Risk of Collision Explained for MCA Oral Exams

Risk of collision is one of the foundational concepts in COLREG-based oral examination questioning. Every collision avoidance rule depends on an accurate assessment of whether risk of collision exists. Candidates who cannot clearly explain how risk is assessed — and what to do when doubt exists — consistently struggle with follow-up questions at all levels of oral exam.

What Risk of Collision Means

Risk of collision is not a binary on/off condition. It exists on a spectrum, and the regulations require you to assess it early and act on it before risk becomes immediate danger. The earlier you identify and respond to risk of collision, the more options you have and the less drastic those options need to be.

COLREG Rule 7 Overview

Rule 7 of the COLREGs governs the determination of risk of collision. It requires every vessel to use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt, risk shall be deemed to exist.

This last point is critically important and often tested. You must not wait until you are certain that collision will occur. If there is doubt, act on it.

Constant Bearing and Decreasing Range

The classical indication of risk of collision is a vessel maintaining a constant bearing with decreasing range — particularly with a large vessel or at close quarters. If you observe a vessel over several observations and its bearing is not appreciably changing while the range is decreasing, risk of collision must be assumed.

However, even a bearing that is changing slowly may still represent a risk of collision, particularly if the closest point of approach is unacceptably small. Bearing change alone is not sufficient clearance.

Radar and ARPA

Radar and ARPA provide objective data on the movement of other vessels — range, bearing, CPA, TCPA, course and speed. When properly used and interpreted, this significantly improves the accuracy of risk assessment. However, candidates must understand the limitations: radar plots take time to build up, ARPA calculations can be affected by manoeuvres, and targets can be missed entirely if radar is not properly adjusted.

Visual Assessment

Visual observation — watching the bearing of another vessel's lights or structure against a fixed reference point on your own vessel — remains a valid and important tool for assessing risk of collision, particularly when radar is not available or at short ranges where radar plotting becomes difficult.

Avoiding Assumptions

Rule 7 explicitly cautions against making assumptions with scanty information. In particular, it warns against assumptions based on small compass bearing changes — a contact that appears to be drawing clear may still represent a risk if the bearing change is insufficient to provide adequate CPA.

Early Assessment

The regulations require early assessment of risk, not last-minute reaction. Good watchkeeping means continuous monitoring of contacts, regular plotting or ARPA checking, and early identification of situations that may develop into risk before they become urgent. This is closely linked to the obligation to maintain a proper lookout under Rule 5.

Common Mistakes

• Assuming a changing bearing means no risk of collision
• Waiting until risk is certain before acting
• Relying on ARPA without verifying against observation
• Not applying the "if in doubt" principle
• Failing to reassess risk after an alteration of course

How Oral Examiners May Test Judgement

Examiners frequently present scenarios with ambiguous contact situations — a vessel drawing slowly right, CPA computed at half a mile, in reduced visibility. They are assessing whether you understand when to act, not just whether you can describe the rules. Strong candidates show they would not wait for absolute certainty before taking early, bold action.