Down by the head – Down by the stern – On even keel.
These expressions mean:
Down by the head – The draught forward exceeds the draught aft.
Such a “trim” will have a detrimental effect upon the ship’s speed and steering.
Down by the stern – The draught aft exceeds the draught forward.
In most cases a certain drag is preferable in connection with the steering of the ship. Too much drag may result in loss of speed. Ships sailing in ballast may need to be trimmed by the stern 1 to 1.5 metres so that the propeller will be sufficiently immersed, say at least two thirds of the diameter, otherwise the power developed may be wasted.
On even keel – The draughts forward and aft are equal.
Down to her marks. This expression means that the vessel has been loaded to her maximum permissible draught, either winter, summer or tropical loadlines, as the case may be. It does not imply that all cargo space has been filled. If both deadweight and cargo space have been fully utilised the ship is “full and down It depends on the stowage factor of the cargo whether the vessel will be full and down.
Upon checking the weight of the cargo loaded by a vessel when down to her marks, there may be a considerable difference with the deadweight capacity for cargo based upon the ship’s capacity plan, after allowance for bunkers, water, stores, etc.
This difference may be explained by incorrect estimate of bunkers, water, stores, dunnage, etc., or incorrect reading of the ship’s draught in choppy water.
Sufficient allowance should be made for the difference in specific gravity of salt and fresh water, the loadlines being based upon loading in seawater.