Introduction – Gas Planning Is the Real Technical Skill

Malta has some of the world’s most accessible deep wrecks: HMS Stubborn (~55 m), Southwold bow & stern (68–73 m), Schnellboot, ORP Kujawiak, and several 90–100+ m sites for expedition-level CCR diving.

The difference between a safe dive and a stressful one is almost always gas planning

This guide breaks down high-level gas planning principles for deep Malta wrecks — not a full maths class, but a practical framework you can apply immediately.

1. Why Gas Planning Is Different in Malta

Malta’s deeper wrecks create a unique environment:

✔ Consistent depth ranges

Most major wrecks sit at clean, flat depth bands (55 m, 70 m, 90–110 m).
This makes gas planning predictable — if you know the profile.

✔ Blue-water ascents

Many wrecks require DSMB ascents with mid-water deco.
Gas planning must allow for imperfect line work or current.

✔ Long runtimes

A “short” 70 m dive can still involve 45–70 minutes of deco.
OC gas adds up fast.

✔ Perfect for CCR

Deep, square profiles are exactly where CCR shines — but bailout planning must be realistic.

2. Trimix Basics for Malta – Simple Rules That Work

Trimix gas planning isn’t about chasing perfect numbers. It’s about:

• Function
• Safety
• Cognitive clarity
• Logistics

A simple way to think about deep wreck mixes in Malta:

For 45–55 m wrecks (Stubborn / Polynesien deeper routes)

Typical back gas:
Trimix 21/35 or 18/45

Why:

• Good END
• Low narcosis
• Moderate helium cost

For 60–70+ m wrecks (Southwold, Schnellboot)

Typical back gas:
Trimix 15/55 or 12/60

Why:

• Keeps END sensible (25–30 m range)
• Enough helium to avoid dense gas issues
• More stable physiology during long bottom times

For 90–100+ m dives (Kujawiak / deeper project dives)

Typical back gas:
Trimix 10/70, 8/80 or expedition mixes depending on PO₂ ceiling

Why:

• Very low nitrogen
• Very low gas density
• Narcosis management becomes critical

These aren’t rules — they’re starting points.
Exact mixes depend on:

• Workload
• Diver experience
• Unit (OC vs CCR)
• Thermocline
• Dive objective

3. Choosing Deco Gases – Keep It Simple, Keep It Useful

New technical divers often over-complicate deco gas choices.

For typical Malta profiles, these cover 90% of use cases:

✔ Nitrox 50 (50% O₂)

Used from ~21 m
Excellent “workhorse” gas for 45–60 m dives.

✔ 80% O₂ or 100% O₂

Used from 6 m
Pure O₂ is great when conditions allow stable holds.

✔ Trimix Deco (rarely needed)

For extremely deep or cold dives.
Most Malta divers won’t need it until 90+ m projects.

For OC:

• 1 deco gas → Tec40
• 2 deco gases → Tec45 / Tec50 / Trimix
• More only for extreme runtimes

For CCR:

Deco gases are bailout gases first, deco gases second.

4. OC vs CCR Gas Planning – The Real Differences

Most recreational or early-tec divers think CCR is “just more bottom time”.
The real difference is deeper:

Open Circuit Trimix – Gas Planning Realities

1. High gas consumption at depth

A 70 m dive on OC burns through:

• Back gas rapidly
• Deco gas rapidly
• And doubles or triples costs

2. Heavy bailout dependence

Your entire plan must assume OC bailout as your exit strategy.

3. Deco gas logistics matter more

If you lose one deco gas, what’s your plan?
OC divers need redundancy at multiple levels.

4. Depth/time trade-offs

Want more time?
Prepare for more helium cost and more deco.

CCR – Gas Planning Realities

CCR fundamentally changes the profile:

1. One-third to one-tenth the gas cost

Your helium lasts many dives, even at 70–90 m.

2. Deco becomes more efficient

Constant optimal PO₂ reduces decompression.

3. Predominant risk = bailout planning

Your loop gives efficiency.
Your bailout plan gives safety.

4. Bottom time flexibility

You can extend the dive safely — but tasks & thermal load still matter.

5. CCR Bailout Planning – The Critical Skill

Many new CCR divers fail at the realistic part of bailout planning:

They plan bailout for calm, perfect conditions – not real ones.

A good CCR bailout plan assumes:

• Stress SAC, not CCR SAC
• Delay before ascent
• Potential current
• Possible deeper start point
• Gas switch issues
• Team separation
• DSMB ascent, not a shot line

For a typical 70 m Malta wreck, bailout might include:

• Deep bailout (e.g., 15/55 or 12/60)
• Nitrox 50
• Oxygen
• BOV access
• Clear switch protocols

6. Example Planning Differences – 70 m Wreck Dive

Not a dive plan — just a comparison.

Open Circuit Example (Southwold Stern, 73 m)

Bottom gas: Trimix 12/60
Deco gases: 50% and 100%
Bottom time: 20–25 min
Total gas carried: 3–4 cylinders
Typical deco: 60–90 min
Primary concern: Gas volume and gas density

CCR Example (Prism2, same wreck)

Diluent: Trimix (e.g., 10/70 or similar)
Setpoints: 1.2–1.3 at depth / 1.4–1.5 ascending
Bottom time: Often 30–40+ min
Bailout: 1–3 cylinders depending on training & team
Deco: Shorter, more controlled
Primary concern: Bailout management & loop discipline

Both are valid.
CCR simply opens more time and reduces cost.

7. Safety Margins – The Most Important Aspect

Gas planning isn’t about minimums.
It’s about margins.

A solid plan includes:

• Accurate SAC
• Realistic stress response
• Failure scenarios
• Lost gas contingency
• Team resources
• Ascent strategy
• DSMB plan
• Thermal/physiological load

This is what separates a deep technical dive from a deep number-chasing dive.

Final Thoughts – Gas Planning Is a Skill, Not an Equation

Technical diving isn’t about chasing the perfect mix.
It’s about making decisions that keep you safe, efficient and focused on the wreck — not your SPG.

Whether you choose OC trimix or CCR, the principles remain:

• Plan with honesty
• Leave margin
• Prepare bailout properly
• Avoid task overload
• Don’t rush depth progression

Malta offers the ideal environment to train these skills — predictable depths, real wrecks, and clean progression from 40 m to 100+ m.