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A Complete Guide to Duct Systems for Marine Applications

Double wall ducts and fittings

Shipbuilding is a highly challenging process especially in terms of installation of ventilation systems and air conditioning. The ventilation system must be resistant to changing weather conditions, high humidity and salinity, while being failure-free and easy in maintenance.

Reliability and maintenance are key aspects of shipbuilding since in the case of some equipment failure at land construction You can easily seek assistance, however, at sea, it is virtually impossible. Employees of vessels must be able to quickly and efficiently repair a failure, otherwise compromised can be a health or life of the ship crew. Since one of the most dangerous situations in on the ship is a fire, the entire ventilation system should be designed and constructed in such a manner that in the case of fire, the fire and smoke do not spread.

The Most Common Duct Systems for Marine Applications are:

  1. Double-wall, insulated spiral ducts and fittings with mineral wool;
  2. Double-wall, insulated spiral ducts and fitting with air insulation;
  3. Single-wall, non-insulated spiral ducts and fittings with EPDM seals.


A complete duct system, both insulated and non-insulated, can be assembled using:

  • spiral ducts: single-wall or double-wall design
  • duct fittings used for joining: female (for joining duct fittings together and male coupling (for joining spiral ducts of the same diameter together), concentric and eccentric reducers (for joining two spiral ducts of different diameters together)
  • duct fittings used for changing the direction of the duct run: bends
  • duct fittings used for branching-off: T-pieces and branches
  • duct fittings used for capping ductwork off: end caps
  • assembly accessories: suspension clamps (for insulated ductwork once-piece clamps CLRU are recommended)

ISOL system consists of 15, 30, 45, 60, 90-degree bends (on the special request we can manufacture any segmented bend from 5 to 85 degree with tolerance  +/-2o), T-pieces, crosses and transition pieces, reducers, concentric and eccentric reducers, couplings, branches, offsets etc.


Isol system

ISOL system - bends, reducers, T-pieces, couplings and endcaps.

Isol safe system

ISOL safe system - bends, reducers, T-pieces, couplings and endcaps.


Both double-wall and single-wall ductwork are manufactured from galvanized steel sheet as a standard, available also aluminium duct system, both insulated and non-insulated when You aim for a more lightweight ventilation system. 

Insulation layer used in ISOL system components is mineral wool classified as a non-combustible material, approved and certified to be used for marine applications. In the ISOL safe system duct fittings, instead of mineral wool, air is used as a thermal insulator, which leads to the lower weight of the ventilation installation.


Duct fittings are provided with factory-installed EPDM rubber seals. Seals are securely fitted on the duct fittings' ends, therefore, eliminating the need for any additional sealants during the ductwork assembly. The seals adhere closely and tightly to the duct wall. It is attached to the end of the fitting, running reliably mounted along the turned-out edge of the fitting. Such a design ensures that the gasket always remains in its place, regardless of installation conditions.

Rubber seals

Rubber seals are factory-installed on the duct fittings.

This material is very resistant to ozone and UV exposure as well as varying temperatures, thus contributing to extended durability. The gasket supports temperatures ranging from - 30˚C to +100˚C.

Dimensions and sizes

Spiral ducts are available as 3-meter lengths (standard), on the request duct can be manufactured in the length from 1 m to 6m. Ducts are spirally rolled with a sheet metal tape, 137 mm wide.

Tubeformer for ducts

Spiral ducts are manufactured using tubeformers.

Double-wall system components: Inner diameter 80-400mm, outer diameter 100-500 mm
Single wall system components: 80-1600 mm (other dimensions on request).

Ducts and fittings with 16mm insulation thickness:
Inner diameter in accordance with the European standard 1506.
Outer diameter equals nominal inner diameter + 32 mm

Double wall insulated sizes

Double-wall spiral ducts - diameter range

Both inner and outer diameter are manufactured in accordance with standard dimensions of the SPIRAL system – the European standard 1506.


Spiral duct and fittings equipped with rubber seal provide airtightness class D (certificate No. 0103/07) as defined in the EN 12237 standard, provided that the assembly is correctly carried out (for assembly, storage and transport instructions, see our Good Practices).

Airtiggtness class testing

All SPIRAL® system components are tested for their airtightness using the following diagram.

SPIRAL® system of circular ducts and fittings with factory-fitted gaskets is certified by RISE Research Institutes of Sweden AB (former SITAC) for tightness class D – certificate No. 0103/07 as defined in the PN-EN 12237 standard.


Double-wall ducts consist of an outer duct and inner duct with a mineral wool insulation layer between them. The inner duct can be manufactured as a standard spiral duct - SPRI or as a perforated duct for better sound insualtion properties - SPRPI. Double-wall design also referred to as double-jacketed, mean inner-outer duct with a layer of insulation with mineral wool between the inner and outer wall. Inner walls of duct fittings are manufactured in pressed design for smooth airflow (with small exception, check the catalogue for details). Outer walls are manufactured in pressed design or in segments, depending on the diameter:

Duct fittings are of double-wall design with air insulation between and equipped with EPDM rubber seals on the fitting's ends boon both outer and inner diameter.


Double wall bend mineral insultion 10 mm

BPLI-90 Double-wall bend - 10mm mineral wool insulation.

Insulated fittings with 16mm insulation: outer jacket is manufactured from segments.
Insulated fittings with 10mm insulation: outer jacket in diameter 100, 125, 150, 160, 200 mm are manufactured in pressed design, the remaining diameters are made of segments.

Double wall bend air insulated

BPLIL-90 Double-wall bend - air insulation.

IZOL®safe-system consists of inner and outer galvanised wall, and air in the middle. The distance between inner and outer walls is maintained by means of special spacer. 

More about Insulation Solutions - You can find here

And more details about Preinsulated Ductwork Systems -  You can find here.