The vertical distance from the waterline to the main deck edge, indicating reserve buoyancy and load line compliance.
In practice
The assigned freeboard is marked on the ship's sides as the load line or Plimsoll mark. The mark comprises a series of lines indicating maximum permitted draughts in different seasonal zones and water densities: summer, winter, tropical, fresh water, and others. Exceeding the assigned freeboard by loading beyond the relevant load line is a serious statutory offence under the law of the flag state and is routinely checked by port state control officers during inspections. The chief mate calculates draught and freeboard figures using the ship's stability booklet and loading computer to ensure compliance before the vessel departs any berth.
Regulatory detail & full definition
Freeboard is the vertical distance measured amidships from the uppermost continuous deck (freeboard deck) down to the waterline. It represents the reserve buoyancy available to the vessel and is a direct measure of her ability to resist flooding and maintain stability in heavy weather. The Load Line Convention 1966 (LL 66), as amended, establishes the international framework for calculating and assigning minimum statutory freeboards to vessels based on their dimensions, structural strength, stability, and type.
The assigned freeboard is marked on the ship's sides as the load line or Plimsoll mark. The mark comprises a series of lines indicating maximum permitted draughts in different seasonal zones and water densities: summer, winter, tropical, fresh water, and others. Exceeding the assigned freeboard by loading beyond the relevant load line is a serious statutory offence under the law of the flag state and is routinely checked by port state control officers during inspections. The chief mate calculates draught and freeboard figures using the ship's stability booklet and loading computer to ensure compliance before the vessel departs any berth.