Speed and distance measuring devices
What is being checked
The inspector is checking whether speed logs provide reliable through-water and over-ground data to navigation systems and officers understand which reference each display and consumer uses, with officers able to configure, cross-check, test and respond to failure of the actual equipment fitted.
Ready onboard
0/6 completePractice questions
Answer aloud, then open the preparation point.
1What safety function does speed and distance measuring devices provide?
Speed logs provide reliable through-water and over-ground data to navigation systems and officers understand which reference each display and consumer uses.
2How is the complete function tested?
Use built-in tests, compare GNSS, radar and known-distance performance where appropriate, verify zero or bias and confirm outputs to radar, ECDIS and VDR.
3What is its principal limitation?
Water-track data is affected by current, aeration and loading; ground-track data may depend on GNSS and share its failures.
4What is your response if it fails?
Select an approved alternate input, enter manual speed only under controlled procedure, mark the limitation and assess every dependent radar, ECDIS and recording system.
5Show the latest test and operational evidence.
Link the dated record to the actual unit, test method, result, defect response and restoration; a panel lamp test alone is not sufficient where the full signal path can be tested.
Where an observation may arise
The responsible officer cannot explain safe use, limitations or failure response.
Testing does not prove the required operational function or remote indication.
Officers cannot identify whether a displayed speed is water- or ground-referenced.
Radar or ECDIS receives an unsuitable or failed speed source.
Persistent disagreement is not investigated or recorded.
Master's practical note
Trace the speed source into each radar. The most serious error may be a healthy log feeding the wrong reference into true-motion and vector calculations.
Equipment boundary and references
Equipment boundary: Required axes and performance depend on ship size, construction date and approved installation. GNSS-derived speed is not independent during GNSS interference.
References
- OCIMF SIRE 2.0 Question Library Part 1, Version 1.0, Question 4.1.8
- SOLAS Chapter V regulation 19
- IMO Resolution MSC.96(72)
- ICS Bridge Procedures Guide
Last reviewed: 2026-09-11