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Marine & Station Keeping
Moonpool Doors and Gates
Moonpool Doors and Gates close the hull opening under the drill floor and guard its edges. The Category covers hydraulic hatches that open downward into the moonpool, sliding and hinged doors, their locking cylinders and power units, and the safety gates, barriers and handrails that keep people and equipment from falling into the opening.
What doors and gates do
Closed moonpool doors stop waves and spray rising into the moonpool area. They also give the crew a working deck over the opening and reduce the risk of dropped objects into the sea. On many drillships each door leaf hinges at the moonpool edge and opens downward, driven by hydraulic cylinders. Separate locking cylinders or bolts hold the leaves shut against wave slam from below. Sliding doors move sideways on tracks instead. Gates and barriers around the moonpool edge close off the drop when the doors are open.
Configurations
| Type | How it moves | Notes |
|---|---|---|
| Downward-opening hatch | Hinges down into the moonpool | Common on drillships, leaves hang in the moonpool when open |
| Sliding door | Moves sideways on tracks | Needs clear deck space beside the opening |
| Hinged upward door | Folds up onto the deck | Older and smaller moonpools |
| Safety gate or barrier | Swing, slide or lift | Interlocked with door and cart movement |
MacGregor is one well-known maker of moonpool hatch systems.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Clear opening | Must pass your BOP and trees | m by m (ft by ft) |
| Deck load when closed | Equipment and people on top | kN/m² (psf) |
| Wave slam design load | Load from below in the moonpool | kN/m² (psf), per design |
| Cylinders per leaf | Redundancy and force | Count, bore and stroke |
| Locking | Holds leaves shut | Hydraulic locks, fail-safe option |
| Hydraulic pressure | Power unit fit | bar (psi) |
Standards and class
Class approves moonpool doors and their supports as part of the hull structure, using the society's hull and closing appliance rules, and surveys them with the hull. The design load case includes wave slam in the moonpool and deck loads on the closed doors. Hydraulic cylinders and piping follow the society's machinery rules. Gates and handrails follow the rig's safety case and the flag state's requirements for guarding openings.
Failure modes and inspection
- Leaf structure cracks and dents from wave slam and dropped objects. Inspect welds at hinges and edges with magnetic particle testing.
- Hinge pins and bushings wear and seize. Measure clearances and check grease paths.
- Cylinder rods score and pit, and seals leak. Inspect rods and ask for the last rebuild.
- Locks and latches stop engaging fully as parts wear. Function test every lock with the doors under load.
- Seals on the coaming tear or harden. Check the seal and its seating.
- Limit switches and interlock sensors fail in spray. Test each one against the control logic.
Documentation
- Class design approval and the drawings it covers.
- General arrangement drawing with the opening and coaming dimensions.
- Hydraulic schematic and cylinder data.
- OEM service history and the last cylinder rebuild.
- Interlock and control logic description.
- Inspection reports for structure and hinges.
Integration
Doors fit one moonpool opening and coaming, so a used door set usually only fits a sister rig. Otherwise a new coaming, frame or hinge mounting is needed, with class approval. Check that your hydraulic power unit gives the pressure and flow the cylinders need. Then confirm that the interlocks connect to your carts, handling systems and drill floor controls.
Refurbishment and the used, surplus or refurbished choice
A refurbishment renews pins, bushings and seals, rebuilds the cylinders, repairs the structure and ends with a function test of opening, closing and locking under class. Unused surplus door sets from cancelled newbuilds suit sister rigs. A used set that does not fit is still a source of cylinders, locks and seals. Gates and barriers are simpler items and are often reused. The carts that pass over the opening are in Moonpool Trolleys and Carts.
FAQ
Frequently asked questions
How do moonpool doors work on a drillship?
On many drillships the moonpool doors are hydraulic hatches that open downward into the moonpool, each leaf moved by cylinders. Separate locks hold the leaves shut against wave slam from below. Some rigs use sliding doors on tracks instead.
Can used moonpool doors fit a different rig?
Only if the opening size and coaming match, which usually means a sister rig. Otherwise expect a new frame or coaming and structural work approved by class. The cylinders, locks and seals from a set that does not fit are still useful as spares.
What should I check on used moonpool hatch cylinders?
Check the rods for scoring and pitting, the seals for leaks, and the pins and bushings for wear. Ask for the pressure rating, bore and stroke and the last rebuild record. Leaking or pitted cylinders need a rebuild by a hydraulic workshop before use.
Are moonpool doors class items?
Yes, class approves moonpool doors and their supports as part of the hull structure and surveys them with the hull. The design covers wave slam from below and deck loads on top. A replacement door set needs class approval of its drawings and a survey after fitting.
Looking for moonpool doors and gates?
Tell us what you need and we will find out what is available. We reply within one business day.