HARD RIGHT RUDDER 6 KTS
This maneuver is made at 6 knots so a feel of the turning radius of the ship can be gotten at normal maneuvering speeds rather than in the full sea speed conditions with which the seagoing mariner is more familiar. During the turn do not change engine speed, and remember that the rate of turn will be affected by both current and wind. Record the data as shown on the sample data sheet. At the same time, observe the area required to make this turn and compare it with a known reference length, such as the distance from the bridge to the bow, for future use when judging whether a vessel has sufficient room to turn in an anchorage or harbor.
Keep in mind that the depth under the keel will cause the turning diameter to increase until, in shallow water, it may be as much as twice the diameter found for the same ship in deep water. Since for practical purposes the rate of turn is about the same whether maneuvering in
This maneuver is made at 6 knots so a feel of the turning radius of the ship can be gotten at normal maneuvering speeds rather than in the full sea speed conditions with which the seagoing mariner is more familiar. During the turn do not change engine speed, and remember that the rate of turn will be affected by both current and wind. Record the data as shown on the sample data sheet. At the same time, observe the area required to make this turn and compare it with a known reference length, such as the distance from the bridge to the bow, for future use when judging whether a vessel has sufficient room to turn in an anchorage or harbor. Keep in mind that the depth under the keel will cause the turning diameter to increase until, in shallow water, it may be as much as twice the diameter found for the same ship in deep water. Since for practical purposes the rate of turn is about the same whether maneuvering in shallow or deep water, the larger area required to complete a turn is not immediately obvious to an observer. For these reasons it is stressed that the shiphandler should carefully observe the turn and compare the turning diameter with a known reference for use when planning maneuvers in the future.
HARD LEFT TURN AT 6 KNOTS
Make the same maneuver but this time turn to the left and again observe the turning diameter. When handling smaller ships, the smaller diameter and greater rate of a low speed turn to the left is apparent to the observer, as compared to the turn to the right. There are disadvantages to turning to the left when maneuvering in confined waters that far outweigh this one advantage of slightly reduced turning diameter.
BACKING AND FILLING
For the purpose of these trials, 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 apparent as the ship moves ahead that the turning diameter for this turn is less than for a turn using constant revolutions, and most ships will turn in about half the diameter required for the turn, 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. 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. You should 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.Do not be fooled by the fact that, during both this backing and filling maneuver and the steady state 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 alternative, 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. Some of the uses of the backing and filling maneuver are discussed in later sections.
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.
