Trim by the Head

Trim by the head is the condition where the forward draught of a vessel exceeds the aft draught, meaning the ship is deeper at the bow than at the stern. This trim condition arises when heavy cargo or ballast is concentrated in the forward holds, or when forward tanks are full and after tanks empty. A modest trim by the head may be required to achieve the minimum propeller immersion in ballast condition, but excessive trim by the head adversely affects steering, increases bow-wave resistance, and can cause the propeller and rudder to emerge from the water on pitching in a seaway, reducing controllability. The CTU Code and individual vessel trim notices define acceptable trim limits. The chief mate monitors and controls trim throughout the loading and discharging sequence by distributing cargo and ballast to achieve the required departure condition. If trim by the head becomes excessive at sea due to fuel consumption patterns or cargo shift, the OOW informs the chief mate who can transfer ballast between tanks to restore acceptable trim. In shallow channels and ports with tight underkeel clearance, excessive trim by the head can cause the bow to touch bottom while the aft draft appears safe—a known grounding scenario. The ECDIS passage plan and pre-arrival calculations should include the anticipated arrival trim to ensure compliance with port authority requirements.