Many instruments are employed today to facilitate navigation; some are relatively simple to use and others require extensive programs of instruction. In the latter categories are some of the modern electronic instruments, computers and mechanical devices available today to assist the navigator.

Navigation instruments are designed to fix position, measure direction and distance, determine speed, measure the depth of water, assist in plotting on charts, and observe the weather elements. Sometimes a combination of various instruments is used simultaneously to yield the required information.

Speed Log

An instrument known as the Speed Log is used to determine the speed of a yacht and the distance traveled through the water usually simultaneously. Various types of logs are used, some operating on a simple mechanical principle and others based on ingenious electromechanical techniques.

Deck Log

A Deck Log is the yachts official record book off the vessels movements which is kept aboard and it's use is generally reserved for longer over-night passages. The layout of the log into hourly or occasional entries is dependant on the type of yacht (MY or SY) and the duration and conditions being experienced. The navigator can prepare a log to suite the vessel and will stress the importance of the log as a yachts official document and as a record of the yachts last fixed position during a voyage.

Depth Sounder Lead Line

To determine water depth a navigator uses either the Lead Line or a electronic echo Depth Sounding. The lead, which consists essentially of a lead weight at the end of a suitably marked line, is used in coastal or shallow waters under conditions of low visibility. The echo sounder, which is found on almost all seagoing yachts, indicates the depth of water by measuring the time interval between the emission of a sonic or ultrasonic signal and the return of its echo from the bottom.

The Magnetic Compass

Whether motor cruising or racing a yacht, a compass is a very useful item of equipment and is one of the oldest instruments used aboard yachts. Although it has been generally supplanted by the Gyrocompass on Motor Yachts, the magnetic compass retains its original role as the basic navigational instrument because it is not subject to electromechanical defects, and, hence, on most seagoing voyages it is a necessary standby instrument. Both the Steering and Hand bearing compasses are graduated from 0 to 360 degrees, the circular card being mounted on a fine point and suspended in a bowl of fluid to dampen the oscillations.

The compass needle will indicate magnetic north, although the chart is aligned to true north. The difference between them is known as Variation or Declination and varies with time and with your location on the earth's surface, and it is indicated on the chart. For the convenience of navigators, the declination in many parts of the world has been measured, and charts have been prepared that show by connected points of equal declination, or Isogonic Lines, the approximate east or west declination for any area. On such charts, the line of no declination, along which the compass points true north, is called an Agonic Line

The majority of steering compasses have a mark on the rim called the 'Lubber Line' to indicate the boat's head and hence help you steer a given course.

Nobody can steer a small craft absolutely accurately but the competent helmsman should be able to keep to within 5 degrees of the required course, with errors in one direction being compensated by errors the other way.

The compass is subject to disturbance called Deviation from ferrous metal objects nearby. These are likely to be few in fiberglass yachts and can be checked by going out and 'Swinging the Compass' to produce a Deviation Chart correcting your steering compass reading to match the yachts course. It is worth checking the effect of any metal fittings being installed by putting them next to the compass and seeing whether the card swings. In a cruising yacht, don't forget to stow things like an outboard engine and even beer cans well away from the compass.

Gyrocompass

The Gyrocompass uses a gyroscope as its directive element, tends to indicate true north. The gyroscope in this compass is a rapidly rotating mass, free to move about one or two axes, perpendicular to the axis of rotation and to each other. Control elements are added to the gyroscope to convert it to a read direction in true degrees. The indications of the master gyrocompass may be repeated in various parts of the yacht, for example, in bearing repeaters, steering repeaters, and radar repeaters.

Azimuth Circle

The Azimuth Circle is an important auxiliary device used for indicating azimuth, or the bearing of an object and its direction measured from the north point. It is a graduated ring with sight vanes that is designed to fit snugly over a compass or a compass repeater. It provides a means of taking bearings of both terrestrial objects and celestial bodies.

Radar (radio detection and ranging)

Radar is an electronic system, used to locate objects beyond the range of vision, and to determine their distance by projecting radio waves against them. A high-frequency radio transmitter sends out a beam of electromagnetic waves, ranging in wavelength from a few centimeters to about 1 m (about 3 ft). Objects in the path of the beam reflect these waves back to the transmitter and can be viewed on a electron tube via the resonant-cavity magnetron. The term radar is derived from the phrase "radio detection and ranging," and this name was used by the U.S. and its allies during World War II for a variety of devices concerned with radio detection and position finding. Such devices not only indicate the presence and range of a distant object, called the Target, but also determine its position, its size and shape, and its velocity and direction of motion relative to your own. Although originally developed as an instrument of war, radar today is used extensively in many peacetime pursuits, which include controlling air and sea traffic, detecting weather patterns, and tracking ships in shipping lanes.

Basic Operation

Radio waves travel at about 300,000 km/sec (about 186,000 mi/sec), or at the speed of light. Radar equipment consists of a transmitter, an antenna, a receiver, and an indicator. Unlike radio broadcasting, in which a transmitter sends out radio waves and receivers intercept them, radar transmitters and receivers are usually located in the same place. The transmitter broadcasts a beam of electromagnetic waves by means of an antenna, which concentrates the waves into a shaped beam pointing in the desired direction. When these waves strike an object in the path of the beam, some are reflected from the object, forming an Echo Signal. The antenna collects the energy contained in the echo signal and delivers it to the receiver. Through an amplification process and computer processing, the radar receiver produces a visual signal on the screen of the indicator, essentially a computer display monitor

Transmitter

To operate radar successfully, the transmitter must emit a large burst of energy and receive, detect, and measure a tiny fraction (about a billionth of a billionth) of the total radio energy, returned in the form of an echo.