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There are a lot of different marine navigation methods, instruments, and systems to navigate the seas. In this article, I'll explain most of them, including the navigational instruments that are most used by sailors today.
What types of marine navigation are there? Celestial navigation, dead reckoning, inertial navigation, and electronic navigation. One can either determine location based on a previous location (dead reckoning), or based on some sort of object (star, landmark, or buoy). Some commonly-used tools are the compass, GPS, radar, and sextant.
That last one is a bit of a cliché, but my guess is that every sailor secretly wants to use a sextant (at least I do). Well, here's the good news: you should. Celestial navigation is old, but not outdated. And that goes for most methods. GPS is definitely better in many ways, like most modern solutions - like pizza delivery. But you still want to know how to make your own.
Marine navigation is the use of navigation techniques to guide a (sail)boat from one point to the next.
All forms of navigation have four steps:
What is a navigation technique? A navigation technique is a way to determine the navigator's position and to set the desired course. There are different methods of locating your position, different plotting methods, and also different ways to determine your course. The system of locating, plotting, and setting a course is called a navigation method.
The most common navigation methods are satnav, dead reckoning, and radar navigation.
Every method has advantages and disadvantages. For example, dead reckoning and radar can be used to determine your location based on just one point or object. But you need a lot of equipment. Celestial navigation is very reliable, but you need clear skies. Satellite navigation is very accurate, but you need a power source.
Celestial navigation is one of the oldest navigation methods. The navigator uses the celestial bodies to determine his location.
With Coastal navigation, the navigator uses the shape of landmarks along the coast, and the direction of the coastline.
With Inertial navigation, you use motion sensors to calculate your new position relative to the starting position. (This is a form of dead reckoning.)
Pilotage simply means fixing your position with a very high frequency and is used in harbors and restricted waters.
Radio navigation uses radio waves to measure the direction to a radio source. For this to work, you need radio towers all over the place. GPS is winning the battle for sure.
Radar navigation is mostly used to avoid collisions when you're close to land or other ships.
Satellite navigation is the most used form of navigation nowadays. This uses multiple satellites to pinpoint your location.
Experienced skippers always have multiple navigation methods at hand: and so should you.
You can use analog or electronic equipment to get your position and plot it. A lot of the electronic instruments are actually just modern replacements for the old tools: they pretty much do the same job (but faster and better). A chartplotter is just a GPS version of a compass, a chart and a ruler (okay, I agree, it's a bit more complicated).
Some serious navigation systemsOld methods are less accurate than GPS - but they are pretty darn close enough! Celestial navigation can be very accurate if you do it right. Old skool methods are a great backup (and also cool to learn). They're always available: during solar flares, outages - some even without equipment.
You can use all kinds of navigation systems. The most used on modern-day boats are:
You can determine your position based on your previous position, or you can look out and use pretty much any kind of landmark, celestial body, and so on, to pinpoint where you're at.
If you use objects, you can do two things with them: you can measure your distance from them. And you can measure the direction to an object. The direction to an object is called a bearing.
If you don't have a compass, you can still get a directional line. Find two charted objects that align (like some rock formations or two buoys). This is called a transit.
By plotting the bearing or transit on a chart, you know along which line you're moving.
Then, if you measure the distance from you to an object, you get a line of position (LOP). If you plot this on a chart, you get a circle or arc.
If you draw two LOPs, they will intersect. This point is called the fix. That's your position. If you plot two or more bearings, you also get a position fix. Want to be very accurate? Use a bearing and a transit.
It's as simple as that. All navigation equipment essentially do one of these two things. Find some lines, make them intersect.
So you need lines to know where you are. A navigation technique is simply the way you chose to get your lines.
Wikipedia here says that using lines of position is just one of the techniques, but I disagree. Satellite, radio, radar - all these methods use some sort of distance or directional lines to tell you where you are.
To get yourself some lines, there are plenty of old skool methods and modern ones as well.
Getting a compass bearing is easy. You find a point on a chart you can see on the horizon, and you point your compass at it. Read the angle on the compass, and simply draw a line in that angle across the point of reference. The classic way is three compass bearing on three widespread objects.
For this method, you need a compass and a marine chart.
You don't have to go overboard when buying a good, reliable compass. It's pretty affordable. If you want to know what I use, read my article here. It's so good, I even have one in my car.
Not sure how to use a compass? Read the complete beginner's guide here.
If you don't have a compass, you can still find your direction by using two landmarks or objects. When two charted points align with your bowsprit, for example, two buoys, you can draw a line through them. Voila, you know your direction. This line is called a transit.
For this method, you need a marine chart.
Radar is different and pretty neat because it only needs one object to get a pretty accurate position. It can get the range and bearing from one object and plot it directly on the chart. So it's extremely useful if you navigate let's say a massive container ship in a crowded, tight port.
For celestial navigation, you need a couple of tools: a nautical almanac, a marine chronometer, and a sextant.
You first use the almanac and chronometer to pick a subpoint. That's the point where the planet or star is currently located above Earth. Then, you take the sextant to measure the angle between the celestial body and the horizon. This gives you the distance between you and the subpoint. Here's your first line of position. A neat circle around the location of a star.
Repeat this process a couple of times with different stars, until you get two or more lines that intersect, giving you the position fix. Also called 'the celestial fix' - which is a pretty rad name.
You need a sextant, chronometer, and almanac for this method.
The easiest and most accurate way to pinpoint a location is by using satellites. A GPS receiver calculates the distance from multiple satellites. This gives you some lines, that are now in the sky instead of on a map. Again, where the lines intersect is where you are.
GPS is extremely accurate and reliable. It can find you within half an inch, and will only fail if there's no power source, very heavy weather, solar flares, and so on. It will work perfectly most of the time.
However, there are some downsides. GPS only tells your current location. It doesn't show any maps, directions, and so on. In combination with electronic chartplotters, GPS is very powerful. This is what's in our cars, sailboats, phones and so on.
It also can't tell you which direction you're pointing towards. So you can't use it to measure bearings.
GPS is an American technology, and China, Russia, and Europe have their own variants, although they are not as widely supported.
You need at least a GPS receiver, plus a marine chart or a chartplotter.
Nowadays, you can get a reliable, easy-to-use chartplotter, made by a reputable brand, with all the functionalities of an advanced marine GPS, at a fraction of the price. Click here to read my recommendation.
An echo sounder is a sonar that's used to determine the water depth. It uses sound waves and measures the delay of the reflections. This tells the distance to the bottom.
Echo sounding can be used to estimate a location but it's not very accurate. You also need some sort of bearing. Then check the chart and your current depth. Check at what point your depth and the bearing intersect.
You can use sounding by itself to estimate a location, but it's a bit tedious. You literally measure a lot of points and draw up your own depth chart. Then compare it to an existing chart to estimate your location.
For this method, you need a sonar device, fishfinder, or MFD (multi functional display).
If you're sailing in a port or bay, there are lots of other vessels and objects to avoid. So you want to stay on course accurately. To do this, you need to monitor your position very carefully. If you want to avoid to have to plot your position every minute, you could use parallel indexing to stay on course.
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Parallel indexing is simple. Take a fixed object. Through it, draw a line that's parallel to your course. Then monitor the echo of the object on the radar. As long as it stays glued to the line, you're on course.
You need a radar for this method.
You can also measure the distance from your old position. For this, you need your course and speed. This is called dead reckoning. It's the same principle. Your old position is the 'object'. Your course is the angle (bearing), and your speed is the distance, giving you a line of position.
You need an inertial navigator for this method. (Or the old skool chronometer and chip log.)
This method isn't used a lot, but it can be handy. We check when the top of the lighthouse appears on the horizon. If we know the height of the lighthouse, and our eye height, you can calculate how far away we are. Using some algebra, involving the curvature of the Earth. Most navigational almanacs (including Reeds Nautical Almanac - Rising and Dipping distances) contain some sort of a table that gives you the distance.
If you have the distance, that's a line of position. Then just point your compass at it for the bearing, and you have your fix.
You need a sextant and nautical almanac for this method.
What did early explorers use to navigate? The most common tools for ancient navigators were:
The astrolabe is an ancient navigation instrument that measures the inclined position of stars or planets. It can be used during day and night. It was used during the Middle Ages and literally means 'the one that catches the heavenly bodies'.
The back staff measures the altitude of the sun using its shadow. It was invented in the 16th century. Before that, navigators had to directly stare into the sun to measure its altitude. Which is not great for your sight in the long term. This instrument creates a projection using the sun's shadow. It's way better to look at that.
The octant and sextant measure the angular distance between two visible objects. Usually, it's the distance between the horizon and the sun. Both tools are used for celestial navigation and work roughly the same.
The octant has a smaller angle than the sextant, and it couldn't be used to measure the angle between the sun and the moon, because the angle was too wide. That's when the sextant was invented.
A chip log is a wooden board attached to a line. This line has knots. The navigator throws the log overboard and counts the number of knots over a certain time. This gives him the ship's speed.
This is also where the word 'knots' (for nautical speed) comes from.
How did sailors navigate by the stars? If a navigator knows where a star is located above Earth, he can determine his distance from that particular subpoint. He needs a tool to measure the angle between the star and the horizon, like a sextant or astrolabe. Now he has a line of position. When repeated, he can triangulate his position (the celestial fix).
What types of navigation or other tools do sailors use today? Most sailors use multiple navigation methods. Most ships use some form of GPS, chartplotting, a compass, radar, and echo sounding (sonar). The primary navigation method depends on the situation. A compass is very suitable for open seas. In coastal waters or harbors, radar and sonar are typically used more often.
What tools did ancient navigators use? Ancient navigators used the following tools for fixing a location: astrolabe, back staff, octant, sextant, and compass. To determine their course and speed, they used a chip log, marine charts, and a chronometer (timekeeper). The Dutch used a pendulum clock instead
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Unlike the roads and highways that we drive on, the waterways we go boating on do not have road signs that tell us our location, the route or distance to a destination, or of hazards along the way. Instead, the waterways have AIDS TO NAVIGATION (or ATONs), which are all of those man-made objects used by mariners to determine position or a safe course.
These aids also assist mariners in making a safe landfall, mark isolated dangers, enable pilots to follow channels, and provide a continuous chain of charted marks for precise piloting in coastal waters. The U.S. Aids to Navigation System is intended for use with nautical charts, which provide valuable information regarding water depths, hazards, and other features that you will not find in an atlas or road map.
The term "aids to navigation" includes buoys, day beacons, lights, lightships, radio beacons, fog signals, marks and other devices used to provide "street" signs on the water. Aids To Navigation include all the visible, audible and electronic symbols that are established by government and private authorities for piloting purposes.
The Coast Guard is the agency responsible for maintaining aids to navigation on U.S. waters that are under federal jurisdiction or that serve the needs of the U.S. armed forces. On bodies of water wholly within the boundaries of a single state, and not navigable to the sea, the Coast Guard grants the state responsibility for establishing and maintaining aids to navigation. The U.S. Corps of Engineers is responsible for many of the canals, dams, locks, and other man-made waterways in the country. The Corps also is responsible for the regulation of mooring buoys in all navigable U.S. Waters.
The individual Coast Guard districts also may grant permission to private groups and citizens to place "Private" Aids to Navigation. These aids allow individuals or organizations the ability to mark privately maintained channels, zones or waterways. These aids must be pre-approved, and must be maintained by the individual or organization.
The term "aids to navigation" encompasses a wide range of floating and fixed objects (fixed meaning attached to the bottom or shore), and consist primarily of:
Both Buoys and Beacons may have lights attached, and may have a sound making device such as a gong, bell or horn. Both Buoys and Beacons may be called "marks".
Caution: Do not count on floating aids to always maintain their precise charted positions, or unerringly display their characteristics. The Coast Guard works constantly to keep aids on station and functioning properly, but obstacles to perfect performance are so great that complete reliability is impossible. Only use floating aids for use as a navigation fix when you cannot see a fixed point of reference.
Depending on where you boat in America, you may see several differences in how navigational marks are colored, numbered, or lighted. Regardless of the location, buoys and beacons are placed in very specific locations, to mark either a particular side of a waterway, or some other navigational feature. The primary system in use is referred to the "U.S. Aids to Navigation System". The U. S. Coast Guard maintains this system in conformance to the International Association of Lighthouse Authorities (IALA), which is an international committee which seeks to ensure safe navigation, primarily through the use of common navigation aids and signals.
The "LATERAL" system is the familiar RED RIGHT RETURNING system, meaning that on all navigable waters returning from sea, the red even-numbered marks are on the starboard (right) side of the channel and the green odd-numbered marks are on the port (left) side of the channel. Numbers on the marks ascend when traveling from sea to harbor--if you don't have a compass and become disoriented on the water, you will always know you are heading upstream if the buoy numbers get larger as you travel.
Port side numbered aids are green in color, odd numbered and may be lighted. Port side marks are located on the left side of the waterway as you travel upstream, and the buoy numbers will increase as you head upstream. (Chart depictions are shown next to the marks) Port-Side Buoys have a cylindrical above-water appearance, like a can or drum floating on its axis. Commonly referred to as "CAN" buoys. Beacons - Port side beacons have square marks attached to them, with two shades of color and a reflective border.
Starboard aids are red in color, evenly numbered and will be on your right side as you travel upstream. Buoy numbers increase as you head upstream, and may have a red light. Starboard-side buoys have an above-water appearance like that of a cylinder topped with a cone, pointed end up. The cone may come to a point or be slightly rounded. Commonly referred to as "NUN" buoys. Starboard-side Beacons have triangular marks attached to them, with two shades of color and a reflective border.
For the sea buoys that delineate channels off the coast of the United States, and for the Intracoastal Waterway (ICW), red is on the right (shore side) when proceeding clockwise around the U. S. from the East Coast to the Gulf Coast, or proceeding north along the West Coast.
ICW marks are further identified by a small yellow reflector at the bottom of the mark. The same port and starboard marks shown above will look like the following.
Numbers on the marks ascend when traveling in this direction. Where the IALA-B and ICW marks meet, one must be very careful to observe the change in meaning by referral to local charts.
These diamond shaped marks are used to help the vessel operator determine location on a nautical map. When you see a dayboard, and find the corresponding mark on the chart, you know your precise location. They may be lettered, and may be lighted with a white light. Their color reflects that of nearby lateral marks.
These marks are used to mark fairways, mid-channels, and offshore approach points. They have unobstructed water on all sides. These marks may be lettered, and may be lighted with a white light. They may also have a red top mark.
These indicate a danger which may be passed on all sides. They are erected on, or moored on or near danger. They should not be approached closely without special caution. They may be lighted, and they may be lettered.
Special marks have no lateral significance (meaning they don't tell you which side of the channel or river you may be on). These marks are used to mark a special feature or area. These include area limits for anchorages, fishing grounds, or dredging/spoil areas. These buoys may be lighted, and if they are it will be a fixed or flashing yellow light. Shape is optional, but usually follows the shape of the navigation buoys that it is positioned near.
Mooring buoys come in two different shapes; spherical and cylindrical. Both have white bodies with a solid blue horizontal band on the center of the buoy. Mooring buoys may have a white reflector, or a white light attached to them. Mooring buoys are the ONLY buoys to which you may legally tie your boat. Buoys are generally placed in marked anchorage areas, and you must take caution if you are traveling near buoy areas. Check your state boating guide for particular operating restrictions in anchorage areas.
These are pairs of unlighted or lighted fixed aids that when observed in line show the pilot to be on the centerline of a channel.
Regulatory Marks re designed to assist boaters by informing them of special restrictions or dangers that they are approaching. Regulatory marks are white "can" buoys that have an orange shape on them. The mark will give either a warning or instructions on how to proceed. The shape determines what type of mark it is.
This system was originally intended for use by states on lakes and inland waterways that weren&#;t covered by nautical charts. The buoys used in the Uniform State Waterway Marking System (USWMS) used colors, shapes and marking patterns that differed greatly from the U.S. Aids to Navigation System (ATONS).
In , the U.S. Coast Guard decided to phase out the USWMS to avoid potential confusion of boaters and instead, favored using the more widely recognized ATONS. By , the USWMS was completely phased out. Below are a few of the differences from the federal system you should know about.
Here's a summary of the important changes regarding the phase out of USWMS:
The state system differs in several ways, in case you happen to encounter them. These aids also assist mariners in making a safe landfall, mark isolated dangers, enable pilots to follow channels, and provide a continuous chain of charted marks for precise piloting in coastal waters. The U.S. Aids to Navigation System is intended for use with nautical charts, which provide valuable information regarding water depths, hazards, and other features that you will not find in an atlas or road map.
Red-topped White Buoys
Black-striped white Buoys - Inland Waters Obstruction Mark
Black-topped White Buoys
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