Timber cargo is lumber carried uncovered on a vessels freeboard deck. Vessels which commonly carry timber on deck can be assigned deeper loadline draughts, if they meet certain criteria. This reflects the low permeability and inherit bouyancy provided by the timber. Similar products, such as wood chips or paper pulp, will not qualify (as they are water absorbant).
The plimsoll mark of a timber cargo vessel will have two scales. An additional set of timber freeboard marks are set aft of the plimsoll, and apply when timber cargo is present (otherwise, the standard freeboard marks apply).