Safe Speed Explained for MCA Oral Exams

Safe speed is one of the most frequently misunderstood concepts in MCA oral exam preparation. Candidates often assume it is simply about going slowly, or that it means following a posted speed limit. In reality, safe speed is a dynamic, situational assessment that reflects the entire watchkeeping environment — and examiners know it.

What Safe Speed Means

Safe speed is the speed at which a vessel can take proper and effective action to avoid a collision and stop within a distance appropriate to the prevailing circumstances and conditions. It is not a fixed number. It varies with conditions, vessel characteristics, and environment. A speed that is safe in clear weather in open ocean may be entirely unsafe in restricted visibility in a busy shipping lane.

Why Safe Speed Is Not Just a Number

This is the key point that separates strong candidates from weak ones in oral exams. Many candidates, when asked what safe speed they would maintain in a particular scenario, give a figure: "I would reduce to eight knots." This answer misses the point entirely unless it is accompanied by an explanation of how that speed was assessed against the relevant factors.

Safe speed is a judgement, not a measurement. The examiner is testing whether you understand the factors that go into that judgement.

COLREG Rule 6 Factors

COLREG Rule 6 sets out the factors that every vessel must take into account when determining a safe speed. These fall into two groups: factors applicable to all vessels, and additional factors for vessels using radar.

For all vessels, the factors include: the state of visibility; the traffic density, including concentrations of fishing or other vessels; the manoeuvrability of the vessel, paying particular attention to stopping distance and turning ability; the presence of background light at night; the state of wind, sea and current and proximity of navigational hazards; and the draught of the vessel in relation to available depth.

Visibility

Visibility is typically the most immediately impactful factor. In clear visibility with good radar, a vessel can maintain a higher speed and still have sufficient time to assess and avoid collision. In fog or other restricted visibility, even a modest speed may be unsafe if stopping distance exceeds detection range.

Traffic Density

In congested waters — a busy Traffic Separation Scheme, a port approach, a fishing ground — the density of vessels increases the risk of encounter. Safe speed must reflect the time available to assess multiple contacts simultaneously.

Manoeuvrability

Larger vessels, deeply laden vessels, and vessels with restricted manoeuvring capability require longer stopping distances and wider turning circles. Safe speed for a laden VLCC in restricted visibility is very different from safe speed for a small coastal vessel. The vessel's own characteristics are a central part of the assessment.

Radar Limitations

When radar is in use, additional factors apply: the characteristics, efficiency and limitations of the radar sets; any constraints imposed by the radar range scale in use; the effect on radar detection of sea state, weather and other sources of interference; the possibility that small vessels, ice and other floating objects may not be detected by radar at adequate range; the number, location and movement of vessels detected by radar; and the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.

Stopping Distance

Safe speed is ultimately constrained by stopping distance. If radar detection range for a particular target type is X miles, safe speed is the speed at which the vessel can stop within a distance significantly less than X miles — allowing time for detection, assessment, decision-making and action. In restricted visibility, this often means much slower speeds than many candidates assume.

How to Explain Safe Speed in an Oral Exam

Structure your answer around the Rule 6 factors relevant to the scenario presented. Describe the conditions, identify which factors are most significant in that context, and explain how those factors lead you to a speed judgement. You do not need to quote every factor for every scenario — demonstrate that you can assess contextually.

Common Mistakes

• Stating a specific speed without explaining the factors considered
• Ignoring radar limitations when radar is in use
• Failing to mention stopping distance as part of the assessment
• Treating safe speed as a one-time decision rather than a continuous re-assessment