SPEED LOG

Marine Speed Log:

 

A marine speed log is a device used to measure the speed of a vessel through the water (known as speed over ground or SOG) and sometimes relative to the seabed (referred to as speed through water or STW). It is a crucial tool for marine navigation, ensuring the vessel’s safe operation, fuel efficiency, and compliance with maritime regulations.

 

The marine speed log provides essential data to the vessel's crew, enabling them to make informed decisions about route planning, fuel consumption, and maintaining a safe speed. There are different types of speed logs that vary based on technology, mounting methods, and application.

 

How a Marine Speed Log Works:

A speed log typically uses sensors or transducers that measure the speed of the vessel through water or over the ground. These devices can either use mechanical or electronic principles to calculate speed and display it for the crew.

 

Mechanical Speed Log: These older systems use a rotating impeller or paddlewheel, which is towed or mounted on the hull, that spins as the vessel moves through water. The rotation speed is measured and converted to speed data.

 

Electronic Speed Log: These modern systems use various technologies, including ultrasonic, electromagnetic, or Doppler radar sensors to measure the vessel's speed. These systems are typically more accurate, reliable, and less prone to mechanical failure.

 

Types of Marine Speed Logs:

 

Electromagnetic Speed Log:

Description: Electromagnetic speed logs measure the water flow relative to the hull of the vessel using electromagnetic fields. A sensor on the hull detects the movement of the water particles as the vessel moves, and the data is converted into speed readings.

Advantages: High accuracy, low maintenance, and no moving parts.

Uses: Widely used on commercial vessels, offshore platforms, and yachts.

Disadvantages: Requires a power supply, and performance may be affected by the presence of marine growth on the sensors.

 

Doppler Speed Log (Acoustic Speed Log):

Description: Doppler speed logs use sound waves to measure the relative velocity between the vessel and the water or seabed. A transducer emits sound waves that bounce off the water or seabed, and the Doppler shift in the reflected signal is used to calculate speed.

Advantages: Accurate, no moving parts, unaffected by marine growth or fouling, and can measure both the vessel’s speed through water and relative to the seabed.

Uses: Commonly used in both commercial and military vessels, as well as in scientific research applications.

Disadvantages: Requires periodic calibration and can be expensive.

 

Mechanical Speed Log (Paddlewheel or Impeller Type):

Description: A mechanical speed log uses a paddlewheel or impeller mounted on the hull of the vessel, often underwater. As the vessel moves through the water, the impeller spins, and this rotation is used to measure the speed of the vessel.

Advantages: Simple technology, low cost, and reliable in most conditions.

Uses: Mostly used in smaller boats or as backup systems on larger vessels.

Disadvantages: Prone to fouling, wear, and tear, and can be affected by marine growth.

 

Ultrasonic Speed Log:

Description: Ultrasonic speed logs use sound waves to measure the vessel's speed relative to the water. A pair of ultrasonic transducers is mounted on the hull, and the time it takes for the sound waves to travel between the transducers is measured to calculate the vessel's speed.

Advantages: Highly accurate, with no moving parts, and little maintenance required.

Uses: Found in a variety of vessels, including yachts, commercial ships, and naval vessels.

Disadvantages: Can be expensive and requires good installation for optimal performance.

 

Integrated Speed Log (Multi-Function System):

Description: Modern speed logs are often integrated with other navigation and monitoring systems, such as GPS, radar, and autopilot. These systems combine speed measurements with data from other sensors to provide comprehensive navigation data, such as speed over ground (SOG) and speed through water (STW).

Advantages: Provides more comprehensive data for navigation and efficiency. Allows for integration with other systems on the vessel.

Uses: Commercial vessels, luxury yachts, and large marine platforms.

Disadvantages: Can be more expensive due to advanced features and integration.

 

Key Components of a Marine Speed Log System:

 

Sensor/Transducer: The primary component that measures the speed by detecting movement (using either mechanical, electromagnetic, ultrasonic, or Doppler principles).

 

Processor/Display Unit: The data collected by the sensor is processed and displayed on a digital readout or integrated into a chart plotter or navigation system.

 

Calibration and Maintenance System: Regular calibration is required for the sensor to ensure accurate readings. Maintenance often involves checking for fouling, cleaning, and ensuring the sensor is correctly aligned.

 

Top Brands of Marine Speed Logs:

 

Furuno:

Furuno is a well-known brand in marine electronics and offers a wide range of speed log systems, including Doppler, electromagnetic, and mechanical types.

Popular Models:

Furuno DS30/DS50/DS80 Speed Log: A versatile and reliable Doppler speed log that offers both speed through water and speed over ground measurements.

Furuno Series: Electromagnetic speed logs designed for ease of installation and maintenance.

Features: Furuno speed logs are known for their durability, high accuracy, and ease of integration with other navigation systems.

 

Simrad:

Simrad, part of the Navico group, offers high-quality marine speed logs, including Doppler and electromagnetic types, suited for professional and recreational marine use.

Popular Models:

Simrad PI50 Speed Log: A highly accurate electromagnetic speed log that integrates with Simrad’s other navigation systems.

Simrad IS20 Speed Log: A simpler, more affordable model designed for smaller vessels and recreational boats.

Features: Simrad systems are known for high accuracy, robust construction, and integration with other navigation and autopilot systems.

 

Kongsberg (formerly Kongsberg Maritime):

Kongsberg is a leading manufacturer of advanced marine systems, including high-end Doppler and electromagnetic speed logs used in commercial shipping and offshore platforms.

Popular Models:

Kongsberg Seapath 300: An advanced integrated speed log and heading system with GNSS and Doppler capabilities.

Features: Offers high-precision measurements, long-term reliability, and seamless integration with dynamic positioning and other advanced navigation systems.

 

JRC (Japan Radio Company):

JRC offers several marine speed log systems, including Doppler and mechanical speed logs, widely used in commercial and military vessels.

Popular Models:

JRC JLN-7400 Doppler Speed Log: A high-precision Doppler radar-based speed log with excellent measurement capabilities.

Features: Known for robust, reliable systems, often used in large vessels and commercial shipping.

 

Advantages of Marine Speed Logs:

Accurate Speed Measurement: Provides precise data on a vessel's speed, essential for safe navigation, route planning, and fuel efficiency.

No Magnetic Interference: Unlike traditional magnetic compasses, modern speed logs are unaffected by magnetic fields.

Versatility: Available in mechanical, electronic, and integrated forms, catering to a wide range of vessel types and applications.

Integration with Other Systems: Many modern speed logs can be integrated with GPS, radar, and autopilot systems, offering a complete navigation package.

 

Disadvantages of Marine Speed Logs:

Cost: High-precision Doppler and electromagnetic systems can be expensive, especially when integrated with other navigation systems.

Maintenance: Mechanical systems, such as paddlewheels, can be affected by fouling and wear over time.

Installation: More advanced systems may require professional installation, especially integrated systems or Doppler systems.

 

Conclusion:

Marine speed logs are essential tools for any vessel, providing vital information about the vessel’s speed and helping ensure safe and efficient navigation. Whether on small recreational boats or large commercial ships, choosing the right type of speed log—whether mechanical, Doppler, electromagnetic, or ultrasonic—depends on the vessel's needs, budget, and operating conditions.