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CCR setup

Activating CCR mode

In Settings → CCR mode, toggle the switch to on. The app does several things:

  1. Saves your OC cylinder configuration so you can switch back
  2. Loads or creates CCR cylinders — diluent, O₂, and a default bailout
  3. Shows the Closed Circuit Setup card on the main plan page with setpoints, switch depth, and bailout mode
  4. Disables Auto-set GF Low (the Andy Davis method doesn't apply to CCR — see the method article)
  5. Marks the result as stale so you'll recalculate with the new mode

If CCR was previously configured for this plan, your saved cylinders and setpoints are restored. Otherwise, sensible defaults are created.

Default CCR setup

If this is the first time you've enabled CCR for a plan, you get:

Role Default mix Size Fill
Diluent (bottom) 18/60 hypoxic trimix 3.0 ℓ 232 bar
Oxygen 100/0 3.0 ℓ 200 bar
Bailout 21/35 trimix 11.1 ℓ 232 bar

These are starting points — adjust to your actual unit, mix, and bailout configuration.

Cylinder roles in CCR

Diluent

Has the bottom role in CCR. The diluent fills the loop above water and supplements during descent when the loop volume falls. Its mix determines:

  • Maximum depth — the diluent's O₂ % limits CCR max depth (at any depth, the loop PPO₂ ≤ raw diluent PPO₂ × 1.0 = the diluent partial pressure during a flush)
  • Bailout EAD — if you bail out to OC on the diluent, your immediate gas at that depth is the raw diluent
  • Loop density — denser diluent means denser loop

The "best diluent" calculator can compute a diluent that satisfies both narcosis and density constraints at your max planned depth. Its oxygen fraction follows the diluent O₂ strategy you choose — a fixed 10 %, or one set so the diluent PPO₂ at depth is 1.0 ata — see the Best mix calculator.

Oxygen

Pure O₂ (1.00 / 0). Used by the loop solenoid to maintain setpoint. O₂ consumption is not calculated — the app records the cylinder for reference only, and you monitor your supply in the water. See Oxygen & scrubber for why.

You can adjust:

  • Cylinder size (typically 1.5 or 3.0 ℓ for CCR)
  • Fill pressure (typically 200 bar)

Bailout

OC gas carried in case of a loop failure. The deco algorithm does not use bailout in normal operation — only displays it for reference and sufficiency-check purposes. Multiple bailout cylinders are common (e.g., 21/35 deeper, 50/0 mid, 100/0 final).

Bailout sufficiency is checked separately — see Bailout planning.

CCR setup card on the main page

When CCR mode is active, a dedicated card appears between Cylinders and the Dive profile:

Setpoints

Four input fields:

  • Surface SetPoint — used surface → switch depth on descent, and from switch depth → surface on ascent (typical: 0.7)
  • SP switch depth — depth at which descent switches from surface SP to bottom SP (typical: 20 m)
  • Bottom SetPoint — used below the switch depth during the bottom phase (typical: 1.3)
  • Deco SetPoint — used at all decompression stops (typical: 1.3 or 1.5)

A per-segment SP override is possible from the segment editor.

Bailout mode

Two options:

  • Independent — each diver carries enough bailout to ascend solo on OC from max depth. The app validates this.
  • Group — bailout is the team's collective gas; sufficiency is the team's responsibility. The app does not validate group totals — that's a planning step done outside the app.

If you select Group, a warning banner reminds you that gas validation is your responsibility.

Switching between OC and CCR

Each plan has both an OC and a CCR cylinder configuration, preserved separately:

  • Switch OC → CCR — your OC cylinders are saved; CCR cylinders restored or initialized
  • Switch CCR → OC — your CCR cylinders are saved; OC cylinders restored

This lets you compare the same dive on OC vs CCR easily. Switching does not auto-recalculate — you'll see "Press Calculate" until you re-trigger the algorithm.

Settings specific to CCR

In Settings → CCR:

Setting Default Range What it controls
Bailout switch time 2 min 0–5 Mandatory pause when switching to bailout
Diluent O₂ from target PPO₂ Off On / Off Best-diluent O₂ strategy. Off = fixed 10 %; on = diluent O₂ set so its PPO₂ at depth is 1.0 ata (≈ 9 % at 100 m)

Plus the standard algorithm settings (GFs, ascent rates, stop interval) all still apply.