Marine compressor sizing: duty first, model second

The most common mistake in marine compressor sizing is to look at power and price first, then try to fit the duty afterwards. Air circuits on a vessel differ enough that reversing the order produces a machine with "enough capacity, wrong duty".

Step 1 — identify the circuit

• Starting air: 30–40 bar, intermittent, highest reliability requirement — a piston duty;
• Instrument air: 7–8 bar, dry and clean, needs desiccant drying and fine filtration;
• Deck service air: 7–10 bar, fluctuating demand, compact units suit retrofits;
• Nitrogen feed: 8–13 bar, continuous, oil carry-over directly affects generator life.

Step 2 — cooling and power

With sea or fresh water available, water cooling is preferred for continuous duty. Air cooling suits well-ventilated engine rooms up to 45 °C ambient, and is limited to 110 kW; 132 kW and above require water cooling. Confirm 380 / 440 / 690 V and 50 / 60 Hz — offshore projects often add 690 V and 30-year design life.

Step 3 — class society and documents

The society determines pressure-part materials, survey method and onboard documentation. We hold CCS type approval, BV Mode II, ABS and RS approvals, with design and survey coverage across 10+ societies; LR, KR and RINA have delivered-vessel certificates. Where another society or MED is specified, we confirm the certification route and schedule before order.

Step 4 — margin and interfaces

Allow roughly 10% capacity margin over peak demand and size receivers for peak shaving. On retrofits, check base dimensions, flanges and cable entries so the new unit is interchangeable and dock work stays minimal.