Where should I start to approach the rebreather world

[tbone1004]

Can you not get the 7L 232 bar steel Fabers?

sadly not

 

[Wibble]

There's those lovely 8.5 litre cylinders in the other thread. Perfect for sidemount.

 

[Marie13]

There's those lovely 8.5 litre cylinders in the other thread. Perfect for sidemount.

The LP50s are lovely and light for SM when you want redundancy but are doing shallow dives. I have two pairs and people keep trying to buy them from me.

 

[rjack321]

The LP50s are lovely and light for SM when you want redundancy but are doing shallow dives. I have two pairs and people keep trying to buy them from me.

They are also good as CCR BO for wreck dives up to 60m, ~25mins bottom time. One with 18/45 the other with 50%

 

[stuartv]

That's annoying. Those HP aluminum cylinders (i.e. 232 bar) are nice because there's a bit heavier than their LP (208 bar) cousins, so don't float as much. Being small they're great for the shallower dives.

A side benefit is you don't need all that gas, so you can use it for proving it works on all dives with fewer topoffs. Nothing quite like loop off, bailout in mouth, then... nothing! I could have sworn that I'd turned it on before jumping; still, better to prove it in a test than add to an incident pit when you really need it!

I plan my dives based on how much gas I'm carrying. "you don't need all that gas" does not compute. If I were using bigger BOs, then I would allow myself a longer Max TTS... So, I would still need "all that gas".

My RMV is not all that great, either. Having more gas (than what I current carry in AL80s) might allow me to have a Max TTS that is actually as long as some of the people I have dived with. It sucks being on CCR and still being the limiting factor/person in the dive - because my RMV is crap.

 

[Wibble]

I want bottom time!

There is a limit to this though. For the example of a 60m/200' dive, I'd go for 40 mins rather than 50 mins because the deco really bites as the slower compartments fill, e.g. 40 mins BT is a two-ish hour dive, 50 mins BT is getting on to a three hour dive.

As ever it's constrained by how much bailout can you carry; a couple of 'full' ali80s and it's possible to get out of dodge for the 40 min dive, but the 50 min one is pushing it... a lot.

It's more likely that a 3 hour runtime would be on a lazy shot, so lots of gas available. If not, need to make damn sure there's a drop tank and a signal -- small yellow blob -- and a pre-arranged procedure with the skipper to drop it down the line if the signal's shown.

Hate floating stages. They get caught in wrecks :-( Sidemounting is the solution.

 

[JonG1]

Tight on the 65 though Wibs, been playing with adding in 36% in a 300b 3L to cover the middle stops for Malin, it can be racked then and still only carrying the usual 2x80s for the bulk of dives.

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 50/75

Dec to 60m (6) Diluent 15/55 0.70 SetPoint, 10m/min descent.
Level 60m 34:00 (40) Diluent 15/55 1.30 SetPoint, 15m ead, 23m end
Asc to 33m (43) Trimix 15/55 -7m/min ascent.
Stop at 33m 0:09 (44) Nitrox 36 1.51 ppO2, 25m ead
Stop at 30m 2:00 (46) Nitrox 36 1.40 ppO2, 22m ead
Stop at 27m 2:00 (48) Nitrox 36 1.30 ppO2, 20m ead
Stop at 24m 2:00 (50) Nitrox 36 1.20 ppO2, 17m ead
Stop at 21m 2:00 (52) Nitrox 36 1.09 ppO2, 15m ead
Stop at 18m 3:00 (55) Nitrox 36 0.99 ppO2, 13m ead
Stop at 15m 5:00 (60) Nitrox 65 1.59 ppO2, 1m ead
Stop at 12m 7:00 (67) Nitrox 65 1.40 ppO2, 0m ead
Stop at 9m 10:00 (77) Nitrox 65 1.22 ppO2, 0m ead
Stop at 6m 17:00 (94) Nitrox 65 1.03 ppO2, 0m ead
Stop at 3m 35:00 (129) Nitrox 65 0.84 ppO2, 0m ead
Surface (132) Nitrox 65 -1m/min ascent.

OTU's this dive: 149
CNS Total: 58.7%
Gas density: 4.6g/l

424.2 ltr Trimix 15/55
601.2 ltr Nitrox 36
1795.2 ltr Nitrox 65
2820.5 ltr OC TOTAL

 

[stuartv]

I want bottom time!

There is a limit to this though. For the example of a 60m/200' dive, I'd go for 40 mins rather than 50 mins because the deco really bites as the slower compartments fill, e.g. 40 mins BT is a two-ish hour dive, 50 mins BT is getting on to a three hour dive.

As ever it's constrained by how much bailout can you carry; a couple of 'full' ali80s and it's possible to get out of dodge for the 40 min dive, but the 50 min one is pushing it... a lot.

It's more likely that a 3 hour runtime would be on a lazy shot, so lots of gas available. If not, need to make damn sure there's a drop tank and a signal -- small yellow blob -- and a pre-arranged procedure with the skipper to drop it down the line if the signal's shown.

Hate floating stages. They get caught in wrecks :-( Sidemounting is the solution.

I have yet to plan or do a dive where I was not carrying all the BO I needed. At this stgae of my diving, I will not rely on using gas hung on a shot line. That would only be for a case where I screwed up badly in my gas calculations and end needing a lot more than I thought I would need.

Any my only point was that "dive times will extend to include all available gas." So, it does not compute - to ME - to say that I'm carrying BO I "don't need." If I'm carrying it, then I already figured out how long I can dive with that much gas (with suitable safety margins, of course) and that is my dive time limit.

If I limit my dive for some other reason - like a buddy that has planned out their dive and can't stay as long as me for some reason - THEN I would have "extra gas".

 

[KenGordon]

Tight on the 65 though Wibs, been playing with adding in 36% in a 300b 3L to cover the middle stops for Malin, it can be racked then and still only carrying the usual 2x80s for the bulk of dives.

DIVE PLAN
Surface interval = 5 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 50/75

Dec to 60m (6) Diluent 15/55 0.70 SetPoint, 10m/min descent.
Level 60m 34:00 (40) Diluent 15/55 1.30 SetPoint, 15m ead, 23m end
Asc to 33m (43) Trimix 15/55 -7m/min ascent.
Stop at 33m 0:09 (44) Nitrox 36 1.51 ppO2, 25m ead
Stop at 30m 2:00 (46) Nitrox 36 1.40 ppO2, 22m ead
Stop at 27m 2:00 (48) Nitrox 36 1.30 ppO2, 20m ead
Stop at 24m 2:00 (50) Nitrox 36 1.20 ppO2, 17m ead
Stop at 21m 2:00 (52) Nitrox 36 1.09 ppO2, 15m ead
Stop at 18m 3:00 (55) Nitrox 36 0.99 ppO2, 13m ead
Stop at 15m 5:00 (60) Nitrox 65 1.59 ppO2, 1m ead
Stop at 12m 7:00 (67) Nitrox 65 1.40 ppO2, 0m ead
Stop at 9m 10:00 (77) Nitrox 65 1.22 ppO2, 0m ead
Stop at 6m 17:00 (94) Nitrox 65 1.03 ppO2, 0m ead
Stop at 3m 35:00 (129) Nitrox 65 0.84 ppO2, 0m ead
Surface (132) Nitrox 65 -1m/min ascent.

OTU's this dive: 149
CNS Total: 58.7%
Gas density: 4.6g/l

424.2 ltr Trimix 15/55
601.2 ltr Nitrox 36
1795.2 ltr Nitrox 65
2820.5 ltr OC TOTAL

If you bail out will you really be using 50/75? Why not just stick with the bottom gas Rather than a third, awkward, cylinder?

 

[JonG1]

I always plan BO on regular GFs, I run a 90/90 backup computer, but the extra gas could cover hypercapnia, or avoid a subsidiary issue such as DCS.

Generally I aim to dive 2 BOs for simplicity on normoxic and cut times to suit , but a racked 3l 300b isn't too much mither for a bit longer on a decent target, such as the Malin wrecks.

I've also slung it on top of a stage and it's really not an issue, due to its diminutive size.