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On board the USS Porter (DDG-78), Lieutenant (junior grade) Enrique Portillo (left) trains Boatswain's Mate First Class Derrick Manzano on the use of a maneuvering board, a key tool for avoiding collisions at sea.
U.S. Navy (Ford Williams)
Bluejacket's Manual - Collision at Sea Avoidance
Non-mariners often ask how ships on the open ocean manage to collide with each other. Most collisions occur in more confined waters, such as the shipping channels approaching busy ports, where many vessels converge on their way in or out. But ships sometimes do collide on the open sea.
By Lieutenant Commander Thomas J. Cutler, U.S. Navy (Retired)
Avoiding collisions is complicated by the facts that the open sea has no traffic signs or signals, no designated travel lanes, and no streetlights or headlights to illuminate the way. Further, although mandated light arrays are designed to help mariners identify a ship's aspect, they can sometimes be confused by spurious or even necessary lights (particularly on aircraft carriers or fishing vessels). The bottom line is that, unlike on land, the open sea is an undefined plane on which vessels can be variously oriented, and it is easier to get into trouble than one might imagine.
Despite the challenges mariners face, there are practices that can significantly mitigate the risk of collision. The first is knowing one's ship. A shiphandler must know and appreciate such factors as
• How many rudders and propellers (screws) a ship has (a ship with twin rudders and screws is much more maneuverable than one with only one of each)
• What kind of propulsion she employs (ships with gas turbines are able to respond more quickly than a steam-driven ship)
• What is her displacement (the heavier the ship, the more distance required to slow or stop her)
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