Floating cranes are the workhorse of marine lifting operations. They come in many different forms and sizes, either on modified barges, installed to semi-submersible platforms or installed to specially modified vessels. The latter are often built or need to be modified in order to take the high loads and hull stresses involved when carrying out often very heavy lifting operations.
When lifting at sea, either inshore of offshore, there are many considerations that must be taken into account over and above those for similar operations on land.
Firstly, the floating crane is mounted, usually, to a body that need not be at rest. It will be subject to “static” reactions to changes in load moment, countered by buoyancy shifts or ballast movement.
It will also experience “dynamic” reactions as a result of wave action on the floating body causing it to, primarily, heave, pitch and roll.
As a result of this, the floating crane’s lifting capacity is a function of the environmental conditions in a similar, but much more restrictive way, as a land-based crane.
When lifting items into or out of the water, the progressive change in buoyancy and submersion will have an effect on the load being lifting. Considerations such as sea state, entrapped water, centre of buoyancy shifts all must be considered to ensure a safe lift.