JRC JLN-205 Doppler Speed Log

Complete Marine Technical Guide for Accurate Vessel Speed Measurement

Product Identification

The JRC JLN-205 Doppler Speed Log is a highly reliable marine navigation instrument designed to accurately measure a vessel's speed through water and distance traveled. Utilizing Doppler ultrasonic technology, the JLN-205 provides real-time speed information essential for safe navigation, collision avoidance, route monitoring, and integrated bridge operations.

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Product Introduction

Modern vessels require precise speed information for navigation, voyage planning, maneuvering, and integration with radar, ECDIS, AIS, autopilot, and voyage data recording systems.

The JRC JLN-205 is a professional Doppler Speed Log capable of continuously measuring:

• Speed Through Water (STW)
• Distance Run
• Fore/Aft Speed Components
• Port/Starboard Speed Components
• Speed Data for Integrated Bridge Systems

The system is widely installed on:

• Cargo Ships
• Tankers
• Bulk Carriers
• Container Vessels
• Passenger Ships
• Offshore Support Vessels
• Naval Ships

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Main Product Image

The image above shows a complete JRC JLN-205 Doppler Speed Log system including display unit, signal processor, and electronic interface modules.

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What Is a Doppler Speed Log?

A Doppler Speed Log is a marine navigation device that measures vessel speed using the Doppler Effect.

The system transmits ultrasonic signals through the ship's hull into the water. When these signals reflect from particles suspended in the water, the frequency shift is measured and converted into speed information.

Unlike GPS speed measurement, Doppler logs measure actual vessel movement relative to the water mass, providing critical navigation data even when GPS signals are unavailable or degraded.

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Typical Doppler Measurement Principle

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Main Features

High Accuracy Speed Measurement

Provides accurate speed-through-water data for navigation and maneuvering.

Doppler Ultrasonic Technology

Uses proven Doppler signal processing technology for reliable measurements.

Distance Calculation

Automatically calculates cumulative distance traveled.

Multiple Data Outputs

Compatible with:

• ECDIS
• Radar
• AIS
• Autopilot
• Voyage Data Recorder (VDR)
• Integrated Navigation Systems

Compact Operator Display

Dedicated LCD display provides:

• Vessel Speed
• Distance Run
• Alarm Status
• System Diagnostics

Built-in Self Diagnostics

Continuous monitoring of system health and sensor operation.

IMO-Compliant Navigation Equipment

Suitable for vessels requiring SOLAS-compliant navigation instrumentation.

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Display and Control Unit

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Main Components

The JRC JLN-205 system consists of several major components:

1. Display Unit

Located on the bridge.

Functions:

• Speed indication
• Distance display
• Alarm monitoring
• System configuration

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2. Log Signal Processor

Acts as the system's central processing unit.

Functions:

• Signal processing
• Doppler frequency calculation
• Sensor data conversion
• Output generation

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3. Hull-Mounted Transducer

Installed below the waterline.

Functions:

• Ultrasonic transmission
• Signal reception
• Water speed measurement

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4. Interface Unit

Provides communication with:

• Radar
• ECDIS
• AIS
• VDR
• Integrated Bridge Systems

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5. Power Supply Module

Provides stable operating voltage to the entire system.

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System Components

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Marine Applications

The JRC JLN-205 is used for:

Navigation

Continuous vessel speed monitoring.

Collision Avoidance

Provides accurate speed information to navigation systems.

ECDIS Integration

Improves route monitoring and voyage planning.

Autopilot Operation

Provides speed inputs required by steering systems.

Dynamic Positioning Support

Assists DP systems with vessel motion information.

Voyage Recording

Supplies speed data to Voyage Data Recorders.

Harbor Maneuvering

Supports safe vessel maneuvering during docking operations.

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Common Problems & Troubleshooting

1. No Speed Indication

Possible Causes

• Transducer failure
• Signal processor malfunction
• Power supply problem

Corrective Actions

• Check transducer connections
• Verify power supply
• Inspect processor status indicators

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2. Speed Reading Fluctuates

Possible Causes

• Air bubbles beneath hull
• Marine growth on transducer
• Excessive turbulence

Corrective Actions

• Clean transducer face
• Inspect hull condition
• Verify transducer installation

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3. Speed Reading Too Low

Possible Causes

• Fouled transducer
• Sensor alignment issue
• Weak ultrasonic signal

Corrective Actions

• Clean transducer
• Perform calibration
• Verify signal strength

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4. Communication Failure

Symptoms

• No speed data on ECDIS
• Radar speed input lost
• VDR data interruption

Solution

• Check serial communication ports
• Verify NMEA output settings
• Inspect interface cables

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5. Distance Counter Not Updating

Possible Causes

• Processor fault
• Data calculation error
• Internal memory issue

Solution

• Restart system
• Check software configuration
• Verify processor diagnostics

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Maintenance Tips

Proper maintenance ensures long service life and reliable performance.

Daily Checks

• Verify speed indication
• Check alarm status
• Confirm display readability

Weekly Checks

• Inspect external connections
• Verify communication outputs
• Review system alarms

Monthly Checks

• Confirm calibration values
• Test integrated navigation interfaces
• Check processor diagnostics

Dry Dock Maintenance

During dry dock periods:

• Clean transducer surface
• Inspect transducer housing
• Check mounting condition
• Verify waterproof integrity

Annual Maintenance

Recommended:

• Functional testing
• Calibration verification
• Communication testing
• Output verification

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Why Ships Still Use Doppler Speed Logs

Although GPS provides speed-over-ground information, Doppler Speed Logs remain essential because they provide:

Speed Through Water

Critical for navigation calculations.

Independent Speed Source

Provides redundancy if GPS becomes unavailable.

Autopilot Support

Improves steering performance.

Accurate Maneuvering Data

Essential during docking and restricted-water navigation.

Regulatory Compliance

Required on many SOLAS-class vessels.

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Frequently Asked Questions (FAQ)

What does the JRC JLN-205 measure?

The system measures vessel speed through water and distance traveled using Doppler ultrasonic technology.

Is it different from GPS speed?

Yes. GPS measures Speed Over Ground (SOG), while the JLN-205 measures Speed Through Water (STW).

Can the JLN-205 connect to ECDIS?

Yes. The system provides navigation data outputs compatible with ECDIS and other bridge equipment.

What happens if the transducer becomes fouled?

Speed accuracy may decrease, and unstable readings may occur.

Is periodic calibration required?

Yes. Regular verification and calibration checks are recommended during annual inspections and maintenance periods.

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Short Product Description

The JRC JLN-205 Doppler Speed Log is a professional marine navigation instrument designed to provide highly accurate vessel speed-through-water and distance measurements. Utilizing advanced Doppler ultrasonic technology, the system integrates seamlessly with ECDIS, radar, AIS, autopilot, and VDR systems, making it a trusted navigation solution for commercial and offshore vessels worldwide.

SM MARINE SERVICE™

Marine Automation & Navigation Equipment Supplier

Available Condition:

• New Equipment • Used Equipment • Refurbished Equipment • Reconditioned Equipment

Stock Location:

• Bangladesh • China

Services:

• Worldwide Shipping • Technical Support • Spare Parts Supply • Marine Equipment Sourcing

Contact Information

SM MARINE SERVICE™
Samir Market, DT Road, Pahartali, beside CDA Market, Chattogram, Bangladesh

Mobile / WhatsApp / Viber: +88 01818 929292

Email: info@smmarineservice.com

Website: www.smmarineservice.com