Deep Water Route
The routeing measure surveyed for draught-constrained ships, how it differs from a traffic lane, and where its use is mandatory rather than recommended.
A deep water route is a route within defined limits that has been accurately surveyed for clearance of the sea bottom and submerged obstacles to a stated minimum depth of water. It exists for ships whose draught constrains their choice of water, and it is a distinct routeing measure from a traffic lane even where the two overlap.
The distinction that matters operationally is whether use is mandatory. In the Straits of Malacca and Singapore, Rule 1 of the Rules for Vessels Navigating Through the Straits of Malacca and Singapore requires eastbound deep draught vessels to use the designated deep water routes, and Rule 2 asks them to avoid overtaking within those routes in the Phillip Channel and the Singapore Strait . In that system the deep water routes lie inside the eastbound traffic lane rather than alongside it.
A deep water route does not guarantee a particular clearance to a particular ship. The surveyed depth is a datum, and the master still applies the applicable under-keel clearance requirement, allows for squat at the intended speed, and works to the state of tide. The full article will cover the definition in IMO ships’ routeing, the adoption procedure, the interaction with COLREG Rule 10, and the principal routes in force.