Backing and filling, this common maneuver is started with the vessel dead in the water. The engine is brought to half ahead and the rudder is put hard right. It will be immediately apparent as the ship moves ahead that the turning diameter for this accelerating turn is significantly less than for a turn using constant revolutions, and most ships will turn in about half the diameter required for the turn in maneuver, assuming both turns are made in the same depth of water.
When the vessel has picked up a good swing and some headway (the amount of swing depending on the sea room available for the turn), the engine is put half astern (or full astern for low-powered or deeply laden ships). The rudder becomes less effective as the ship loses headway, so it is first put amidships and then hard left as the ship begins to gain sternway. Again, the duration of backing and amount of sternway depend primarily on the space available for the turn, but the vessel can be turned in about one - and -a - half-times her own length if required, by reducing the amount of ahead and astern speed the vessel is allowed to develop. Again observe the diameter required to make this turn, and get a feel for the maneuver and the time required to reduce headway. The effectiveness of the rudder while the ship is going astern can also be ascertained at this time.
1. HALF AHEAD/HARD RIGHT.
2. HALF ASTERN/HARD RIGHT.
3. HALF ASTERN/HARD LEFT.
4 and 5. HALF AHEAD/HARD RIGHT.
6. TURN COMPLETED.
REPEAT 2, 3, 4, AND 5 AS REQUIRED.
Do not be fooled by the fact that, during both this backing and filling maneuver and the steady turns, the ship at first develops a good swing and then appears to be losing that swing as the rate of turn decreases. This effect is sometimes misunderstood and the shiphandler feels that the ship is going to stop swinging. The rate of turn will only decrease until the forces affecting the ship reach a state of equilibrium, after which a constant rate of turn is maintained. Be patient,
Do not attempt to back and fill to the left unless you have no other altemative, as a ship will normally lose her swing in that direction when the engine starts turning astern. An excessive number of engine maneuvers are required to back and fill to the left, and in many cases the ship simply will not make the maneuver. There is not much point in collecting data during this maneuver. The rate of turn and the turning diameter required to reverse the vessel's heading are more a factor of the shiphandler's skill than the ship's characteristics, so comparisons are not particularly meaningful.
Also, remember if you can, to use the wind and current to help maneuver the ship.
