Info Helium is expensive and deep air is not my thing. -Let's talk about "Big" dives.

[SelfDiver]

Helium prices have gone up, way up.
Here are some things we can do with Nitrox to practice for the BIG dive.

What is a BIG dive? A big dive involves decompression, multiple tanks, multiple mixes or complicated logistics.
Doing an S-drill and SMB launch is nice practice but that is different than being in the water for more than 2 hours with multiple tanks.

Plan a dive to 40 meters on Air with 40 minutes bottom time.
Total Dive time is 100 minutes with ~35 minutes spent with deco 50% between 6-3meters.
This is an affordable dive with 4 X AL80 tanks. Even renting a twinset should be doable.
You will struggle at 80 meters with a team If you can't plan and execute this dive.
The gear configuration is similar to a Trimix dive to 100 meters.

The shallower deco dives on Nitrox are a cheaper way to achieve mastery in the process and procedures needed for big dives.
The depth is only one aspect of big dives. The real hindrance is logistics.
- How do you enter the water with 4 tanks?
- Do you need a safety/helper diver?
- Twinset or sidemount?
- Drysuit?
- DPV to get to the dive site?
- Staging deco or carry with you? leaving bottles along the way forces you return to the same spot for ascent or incur a penalty.
- Deep wrecks? Wall dive? are you comfortable navigating at 100 meters?
- Are you comfortable sitting at 3 meters for 30 minutes with your deco regulator?
The answers are easier to figure out at 40 meters than at 100 meters.
The Tech course or certification is not sufficient to be comfortable with all the logistics involved.
I am not casually doing dives to 100 meters with 2 hours of deco on a daily basis.
The practice is good for me. I can run drills while sitting at 3 meters for 30 minutes.

These cheaper dives also allow you to be a safety/helper diver for others who are doing expensive dives.
Agree to carry tanks, in and out of the water for eachother.
Agree to meet the divers at 40m and help in the ascent in case they need it.

Do the shallow dives like they are big Trimix dives and practice for when you finally get some cash for Helium.

 

[arew+4]

Why not go to rebreather?

 

[PfcAJ]

Why not go to rebreather?

You still need all those tanks for bailout. RB doesn’t really change what you need to bring with you, it just changes what you actually use.

 

[DiveLikeAMuppet]

Any practice is better than no practice but I’m not sure it really prepares you for very deep dives, especially not on OC.

40 minutes bottom time on air at 40 meters and 2 deco gases is just a normal wreck dive here - jump off the boat, possibly solo, drifting deco under a DSMB… even though I would go for 50% and 100% at 6m, deco at 3 in the ocean might be a no no.

I think you would still need to dive a lot in the 60 - 80 meter range to stay marginally current for 100 m - as the bottom times become shorter and deco increasingly more committing. Not sure that’s achievable with current helium prices either, or what would be the point of OC helium at 100 meters . For CCR it doesn’t matter, you fill bailout once every few years.

 

[rx7diver]

... Plan a dive to 40 meters on Air with 40 minutes bottom time.
Total Dive time is 100 minutes with ~35 minutes spent with deco 50% between 6-3meters. ...

Hmm. How about 40 msw (130 fsw) on air for 40 min BT, and stay on air until 20 fsw where you switch to oxygen, where you deco out? (Don't forget to cycle back to air periodically if you need to.)

Or 40 msw (130 fsw) on nitrox (EAN28?) for 40 min BT, and stay on this nitrox until 20 fsw where you switch to oxygen, where you deco out? (Don't forget to cycle back to nitrox periodically if you need to.)

Either is an affordable dive and simple. And either should give you less deco time (and better? deco).

ETA: IANTD has (or used to have) an "Advanced Deep Air" course (air for bottom gas, and two deco gases) and a "Technical Nitrox" course (EAN for bottom gas, and two deco gases). The second course (especially) was promoted as a way of teaching divers necessary skills in advance of tri-mix (especially for divers who don't want to do *Advanced* Deep Air-levels of deep air diving).

rx7diver

 

[Still Kicking]

Nm

 

[justinthedeeps]

How important is your practice depth and bottom time on these mocked up air dives?

Why not just set your GFs to like 20/40, max at 30 metres (or less), launch your SMB, then go thru a deco plan that you would get on a much deeper dive with normal GFs?

 

[justinthedeeps]

How many trimix twinsets do you need to [re]fill before you paid as much for gas alone as a whole rebreather costs (~$9k)?

Assuming $3.50/cuft

Looks like about ~30 refills of a 2x 12L (~200cf) 15/55 twinset from 50 bar back up to 237 bar (near ~$300)

~20 refills of 10/70 @ near $400 per fill/dive?

 

[broncobowsher]

If you want to keep current with diving deep, rebreather is the way to go. Yes, the up front costs are high. But it opens up a lot of options. One of the good ones is when plans get changed on you. Weather changed, the 60m dive is out but a 30m is the backup plan. You are not blowing $400 in helium on an air dive. But it doesn't matter if you blow $15 in Helium on a shallow dive. You still get a dive even if it wasn't the one you were planning on in the first place.

And when people price a rebreather against the cost of helium fills, the math actually works out better. The math makes the assumption that you throw the rebreather in the trash can when you are done. If you calculate the actual cost of what you spend vs. what you could sell it for, the pay off is a lot sooner. And you are further ahead.

Multi day trips no longer require a truck to haul multiple sets of doubles and multiple deco bottles. A couple sets of little 3L rebreather bottles and a keg of sorb will have you diving for days.

 

[grantmac]

Multi day trips no longer require a truck to haul multiple sets of doubles and multiple deco bottles. A couple sets of little 3L rebreather bottles and a keg of sorb will have you diving for days.

This last point right here is what has me looking hard at CCR sooner than originally planned. I like to dive in places where bringing a whole truck full of tanks just isn't feasible.
Do I invest in a gas compressor (maybe) or consider CCR?