- With reference to dry-docking:
(a) state what is meant by the critical period on settling onto the dock blocks;(3)
(b) explain the reasons why this period is considered critical;(5)
(c) state how the danger is reduced.(2)
(a) Meaning of the critical period on settling onto the dock blocks (3 marks)
The critical period is the interval between the vessel first making contact with the keel blocks and the time when the vessel is fully supported by the blocks, with buoyancy no longer carrying a significant portion of the weight.
(b) Reasons why this period is considered critical (5 marks)
- Large stresses on the hull – uneven support while weight transfers from water buoyancy to keel blocks.
- Risk of excessive trim or list – if not properly aligned, the vessel can heel or trim suddenly.
- Danger of structural damage – bilge keels, shafting, or rudder may be strained if the vessel settles incorrectly.
- Instability risk – as buoyancy decreases, stability margins are temporarily reduced.
- Personnel and dock safety – incorrect settling can endanger workers and cause dock structure damage.
(c) How the danger is reduced (2 marks)
- Proper trim and stability preparation – slight stern trim and stability within safe limits before docking.
- Accurate docking plan and supervision – correct placement of keel blocks and careful control of de-ballasting under dockmaster’s direction.