Here’s rule 7: Risk of collision
(a) Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist.
(b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.
(c) Assumptions shall not be made on the basis of scanty information, especially scanty radar information.
(d) In determining if risk of collision exists the following considerations shall be among those taken into account:
(i) such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change;
(ii) such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range.
Risk of collision
Rule 5: Look-out and Rule 7 are closely linked. Under Rule 5 you should use all available means to collect information on your situation by applying Rule 5 and use that information and apply it to Rule 7 to continuously to asses if a risk of collision exists.
When applying Rule 7 you must continuously use information collected to assess if a risk of collision exists.
To assess the risk of collision you must ask yourself:
- Is a collision possible, because of the action (or lack of) of another vessel in the immediate area? This statement includes your own vessel.
- Is a collision probable? If so, the risk of collision is already here and you need to act as a matter of urgency.
This risk-assessment process is essential if you are to take appropriate action in ample time.
Risk-assessment techniques include:
- Look and listen – as with keeping a lookout, you must use all the information and equipment available to determine the risk of collision.
- Use a hand bearing compass to check the bearing of approaching vessels is changing in regular intervals. A steady bearing indicates the risk of collision but a risk of collision may exist even with a bearing change, particularly at close range and with larger vessels.
- Use your radar.
- With ARPA, use relative vectors to determine the risk of collision.
- Is the target passing ahead or astern or are you going to collide? Remember the primary information you need to answer these questions is relative information.
- Do not trust ARPA to give you an accurate CPA. Take 0.5 nautical mile off each indication to be safe and, if the CPA is already 0.5 nautical mile, then assume a risk of collision exists.
- Do not just rely on a change of bearing as an indicator of clearance. As a target ship approaches, its change of bearing should accelerate significantly. If the change of bearing does not accelerate then there is a risk of collision.
Do not relax – keep monitoring the situation until the target ship is passed and clear.
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