Grades 6–8 · Machines
How can a dry dock leave a huge ship standing on land?
A fixed dry dock is a basin that can be opened to the water and then sealed. When it is flooded, a ship can float inside. Prepared blocks lie below the hull in carefully chosen positions.
In the diagramThe ship’s weight follows a new support pathFlooded basinDrained basinbuoyancy carries weightblocks carry weightA fixed graving dock drains around prepared hull supports.
After the entrance is closed, pumps remove water from the basin. The falling water surface lowers the floating ship until it contacts the blocks. As the water falls farther, less of the hull remains submerged, so buoyancy supports less of the ship’s weight.
The blocks take over that load and pass it into the dock floor and ground. They must line up with parts of the hull able to carry the forces. Removing the water does not make the ship lighter; it changes the route through which the weight is supported.
With the basin drained, workers can reach hull areas normally underwater. To refloat the vessel, the dock is filled in a controlled way until buoyancy again carries the load. A ship can therefore reach a dry workspace without a crane lifting its full weight.
About this explanation
Starting knowledge: Understand buoyancy as an upward force and distinguish a load from its supports.
Sources
- Naval Sea Systems Command — Meeting the mission: Integral step to docking a ship is teamwork