From the collision of the USS Washington (BB-56) and the USS Indiana (BB-58) in 1945 to the deadly ramming of the USS Hobson (DD-464) by the USS Wasp (CV-18) in 1952, from the infamous HMAS Melbourne/USS Frank E. Evans (DD-754) tragedy of 1969 to the fatal encounter of the USS Fitzgerald (DDG-62) with the container ship ACX Crystal in 2017, ship collisions have left an indelible stain on the U.S. Navy’s history. Non-mariners are prone to ask: How it is that ships manage to collide in the open ocean? While 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, ships do sometimes collide on the open sea.
Avoiding collisions is complicated by the fact that the open sea has no traffic signs or signals, no designated lanes of travel, and no streetlights or headlights to illuminate the way. Further, mandated light arrays designed to help mariners identify a ship’s aspect can sometimes be confused by spurious or even necessary lights (particularly on aircraft carriers or fishing vessels). The bottom line is that 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 unique challenges that mariners face, there are practices that can significantly mitigate the risk of collision. The first is knowing one’s ship. A ship with twin rudders and screws (propellers) is significantly more maneuverable than one with only one of each. Other key factors are what kind of propulsion she employs (ships with gas turbines can respond more quickly than steam-driven ships) and her displacement (the heavier the ship, the more distance required to overcome inertia and slow or stop her). Beyond those basics, a capable mariner also will know things such as the ship’s tactical diameter (turning radius for a 180-degree turn), her pivot point (rotating point as the ship turns), and her advance (distance gained in the direction of the original course) and transfer (distance gained perpendicular to that original course for various speeds).
Among the most important antidotes to collisions at sea are the nautical rules of the road. These internationally accepted rules of behavior consider those things that pertain to vessels when operating in the vicinity of one another. Problems created by the lack of defined paths on the open sea are solved by the universal adherence to standard practices. For example, when one ship is overtaking another, it is up to the overtaking vessel to maneuver, while the other must maintain course and speed to avoid confusion. And when two ships are in a crossing situation, the one having the other on her starboard side must yield. When these rules are understood and adhered to, the risk of collision is nearly nil.
The rules of the road also establish standard light configurations that help mariners understand a vessel’s aspect (i.e., being able to discern whether one is looking at a ship’s starboard or port side or knowing whether she is heading toward or away). Additional lights can warn that a vessel is incapable of normal maneuvering because she is trawling, recovering aircraft, has lost steering control, etc. In daylight, these lights are replaced by dayshapes (black balls, cones, etc.).
Besides taking advantage of available technological advantages, such as the modern Automatic Identification System (AIS), knowledge of certain basic techniques can greatly enhance a mariner’s chances of remaining collision-free. For example, when encountering another vessel, the prudent mariner will use his or her compass to shoot periodic bearings and use radar to check the range. If, for example, the bearings to a ship on the port bow are increasing, she will pass ahead; if they are decreasing, she will pass astern. If these observations reveal that the vessel is CBDR (constant bearing, decreasing range) collision is inevitable unless one or the other adjusts course and/or speed.
One of the most useful tools for avoiding collisions is the maneuvering board. While the user is actually employing polar-coordinate/vector geometry, only simple arithmetic is required, because the calculations are made graphically. Using only dividers and parallel rulers, one can use ranges and bearings to other vessels to not only predict how close they will come (known as CPA, for closest point of approach), but also to predict what effects changes in course and/or speed will have. Though the boards are a bit intimidating when first encountered, with practice mariners learn the almost magical qualities that maneuvering boards extend to users.
Perhaps most important of all is crew readiness, accomplished through effective training and individual fitness. Watch teams must have the knowledge and skills required to keep ships safe at sea. And each individual must be adequately rested to ensure that he or she is alert and functioning at a high level of efficiency while on watch. It is no exaggeration to describe these requirements as matters of life and death. To cut corners in either of these two areas is to risk serious injury and death, something that has been proven on too many occasions.
Thucydides is often quoted as saying, “A collision at sea can ruin your entire day.” While the famous Greek historian never actually wrote those sardonic words, he did quote Athenian leader Pericles as having said, “Seamanship is an art like any other; it is not something which can be picked up in one’s spare time.” A valuable lesson learned more than 2,000 years ago.