - better for muscle memory to stick with the CCR. Plus, it's a lot more fun to dive... who want's to go back to all of that noise?