Module 5 - COLREGs
Rule 7 — Risk of Collision
Rule 6 first requires a safe speed that lets the vessel take proper and effective avoiding action and stop within an appropriate distance. Visibility, traffic density, manoeuvrability, background lights, wind, sea, current, hazards and draught all affect that decision; operational radar adds its own detection, scale and performance factors.
Rule 7 then requires all available means appropriate to the conditions to determine whether collision risk exists. If there is any doubt, risk is deemed to exist. Proper use of operational radar includes long-range scanning and systematic plotting or equivalent observation; assumptions must not be based on scanty information, especially scanty radar information.
A compass bearing of an approaching vessel that does not appreciably change is strong evidence of risk when range is decreasing. It is not a complete clearance test: risk can still exist despite appreciable bearing change when the other vessel is very large, towing or already close. Continue bearings or systematic radar observations and assess CPA, TCPA, aspect, rate of closure and uncertainty together.
AIS can improve awareness or identification but MCA guidance says collision-avoidance decisions should be based primarily on systematic visual and/or radar observation. Trying to negotiate a non-COLREG passing plan by VHF can waste time, misidentify the vessel or produce misunderstanding; comply with the Rules and take observable action.
- Choose a safe speed that preserves detection, assessment and manoeuvring time
- Use repeated systematic observations and deem risk to exist if doubt remains
- No appreciable bearing change indicates risk; bearing change alone does not always prove clearance
- AIS and VHF cannot replace COLREG-compliant visual or radar assessment
Watch for this: Write timed bearings down. The record makes a trend easier to see and reduces the temptation to reinterpret a worrying contact from memory.
Optional quick check
Section 3 of 9
The bearing changes noticeably, but the target is a very large vessel already at close range. What is the sound conclusion?
Apply Rule 7 to complete encounters
The COLREGs module links lookout, safe speed, risk assessment, avoiding action and vessel responsibilities.