Marine and Offshore HVAC Duct Guide — Naval, Cruise, FLNG, AUKUS Submarine Programme and Class Society Approval

Why marine and offshore HVAC ductwork is different

The HVAC ductwork that keeps an office tower in Sydney comfortable would be unrecognisable on the deck of a cruise ship in the Tasman Sea, in the engine room of a tanker on the Bass Strait passage, or inside a pressure hull at depth. The same physics of air movement applies, but the material specification, fabrication tolerance, fire integrity, motion tolerance, weight budget, hazardous-area treatment and approval pathway are all different — usually by an order of magnitude. This guide walks through the engineering, regulatory and procurement reality of HVAC ductwork for marine and offshore facilities, with specific attention to the projects driving Australian shipyard demand in 2026 and beyond: the AUKUS submarine programme, continuous Naval Shipbuilding Plan surface vessel work at Henderson WA and Adelaide SA, FLNG and FPSO operations on the Northwest Shelf, and the steady through-life maintenance and refit pipeline for commercial shipping calling Australian ports.

Marine and offshore HVAC ductwork is unique on six axes. First, corrosion: salt spray, chloride-laden humidity, and the chronic moisture exposure of a deck plant or open machinery space drive material selection beyond what any landside HVAC would require. The marine atmosphere chloride deposition rate exceeds even severe coastal industrial environments by a factor of three to five times, and standard galvanised duct rated for 25-year landside service can pit through within 18–36 months on weather-deck exposure. Second, motion: vessels pitch, roll, heave and yaw, while floating production units survive cyclonic storm events with motion that no fixed building duct support is designed to absorb. The Northwest Shelf cyclone season delivers significant wave heights of 9–15 metres in design conditions, with corresponding accelerations on FPSO and FLNG hulls that drive expansion-joint selection, hanger spacing and damper actuator margin. Third, space: every cubic centimetre on a submarine, naval combatant or process module is contested by competing systems, and HVAC routing is squeezed into spaces that landside engineers would dismiss as impossible. Submarine HVAC duct is commonly routed inside the structural pressure hull frame, with fabrication tolerance below ±2 mm to make the geometry close. Fourth, fire and explosion safety: SOLAS Chapter II-2 and IEC 60079 hazardous-area zoning impose layered requirements on duct integrity, damper certification and the gas-tight separation of safe and hazardous areas. The single biggest fire on a ship begins in the galley exhaust or engine room, so the integrity of the duct system in those routes is the difference between a contained incident and the loss of the vessel. Fifth, weight: every kilogram of duct steel reduces payload, deadweight or operational range, so engineers chase thinner stainless gauge, FRP composite alternatives and shorter run lengths. On a typical mid-size FPSO, total HVAC duct weight including insulation and supports runs 250–500 tonnes, comparable to a major piping system in mass. Sixth, approval: a marine or offshore duct module cannot simply be built and installed; it must be approved by a class society surveyor, witnessed at a Factory Acceptance Test, certified for fire integrity, and finally signed off at sea trial.

SBKJ has supplied HVAC duct fabrication machinery to shipyards, naval primes and offshore module fabricators across Australia, Asia, the Middle East, Europe and the Americas. Our auto duct lines, spiral tubeformers and TDF flange machines are configured for the stainless steel, FRP and special alloys that marine and offshore projects demand, and the FAT pathway is built around the witnessing requirements of ABS, DNV, Lloyd's Register and Bureau Veritas. This guide is the working document our engineers use when an Australian shipyard procurement team or naval prime quality lead phones us to ask what they should specify. It is also the reference we share with consulting naval architects, marine engineers and offshore HVAC consultants who need a single document covering the regulatory, material, fabrication and approval pathways for an unfamiliar marine or offshore project.

The audience for this guide is multi-disciplinary by nature. A naval architect coordinating the fire safety plan needs the SOLAS Chapter II-2 mapping. A marine engineer responsible for engine room ventilation needs the ISO 8861 calculation basis. An offshore HVAC consultant on a Northwest Shelf FLNG project needs the API RP 500/505 zone classification practice. A defence-prime quality manager on an AUKUS programme needs the MIL-S-901 shock testing and the class society type approval pathway. A shipyard procurement engineer at Henderson WA or Adelaide SA needs the lead time, FAT logistics and material sourcing reality. The sections that follow address each of these audiences without assuming background in the other disciplines.

Marine vs offshore — the categories that drive specification

The first decision in any marine or offshore HVAC project is to identify which category of platform you are designing for, because each category triggers a distinct regulatory and engineering pathway.

Commercial shipping

Cargo, container, tanker and bulk carrier ships are SOLAS-flag vessels classed by one of the IACS members. Their HVAC ductwork serves accommodation, engine room, cargo control room, galley, and — for tankers and gas carriers — the pump room and tank-deck areas where hazardous-area zoning applies. Specification is dominated by ISO 7547 (accommodation comfort), ISO 8861 (engine room ventilation), and SOLAS Chapter II-2 (fire safety, damper certification, A/B/H class division integrity). LNG carriers and chemical tankers add IEC 60079 hazardous-area requirements around tank deck and pump room, and the IMO IGC Code (gas carrier) and IBC Code (chemical tanker) layered requirements. Bulk carriers and container ships have the simplest HVAC scope: accommodation block plus engine room, with relatively modest galley exhaust and limited hazardous-area scope. Modern post-Panamax container ships nonetheless run engine room ventilation totals of 200,000–400,000 m³/h, with multiple parallel fan trains and significant duct cross-sections. Tanker HVAC is more involved due to the cargo deck zoning and cargo control room positive pressurisation. LNG carriers are the most demanding subset of commercial shipping HVAC, layered with ATEX/IEC 60079 zoning around the cargo containment system.

Passenger and cruise vessels

Cruise ships, ferries and ro-pax vessels carry the same SOLAS framework but multiply the accommodation HVAC demand by an order of magnitude. A modern cruise ship has 2,000–6,000 occupants, hundreds of cabins, large public spaces, theatres, casinos, swimming pools, galley clusters, hospital wards, and crew quarters — each with distinct ventilation rate, temperature and humidity targets. Post-COVID, infectious disease control has become a procurement-grade requirement, with elevated outdoor air, MERV-13+ or HEPA-grade filtration on key recirculation paths, and zonal isolation capability so an outbreak in one section does not cross-contaminate an adjacent zone. Galley exhaust is a project unto itself, with grease-laden vapour control, fire suppression integration, and bulkhead penetration of A-class divisions handled by type-approved dampers. The total HVAC fan capacity on a 4,000-passenger cruise ship typically exceeds 2,000,000 m³/h, with tens of central air handling units, hundreds of fan coil units, and multiple kilometres of stainless and galvanised duct distributed across 12–18 decks. Ferry and ro-pax vessels are smaller in passenger count but carry the additional complexity of vehicle deck ventilation, where carbon monoxide build-up during loading and unloading drives 10+ ACH extract rates with explosion-protected components on car deck level due to fuel vapour risk.

Naval surface combatants

Frigates, destroyers, offshore patrol vessels and amphibious ships follow a parallel naval rule set rather than commercial SOLAS. The Australian Naval Shipbuilding Plan covers the Hunter-class frigates, Arafura-class OPVs, Evolved Cape-class patrol boats, and the future general-purpose frigate programme, with build at Henderson WA (Civmec, Austal, Luerssen Australia) and Adelaide SA (BAE Systems Australia, ASC). HVAC for naval surface vessels integrates damage control, NBC (nuclear, biological, chemical) citadel protection, electromagnetic compatibility, and shock and vibration tolerance per MIL-S-901. The duct material specification typically defaults to 316L stainless steel for outboard and weather-deck supply, with selective use of non-magnetic alloys in spaces where electromagnetic signature management is a concern. Naval HVAC is also more pressure-redundant than commercial HVAC: combat damage scenarios may eliminate the primary fan train, and the duct system has cross-connect redundancy with secondary fans on a separate electrical bus, with isolation dampers managed by the platform combat management system. Hunter-class frigate HVAC fabrication scope at the BAE Systems Australia Maritime Osborne yard is one of the larger ongoing stainless-steel duct projects in the southern hemisphere through the late 2020s, with Arafura-class OPV fabrication at Henderson contributing further demand.

Submarines

The AUKUS programme — Australia, United Kingdom and United States — has placed the submarine HVAC question at the centre of Australian naval shipbuilding strategy. Australian build of conventionally armed nuclear-powered submarines is planned for South Australia, with workforce, supply chain and quality systems being established at Adelaide and Henderson WA. Submarine HVAC is the most demanding ductwork environment on Earth: confined space, sealed pressure hull, atmosphere revitalisation tied to CO2 scrubbing and oxygen generation, magnetic and acoustic signature management, extreme shock and vibration tolerance, NBC citadel protection, and damage-control compartment isolation. Material defaults to non-magnetic stainless for many runs, with shock-mounted hangers, expansion joints rated for sustained motion, and full traceability of every metre of duct from coil heat number through fabrication to compartment installation. The fabrication tolerance band on submarine HVAC duct is approximately one-third of commercial marine tolerance, the leak rate target is approximately one-tenth, and the documentation pack supporting each duct module typically runs to several hundred pages of mill certificates, weld procedure qualification records, NDT (non-destructive testing) reports, dimensional inspection records, surface finish records and traceability tags. The audit trail extends from coil purchase through finished installed component for the full operational life of the boat.

Offshore production — fixed platforms, FPSO, FLNG

Fixed offshore platforms, Floating Production Storage and Offloading (FPSO) units and Floating Liquefied Natural Gas (FLNG) facilities are the offshore equivalent of mid-sized industrial chemical plants — but stationed at sea, exposed to cyclonic weather, and with all auxiliary infrastructure including living quarters compressed onto the same hull or jacket. HVAC system scope covers process modules (typically Zone 1 or Zone 2 hazardous-area), utility modules, control rooms (typically pressurised safe haven), accommodation modules (large hotel-grade HVAC), helideck, and life-support areas. The Australian Northwest Shelf hosts the Prelude FLNG (Shell), Ichthys floating offload (INPEX), Pluto LNG (Woodside), Wheatstone (Chevron), and Gorgon (Chevron) along with multiple smaller fixed platforms; the Bass Strait hosts the legacy ExxonMobil/Esso fields; and the Bonaparte Basin and Browse Basin host current and planned developments. The HVAC scope on a major FPSO or FLNG project is typically broken into separate procurement packages for process module HVAC (handled by the topside EPC contractor), accommodation module HVAC (often handled by a specialist accommodation builder), helideck HVAC and fire protection (specialist subcontract), and the marine systems HVAC inside the hull (handled by the FPSO conversion or new-build yard). Each package has different class society interface, different material specification, different lead time and different fabrication facility. Coordinating the duct-package interfaces is one of the larger engineering management challenges on FPSO and FLNG projects, and the failure to align material specification at module interface points is a recurring source of late-stage rework.

Offshore construction — jack-up rigs, drillships, semisubmersibles

Drilling rigs and offshore construction vessels share much of the offshore production ruleset but carry additional considerations for transit between deployments, transient hazardous-area definition during well control events, and the much higher rate of personnel turnover. Their HVAC plant is typically more standardised and more aggressively weight-budgeted, with skid-mounted air handling units and shorter, higher-velocity duct runs.

The regulatory framework — IMO, SOLAS, class societies and Australian context

The HVAC engineer working on a marine or offshore project navigates four overlapping rule layers, each issued by a different authority and each with different update cycles.

International Maritime Organization (IMO) — the umbrella

The IMO sets the international rules that flag states adopt into national law. The most relevant IMO instruments for HVAC are SOLAS (Safety of Life at Sea), MARPOL (pollution prevention, with HVAC implications for engine room ventilation and EEDI/CII), and the various code sets (IGC, IBC, IGF) for gas carriers, chemical tankers and gas-fuelled vessels. The single most cited HVAC reference is MSC.1/Circ.1166, the IMO Maritime Safety Committee circular giving guidance on uniform interpretation of SOLAS regulations applicable to HVAC arrangements on passenger ships. It is not a binding rule on its own but is cited in nearly every class society HVAC interpretation as the baseline.

SOLAS Chapter II-2 — fire safety, the dominant duct constraint

Chapter II-2 of SOLAS is the regulation that drives most fire-related HVAC ductwork detailing. It defines:

• A-class divisions — A-60, A-30, A-15 and A-0 — being non-combustible structural fire divisions that maintain integrity for 60, 30, 15 or 0 minutes during a standard time-temperature fire test.
• B-class divisions — non-load-bearing fire-resistant divisions, typically B-15 — used for cabin and corridor walls.
• H-class divisions — a higher hydrocarbon fire integrity standard tested against the rapid-rise IMO hydrocarbon curve, used on tankers, FPSOs and platforms where fire scenarios involve hydrocarbon pool or jet fire rather than the slower cellulosic curve.
• Fire damper requirements at every duct penetration of an A, B or H division — type-approved units with rated thermal trip and gas-tight closure.
• Smoke control routes — the use of HVAC ducts as part of smoke evacuation strategy in passenger spaces, with positive pressurisation of stairways and refuge zones.

Class societies — the technical assessors

The seven principal IACS member societies that approve marine and offshore HVAC components in 2026 are:

• ABS (American Bureau of Shipping) — dominant in US-flag, offshore production and a large share of the global naval market. Reference: ABS Steel Vessel Rules, with HVAC provisions in Part 4 Chapter 2.
• DNV (formerly DNV GL) — strong on offshore (DNV-OS-D202 covers Marine HVAC), Norwegian and Northwest European fleets, and a significant share of LNG carrier and FLNG work.
• Lloyd's Register — UK origin, broad commercial and naval scope, strong presence on Australian Naval Shipbuilding Plan vessels via UK supply chain.
• Bureau Veritas (BV) — French origin, strong on cruise ships and European-built passenger tonnage.
• ClassNK (Nippon Kaiji Kyokai) — Japanese, with strong commercial shipping presence in the Asia-Pacific region.
• RINA — Italian, strong on cruise ships and Mediterranean-built tonnage.
• KR (Korean Register) — Korean-flag and Korean-built tonnage, increasingly active in offshore and LNG.

Each society publishes its own HVAC interpretation of IMO SOLAS, with type approval procedures for fire dampers, fans, air handling units, and — increasingly — pre-fabricated ductwork modules. Class society survey of HVAC starts at concept design (drawing approval), continues through fabrication (FAT witnessing on critical components), and concludes with onboard survey and sea trial sign-off.

Australian context — AMSA, Defence and offshore regulators

For Australian-flag commercial vessels and offshore facilities in Australian waters, the Australian Maritime Safety Authority (AMSA) recognises all IACS member societies and adopts SOLAS into Australian law via the Navigation Act 2012 and the Marine Order series. For offshore petroleum facilities, NOPSEMA (the National Offshore Petroleum Safety and Environmental Management Authority) regulates safety case and safety management systems, with HVAC integrity feeding into the SCE (Safety Critical Element) register. For naval and AUKUS programmes, the Australian Department of Defence, the Naval Shipbuilding and Sustainment Group (NSSG, formerly NSC), and the prime contractors (BAE Systems Australia, ASC, Lockheed Martin Australia, BAE Systems Maritime UK, General Dynamics Electric Boat) layer defence-side approvals on top of the class society pathway.

Hazardous-area classification — IEC 60079 and API RP 500/505

For tankers, gas carriers, FPSOs, FLNG, fixed platforms and any vessel handling flammable cargo or fuels, hazardous-area classification dictates HVAC routing, fan and damper specification, and the gas-tight separation of safe and hazardous areas.

The international zoning system per IEC 60079-10-1 defines:

• Zone 0 — explosive atmosphere present continuously or for long periods. Examples: inside a cargo tank, inside a pump casing.
• Zone 1 — explosive atmosphere likely to occur during normal operation. Examples: tank deck on a tanker, certain process module areas on an FPSO.
• Zone 2 — explosive atmosphere unlikely to occur in normal operation, and if it does, only short duration. Examples: enclosed areas next to Zone 1, with mechanical ventilation.

The US/IEEE/NEC equivalent is Class I Division 1 (continuous or likely) and Class I Division 2 (unlikely, short duration). API RP 500 and API RP 505 are the recommended practices for zone classification on offshore production facilities, widely adopted by Australian and international operators alike.

From an HVAC duct perspective, hazardous-area classification drives:

• Physical separation of safe-area and hazardous-area HVAC by gas-tight bulkheads, with no shared plenum.
• Explosion-protected fan motors (Ex d, Ex e, Ex n) on extract from hazardous areas.
• Intrinsically safe sensor and damper actuator wiring per Ex i standards.
• Fire-and-gas damper coordination — closing on F&G alarm to prevent gas migration through ductwork.
• Pressurisation strategy for safe havens (control rooms, accommodation) — typically maintained 25–50 Pa positive against the surrounding atmosphere, with overpressure relief and gas detection on intake.

The AGCS (Aviation General Cargo Standard) helideck guidelines and API 14C process safety standard layer on additional requirements where helidecks and process modules are co-located on the same hull.

Material requirements — stainless, cupronickel, FRP and galvanised

Materials drive most of the cost and most of the long-term performance of marine and offshore HVAC ductwork. The four families used in 2026 production are:

316L stainless steel — the marine atmosphere default

For supply duct exposed to marine atmosphere — weather deck, accommodation outboard, engine room intake, helideck — 316L stainless is the practical minimum because chloride-induced pitting attacks lower-grade stainless and rapidly destroys carbon steel. The 'L' designation (low carbon) prevents chromium carbide precipitation in welded zones and preserves corrosion resistance through fabrication. Typical sheet gauge for marine HVAC supply duct is 0.7–1.2 mm depending on size and pressure class. SBKJ auto duct lines are configured to handle 316L on the same line as galvanised, with appropriate roller hardness, lubricant and tooling clearance. For especially aggressive service — direct splash zone on offshore platforms, hot/humid tropical accommodation outboard duct, salt-laden weather-deck plant — Super Duplex (UNS S32750) and 6Mo (UNS S31254) grades are sometimes specified, with a 30–60% cost premium over 316L. Naval programmes including AUKUS may also specify low-magnetic-permeability variants of 316L (typically with controlled delta-ferrite content below 0.5%) for spaces where magnetic signature is managed.

Cupronickel 90/10 — legacy naval and seawater spaces

Cupronickel 90/10 (90% Cu, 10% Ni, with small additions of iron and manganese) has been used in legacy naval HVAC ductwork and in seawater-cooled spaces on commercial ships. Its biofouling resistance and chloride tolerance are excellent, but cost is significantly higher than stainless, and modern naval programmes (including AUKUS) are largely defaulting to stainless or specialised alloys for new build. SBKJ tubeformers can be configured to handle Cu-Ni for retrofit and refit projects.

FRP composite — weight-sensitive offshore and chemical service

Fibre-reinforced polymer (FRP) composite ductwork — typically vinyl ester or polyester resin with glass reinforcement — is used in some offshore weight-sensitive areas and in process modules where chemical aggressiveness exceeds stainless tolerance. FRP duct is dimensionally lighter than stainless for equivalent stiffness, has excellent chemical resistance, and is non-magnetic. The trade-offs are higher fire-rating complexity (most FRP is combustible and needs fire-rated coating or sleeving at A/B/H division penetrations), higher unit cost, and limited ability to absorb impact damage. SBKJ supports FRP-compatible fabrication via dedicated pultrusion partner equipment when projects require.

Hot-dip galvanised G275 — protected accommodation interior

For accommodation interior duct that is not exposed to direct marine atmosphere — internal supply branches, interior return paths, intra-cabin distribution — hot-dip galvanised G275 (275 g/m² zinc coating per AS 1397 or equivalent EN 10346) is acceptable and meaningfully cheaper than stainless. Many cruise ship and ferry projects use galvanised for the bulk of internal duct volume, reserving stainless for outboard and humidity-exposed sections. The cost trade-off favours galvanised by approximately 60–75% per square metre of duct surface against 316L; for a major cruise ship project with 20,000+ m² of accommodation duct, this is a multi-million-dollar line item. Class societies recognise galvanised duct in protected interior service, but the engineer must demonstrate that the duct is not exposed to marine atmosphere through the design service life. Typical practice is galvanised inside the citadel/accommodation envelope with stainless transitions at every weather-deck or outboard penetration. SBKJ machinery is configured to switch between galvanised and stainless coil quickly, with tooling profile, lubricant and PLC programme stored as material recipes that operators can select at the HMI.

The AUKUS submarine programme and Australian shipyard demand

The AUKUS announcement of September 2021, and the subsequent optimal pathway announcement of March 2023, established Australia's path to a sovereign nuclear-powered submarine capability. The programme has three phases relevant to HVAC ductwork demand:

1. Through 2027 — increased US and UK submarine port visits and rotational presence, with Australian crew embarked, building workforce competency at HMAS Stirling (Garden Island, WA).
2. Late 2020s through 2030s — Australia acquires Virginia-class submarines from the United States to bridge capability while Australian build ramps up.
3. Late 2030s onward — Australian build of the SSN-AUKUS class at Adelaide SA (Osborne Naval Shipyard, ASC), with extensive supplier development and workforce training in the meantime at Adelaide and Henderson WA.

The HVAC ductwork demand profile across these phases is:

• Sustainment and refit — through-life HVAC component supply, retrofit and refit of visiting US/UK submarines and the eventual Virginia-class fleet at HMAS Stirling.
• Module fabrication ramp — Australian fabricators including ASC, BAE Systems Australia, Civmec, Austal and Luerssen Australia building competency in submarine-grade HVAC module work, often via subcontract to UK and US primes.
• Sovereign build — full HVAC duct fabrication for SSN-AUKUS at Osborne, with material traceability, FAT witnessing and class/defence approval pathways embedded in the supply chain.

SBKJ is positioned to supply the auto duct lines, spiral tubeformers and TDF flange machinery that Australian shipyards and module fabricators need to scale stainless-steel HVAC duct production to AUKUS-grade quality and traceability.

Naval shipbuilding HVAC specifics — damage control, NBC, magnetic signature, shock

Naval HVAC ductwork carries five engineering loads that commercial HVAC does not:

Damage control and compartmentalisation

Naval vessels are designed to remain operational after battle damage. HVAC ductwork must respect the watertight and gas-tight compartment boundaries of the damage-control plan, with isolation dampers at every penetration that close on damage-control alarm. Duct routing avoids creating cross-compartment leak paths that could compromise compartmentalisation under flooding or fire. The damage-control isolation damper is a more aggressive specification than commercial fire damper: it must close fully and seal gas-tight against compartment overpressure of typically 30–50 kPa (compared to a few hundred Pascals on commercial systems), it must do so within 1–2 seconds of alarm signal, and it must do so reliably after sustained shock and vibration exposure. The fabrication standard for the duct adjacent to the damper, including the connection geometry and the support detail, is correspondingly tighter.

NBC (nuclear, biological, chemical) protection

Modern naval vessels include a citadel — a sealed gas-tight zone within the ship — pressurised with filtered air to prevent chemical or biological agent ingress. HVAC ductwork into the citadel passes through filter banks (HEPA + activated carbon for chemical agents), with overpressure plenums and quick-acting isolation dampers on alarm. AUKUS submarines and Australian Hunter-class frigates both have citadel architecture.

Magnetic signature management

For submarines and mine-countermeasure vessels, ferromagnetic material in the structure increases magnetic signature and detectability. Non-magnetic 316L stainless (with controlled delta-ferrite content) and specific austenitic stainless grades are used for HVAC duct in signature-critical spaces. The duct fabrication line must be configured to avoid contamination of non-magnetic material with carbon steel particulate from adjacent processes.

Shock and vibration tolerance — MIL-S-901

Naval HVAC duct hangers, fixings, fans and equipment frames are typically tested or calculated to MIL-S-901 shock requirements (lightweight, mediumweight or heavyweight class depending on installation) and to MIL-STD-167 vibration limits. The fabrication tolerance is tighter than commercial: weld quality, hanger spacing, expansion joint behaviour and damper actuator margin all have to survive the design shock event without permanent deformation or function loss. Submarine HVAC components escalate the shock requirement further with extended-duration high-amplitude shock simulating the survivability case for a near-miss underwater detonation. The qualification pathway is typically a combination of finite element calculation (for large or unique components) and hammer-table or barge-test physical shock testing (for serial components and smaller assemblies). The cost of qualification is significant — six-figure USD per component family is typical — and drives strong preference for re-using qualified standard items rather than introducing new component variants.

Electromagnetic compatibility (EMC)

Duct routing avoids creating loop antennas or interfering with combat system signal paths. Bonding and grounding of the duct system to ship structure is specified, and stainless duct can act as both an EMI shield and a current path that must be designed not to introduce noise into nearby cable runs.

Submarine HVAC — atmosphere, signature, confined space

Submarine HVAC is the most demanding ductwork environment in marine engineering, integrating mechanical ventilation with atmosphere revitalisation chemistry.

Atmosphere monitoring and revitalisation

A submerged submarine is a sealed gas-tight environment. Crew respiration and equipment off-gassing build CO2, deplete O2 and accumulate trace contaminants (CO, hydrogen, hydrocarbons, refrigerant leakage). The atmosphere control system includes:

• CO2 scrubbing — typically MEA (monoethanolamine) absorption or solid-bed amine, with scrubbed air returned to the HVAC distribution.
• O2 generation — typically electrolytic from seawater on nuclear submarines, with O2 introduced to the HVAC supply.
• CO/H2 catalytic burners — handling trace combustibles.
• Aerosol and particulate filtration — including HEPA and activated carbon for chemical contaminants.
• Continuous gas monitoring — O2, CO2, CO, H2, refrigerant, and combustible gas at multiple points throughout the boat.

HVAC ductwork integrates with all of the above; duct sizing, leakage class and material chemistry are all coordinated with the atmosphere chemistry plan.

Confined-space ventilation

Submarine compartments are confined spaces with limited egress. Ventilation rates are calculated for crew metabolic load, equipment heat dissipation and atmosphere control system airflow, with redundancy on the supply side so a single fan failure does not produce hypoxia. Damage-control compartment isolation dampers are quick-acting and tested to seal against the design hull deflection after shock event.

Signature — acoustic and magnetic

Acoustic signature management drives HVAC fan selection (low-noise, vibration-isolated, often with active noise cancellation on key supply paths) and duct construction (lined ducts with acoustic absorptive insulation, smooth internal flow paths to minimise vortex shedding noise). Magnetic signature drives non-magnetic material selection.

Cruise ship HVAC — passenger comfort and infectious disease control

Cruise ship HVAC has been transformed by post-COVID infectious disease control requirements layered on top of the existing comfort, fire safety and weight-budget constraints.

Passenger comfort — ISO 7547

ISO 7547 specifies the design ambient conditions and the air change rates expected for accommodation comfort on commercial vessels. Cruise ships generally exceed the ISO 7547 minimum, with cabin design conditions in the 22–24 °C summer and 21–22 °C winter range, supply air at 14–18 °C, 30–60% RH band, and 8–12 ACH typical with higher rates in galley, hospital and theatre spaces.

Infectious disease control — post-COVID

Cruise lines and class societies now expect higher outdoor-air fractions on key recirculation paths, MERV-13 to MERV-14 filtration on accommodation supply (and HEPA on hospital, isolation and life-support areas), and zonal isolation capability so an outbreak in one accommodation block can be HVAC-isolated from adjacent blocks. UV-C in-duct disinfection is increasingly specified on return air paths. Duct material in life-support and hospital paths often defaults to 316L stainless for cleanability.

Galley exhaust

Galley exhaust on a cruise ship handles thousands of meals daily across multiple kitchen clusters. The duct system carries grease-laden vapour that requires continuous scheduled cleaning, fire suppression integration (typically wet chemical at the hood and dry chemical or CO2 in the duct), and bulkhead penetration of A-class divisions handled by type-approved fire/grease dampers. Stainless construction is universal, with welded longitudinal seam to prevent grease leakage and external duct fire spread. Galley exhaust is the single highest fire-risk HVAC route on any vessel, and the construction specification reflects that: continuous welded longitudinal and transverse seams, no Pittsburgh or snaplock joints anywhere in the run, smooth internal finish to minimise grease deposition, accessible cleaning ports at every elbow and on every straight section over 3 m length, and redundant fire suppression that includes both internal duct extinguishing agent and external fire protection rating. The fan station at the discharge is typically segregated from accommodation areas with multi-hour fire-rated separation, and the duct fire-rating from the hood through to the discharge point is engineered as a single integrity envelope.

LNG carrier HVAC — cargo machinery, BOG, ATEX zones

LNG carriers have highly specialised HVAC requirements driven by cargo properties (cryogenic, flammable, evaporative) and the resulting hazardous-area zoning.

• Cargo machinery space ventilation — high air change rates (typically 30+ ACH) for cargo pump and compressor rooms, with extract-only fan strategy and gas detection at the extract plenum.
• BOG (boil-off gas) management — Zone 1 and Zone 2 areas around the cargo tank dome and any GVU (gas valve unit) require explosion-protected HVAC components and fire-and-gas damper coordination.
• Tank deck zoning — IGC Code zone definitions are tighter than IEC 60079 generic zoning, with specific distances from cargo tank and dome.
• Accommodation pressurisation — accommodation block sealed and pressurised against cargo deck, with gas detection on intake and shutdown logic on combustible gas alarm.

FPSO and FLNG — process modules, accommodation, helideck, life support

FPSO (Floating Production Storage and Offloading) and FLNG (Floating Liquefied Natural Gas) facilities combine all of the offshore production HVAC challenges with marine vessel constraints. Australian operations on the Northwest Shelf include Shell's Prelude FLNG (the largest floating structure ever built), INPEX's Ichthys floating offload terminal, Woodside's Pluto operations, Chevron's Wheatstone and Gorgon facilities. Bass Strait operations are dominated by ExxonMobil/Esso legacy fields. The Bonaparte Basin and Browse Basin host current and planned developments.

Process module HVAC

Process modules are typically Zone 1 or Zone 2, with extract-only ventilation strategy, explosion-protected fan motors, fire-and-gas damper coordination, and routing that respects zone boundaries. Duct material is typically 316L stainless or FRP composite depending on chemical service. Massive air volumes (multiple 100,000 m³/h fan stations are common) drive large duct cross-sections and dedicated fan houses. The extract-only ventilation strategy is fundamental to offshore process module HVAC: the module is held at slight negative pressure relative to the surrounding open-air environment so that any process gas leak migrates outward through louvres rather than inward to non-hazardous areas. Supply air enters via natural-ventilation louvres or filtered intakes from the upwind side, sweeps across the module, and is extracted through Ex-rated fan stations at the downwind end. Calculation of the required extract rate is done per API RP 14C and the relevant class society offshore HVAC rule, factoring in the largest credible release scenario (typically a small-bore connection failure on a high-pressure line) and the dilution time-to-LEL target. Typical Australian Northwest Shelf process module extract rates are 12–30 ACH on enclosed modules, with naturally ventilated modules achieving similar dilution through wind-driven flow through louvres.

Accommodation modules

Accommodation modules house 100–250 personnel on a typical FPSO, with hotel-grade HVAC standards, citadel-style pressurisation against the surrounding hazardous area, gas detection on intake, and fire/gas isolation on alarm. Material defaults to galvanised G275 internally and 316L stainless for outboard and humidity-exposed sections. Accommodation pressurisation is typically 50 Pa positive against the surrounding hazardous-area atmosphere, with continuous gas detection on the outdoor air intake and an automatic shutdown logic that closes the intake fire/gas damper, isolates the supply fan and reverts the accommodation envelope to a sealed state on combustible gas alarm. The accommodation HVAC must continue to function during this isolation period via a smaller emergency air system to maintain liveable conditions for the muster duration. Helideck-adjacent accommodation has the additional consideration of jet fuel vapour ingress during refuelling abort scenarios, with the intake gas detection extended to monitor for jet fuel hydrocarbons as well as production gas.

Helideck

Helidecks integrate fire suppression, ventilation of helicopter refuelling areas, and AGCS guideline compliance. HVAC interfaces with the deck-integrated foam fire suppression system and the helicopter refuelling vapour-control plenum.

Life-support and critical safe areas

Control rooms, computer rooms, telemetry rooms, electrical switchrooms and the muster/refuge areas are designated safe haven and are HVAC-pressurised, gas-tight, with filtered intake and fire/gas alarm integration. These spaces follow API RP 500/505 and the operator's specific safety case.

Helideck heating, ventilation and fire suppression

Helideck HVAC is a specialised sub-discipline. Australian offshore operations use AGCS guidelines and Civil Aviation Safety Authority (CASA) requirements on helideck integrity. The HVAC scope covers:

• Refuelling vapour extraction during fuel transfer.
• Heating of pilot rest and refuelling control rooms in cold-water operations (less critical in tropical Australian context, more critical in southern operations).
• Coordination with the deck-integrated fire suppression system — typically high-expansion foam — including damper closure on fire alarm and post-incident smoke clearance.
• Helicopter refuelling abort scenarios — mass airflow extraction to clear flammable vapour.

Ventilation rates per ISO 7547 and ISO 8861

Marine ventilation rates are calculated per the relevant ISO standard or class society rule, with the following typical targets in 2026 practice:

• Accommodation cabins — 8–12 ACH per ISO 7547, with outdoor air component meeting IMO and class society minimums.
• Public spaces (lounges, dining) — 10–15 ACH, with higher rates for theatres and casinos.
• Galley — 30–60 ACH on extract, with makeup air sized for door-balanced operation.
• Engine room — 30–60 ACH per ISO 8861, depending on installed power and cooling demand.
• Cargo holds during loading — up to 200+ ACH for sensitive cargoes (chemical, fruit, vehicle), often via dedicated rotary-driven fans.
• Battery rooms — 6–10 ACH minimum, with hydrogen detection and explosion-protected components.
• Hazardous-area extract — flow rate calculated to maintain dilution below LEL fraction, typically 12+ ACH minimum with continuous monitoring.

Fire dampers, smoke control and bulkhead penetrations

Every HVAC duct penetration of a fire-rated division must use a type-approved damper or sleeve maintaining the rated fire integrity.

A-class divisions

A-60 dampers are the most common requirement on cruise ships and naval surface vessels. Type approval is via class society (ABS, DNV, LR, BV) and Marine Equipment Directive (MED) marking for European-flag vessels. The damper must close on thermal trip (fusible link or electric actuator with thermal sensor), seal gas-tight, and maintain the rated fire integrity for the full duration.

B-class divisions

B-15 dampers are used for cabin and corridor wall penetrations. Lower thermal mass than A-class but still type-approved.

H-class divisions

H-class (H-60, H-120) dampers are tested against the rapid-rise IMO hydrocarbon time-temperature curve and used on tankers, LNG carriers, FPSOs and offshore platforms. Construction is heavier with higher-grade insulation and shock-tested actuators.

Smoke control

HVAC duct on cruise ships and large passenger vessels often doubles as smoke evacuation route, with positive pressurisation of stairways and refuge zones during fire emergency. The duct fire integrity, damper actuation logic and fan capacity all coordinate with the fire safety plan approved by the class society.

Chilled water plant integration with HVAC distribution

Marine and offshore HVAC distribution is typically chilled-water based, with central chiller plant feeding terminal AHUs and fan coil units distributed through the vessel. Chilled water piping runs in parallel with HVAC ductwork, sharing the same support and routing constraints. The duct fabrication scope on a typical project covers:

• Supply and return duct from AHU to room terminals.
• Outdoor air intake duct, often with louvred weather-deck termination.
• Exhaust duct to weather deck or safe zone, with weatherproof termination and back-draught damper.
• Galley grease-laden vapour exhaust (separate, welded stainless).
• Toilet/sanitary exhaust (typically galvanised, smaller cross-section).
• Battery room and hazardous-area extract (Ex-rated components).

SBKJ machinery for marine and offshore projects

SBKJ supplies a configured set of HVAC duct fabrication machinery for marine and offshore projects, with stainless-steel handling, FAT witnessing and class society approval pathways included. The machinery configuration for a marine or offshore project differs from a standard commercial line in five ways: tooling material is upgraded for stainless wear life, lubricant chemistry is selected to avoid stainless contamination, PLC programmes hold separate material recipes for galvanised and stainless, the FAT script includes class society witness points, and the documentation pack includes mill certificates, weld procedure qualification, and material traceability to the buyer's project standard.

SBAL-V auto duct line — stainless variant

The SBAL-V auto duct line in stainless variant produces 316L rectangular duct with TDF flange, Pittsburgh seam and laser-welded longitudinal seam options. Tolerance class meets SMACNA, EN 1505 and class society requirements; output is matched to the buyer's coil specification at quotation. The line accepts coil widths to 1,550 mm and stainless thicknesses to 1.5 mm, with PLC-controlled tooling positioning and full traceability of every metre of output to coil heat number for naval and AUKUS-grade quality plans. See the auto duct line catalogue.

SBTF stainless tubeformer — engine room and exhaust

The SBTF stainless tubeformer produces spiral round duct in 316L stainless, suitable for engine room ventilation, exhaust paths and hazardous-area extract. Diameter range 80–2,500 mm, wall thickness up to 1.5 mm stainless. The tubeformer's spiral lock-seam geometry is a recognised low-leakage construction for class society approval, with leak class corresponding to SMACNA Seal Class A. For higher leak class requirements (welded-seam duct), the SBTF integrates with plasma and TIG welding heads on the seam track. See the spiral tubeformer catalogue.

TDF flange — tight pressure class

For higher pressure classes typical of naval and offshore systems (1,000–2,500 Pa), the SBKJ TDF flange machine produces the integral duct flange in stainless or galvanised, with precision corner formation and consistent gasket seat. TDF flange is the preferred jointing method for class-approved ductwork because the flange profile is repeatable and the leakage class is consistent. The TDF jointing system also reduces shipboard erection time compared with bolted angle flanges, an important factor on shipyard schedules where HVAC is one of many trades competing for compartment access.

Welding integration

For welded longitudinal seam stainless duct (galley exhaust, hazardous-area, naval and submarine), SBKJ integrates plasma and laser welding stations with the auto duct line. The welding scope covers ASME Section IX qualified weld procedures, AWS D1.6 stainless welding, and class society type-approved weld qualification records. For projects requiring radiographic inspection of welds (typical on submarine and naval), the production line includes an inline NDT bay where every duct module can be 100% radiographically inspected before shipment. See our companion guide on welding methods in HVAC duct fabrication for detailed weld procedure discussion.

Procurement, lead time and FAT — the marine project reality

Marine and offshore HVAC procurement runs on shipyard schedule discipline. The typical project sequence is:

1. Class society drawing approval — 4–8 weeks from issue of HVAC drawings to class society stamp.
2. Material procurement — 8–16 weeks for 316L coil and special alloys depending on global mill availability.
3. Fabrication machinery purchase — 90–120 days for an SBKJ auto duct line from purchase order to bill of lading, with class society type approval witnessing built into the FAT schedule.
4. FAT at SBKJ partner production facility — witnessed by ABS or DNV surveyor (or BV/LR/RINA depending on project), with prime contractor quality witness for defence projects.
5. Ocean freight to Australian shipyard — 30–45 days to Henderson, Adelaide, Sydney or Melbourne, with ISPM-15 fumigated crating and chloride/humidity protection.
6. On-site commissioning — SBKJ engineers supervise installation, commissioning, operator training and first-article fabrication, with class society survey of the fabrication facility before serial production.
7. Serial production — duct module fabrication against approved drawings, with material traceability tags, in-process inspection records and final QA sign-off forms for class society audit.
8. Onboard installation — duct modules erected against approved drawings, with leak test per class society procedure and air balance per ISO 7547/ISO 8861.
9. Sea trial sign-off — class society on-board survey of HVAC for sea trial readiness, defects punch-listed and cleared before vessel handover.

Henderson WA and the Australian shipbuilding precinct

The Henderson shipbuilding precinct south of Perth is the geographical heart of Australian naval and offshore fabrication. Companies operating at Henderson in 2026 include:

• Civmec — large fabrication and assembly halls, naval surface vessel module work, offshore module fabrication.
• Austal — aluminium hull fabrication, Cape-class patrol boats, Evolved Cape-class patrol boats.
• Luerssen Australia — Arafura-class OPV programme.
• BAE Systems Australia Henderson — naval sustainment, refit and through-life maintenance.
• BAE Systems Australia Maritime — Hunter-class frigate work shared with Adelaide.

The Adelaide shipbuilding precinct at Osborne Naval Shipyard hosts ASC (Australian Submarine Corporation) and BAE Systems Australia Maritime, with the Hunter-class frigate Programme and the future SSN-AUKUS submarine build planned at the Osborne South Yard. Both Henderson and Adelaide are scaling fabrication capacity, workforce and supply chain to meet the AUKUS programme demand.

SBKJ is engaged with Australian shipyard and module fabricator procurement teams as the supplier of choice for stainless-steel HVAC duct fabrication machinery, with the FAT witnessing pathway, class society type approval and Australian engineering support at our Box Hill North VIC office. See our Australia regional page for shipyard project context.

Comparing material choices — galvanised vs stainless

For projects mixing stainless and galvanised duct, our companion guide Galvanised vs Stainless Steel Duct covers the full cost, durability and fabrication trade-offs.

Onboard installation, leak testing and air balancing

The duct module that leaves the fabrication facility is only halfway through its compliance journey. Onboard installation, leak testing, air balancing and class society survey are the second half, and they happen on the shipyard schedule alongside dozens of other trades competing for compartment access.

Installation against approved drawings

Duct erection on a ship or offshore facility is done against drawings approved by the class society. Each module has a unique identifier traceable to the fabrication record, and the installation team reports against the approved isometric to confirm that what was built matches what was drawn. Deviations are managed through a formal Field Change Notice (FCN) procedure with class society re-approval if the deviation crosses an engineering threshold (material change, pressure class change, route change through fire division).

Leak testing

Once installed, the duct system is leak tested per the class society procedure. Typical practice is pressurising sections to 1.25 times working pressure, isolating supply, and measuring pressure decay over a defined hold period. Acceptable leak rates depend on the duct seal class (A, B or C per SMACNA, with corresponding class society interpretation) and the service the duct supports. Hazardous-area extract duct is typically held to seal class A (effectively zero measurable leak) to ensure that any cargo or process gas in the extract stream is safely conveyed without leakage into safe areas. Galley exhaust duct is tested for both pressure integrity and grease leak resistance, with the latter typically a smoke or visual inspection after thermal exposure.

Air balancing

After leak test, the duct system is air-balanced against the design intent. Air balancing involves measuring flow at every grille and diffuser, adjusting volume control dampers and balancing dampers, and producing a Test, Adjust and Balance (TAB) report showing actual versus design flow at each terminal. Class society survey of air balance is standard practice on accommodation HVAC, with documented sign-off of TAB report before sea trial. Engine room HVAC is typically air-balanced under load conditions during sea trial itself, with engine running at design conditions and the engine room HVAC at full design flow.

Sea trial sign-off

Sea trial is the final integrated test of the HVAC system. With the vessel underway, the HVAC plant is run through start-up, normal operation, fire alarm response, gas alarm response, blackout response and re-start. The class society surveyor witnesses the trial and signs off the HVAC for handover. Defects raised during sea trial are punch-listed and cleared before vessel acceptance. For naval and AUKUS programmes, the prime contractor quality team and the eventual operator (Royal Australian Navy) also witness sea trial and contribute to the punch list.

Lessons from common project failures

Six recurring project failures account for the majority of HVAC duct disputes on Australian marine and offshore projects:

1. Material specification ambiguity at module interface — adjacent modules built by different subcontractors meet at a flange and the material specification doesn't match. Resolution requires a transition piece and re-approval; rework cost typically 5–10x the avoided cost of consistent specification.
2. Late class society drawing approval — drawings issued late or returned for re-work delay fabrication start. The class society approval cycle should start at concept design, not after detailed engineering is complete.
3. Coil specification mismatch — the coil width and thickness ordered does not match what the fabrication line is configured for. Resolution is either re-procurement (long lead time) or accepting downgraded output (compromised tolerance). Specifying the line and the coil together at procurement stage avoids this.
4. FAT witnessing schedule slip — class society surveyor unavailable on the FAT date, causing fabrication line shipment delay. SBKJ coordinates surveyor scheduling 4–8 weeks in advance to avoid this.
5. ISPM-15 crating non-compliance — non-compliant crating impounded at Australian customs, with demurrage at port-storage rates while replacement crating is arranged. ISPM-15 stamp on every wood component avoids this.
6. Onboard fit-up issue against approved drawings — duct module dimensions do not match installed structural geometry. Resolution requires field cutting and re-welding under class society witness; cost is significant and schedule impact is days to weeks per occurrence. Tight fabrication tolerance and 3D scanning of installed structure before fabrication start avoid this.

Adjacent industry guides

Marine and offshore HVAC shares engineering vocabulary with two adjacent industries we cover in dedicated guides:

• Mining ventilation HVAC duct guide — the underground mining industry shares hazardous-area, high-airflow and corrosion-resistant duct requirements with offshore facilities.
• Hydrogen production HVAC duct guide — green hydrogen facilities share Zone 1/Zone 2 hazardous-area requirements and Ex-rated component coordination with FLNG and LNG carriers.

FAQ — marine and offshore HVAC ductwork

Which class societies approve marine and offshore HVAC ductwork?

The seven IACS members covering marine and offshore HVAC are ABS, DNV, Lloyd's Register, BV, ClassNK, RINA and KR. For Australian-flag vessels and Australian-waters offshore facilities, AMSA recognises all IACS members. AUKUS and naval programmes layer defence approvals from the Australian Department of Defence and the relevant prime contractor.

What materials are used for marine HVAC ductwork?

316L stainless for marine atmosphere, cupronickel 90/10 for legacy naval and seawater applications, FRP composite for weight-sensitive offshore and chemical service, and hot-dip galvanised G275 for protected accommodation interior. SBKJ machinery handles all four families with appropriate tooling.

What is the lead time for class-approved marine HVAC duct fabrication machinery?

For an SBKJ auto duct line configured for stainless steel and class society approval, plan for 90–120 days from purchase order to bill of lading. Class society witnessing of the FAT is built into the schedule. Ocean freight to Australian shipyards adds 30–45 days.

How does AUKUS affect HVAC duct supply chain in Australia?

AUKUS drives demand for naval-grade HVAC fabrication capacity at Henderson WA and Adelaide SA. SBKJ supplies the machinery — auto duct lines, spiral tubeformers, TDF flange equipment — tuned for higher tolerance and full traceability that naval and defence-prime quality plans require.

What are A-class, B-class and H-class fire divisions?

SOLAS Chapter II-2 fire integrity classes. A-class (A-60, A-30, A-15, A-0) maintains structural integrity for that minute count under cellulosic fire test. B-class is non-load-bearing fire-resistant, typically B-15. H-class is hydrocarbon fire integrity for tankers, FPSOs and platforms. Every duct penetration of a fire division uses a type-approved damper.

What ventilation rates apply to ship spaces?

ISO 7547 for accommodation typically 8–12 ACH; ISO 8861 for engine rooms 30–60 ACH; cargo hold loading up to 200+ ACH; galley extract 30–60 ACH; battery rooms 6–10 ACH minimum with hydrogen detection.

Where is FAT witnessed for marine HVAC machinery?

At the SBKJ partner production facility, with class society surveyor (most commonly ABS or DNV for Australian projects) witnessing against the contract performance specification. Defence and AUKUS projects add prime contractor quality witness.

What hazardous-area zones apply offshore?

Zone 0 (continuous), Zone 1 (likely in normal operation), Zone 2 (unlikely, short duration) per IEC 60079, or Class I Division 1/2 per US standards. API RP 500 and 505 cover offshore zone classification. HVAC components in hazardous areas must be Ex-rated and the safe/hazardous separation must be gas-tight.

How SBKJ supports your marine or offshore project

SBKJ Group is an Australia-based supplier of HVAC duct fabrication machinery, headquartered in Box Hill North VIC, supporting shipyards and module fabricators across the Australian naval shipbuilding precinct, Northwest Shelf offshore operations, and offshore vessel through-life maintenance and refit. We supply auto duct lines, spiral tubeformers and TDF flange equipment configured for 316L stainless, FRP and galvanised, with class society type approval pathways, FAT witnessing coordination, and Australian engineering support.

For procurement teams at Australian shipyards, naval primes, offshore operators and module fabricators, our engineers provide:

• Configured machine specifications matched to your project's coil and tolerance requirements.
• FAT witnessing coordination with ABS, DNV, Lloyd's Register, BV or your nominated class society.
• Defence-side prime contractor quality witness coordination for AUKUS and Naval Shipbuilding Plan projects.
• Documentation pack including class society type approval, ISO 9001 certificate, FAT signed report, mill certificates, weld procedure specifications, and PLC programme backup.
• On-site commissioning, operator training and first-article fabrication supervision at Henderson WA, Adelaide SA, Sydney, Melbourne or your project location.
• Through-life spare parts continuity guaranteed for at least 10 years from commissioning.

Talk to an SBKJ marine engineer about your project →