5. Answer the following questions.

1. What is a nautical chart?

2. What charts are usually used at sea?

3. What are bearings used for?

4. How can the ship’s position be fixed in shallow waters?

5. How can a navigator identify which light he is looking at?

6. What is the period of the light?

7. What are buoys?

8. What is a Nautical Almanac? What is it used for?

9. What is GPS?

10. What is the difference between course, heading, and track?

11. What is drift?

6. Answer whether the following sentences are true or false. Correct the false ones.

1. In piloting, the navigator guides a ship largely by the bearings of landmarks.

2. By day, mariners can still take visual bearings from lighthouses.

3. Port-side buoys are green.

4. Also a navigator may measure with a compass the altitudes of two or more celestial bodies.

5. The GPS receiver uses data collected from three or four satellites and presents it in navigation displays.

6. Floating navigational aids which are anchored or moored are called lighthouses.

7. The course is the direction of a straight line between a point of departure and a present position.

8. From scales on the chart the navigator can measure directly, without computation, the distance that the ship has traveled.

9. Starboard buoys are topped by a flashing red light.

10. Lighthouses are rarely more than 60m high, because their light could be seen in clouds in poor weather.

7. Sound.

Sound is a relatively new feature for aids to navigation, the first bell and whistle buoys being installed around the late 1850s. And they make sense. On a sailboat at night or in a fog, when there is nothing to see, you listen. You listen very carefully.

The chart always notes the type of sound-making device a buoy has. A bell uses many clappers to strike one bell, each producing a similar tone. Gongs have three or four small bells, each with its own clapper and each producing a different tone. A whistle uses the buoy's up-and-down motion to push air through an orifice, producing a sorrowful moan. A horn is the only sound-making device on a buoy that does not depend on the sea's motion. It uses electric power to make a tone that is similar to, but steadier than, a whistle.

Lighthouses, light towers, and beacons also use sound to help identify themselves, and are so marked on the chart. The type and characteristics of their sounds are different from a buoy's, and their range is greater. Horns use multiple horns (rather than a buoy's single) of different pitch to produce an almost musical tone. A diaphone gives a tone that starts with a higher pitch and ends on a lower. A siren may sound like a police siren, but is usually an even tone similar to that of a single horn.

Charts tell only what sound-making device is used, with no information about the sound's characteristic pattern—the number and length of blasts per period. The Admiralty List of Lights and Fog Signals, or an almanac such as the Macmillan & Silk Cut Nautical Almanac, will describe each light and buoy. It will also tell if the sound device operates only during reduced visibility, or at all times.

What it can't tell you, and no one can, is how the sound will travel. A foghorn's blast can go great distances downwind, while being inaudible just a short distance upwind. Range, loudness, and apparent direction can all vary due to wind or atmospheric conditions. So give them a chance. Be quiet. And listen.