A stone dry dock is a fixed basin that admits a floating vessel, closes off the surrounding water and is pumped down to expose the hull. As the water falls, the vessel settles onto prepared supports. The animation illustrates that sequence, while the calculator estimates a rectangular basin’s water volume and the pump rate needed for a selected drainage time.
Stone Dry-dock Interactive Calculator
Enter dock dimensions, estimated gate leakage and target pump-out time. The calculator gives a first-pass rectangular basin volume and pump-rate balance.
Equation Used
- Rectangular full basin at the entered depth.
- Constant leakage and pump rate.
- Vessel displacement and sloped floor volume are not deducted.
The drawing follows Hiscox movement 816: a gated stone basin is pumped down until the vessel settles on bearing blocks and is shored from the walls.
How the dry dock works
The vessel enters the flooded basin and is positioned over bearing blocks. The entrance is closed, pumps remove water, and support transfers from buoyancy to the blocks. Shores between the walls and hull are shown after block contact.
The animation keeps an illustrative draft constant while the vessel floats. Once its keel reaches the blocks, the vessel stays in place as the remaining water drains to the basin floor. This explains the sequence; it does not calculate hydrostatic stability or hull reactions.
Main parts
- Basin and floor: contain the water and support the docking arrangement.
- Gate: isolates the basin from the surrounding water.
- Pumps: remove water while leakage adds to the required flow.
- Bearing blocks: support the vessel as buoyancy decreases.
- Wall-to-hull shores: illustrate lateral support.
Actual block locations, contact pressures, stability and gate loads require the vessel’s docking plan and site-specific engineering. They are not determined by the volume calculation.
Where the arrangement is useful
A drained fixed basin gives access to a vessel’s underwater surfaces for inspection and work. The same basic flood, position, isolate and drain sequence also explains how a graving dock differs from a floating dock or a lifting platform.
The calculator is useful for checking the arithmetic of a first-pass water-volume and flow balance. It does not rate a dock for a vessel, select a pumping plant or establish when people can enter the drained basin.
Basin volume and pump-rate balance
For length L, width W and water depth H, the rectangular volume is V = LWH. For target time t, the net drainage rate is V/t. Required pumping rate is Q = V/t + Qleak.
With dimensions in metres and time in hours, volume is in m³ and flow rates are in m³/h. Leakage share is 100 × Qleak/Q.
For a known constant pump rate greater than leakage, the same balance can be rearranged as t = V/(Q − Qleak). Real drainage differs when flow changes with head, leakage varies, or actual basin shape and vessel displacement differ from this full rectangular volume.
Worked example: a rectangular flow estimate
For a hypothetical basin 220 m long, 32 m wide and 11 m deep, assume constant leakage of 300 m³/h and a target time of 4 hours.
- Volume = 220 × 32 × 11 = 77,440 m³.
- Net drainage rate = 77,440/4 = 19,360 m³/h.
- Required pump rate = 19,360 + 300 = 19,660 m³/h. Leakage is about 1.53% of that rate.
If four hypothetical pumps each deliver 5,000 m³/h at the actual operating head, their combined 20,000 m³/h gives about 3.93 hours under this balance. With only three available, the estimate becomes 77,440/(15,000 − 300) ≈ 5.27 hours. That arrangement would not maintain the 4-hour target with one pump unavailable.
These are arithmetic examples, not a pump specification or vessel-docking procedure. Vessel displacement, basin details and changing pump performance remain excluded.
Fixed basins and other lifting arrangements
| Arrangement | Basic method |
|---|---|
| Graving dock | Close and drain a fixed basin around a supported vessel. |
| Floating dock | Change the buoyancy of the dock structure to lift its supported load. |
| Marine railway | Move a vessel-supporting cradle along an inclined track. |
| Vertical ship lift | Raise a supporting platform. |
Capacity, cost, drainage or lifting time and suitability depend on each installation. The rectangular basin calculation does not compare their structural capacities or economics.
Frequently asked questions
Does basin volume deduct the ship’s displacement?
No. It is L × W × H for a full rectangular basin. Vessel displacement and details such as stepped walls, sumps and sloping floors are not included.
Why is leakage added to the pump rate?
The pumps must remove the planned basin volume and the water entering during drainage. With constant leakage, its flow is added directly to V/t.
What does leakage share mean?
It is leakage divided by the required total pump rate, expressed as a percentage. It is not a percentage of gate damage or a seal-acceptance criterion.
Why might actual pump-down take a different time?
Actual water volume, pump flow at changing head, leakage and residual water can differ from the constant values assumed here. Use actual geometry and pump data for a project estimate.
Does the animation calculate block loads or vessel stability?
No. It illustrates floating at a constant draft, contact with bearing blocks and subsequent drainage. It does not calculate support reactions, hull stresses or stability during docking.
Does a small total-flow margin provide one-pump-out redundancy?
Not necessarily. Recalculate the net drainage rate using only the available pumps. In the example, losing one of four 5,000 m³/h pumps extends the estimate beyond the 4-hour target.
References
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