Every good seaman knows that the wind affects turning. The freeboard and superstructure act as a sail area especially at low speeds. As the pivot point is well forward when a ship is moving ahead, the pressure acting on the greater exposed area abaft this point tends to turn the ship into the wind. Ships with high freeboard, tend to turn into a wind more rapidly and turn out of a wind more slowly than under no wind conditions. When going astern, the pivot point moves aft, and the stern to seeks the wind. The stronger the wind, the more likely to back into the wind. This can be used to help when turning in restricted waters. In the case where the sail area of a ship's superstructure and free-board (high bow, low stern) is forward, the effect of the wind on the ship going slowly ahead is less. A ship with these characteristics, will back into the wind even more.
Any sea forward of the beam will slow the motion of the ship over the ground to more or less , any sea from abaft the beam will accelerate it. The affect of the sea on steering is to cause a ship to seek the trough. If the sea is on the bow or quarter, it may be necessary to carry either right or left rudder in order to maintain your course.
Current affects the underwater body of the ship. It is important because its existence may not always be realized. Known ocean currents may be shifted, accelerated, diminished, or even reversed by winds steadily in one direction over a long period of time. Currents in harbors, straits, and bays are caused by the action of the tides. The current may be reduced or reversed by the tide. The direction and probable force of currents in ports and along coasts may be determined by study your tide tables and current charts. Looking at the shape of the shore line and of the direction in which buoys and other anchored navigational aids are leaning will give a good check on the force and direction of the current running at any given time.
The general effect of a current on the underwater body of a ship is to move it in the same direction in which the current is running. When turning in a current, the ship, at the completion of the turn, may be well down in the direction of the current from her position when the turn was started. When held by an anchor, the ship usually assumes the position where the current has the least underwater area on which to act. For this reason, an anchored ship heads into the current unless the wind or sea is strong enough to overcome its effect. For the same reason, a ship at anchor will swing with the change of the tidal current. Current can be used to cant a ship or to move her toward a dock. Steering is easier when heading into a current than when going with it.
Shallow water will modify the normal action of screws and rudder in steering or turning a ship. She may be sluggish in answering her rudder, or she may take a sudden sheer to one side. High speeds can be made in shallow water by the use of excessive power, but you have to watch your wake. The best seamanship in harbors and rivers is constant watchfulness, foresight, slow but steady speed, having an anchor ready for letting go.
When maneuvering at slow speed or turning at in a confined space in shallow water, the effects from the rudder and propellers may not occur. Since water cannot flow easily from one side of the ship to the other, the sideways force from the propellers may in fact be neutralized you may have eddies build up that will counteract the propeller forces and the expected action of the rudder. If the attempt to turn in shallow water with ahead revolutions on one shaft and astern on the other fails, or if the turn is very sluggish, the situation will be worse if the revolutions are increased.
