Cylindrical watertight enclosures — up to 4 m diameter and 12 m length — housing complete plantroom equipment beneath the water surface. Each vessel is sized within road-transport envelopes so it can ship on a standard flatbed and be lifted into place as a single piece. Not a converted shipping container: it is an engineered pressure-vessel built specifically for submerged service. We design, fabricate and commission these plantrooms for ports, reservoirs, offshore platforms, aquaculture and any installation where surface real estate is constrained or visual impact is unacceptable.
Zero footprint, thermal stability, acoustic isolation, visual non-impact and natural cooling.
Watertight integrity, hydrostatic pressure, marine corrosion, maintenance access and ATEX compliance.
Packaged plantrooms for marine, freshwater and oceanographic research.
Water recycling and filtration plantrooms for hyperscale, edge and cable-landing data centres.
A Complete Plantroom in a Submerged Cylindrical Pressure Vessel
An underwater plantroom is a cylindrical watertight enclosure built as a pressure-rated cylinder with dished ends — up to 4 m in diameter and 12 m in length, sized within a compact road-transportable envelope so it can be shipped to site on a standard flatbed and lifted into place as a single piece. It is not a converted shipping container: the cylinder geometry is mandatory because pressure vessels under hydrostatic load must be cylindrical with dished ends, since a rectangular shell would require uneconomic plate thicknesses and large internal stiffening. The enclosure houses a complete plantroom — pumps, valves, dosing skids, instrumentation, control panels and even compact treatment units — and is installed below the water surface in a basin, reservoir, port, lake or offshore location.
Schematic cross-section — horizontal cylindrical shell with dished ends, top hatch, ballast saddles and the power/SCADA umbilical that connects the vessel to its surface tie-point.
A Structural Argument Driven by Hydrostatic Pressure
An underwater plantroom is a pressure vessel, not a container conversion. To keep the inside dry the shell must resist the hydrostatic pressure as an external load — and this load grows by 9.81 kPa per metre of submergence. A rectangular shell carries this load primarily in flexure: the flat panels bend inward unless heavily stiffened. A cylinder carries the same load in hoop compression, which steel and FRP both handle with a fraction of the wall thickness.
At 10 m design depth, a rectangular plate enclosure with footprint comparable to a mid-size plantroom would need roughly 18 mm wall plus 100 mm stiffener spacing to meet EN 13445 deflection limits — weighing about 12 t empty. A 2.4 m-diameter cylinder of similar internal volume needs only an 8 mm wall and no internal stiffeners, weighing roughly 4.5 t empty. The cylinder is lighter, cheaper, easier to weld and inherently fatigue-tolerant under wave-loading cycles.
| Property | Rectangular Box | Cylindrical Shell |
|---|---|---|
| Primary stress mode | Plate flexure (bending) | Hoop compression |
| Wall thickness (10 m depth) | ~ 18 mm + stiffeners | ~ 8 mm, no stiffeners |
| Empty weight (mid-size) | ~ 12 t | ~ 4.5 t |
| Pressure code | None standard for > 0.5 barg | EN 13445 / ASME VIII |
| Fatigue tolerance | Poor (panel buckling cycles) | Excellent (membrane stress only) |
| Internal volume utilisation | ~ 95 % | ~ 78 % |
| Lifting / handling | Corner castings | Saddle cradles, lifting lugs |
The 17 % volume penalty of the cylinder is more than recovered in installed cost, weight, weldability and code compliance. For depths above about 2 m, cylindrical is the only economic choice.
Sized Within Road-Transport Limits — Up to 4 m Diameter and 12 m Length
Each vessel is bespoke to its duty, but always engineered within a maximum design envelope of 4 m diameter and 12 m length. Staying inside this envelope is what makes the vessel road-transportable on a standard flatbed, liftable with standard cranes, and shippable to site as a single pre-commissioned piece. Smaller envelopes are used wherever the duty allows — a smaller shell is cheaper, lighter, easier to handle and faster to install.
| Reference | Length (typical) | Diameter (typical) | Internal Volume | Empty Weight | Typical Duty |
|---|---|---|---|---|---|
| Compact | 3 m | 2 m | ~ 7.5 m³ | ~ 2.0 t | Compact pump & dosing skid |
| Standard | 6 m | 2.4 m | ~ 24 m³ | ~ 4.5 t | Full plantroom (pumps, panel, dosing) |
| Large | 12 m | 2.4 m | ~ 50 m³ | ~ 8.5 t | Treatment train + plantroom |
| Large — high diameter | 12 m | 3.5 m | ~ 110 m³ | ~ 14 t | Tall internals (DAF, lamella, MBBR) |
| Maximum envelope | 12 m | 4 m | ~ 145 m³ | ~ 18 t | Largest single-piece submerged plantroom |
All envelopes are pressure-rated for 0–20 m depth as a baseline, with 30 m and 50 m options when site conditions require. Equipment is loaded into the vessel through an end-flange or top-hatch arrangement chosen for the installed orientation. Larger plant duties are met by linking two or more vessels at a seabed manifold rather than exceeding the 4 m × 12 m envelope.
Typical Plantroom Equipment Pre-Integrated
An underwater plantroom is engineered as a complete pre-commissioned skid. Equipment is installed and tested in the shop, the vessel sealed, transported and lowered in. Site work is reduced to mechanical and electrical connections at the umbilical only.
Inlet & outlet pumps, manifold valves, instrumentation. Pumps are installed dry inside the vessel — not flooded submersibles — for service life and maintainability.
Day tanks, metering pumps and chemical injection points for coagulant, flocculant, pH correction or disinfectant. Spill-bunded internal tray.
PLC, HMI, instrumentation marshalling and SCADA gateway. Communications over the umbilical fibre.
Sub-skid DAF for fine TSS or oil removal, integrated with pretreatment. Available in 40' configurations.
Compact biological reactor for ammonia/organic polishing. Air supply via dedicated blower in a dry zone of the vessel.
Multimedia or self-cleaning filter cartridges for polishing duty. Selected for serviceable cartridge replacement during planned hatch openings.
Acid / caustic / lime dosing with day tank, pH probe and reactor section. Reagent selection per site water chemistry.
Leak detection, level sensors, gas detection, emergency vent valves and panic-pull surface alarm. ATEX-classified where required.
Step-down transformer, MCC, UPS and lighting. Single armoured submarine cable from shore or platform.
Where Submerged Plantrooms Replace Surface Plant
Packaged turnkey plantrooms for marine biology, oceanographic, freshwater and environmental research — seawater intake, filtration, sampling, refrigeration, instrumentation and SCADA in a single pre-commissioned vessel.
Research StationsClosed-loop cooling-water filtration, heat-exchange and anti-biofouling plantrooms for hyperscale, edge and cable-landing data centres. WUE 0.01–0.05 L/kWh, 60–70 % cooling-PUE adder reduction vs evaporative.
Data-Centre CoolingSubsea plantroom mounted to platform leg or seabed manifold. Frees deck space and reduces topside weight — a primary Capital expenditure driver on FPSO and platform builds.
Offshore Oil & GasInlet pump and screening plantroom set below low-tide line at a beach intake. No surface structure on the shoreline; reduced visual impact and storm-surge exposure.
DesalinationRecirculating aquaculture system (RAS) plantroom installed within the cage array. Eliminates need for surface walkways and barges; reduces wave-action risk.
AquacultureSubmerged aerator and pump plantroom for shallow reservoir or service-water tank destratification. Whole plant invisible from the dam crest.
Reservoir AerationBerth runoff and bilge-water treatment plantroom mounted under the quay. Treats discharge in place, eliminates pipe runs to a remote shore plant.
Port EffluentService-water and cooling-loop plantroom within the dam intake or cooling-water canal. Constant-temperature operating environment.
Power GenerationOur Six-Stage Delivery Process
Hydrography, soils, design wave, water chemistry, depth envelope, duty cycle.
Plantroom equipment selection and the P&ID, control narrative and instrumentation schedule.
EN 13445 / ASME VIII shell calculations, penetration design, umbilical interface and lifting plan.
Shop-build the vessel, install all equipment, dry pressure-test, run a full factory acceptance test (FAT).
Road or sea transport to site. Crane or marine-lift to the seabed. Diver or ROV connection of the umbilical.
Submerged hydraulic and electrical commissioning, leak survey and operational handover. SCADA tie-in to the shore room.
Standards That Govern Submerged Pressure Enclosures
European unfired-pressure-vessel code governing the cylindrical shell, dished ends, welds and penetrations.
US equivalent — used on platforms operating under US-flag or ABS classification.
Marine structural classification for offshore submerged enclosures; load combinations including wave, current and seismic.
For plantrooms in oil & gas service, the electrical equipment, vent system and gas detection are ATEX-rated.
Hazardous-area electrical equipment, used in combination with ATEX. Covers SCADA panels, lighting and instrumentation.
Marine classification for the lifting frame, ballast and any item routinely lifted to the surface for maintenance.
Zero surface footprint, thermal stability, acoustic isolation, security and sustainability — the eleven reasons to go submerged.
Read AdvantagesWatertightness, hydrostatic pressure, ballast & buoyancy, marine fouling, maintenance access and ATEX — engineering solutions for each.
Read ChallengesPackaged plantrooms for marine biology, oceanography and freshwater research — sampling, filtration, refrigeration and SCADA in one submerged vessel.
Research StationsWater recycling, filtration and heat-rejection plantrooms for data centres — closed-loop cooling that drops WUE by 95–99 %.
Data CentresThe above-surface sister concept — complete plantroom built into a 10', 20' or 40' shipping container shell.
Read MoreEvery underwater plantroom is a one-off — engineered for the duty, depth and water chemistry of the installation site.
Read MoreSubsea plantroom service on platforms and FPSOs — the principal use-case for submerged plantrooms.
Read MoreSubmerged intake plantroom for beach-well and open-intake desalination installations.
Read MoreRecirculating aquaculture plantroom installed within the cage array beneath the working platform.
Read MoreExternal flow, scour, wave-load and internal-process CFD for submerged plantroom design and verification.
Read MoreFrom hydrography and process scoping through pressure-vessel design, fabrication, FAT and wet commissioning — one engineering team, one delivery contract.
Our expertise spans multiple industries with sector-specific water treatment solutions.