By now, many naval officers are familiar with the handling characteristics of the Arleigh Burke (DDG-51)-class destroyer—thanks to ten years' experience and excellent Proceedings professional notes by Rear Admiral Jim Stavridis and Captain Gene Moran (October 1994 [pp. 66-68] and July 2000 [pp. 85-86], respectively). Those two articles should be the foundation for officers wishing to hone their skills on these warships. My intent here is to build on their efforts and show how a slight modification in the use of engines can provide conning officers better control while using opposing engines in a twist.
To quickly review, the DDG-51 has a twin-screw, twin-rudder propulsion plant, with outward rotating controllable, reversible pitch propellers. To twist the ship, the conning officer would order a full—or hard—rudder and ahead 1/3d (or 2/3d) on one engine and back 1/3d (or 2/3d) on the other. The ahead engine's screw wash over that full rudder begins walking the stern to the side of that screw, while the backing bell keeps the ship in position. In theory, you could twist the ship around in her own length using this method. In practice, however, something different happens. When conducting an even twist—i.e., ahead 1/3d on one shaft and back 113d on the other—the backing engine quickly dominates the maneuver and the ship rapidly develops sternway. The effect is even more pronounced when conducting a 2/3d-to-2/3d twist. This is a problem because a DDG-51's sternway will kill your twist and possibly cause difficult maneuvering in tight spaces.
The technique that most DDG-51 conning officers have adopted is to "goose" the ahead engine to compensate for the overly strong backing engine. This counters the stern way, but if left on too long, will generate unwanted headway. If properly applied, you could still twist in your own length—provided you have near-perfect timing on cycling between ahead 1/3d and 2/3d.
Although learning to cycle the ahead engine between 1/3d and 2/3d and properly anticipating the ship will take some practice, they are skills that can be mastered by most. The more challenging situation is when a 1/3d twist will not get the job done. The DDG-51 cannot generate high degrees of twisting force, and it takes only a small amount of wind or current to render the 1I3d twist powerless. Trying to twist against a 15-knot wind pinning you against the pier will take a 2/3d twist to get the stern moving. You will develop sternway—much quicker with the 2/3d twist than with the 1/3d—and, again, the sternway will tend to kill your twist. As in the foregoing example, you can counter the sternway by goosing the ahead engine to a standard bell. Managing the standard-to-2/3d combination, however, is trickier—only the most seasoned conning officers should attempt to do this close to a pier or another ship.
Fortunately, there is another method that offers more flexibility and allows the conn to generate larger twisting forces while maintaining precise control and eliminating any sternway or headway. The solution to countering the heavy backing bell is to redefine the back 1/3d and back 2/3d throttle positions. By experimenting with different settings, you can zero in on the astern throttle setting that will exactly counter the corresponding ahead bell; in so doing, you can find the spot where the ship will twist without generating any sternway or headway. Once you determine the proper throttle positions, simply mark them with small pieces of tape.
The new settings for back 1/3d and back 2/3d are substantially less powerful than the original settings, and it will take practice to get used to them. Even though they offer less astern power, they still can stop the ship quickly when needed. For example, when using the new back 1/3d setting while proceeding to an anchorage, you can maintain ahead 1/3d until 80 yards from the anchorage. At that point, order back 1/3d and you will come to a stop just past the drop bearing. As sternway builds, you will pass the drop bearing again. Let go the anchor and keep the back 1/3d bell on for another 15-30 seconds and you will generate the 0.5 to 1 knot of sternway needed to set the anchor.
Validated while on deployment and in home waters at the Norfolk piers, these new settings provide a dead-even twist—both at 1/3d-to-1/3d and 2/3d-to-2/3d—and offer the added benefit of more precise control of backing bells that can be used in any situation. They can be implemented without changes to your engineering plant, standard commands, and standard operating procedures. A couple of pieces of tape and some training for the lee helmsmen are all that is required.
Commander Mosher is commanding officer of the USS Mahan (DDG-72).