Payload and handling
Three sealed compartments, six hatches, six modules, and a handling concept that needs nothing more exotic than a mobile crane.
The compartment is the product.
Three compartments run from station 2.70 m to 13.50 m at a 3.60 m pitch, each 3.50 × 2.80 × 1.45 m internally — 14.21 m³ apiece, 42.63 m³ in total. Each takes two payload modules of 2.44 × 1.09 × 1.10 m, so the vessel carries six.
Cargo deadweight is 17.0 t, which is 2,833 kg of cargo per module at a reference density of 399 kg/m³ against the gross compartment volume. Module lift including the 237 kg tare is 3,071 kg.
The compartment structure is 8 mm plate stiffened at 300 mm — 2,027 kg each, 6.08 t for the three. That is heavier than a concept study would assume, and deliberately so: the boundary is designed for the loss-of-pressurisation case rather than having that case excluded by assumption.
| Configuration | 3 sealed pressure-balanced compartments |
| Compartment envelope | 3.50 × 2.80 × 1.45 m |
| Volume per compartment | 14.21 m³ |
| Total payload volume | 42.63 m³ |
| Compartment pitch | 3.60 m · stations 2.70 to 13.50 m |
| Cargo deadweight | 17.0 t |
| Payload modules | 6 · 2 per compartment |
| Module envelope | 2.44 × 1.09 × 1.10 m · 4 mm skin |
| Module clearances | 60 mm wide, 60 mm long, 350 mm standing |
| Cargo per module | 2,833 kg |
| Lift mass per module | 3,071 kg |
| Module lifts | 6 scissor tables · 1,670 mm stroke, 250 mm collapsed |
| Reference cargo density | 399 kg/m³ |
| Mounting | Four machined flange mounts per compartment, landing on ring-frame stations |
| Connectors | SubConn / MCBH — 44 bulkhead and 44 cable ends, dry 1-atm junction boxes |
Pressure balance
Dry at one atmosphere, at depth.
The compartments are charged with air to sea pressure as the vessel dives. The structure therefore carries a 1.00 bar design differential instead of the full 2.011 bar head, inside a ±0.15 bar control band with relief at 0.5 bar.
Two things follow. The boundary can be lighter for the same volume, which is what makes 35 m³ affordable inside an 18 m hull. And the inside of a compartment stays a dry, one-atmosphere space — so payload electronics, connectors and mechanisms can be ordinary topside hardware rather than pressure-rated subsea equipment. That is usually worth more to an integrator than any figure on the specification sheet.
Total pressurised volume is 50.74 m³ — the three compartments plus the six access trunks — and the air plant is sized around it.
| Principle | Compartments charged with air to sea pressure when submerged |
| Design differential | 1.00 bar |
| Control band | ±0.15 bar · ±1.49 m of depth |
| Relief setting | 0.5 bar |
| Proof test | 3.017 bar — 1.5× the unbalanced head |
| Boundary plate | 8 mm on 300 mm stiffening |
| Design-case stress | 70.3 MPa · SF 3.06 |
| Loss-of-pressurisation stress | 141.4 MPa · SF 1.52 |
| Material | 5083-H116 · 215 MPa yield |
| Pressurised volume | 50.737 m³ · compartments and trunks |
| Compartment mass, each | 2,027 kg |
| Free air per cycle | 142.78 m³ |
| Compartment charge | 100.70 m³ |
| Main ballast blow | 42.07 m³ |
| Bottles | 13 × 50 L at 300 bar |
| Stored free air | 195 m³ |
| Compressor | 15 m³/h |
| Recharge time | 12.85 h |
| Design margin | ×1.35 on one full cycle |
| Charged-air mass | 123.4 kg — carried in the weight statement |
Deck access
Six hatches, dogged submarine-style.
Each hatch gives a 1.15 × 2.50 m clear opening in a 1.35 × 2.70 m cover of 8 mm plate, stiffened by nine members at 300 mm, 305.8 kg complete. It hinges on the outboard long edge, opens to 95° and is balanced on two gas struts at 1.21 kN, so one person can work it.
Fourteen dogs per hatch at 19.31 kN each bear on a machined seat with a 12 mm nitrile cord. At operating depth the seated load is 653.6 kN — 66.6 tonnes. The closure is fail-safe by geometry: the deeper the vessel goes, the harder the sea holds the cover onto its seat.
Below each hatch is a 1.15 × 2.50 × 0.47 m access trunk carrying the load path from the cover seat down into the compartment top.
| Hatches | 6 upward-hinging, dogged, seated plug closures |
| Clear opening | 1.15 × 2.50 m |
| Cover | 1.35 × 2.70 m · 8 mm plate on 186.5 mm webs |
| Dogs per hatch | 14 at 19.3 kN |
| Seal | 12 mm nitrile O-ring on a machined seat, 100 mm land |
| Opening angle | 95° |
| Balancing | 2 gas springs · 13.2 kN manual effort |
| Uplift, relief valve lifted | 162.5 kN — carried by the dogs |
| Seated load at depth | 653.6 kN · 66.6 t — carried by the seat |
| Opening condition | Surface only |
| Access trunks | 6 · 1.15 × 2.50 × 0.47 m |
Integration
Your module, our mounts.
Modules land on four-point flange mounts. Power and data cross the boundary through SubConn and MCBH penetrations — 44 bulkhead ends and 44 cable ends — into dry 1-atm junction boxes inside the compartment.
The interface is fixed and published: envelope, mount pattern, mass and centre-of-gravity limits, connector map, available power and thermal budget. An integrator can design to it without a conversation. Then we run the stability and trim consequences of that specific fit through the model before anything is cut.
Payload interface control drawings form part of the technical pack released under NDA.
Loading
The whole handling concept is a crane and a pallet.
Open a hatch pair, land the module on its lift, lower it, lock the mounts, mate the connectors, close and dog the covers. No dry dock, no purpose-built shore facility, no bespoke handling frame — the 3,071 kg lift is inside the reach of the mobile crane already standing on most working quays.
What actually fits
Modules cost volume. That is worth saying out loud.
A module is 2.44 × 1.09 × 1.10 m externally in 4 mm skin, which leaves 2.874 m³ inside it. Six of them come to 17.24 m³ — about 40% of the gross compartment volume. The rest goes to module walls, handling clearance and the fact that a rectangular module has to pass a smaller rectangular hole.
That is the real price of modularity and it is not hidden anywhere else in the engineering record either. If the cargo is dense or bulk, the right answer is to stow loose in the compartment and lash by hand through the 1.15 × 2.50 m opening, which recovers the full 42.63 m³. The architecture supports both, and which one suits a given payload is a conversation worth having before a configuration is fixed.
The clearances are asserted by the model rather than assumed: 60 mm wide and 60 mm long through the opening, 350 mm standing inside the compartment. The model does not emit if any of them goes negative.
Bring us the payload and we will size it.
We run your fit through the engineering model and come back with real numbers for it, not a generic figure.