Structures are located at a number of Seaway locks which, when fully raised, overhang the lock wall at a given point, thereby limiting:

(a) The height of a vessel above the water line measured at the vessel's side; and

(b) The height of other structures that are located near the sides of the vessel, such as derricks, crosstrees, antennas, etc.

The following block diagram shows the limits beyond which a vessel's hull or superstructure cannot extend when the vessel is alongside the lock wall.

The limits in the block diagram are based on vessels with a maximum allowable beam of 23.2 m. For vessels that have a beam width less than this and that have dimensions exceeding the limits of the block diagram (measured with the vessel alongside the lock wall), a special permission to transit must be obtained. (Accurate measurements may be required before such permission is granted).

Caution: Masters must take into account the ballast draft of the vessel when verifying the maximum permissible dimensions. Bridge wings, antennas, masts and, in some cases, the samson posts or store cranes could be outside the limits of the block diagram and could override the lock wall. Masters and pilots must take this into consideration and exercise extreme caution when entering or exiting locks to ensure that the vessel does not contact any of the structures on the lock.