The trim of a vessel is calculated by subtracting the forward draft reading from the after-draft reading, as shown in the following example:
Imperial draft marks are six inches tall and are spaced six inches apart, see the diagram below.
3.3 Marine Vessel Tank Measurement Marine vessel tank measurement is essentially the same as that of shore tank measurement. However, there are two situations that are common to marine vessel tanks that are not common to shore tanks. A marine vessel does not always remain upright or level in the water. Nonetheless, the liquid inside the tank will always remain level. Therefore, the issues of list and trim must be taken into consideration. Marine vessels are required to discharge all of their cargo; as a result, their tanks are empty, or almost empty before loading and after discharge. Caution must be exercised when measuring the small quantities on board before loading, OBQ, and after discharge, ROB. See section 3.3.4 GAUGING PROCEDURES – OBQ / ROB. 3.3.1 Terminology Draft is the depth of a vessel below the water line; measured, from the surface of the water to the bottom of the keel. Draft Marks are numbers painted on the forward, amidships and after, stern, part of a ship, that indicate the draft of the vessel at the point.
8 8’ 06” 8’ 03” 8’ 00”
After (stern) draft Forward draft Trim
26' 3" (8.00 m) 16' 5" (5.00 m) 9' 8" (3.00 m) by the stern.
Metric draft marks are ten centimeters tall and are spaced ten centimeters apart, see below diagram. 8 8.10 m 8.05 m 8.00 m
List is the leaning or inclination of a vessel, away from the vertical" expressed in degrees port or starboard. When a vessel is not listing, it is said to be "upright".
Starboard
Port
Starboard
Port
ø
Draft Marks in Meters Draft Marks in Feet
No list Vessel upright
Vessel listed ø ° to port
Trim is the condition of a vessel with reference to its longitudinal or horizontal position in the water. When the keel of the vessel is parallel to the waterline the vessel is said the be on "even keel" . When the stern of a vessel is deeper in the water than the bow, the vessel is said the be "trimmed by the stern" .
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