REPLENISHMENT AT SEA
A small number of ships engage in replenishment operations at sea and this number can be expected to increase if the trend toward greater use of merchant ships to support the navy continues. The ship that maintains course and speed during the maneuver is designated the "large ship," because this ship is usually the physically larger of the two vessels involved. The second vessel is the "maneuvering ship."
Initial planning between the two vessels is done by radio. A base course and speed is determined to put the sea two points on the bow of the "large vessel" that will be away from the operation, to make a lee and minimize rolling and yawing. The steering gear must be tested and inspected prior to operation, and a seaman trained in shifting from bridge to local trick wheel steering must be stationed in the steering gear flat. Sufficient crewmembers are assigned to the deck and bridge, and a good helmsman-preferably experienced in steering during ship-to-ship transfer operations-is assigned to the wheel.
Usually the larger merchant ship maintains the base course and speed throughout the evolution, and all maneuvering is done by the approaching ship. In a heavy sea, it may be prudent to have the larger ship maintain course and speed.
When within 1/2 mile of the large or steadied up vessel, the maneuvering ship comes to a heading that parallels the large ship's wake. Speed is adjusted to be about 3 to 5 knots greater than the speed of the large ship and the approach is begun. There is interaction between ships throughout the maneuver, but it is greatest as the bow of the maneuvering ship passes the larger ship's quarter. This "danger zone" should be passed through before the speed of the maneuvering ship is reduced to the final base speed to minimize the passage and assure good rudder control while in it. High powered naval vessels will often approach at much higher speeds and back down just before coming abeam, but this is not a prudent approach when two merchant ships are involved. It is not practical for merchant ships to back down since the effect on steering will be significant and their backing power is not sufficient to slow a ship from the higher speeds used by naval vessels. A lower powered merchant ship continues at a speed greater than that of the steadied up ship until past the danger zone and then reduces engine speed and slowly loses headway until she is moving at the base speed.
One hundred feet is generally a proper separation distance between ships, although some rigs used for transfer require less separation. Don't allow the ships to be pulled together by constant tension winches during the transfer operation. The maneuvering ship heads a few degrees away from the larger ship to compensate for the pull of these winches and also for the suction effect between the two moving ships.
When in position abeam, the ships pass a distance line forward, marked at intervals to assist in maintaining the required separation distance, and then pass the highline and other rigging required for the replenishment operation. Course is adjusted by giving the helmsman headings to steer rather than using helm orders, to assure that all changes are minimal so the ships don't develop any radical swing while alongside. The continued intership attraction while in this position, caused by the reduced pressure as the water flows between the two ships, presents no problem as long as the specified distance and slight angle is maintained between the ships. If the ships get closer to one another they could be drawn together. The mariner can do little to counter intership suction if the two ships are allowed to get too close.
While alongside the maneuvering ship adjusts speed a few revolutions at a time to match her speed with that of the larger ship. Do not make any large changes in revolutions (such as would result from using the telegraph to change speeds). Use abeam bearings and watch the distance line to maintain the ship's position during the transfer.
To depart, open the angle at the bow slightly and let the maneuvering ship come slowly away from the larger ship, increasing revolutions only enough to overcome any decrease in speed due to the change in heading and rudder. Do not pass ahead of the ship since any machinery failure would result in a collision as the departing ship veers across the other ship's bow. Don't increase ship's speed through the water until well clear ofthe larger ship as this will increases the intership suction.
