Vessel’s Characteristics



The distance traveled in the direction of the original heading measured from the
point at which a helm was first applied. The maximum advance is usually between
3 to 5 ship lengths for a merchant ship of any size going at full ahead and using full


The distance of the center of gravity of the ship from the original track line
measured in the 90º to the original heading. The transfer for a turn of 90º is about
two ship lengths

Tactical Diameter

It is the transfer for a turn of 180º which is almost equal to the maximum transfer. It
is usually about the same distance as the maximum advance.

Drift Angle

It is the angle between the tangent to the turning circle at any point and the fore
and aft line of the ship.

Pivot Point

It is the point about which the vessel pivots with the bow swinging inwards and the
stern swinging outwards. It is about one third (1/3) of the vessels length from
forward when going ahead. When going astern the vessel pivots about
approximately one quarter of the length from astern.

Final Diameter

It is the diameter of a circle traversed by a vessel after turning through 360º and
maintaining the same speed and rudder angle. This diameter is always less than
the tactical diameter. It is measured perpendicular to the original course and
between the tangents at the points where 180º and 360º of the turn have been

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