While on watch you notice a radar echo that seems to appear and disappear oddly, and its bearing barely changes even though you know from AIS that the actual vessel it might correspond to is altering position significantly. Your examiner asks you to explain the phenomenon of an indirect echo.

A. An indirect (false) echo occurs when the main radar beam is reflected off part of the ship's OWN superstructure (such as a funnel, king post, or mast) BEFORE it strikes a genuine target and returns by the same indirect path. The resulting echo is displayed at the TRUE RANGE of the real target (because the total travel time is barely affected) but at a FALSE BEARING — the bearing corresponding to the direction the beam was pointing when transmitted, not the true direction to the target. Indirect echoes typically occur within the ship's known shadow/blind sectors, appear on substantially CONSTANT bearings even as the real target's true bearing changes, and behave abnormally when plotted (because the plot is tracking a geometric artefact, not the target's actual relative motion).

B. An indirect echo is simply a genuine target displayed at its correct range and bearing but with reduced brightness due to rain attenuation — it has nothing to do with the ship's own structure.

C. An indirect echo occurs only when a target beyond maximum range returns its echo after the next pulse has been sent, appearing at a falsely short range — this describes a second-trace echo, not an indirect echo.

D. An indirect echo is caused by energy leaking from the side lobes of the beam, producing an arc of false targets around a single strong echo at the same range as the real target.

A. Nothing — a test lift can proceed immediately after repairs

B. Testing should wait until cargo operations begin

C. The area within the grab's swing radius should be cleared of personnel before the lift

D. Only the crane operator needs to be aware the lift is happening

A. Who must remain clear of the exclusion zone while the lift takes place

B. The lunch schedule for the deck team

C. Only the weather forecast for the next watch

D. The cargo manifest for the next port