Practise for your OOW 3000 oral on a working bridge.

Questions examiners ask

Ten of the most-asked, with what a good answer covers.

One from each of ten lessons. The full set of 280 is in the course, each one after the lesson that teaches it.

1. How do you change over from autopilot to hand steering, and when would you?Often asked

   A good answer covers:

   • In traffic, in restricted visibility, in narrow waters, or whenever the master orders, and with time to spare
   • Have the helmsman at the wheel first, then select hand steering and give a course to steer
   • Check the helmsman is steering well and the rudder indicator follows the wheel
   • Changing back: line up on the course, set the autopilot heading, then select autopilot and watch it hold
   • Test the hand steering after a long spell on the autopilot, and before entering waters that need special caution (SOLAS V/24)

   Practised in the lesson The bridge controls: steering, engines, whistle, VHF, alerts, deck log and VDR.

2. When must the steering gear be tested, and what goes in the test?Often asked

   A good answer covers:

   • Each pump alone, and both together where they can run together
   • Full movement both ways, hard over to hard over, and the time taken
   • Each remote control system, and the emergency or local control
   • The rudder angle indicator agrees with the actual rudder angle
   • The power unit failure and control system alarms
   • Entered in the deck log

   Practised in the lesson Steering gear test before departure.

3. Compare the gyro compass and the magnetic compass. Why carry both?Often asked

   A good answer covers:

   • The gyro seeks true north, has a small and steady error, and feeds the autopilot, radar, ECDIS, AIS and repeaters
   • But it needs power, takes hours to settle after starting, and has speed and latitude errors that need correcting
   • The magnetic compass needs no power and cannot fail electrically, so it is the independent back-up
   • But it points to magnetic north, so it carries variation and deviation, and it is disturbed by steel, cargo and electrical equipment
   • SOLAS requires a magnetic compass on every ship covered, and a gyro on ships of 500 GT and over

   Practised in the lesson The compasses: gyros, repeaters and the magnetic compass.

4. When must navigation lights be shown?Often asked

   A good answer covers:

   • From sunset to sunrise, in all weathers
   • In restricted visibility, by day as well
   • And at any other time it is thought necessary
   • No other lights that could be mistaken for them, spoil their visibility or distinctive character, or hinder the lookout

   Practised in the lesson Sunset: navigation lights and the evening routine.

5. What is a BNWAS for, and how does it work when nobody resets it?Often asked

   A good answer covers:

   • It checks the officer of the watch is awake and on the bridge, and calls help if not
   • After the dormant period, set between 3 and 12 minutes, a visual indication on the bridge
   • Then an audible alarm on the bridge, 15 seconds after the visual one
   • Then, 15 seconds later, the alarm at the master and the back-up officer, and 90 seconds after that (up to 3 minutes on larger ships) at other crew locations
   • The emergency call sends it straight to the master and back-up officer

   Practised in the lesson BNWAS test.

6. Set the radar up from cold for navigation and collision avoidance. Talk me through it.Often asked

   A good answer covers:

   • Check the scanner area is clear of people and obstructions before transmitting
   • Switch on, let it warm up to standby, choose a sensible range before transmitting
   • Brilliance and palette for the light, then gain, then tune, then rain and sea clutter
   • Gain until speckle just shows, then back off until it has just gone
   • Least sea and rain clutter that clears the picture, without losing small targets
   • Check the performance monitor and the heading line
   • North-up, relative motion, sea-stabilised for collision avoidance; speed from the log

   Practised in the lesson Radar: setting up from cold.

7. What is bearing discrimination, and what decides it?Often asked

   A good answer covers:

   • The ability to show two targets at the same range, close together in bearing, as two separate echoes
   • Decided mainly by the horizontal beamwidth: two targets closer in bearing than about one beamwidth merge
   • A longer aerial gives a narrower beam; X-band gives a narrower beam than S-band for the same aerial length
   • Each echo is smeared by the beamwidth, so at long range two ships or a ship and a buoy can paint as one

   Practised in the lesson Radar: target discrimination.

8. What is the difference between a blind sector and a shadow sector, and what causes them?Often asked

   A good answer covers:

   • Blind sector: an arc where the beam is blocked and nothing is detected
   • Shadow sector: an arc where the beam is partly blocked and detection is reduced, so weak targets are lost
   • Caused by masts, funnels, other aerials, cranes and structure near the scanner
   • The nearer and wider the obstruction, the wider and deeper the sector

   Practised in the lesson Radar blind and shadow sectors: find them and record them.

9. How does a SART show on the radar, and how does it change as you close it?Often asked

   A good answer covers:

   • Only on the X-band, 3 centimetre radar; the S-band does not trigger it
   • A line of about twelve dots running outward along its bearing
   • The dot nearest own ship marks the SART, very close to its true position
   • As you close to about a mile the dots become arcs, and very close they become circles
   • Reduce sea clutter and adjust gain carefully so it is not suppressed, and use a range of 6 to 12 miles to see it

   Practised in the lesson Radar: a SART and a racon.

10. How does an echo sounder work, and how do you set it up?Often asked

    A good answer covers:

    • It times a sound pulse from the transducer to the bottom and back, using an assumed speed of sound in sea water
    • It measures below the transducer; below the keel and below the waterline come from the draught and transducer depth entered
    • Set the draught, the datum you want, the range and the gain, and a shallow alarm
    • Check the reading against the charted depth plus the tide

    Practised in the lesson Echo sounder and speed log.

By topic: COLREGs questions and ECDIS questions.