Aid-to-navigation

According to the Coast Guard definition of aid to navigation, it is "any device external to a vessel or aircraft intended to assist a navigator to determine position or safe course, or to warn of dangers or obstructions to navigation."

Under this definition all onboard navigation equipment, such as compasses, radars and so on are not a part of aid to navigation systems. Also, any landmarks (large buildings, mountains, trees, etc.) that weren't built specifically for navigation help are not aids to navigation. Nevertheless, all of the above are certainly a very huge part of the help that sailors (and pilots) use for navigation.

In this section, however, we will only describe the "official" aids to navigation. There are visual aids to navigation, Loran-C (not for much longer, though) and GPS.

Visual aids to navigation
These are the most frequently used types of aids. The color and light scheme is the same in most Western hemisphere nations (including North America's Great Lakes), and in Japan, and it conforms to the International Association of Lighthouse Authorities Region B system. The Eastern hemisphere uses a reversed color and light scheme. This is a lateral system, which means that the aids to navigation in the channels are near the sides. There is one rule to remember: when you're entering a channel from seaward, you must leave solid red aids to starboard, and green ones to port side. If the channel goes parallel to the coast, use the clockwise direction as if it were the one "entering from seaward". Always use your charts to identify specific visual aids.
photo by Ina Kulczynska - Forillon National Park, Quebec, Canada	Lighthouses	These are major structures with distinctive color and light schemes (or sequences). This is so that you will be able recognize were you are with certainty. Many lighthouses also have sound signals - very useful in thick fog. You will find the necessary information (sound, light color and characteristic, name, height and nominal range - the distance at which the light is well visible in clear weather, usually it is around 10 nautical miles) on your charts. It is very advisable to have the Coast Guard Light List in your possession - it contains a lot of information you might find useful (such as the complex flash characteristics some lights show). Remember, the colors do not indicate which side you should pass it on!
	Minor lights/beacons	These are much smaller than lighthouses, but also give light signals. They are single- or multi-pile structures, although sometimes can be also skeleton or masonry towers. They have dayboards which are plywood boards with significant shapes and colors, numbers or letters, and a reflective tape around them.
	Daybeacons	These are structures similar to beacons, except they are unlighted and are usually single-pile.
	Buoys	Buoys can be lighted or unlighted. These are the "floaters" you see on waters. They are attached to a very heavy weight that keeps them in place. Their shape is significant. Your charts will show you all buoys (except for ones used in races), together with the shape and lighting pattern. This is one of the reasons why you should update your charts regularly - placement of the buoys sometimes changes, and there are additions.

Some important information about the shapes, colors, lights and numbers on buoys, beacons and daybeacons
Solid color red buoys and dayboards		When entering from seaward - leave them to starboard; The light on these is always red - usually flashing; They always have even numbers; Dayboards are triangular, pointing up; Unlighted buoys are conical (nuns), lighted ones don't need to be conical, but some are.
Solid color green buoys and dayboards		When entering from seaward - leave them to port side; The light on these is always green - usually flashing; They always have odd numbers (with square outline); Unlighted buoys are cylindrical; lighted ones don't need to be cylindrical, but some are.
Cardinal buoys		Yellow and black conical or cylindrical buoys; If lighted the light is white; They have two conical topmarks - direction of pointing has significance! They are lettered - no numbers; They indicate danger and which way you should proceed to avoid it.
Special buoys (shapes have no significance)
	Isolated danger	Black with one red horizontal band; White light (Fl (2) 5s) or (Fl (2) 10s) - but may have no light; Has two spherical topmarks; Lettered - no numbers; Designates a dangerous area around which the water is navigable - it will be indicated on a chart, including the danger involved.
	Fairway	Red and white vertical stripes White light (Mo (A) 6s) or (LFl 10s) - but may have no light; If there is no light - there is a spherical topmark; Lettered - no numbers; Indicates safe waters; Can be passed on either side, but should be left on port.
	No Anchorage	Square daybeacon; Black anchor symbol on a white background, with a red diagonal stripe running across it; Indicates an area where no anchorage is permitted; These areas are marked on your charts with this symbol:
All of the below, if are equipped with a light it is always a yellow light.
	Cautionary	Yellow; May have a yellow "x" topmark; Indicates dangers such as pipelines, firing ranges, race courses, seaplane bases, and areas with no through channels.
	Anchorage	Yellow; May have a yellow "x" topmark; Marks the perimeter of designated anchorage area - your charts will provide the depths.
	Mooring	White with an orange (may be blue) horizontal stripe; Used for securing or mooring vessels; In bad weather (when you cannot see well) keep in mind that a vessel might be secured to the buoy!
	Information	White with an orange square between two orange horizontal stripes on it; The information inside the square may be about a campsite, locality, marina, and so on.
	Hazard	White with an orange diamond between two orange horizontal stripes on it; The information inside the diamond may indicate shoal, rocks, and so on.
	Control	White with an orange circle between two orange horizontal stripes on it; The information inside the circle may be about a speed limit, wash restrictions, and so on.
	Keep-out	White with an orange diamond between two orange horizontal stripes - two orange stripes inside the diamond form a cross (connecting the corners); This buoy indicates areas where boats are prohibited.
	Scientific (ODAS)	Yellow; May have a yellow "x" topmark; Either the buoy itself, or something in the vicinity collects data (meteorological and other scientific data); The abbreviation in parentheses stands for an Ocean Data Acquisition System.
	Diving	White with the diving flag on it (red square with a diagonal white stripe running across it - from top left to bottom right); It indicates that diving (scuba) activity is in progress - do not approach - may be very dangerous for the diver!
	Swimming	White; Indicates the areas restricted for swimmers; Do not approach - it may be very difficult to see swimmers from a boat!
	Ranges	Very important part of aids to navigation; Always built in pairs; They usually mark the centerline of a channel; The rear range mark is higher than the front one; They are rectangular, twice as tall as wide, have a central vertical stripe; When range marks are lined up ("in range"), that means that you are on the line of position they mark.

Additional info about sound signals

Most lighthouses, many large buoys, and many minor lights have sound signals.
Types of sound signals:
1. wave-actuated whistles
2. bells
3. gongs
4. air horns
5. sirens
6. diaphones
The last three have been replaced with electronic horns.
Types and patterns of sound signals are indicated on the charts.
Many electronic horns now have sensors that turn them on when it is foggy.
Most long-range electronic horns operate at about 300 Hz, and medium-range at 300 - 850 Hz.
The distance at which you can hear a horn depends on the wind, waves (water, not sound), and the weather.

Loran-C

Global Positioning System (GPS)

Systems made up of chains of a master ("M") and two to five secondary transmitting stations ("V" to "Z").
There are eight chains in USA (including two in Alaska), three chains in Canada, and more of these worldwide.
The stations are 200 miles apart from each other, spanning an area of about 1000 miles across.
Many stations operate in more than one chain.
Most stations have antennas 625 to 1350 feet high.
Each chain has a group repetition interval (GRI) at which the stations send pulsating signals.
The receiver selects the chain that gives the best accuracy in the given area, synchronizes with its GRI, and ignores all other signals at different GRIs.
The Loran-C system will be shut down in 2008.

Makes use of the satellites orbiting the Earth, in six orbital planes.
Each satellite orbits the planet every 12 hours, and transmit a signal called a pseudo-random digital code. The code is unique to each satellite (which are named after this code) for timing and identification.
The receiver identifies the satellites based on the copy of the code in its memory.
Two types of codes exist: a course/acquisition code (C/A), and a precision code (P) - only military has access to the P-code.
The receiver needs three satellites to get the latitude and longitude, and four satellites to receive the altitude as well.
Older receivers are single-channel units - they are rather slow and have reduced performance during maneuvers. Newer receivers are multichannel - use several satellites, and their navigational functions are always uninterrupted.