Best Transponders For Easy Boat Installation

The easiest transponder to put on a boat is likely to be a Class B transponder, which is designed for recreational craft installation. Class B transponders have a transmission power of 2W, with a range of about 5-6 miles, and cost about half as much as a Class A AIS, usually priced in the $1,000 range. An even cheaper option is an AIS receiver, which doesn't broadcast information about your boat but allows you to access data being broadcast by others.

AIS transponder types: Class A, B, and B+

AIS transponders are used to receive data from nearby vessels and to transmit your vessel's identity, position, speed, heading, and other relevant information to all other vessels equipped with an AIS system within your range. There are three types of AIS transponders: Class A, Class B, and Class B+. All of them are interoperable, but there are important differences between them in terms of extent, complexity, and price.

AIS Class A transponders are mandated for vessels over 300 tons, fishing vessels over 15m, passenger-carrying vessels, and for the SOLAS Convention. They use the SOTDMA (Self-Organized Time Division Multiple Access) system, which ensures that the transponder first notices how other ships transmit their messages and then adjusts its transmission pattern accordingly. This system also prioritises AIS Class A transmissions, which will always be shown to other ships in the area. AIS Class A transponders have a higher transmission power than Class B transponders.

AIS Class B transponders are for recreational craft installation and have a transmission power of 2W, with a range of about 10 miles. They are less expensive than Class A transponders and transmit less frequently. Class B transponders use the CSTDMA (Carrier Sense Time Division Multiple Access) system, which listens for a few milliseconds to hear whether a large ship is transmitting before it transmits its own message. Information transmitted by Class B transponders can be "seen" by all AIS receiving equipment, and Class B transponders also receive all Class A and Class B AIS transmissions.

AIS Class B+ transponders, also called Class B SOTDMA, use the same SOTDMA technology as Class A transponders. This means they have the same priority when reserving a slot, ensuring they can always transmit, even in high-traffic areas. They have a transmission power of 5W.

Class A AIS transponders: features and requirements

Class A AIS transponders are designed for large commercial vessels such as tankers, tugs, and cargo carriers that traverse the world's oceans and seas. They are indispensable for maritime traffic management, especially in high-traffic shipping lanes, and are required by international maritime law for ships over a certain size. These transponders emit a comprehensive set of data, including vessel identification, cargo type, departure and arrival information, location coordinates, course, speed, rate of turn, and navigational status. The transmission power of Class A transponders is higher than that of Class B, ensuring a longer transmission range. Updates are sent every two to ten seconds when the vessel is in motion and every three minutes when stationary.

Class A transponders are engineered to interface with other navigational tools such as GPS, radars, and the Electronic Chart Display and Information System (ECDIS). They are equipped with a dedicated display screen and a full keyboard, allowing mariners to access and analyse vessel information, input data, and manually override automatic transmissions when necessary. The design of these transponders is tamper-proof and durable to withstand the challenging marine environment.

The key features of Class A AIS transponders include:

• High transmission power (12.5 watts)
• Frequent updates (every 2-10 seconds while underway and every 3 minutes while stationary)
• Comprehensive data set, including vessel identification, cargo type, location, course, speed, and navigational status
• Interface capabilities with GPS, radars, and ECDIS
• Dedicated display screen and full keyboard
• Tamper-proof and durable design

The requirements for Class A AIS transponders are dictated by international maritime law and include:

• Mandatory use for ships over a certain size (typically over 300 gross tonnage)
• The need to transmit a comprehensive set of data, including dynamic and static information
• Integration with other navigational tools such as GPS and radars
• Compliance with SOLAS (Safety of Life at Sea) regulations

Class B AIS transponders: features and requirements

Class B AIS transponders are primarily used by recreational vessels and smaller commercial vessels. They are designed to be user-friendly and easy to install, with compact, self-contained units that can be set up with minimal technical knowledge. Class B transponders transmit key navigational data, including the vessel's identity, position, speed, and course, enhancing marine safety for small vessel operators.

There are two types of Class B AIS transponders:

• Class B CSTDMA 2-watt: These are the traditional Class B units with a transmit range of 5-7 miles. They use the carrier sense system to secure a transmission slot.
• Class B SOTDMA 5-watt: This is a newer type of Class B transponder with a higher transmission power of 5 watts and a typical transmit range of 10-15 miles. They use the same self-organized slot management system as commercial Class A transponders.

Class B transponders have a transmission power of 2W, resulting in a range of about 10 miles. They are designed to meet the needs of smaller vessels, including leisure crafts, fishing vessels, and smaller commercial operators who may not traverse internationally recognized shipping lanes. Class B transponders transmit at a less frequent interval and with reduced power compared to Class A transponders.

Despite the differences in transmission power and range, Class B transponders still provide robust information that enhances marine safety. They meet the basic requirements to inform nearby mariners and coastal authorities of a vessel's presence, movements, and possible intent, reducing the risk of collision. Additionally, Class B transponders have dynamic broadcasting patterns, with transmission intervals that vary based on the speed of the vessel. Faster vessels will have their positions updated and transmitted more frequently than slower or stationary ones, increasing their visibility and reducing the risk of collision.

Class B AIS transponders are an excellent choice for recreational and small commercial vessels looking for a cost-effective, user-friendly option to enhance their navigational capabilities and safety. They provide essential data, including vessel identity, position, speed, and course, while being easy to install and integrate with existing onboard display systems.

Class B+ AIS transponders: features and requirements

AIS transponders are specialised tracking devices that allow ships to broadcast their location, course and other vital information to nearby vessels and maritime traffic monitoring stations. Class B+ AIS transponders, also known as Class B SOTDMA, are an advanced version of the standard Class B transponder. They use the same technology as Class A transponders, which are typically used by larger vessels, and have a higher transmission power of 5 watts. This gives them a longer range of approximately 10-15 miles.

Class B+ transponders have the same priority as Class A devices when reserving a transmission slot, ensuring they can always transmit, even in high-traffic areas. This makes them ideal for smaller vessels that operate in busy waters, providing enhanced safety and visibility. Like Class B transponders, they are designed with ease of installation and user-friendliness in mind, making them a good option for recreational boaters.

When choosing a Class B+ transponder, it's important to consider the options for connecting to other devices. Some transponders feature Wi-Fi and Bluetooth connectivity, while others have a NMEA 2000 interface to integrate with modern plotters, instruments and multifunction displays. Some transponders also come with a GPS antenna included, while others require a separate purchase.

It's worth noting that Class B+ transponders have a higher price point than standard Class B devices, reflecting their increased power and functionality. When deciding between a Class B or Class B+ transponder, boaters should consider their specific needs, budget and the areas in which they typically operate.

AIS transponder installation

AIS stands for Automatic Identification System. It is a remarkable system that allows you to ""see" other boats that are close by, even if they are beyond your visual range. AIS is a fully automated tracking system used to identify and track other vessels visually, as a method of collision avoidance.

There are two classes of AIS: Class A and Class B. The higher-power Class A transmits every 10 seconds or fewer, has its own display and keyboard, is usually meant for ships and other commercial vessels, and costs more. Commercial vessels weighing more than 300 gross tons or over 65 feet, certain passenger vessels, commercial vessels, and ships carrying hazardous cargo are required by U.S. and international law to have AIS.

Class B, for recreational boats, is more affordable (many in the $500 range) and is all that most pleasure boats need. It is fully interoperable with Class A, and both vessels will be able to "see" each other. Class B has lower power and transmits its position every 30 seconds (or every 3 minutes if moving slower than 2 knots).

To install AIS on your boat, you will need to decide whether to install a dedicated AIS antenna or use your existing VHF antenna with a digital splitter. If you install a dedicated AIS antenna, it must be at least 2 meters from any other radio antenna or vertical metal structure. If you prefer to use your existing VHF antenna, ensure it has a vertical radiator, an antenna gain of 3dB or similar, and an impedance of 50 ohms.

• Power: A 2-meter power cable with an attached 10-pin plug is supplied with the AIS transponder. Ensure you fully engage the locking ring to make a watertight seal. Always use a 2A fuse or circuit breaker and do not connect directly to the battery.
• AIS/VHF Antenna or a VHF Antenna with a splitter: The AIS system uses two special "data-only" channels in the VHF frequency range, so almost any VHF antenna can be used to receive and transmit AIS data. However, if you choose to install two antennas, they must be at least 2 meters apart; otherwise, the 25W power of the VHF will damage the AIS receiver.
• GPS: The AIS transponder will ship with its own external GPS, which must have an unobstructed, clear view of the sky. Do not place the GPS antenna near or in the path of a radar or HF antenna.

If you are a competent DIYer with basic wiring skills, installing AIS on your boat should take around 6 to 9 hours.

Frequently asked questions