With reference to arresting the headway of vessels of considerable mass, give reasoned opinions on EACH of the following statements:

Reasoned opinion: This statement is not correct. For a vessel of considerable mass, the ability to run the propeller astern at full power is very significant in arresting headway. The astern thrust of the propeller produces a retarding force that, combined with the hydrodynamic resistance of the hull, decelerates the vessel. The stopping distance and time depend directly on the astern power available: a vessel that can develop full astern power will stop in a shorter distance than one limited to reduced astern power. However, the statement has a grain of truth in that the propeller's astern thrust is relatively inefficient (the propeller is designed for ahead running, and astern the blades work at a poor angle, producing less thrust for the power), and the hull resistance and the "squat"/propeller race effects also matter. Nevertheless, full astern power is a major factor in reducing stopping distance, so the statement is largely wrong - it is consequential. The effectiveness is also limited by the risk of the propeller race affecting the rudder and by the time taken to reverse the engine.

Reasoned opinion: This statement is broadly correct. Adapting the rudder to act as a retarder (e.g. by using a large rudder angle or a special rudder design to create drag) has generally been disappointing as a stopping aid. The reason is that a rudder produces a retarding force only when the vessel is moving and the rudder is angled, but the drag it creates is small compared with the momentum of a large vessel, and the rudder's primary function (steering) is compromised. The hydrodynamic drag of a rudder, even at a large angle, is a small fraction of the vessel's total resistance, and it cannot significantly reduce the stopping distance of a large ship. Moreover, using the rudder as a retarder can cause excessive yaw, loss of control, and stress on the rudder/steering gear. Hence the results have been disappointing, and the rudder is not an effective braking device.

Reasoned opinion: This statement is correct, but only to a limited extent. Transverse thrust units (bow/stern thrusters) produce a lateral force that, when used appropriately (e.g. to create a yawing moment that increases the hull's resistance or to assist in turning), can help reduce the stopping distance, particularly at low speeds where the rudder is ineffective. By using the thrusters to induce a yaw or to increase the effective resistance, the vessel can be slowed more quickly. However, the effect is modest because the thrusters' power is small compared with the vessel's momentum, and they are most effective at low speeds. Their "discreet" (judicious) use, combined with astern power and the rudder, can contribute to a shorter stopping distance, but they are not a primary braking device. Overall, the statement is broadly correct: judicious use of transverse thrust can reduce the stopping distance, especially at low speed, but the main retarding force remains the astern propeller and hull resistance.