Casting in a Narrow Channel - Cast means to turn a ship in her own water. Ships turn in this manner when getting under way in a crowded anchorage. Vessels in restricted anchorages often have to turn in their own water because of nearby anchored vessels or restricted maneuvering space.
The problem of turning twin-screw ships with a single rudder is not difficult. Go ahead on one engine and back on the other, using the rudder when head or sternway has been gained. If the ship is fitted with twin rudders directly behind the propellers, order "hard over" rudder before going ahead on one engine. Back the other engine at the speed necessary to prevent headway or sternway being gained.
In light winds, single-screw ships can be turned easily in restricted waters. Take advantage of the tendency to back to port The first move is to go ahead full with hard right rudder but reverse the engines before much headway is made. Shift the rudder after headway has been lost; back down a short distance, and then go ahead full. The rudder should be ordered right full before the engines ahead begin to turn over. In strong winds, it is advisable to turn so that the tendency to back into the wind can be used to increase the turn.
Most seaman know that an anchor can be used to facilitate and expedite a turn in a restricted space. High-powered vessels normally use their twin screws and engines to turn in places where a single-screw, low powered vessel could use an anchor.
The engines can be operated ahead and astern as before but only slow speeds should be used and little steerway gained. The turn should be made to starboard by pivoting on the anchor when going ahead and by the tendency of the stern to swing to port when backing. Be sure and check your chart to see that a dragging anchor does not foul any cables. If the ship hugs the point, the helmsman will require a small amount of rudder toward the bank to steer a straight course. Less rudder will be necessary as the channel begins to bend and the ship moves away from the bank. The signal, "less rudder," is a helps in determining when to begin the turn in clear as well as in foggy weather. Any slack water or eddies that may be encountered around the turn may make it very difficult to prevent a sheer toward the near bank, particularly in shallow water with a laden ship. The stern may feel the current under the quarter and increase the sheer.
Staying in the bend If the master decides to make the turn in the bend, he has to decide when, If he starts too late, the ship may ground on the bank. If he starts too early, there is danger that the bank suction on one quarter added to the force of the current on the other may give the ship a sheer. The bank cushion under the bow will increase this sheer. If the bow should enter the eddies under the point, the ship may pivot and ground on both sides of the channel at the same time.
Taking the bend side of the channel in the middle is the safest way to turn, with a following current approach the turn on a course a little to the bend side of the middle of the channel. The eddies under the point and the increased current in the bend can be avoided, and the force of the current against the quarter can be used to assist the turn.
Two ships should not try and pass in a narrow channel with a bend. The ship with a head current should stop and wait for the other to clear the bend.
