Landfall Learning
Why We Go
Social Studies
Ship's Log
Reading List
Frequently Asked Questions
Landfall-Learning > Science > Electronics


Once you understand Landfall's electrical systems, we can talk more about the electronic devices or "electronics" that the electrical systems power. These include the GPS, steering systems, radar and communication devices. There are also silent communication devices for general signaling, or for when all else fails.

Global Positioning System (GPS)

The most important of these electronic devices is the Global Positioning System, usually referred to as the GPS. While we also talk about GPS in the navigation tools and navigation methods sections, here we will cover how we use our GPS devices on Landfall.

To review, GPS works by receiving signals from three or more satellites in geosynchronous orbit around the earth. In other words, the satellites maintain the same position in relation to the earth's rotation in their orbit. There are twenty-four of these satellites in constant orbit around the earth. The GPS receiver on the boat takes the data from these satellites to triangulate the receiver's exact position on earth.

We can run a cable from the onboard GPS to send navigational data back and forth to our computer. This allows us to use the power of our laptop computer to store large amounts of data or to build routes on our mapping software, and then transfer that data back to the GPS. Some GPS models, including our main GPS unit, have a built in "Map Plotter" which shows our actual position on an electronic map.

We can also wire the GPS directly to the autopilot so that the autopilot can keep us on a specific course or even turn the boat at the right place.

Not only does the GPS tell us where we are, it can tell us where we have been, how fast and in what direction we are moving, and it can tell us what heading to steer to get to a specific destination. There is also a "man overboard" feature. When this function is selected, the GPS will tell us exactly what to course to steer to track back from the way we just came, even if we were making a number of turns along the way. This can be very useful if something (or someone) falls overboard and we can no longer see it with our eyes.

It takes a relatively long time to turn a sailboat around, and often by the time the boat is turned, the waves have obscured any object that is low in the water, like a person's hat--or a person's head! And of course, it is almost impossible to see anything on the surface of the water at night or in rainstorms.

We consider the "man overboard" feature to be one of the more important safety features on Landfall. Because we will be sailing many miles offshore, hundreds or even thousands of miles sometimes, if one of us falls overboard, the GPS may be the only thing that allows us to find the person and get him back aboard.

Because the GPS is such an important safety device for so many reasons, we carry several different GPS receivers on board as backups in case something goes wrong with the primary GPS.

Steering Systems

Autopilot for Sailboat's Wheel

There are two ways to steer the boat without someone standing at the wheel. One way is with the windvane, which is a mechanical device that uses wind pressure to keep the boat on a constant course in relation to the wind. We will discuss this more when we get to mechanical systems. The other way is using the electronic autopilot.

An electric motor connected to the ship's wheel drives the autopilot. An electronic compass inside the autopilot sends a signal to the autopilot's motor every time the boat starts to drift off the programmed compass course. These course adjustments happen almost constantly as the bow of the boat pushes through the waves. There are buttons on the autopilot's control unit that allow us to change the programmed course any number of compass degrees to starboard or port.


Radar Antenna Radar Display

Radar is an electronic device that emits short pulses of microwave radiation from an antenna. The radiation, like light, is reflected by obstacles. The radar detects the reflected pulses and, from the time delay between when the pulse was sent and the arrival of its reflection, calculates the distance of the obstacle. This process is repeated in every direction as the antenna scans the horizon. The resulting information is displayed on a display screen as a 360 degree pictorial representation of the area surrounding the vessel.

Radar allows us to "see" other ships in the distance, navigational markers, landmasses, and any large objects that may be floating in the water. This is very helpful in avoiding collisions, especially at night and during periods of rain and fog.

The radar system requires quite a bit of electricity to operate, so many sailboats use a special instrument called a "Collision Avoidance Radar Detector" or "CARD". Large commercial ships operate their radar systems continuously. The CARD detects the sound waves sent out by these ships' radar and sounds an alarm on the smaller boat, alerting them that a large ship is approaching, and from what direction.

The biggest danger to a small boat at sea is being run over by a large ship. The CARD alarm allows the crew on the smaller boat to steer clear before the larger ship gets too close for comfort.


Mounted VHF Radio Handheld VHF Radios

There are three types of two-way radios that are commonly carried on vessels. The most common radio is a marine "VHF" (very high frequency). Almost all vessels around the world carry a VHF radio, so no matter where you are you can communicate with other boats in the vicinity. The drawback to marine VHF is its relatively short range of 5-25 miles. So while VHF is good for talking to nearby vessels, it is of no use to talk to people on vessels far away.

The second common type of radio is called a "single-side band" radio, or "SSB". Single-side band has a much greater range than VHF and it is almost as easy to operate. The drawbacks to SSB radios are that they are expensive to buy, and they require a lot of space for the radio equipment and antenna shielding.

The final type of radio commonly used on vessels is the "ham" radio. Basically, ham radio allows you to send a signal and talk to another ham radio operator anywhere around the world. It can also send data, allowing you to log on to the Internet or send and receive email. Unfortunately, these ham systems are complicated to operate (requiring a special license from the FCC, or Federal Communications Commission), they are very expensive, and they take up a lot of space.

There are other less common (and more expensive) forms of communication that can be used on vessels. These use satellites for transmitting the data.

Emergency Locator Beacons


An important safety-related battery operated electronic device called an "Emergency Position Indicator Radio Beacon" (EPIRB) is carried on many boats. The EPIRB is designed to send out a long-range distress signal in the event of a life-threatening emergency or if the crew has to abandon ship at sea. When activated, the EPIRB broadcasts a unique, repeating SOS signal that can be detected from virtually any point on earth. When properly registered, the signal includes a description of the vessel and its location. This critical information is routed directly to rescue units on the ground, reducing search time dramatically. It is recommended that sailors venturing outside reliable VHF radio range, about 20 miles offshore, carry an EPIRB on board. The signal is transmitted on a frequency constantly monitored by rescue services and commercial airliners around the world. Even if not properly registered, the outgoing signal includes the serial number of the device and its location in latitude and longitude. The serial numbers of all EPIRBs are registered with the Coast Guard, so that they can identify the vessel in trouble.

Landfall carries a VHF radio, GPS, radar, an autopilot, and an EPIRB.

Silent Communications

Signal Flags

Radio devices that can be carried aboard vessels are not our only means of communication. Time-honored methods used to send signals to other vessels are still in common use today.

If you go to any seaport, you will see boats flying flags. The flag on the stern of a boat is the flag of the nation where the boat is registered. For instance, Landfall is registered in the United States, so we fly the American flag from her stern. If we were visiting a foreign port, then we would fly a second flag from the side of the mast. That flag would be the national flag of the country we are visiting.

There are also 37 different signal flags, shown to the left. A signal flag is used to send a message to other boats. These flags are of all different designs and colors. In fact, there is a different flag for every letter of the alphabet and for each of the numbers 0-9. To send a message, you simply use the flags representing the letters and numbers to spell out the message, and hoist the flags up the mast.

Only a few colors can be readily distinguished at sea. These are: red, blue, yellow, black, and white; that is why these flags use only these colors. The captions beside each flag describe the letter the flag stands for as well as the international signal it represents.

Notice that the flags aren't named after the standard ABCs. Instead, they use the International Radio Operators Alphabet, also sometimes called a phonetic alphabet. Which, since they are transmitting a signal, is very appropriate.

We also use this alphabet when talking on the VHF radio, if there is a lot of static.

The solid yellow flag is commonly called a quarantine flag. The quarantine flag is used to notify the customs officials of a new port that you have just entered their waters. Once the customs officials have cleared the ship and crew (admitted them into the country) the quarantine flag is taken down.

Running Lights

All boats are required to show "running lights" when underway at night. These lights are set up in a standard pattern so that other vessels can tell what type of vessel you are and in what direction you are traveling. There is a red light on the port bow, a green light or the starboard bow, and a white light on the stern. So when it is hard to see other boats at night, if we look out from the port bow and see the green light of another ship, we know that we are going to cross paths and should take care. If we look in that same direction and we see the vessel's red light, we know that the other ship is moving away from us and we are safe. If we look out from our starboard bow, the colors would mean the opposite.

The simple rule is that if we are looking over either our green or red light and see the opposite color on an approaching ship, then we will cross paths. If we see the same color as the light we are looking over, then we are moving away from each other and we are safe.

Signal Flares

We also carry signal flares on Landfall. Signal flares are used in the event of an emergency, to let nearby vessels know that there is a vessel in distress.