Constrained by Draught (CBD)

A power-driven vessel severely restricted in its ability to leave its course because of its draught in relation to the available navigable water.

The status depends on both depth and width: a deep-draught vessel in a channel may be unable to alter course without losing adequate under-keel clearance or leaving the water it can safely navigate. Size or deep draught alone does not automatically establish the status in open, sufficiently deep water.

This is a defined collision-regulation term distinct from a vessel restricted in its ability to manoeuvre by the nature of its work. Prescribed optional signals can make the condition apparent, but other vessels must assess the full situation and applicable rules rather than treating the display as an absolute right of way.