SPEED LOG
A Speed Log is a marine navigation instrument that measures a vessel’s speed through water (STW) or speed over ground (SOG). As per SOLAS Chapter V, Regulation 19 and IMO performance standards, ships must be fitted with an approved speed and distance measuring device to support safe navigation and collision avoidance.
Is a speed log mandatory under SOLAS?
Yes. SOLAS Chapter V, Regulation 19 requires ships of 300 GT and above to be fitted with a speed and distance measuring device.
What is the purpose of a speed log?
A speed log provides accurate vessel speed data essential for safe navigation, voyage planning, collision avoidance, and ECDIS operation.
What types of speed logs are approved by IMO?
Common IMO-approved types include:
Doppler Speed Log
Electromagnetic Speed Log
Impeller (Paddle Wheel) Speed Log
What is the difference between STW and SOG?
STW (Speed Through Water): Measured by the speed log
SOG (Speed Over Ground): Derived from GPS
Both are used for different navigational purposes.
Can GPS replace a speed log under SOLAS?
No. GPS cannot replace a speed log. SOLAS requires a dedicated speed and distance measuring device.
Is speed log input required for ECDIS?
Yes. Speed log input is required for accurate ECDIS calculations, including position prediction and safety alarms.
Does a speed log require regular calibration?
Yes. IMO recommends periodic calibration and performance checks to ensure accuracy.
What happens if the speed log fails?
The failure must be recorded, and alternative means (such as GPS speed) may be used temporarily until repairs are carried out, subject to flag and class approval.
How is speed log compliance checked during inspections?
PSC and Class surveyors verify:
Operational status
Correct data output
Integration with bridge systems
Alarm functionality
Can speed log data be integrated with other systems?
Yes. Speed logs interface with ECDIS, radar, AIS, voyage data recorders (VDR), and autopilot systems.
Conclusion
The speed log is a SOLAS-mandated navigation instrument that plays a vital role in safe ship operation. Compliance with IMO performance standards, proper calibration, and seamless integration with bridge systems ensure accurate speed data, supporting safe navigation and regulatory compliance at sea.