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Rule 7: Risk of collision

  1. 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.
  2. 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.
  3. Assumptions shall not be made on the basis of scanty information, especially scanty radar information.
  4. In determining if risk of collision exists the following considerations shall be among those taken into account:
    1. such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change;
    2. 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.

What this means:

Rule 7: Risk of collision – Our plain English guide to help you understand & remember this rule.

Well, you know what they say about assumptions? This rule confirms that we cannot make any and assume the worst unless we explicitly know otherwise.

It also reaffirms some wording in Rule 5 – Look out, particularly the requirement to use Radar (if fitted), but not rely on it if it produces unverifiable results.

It also introduces the concept of a constant bearing as a means to monitor for and understand collision risk.

Constant bearing test

We can use some methods and tools to understand the risk of collision with observed vessels to the side of us that pose a crossing risk.

Static bearings

If another vessel approaches, our relative bearing to that vessel will remain unchanged if we are on a converging course. As our paths come together, the bearing between us will remain stable, a crucial indicator of a collision course.

Checking the bearing

Many suggest lining up the observed vessel with a stanchion of another part of our boat; however, this is fraught with risk. The relative angle to the other vessel will change if our heading changes or if we move somewhere else on the boat, potentially leading to a false sense of security.

Using a handheld compass

The simplest and most effective way to check a bearing to another vessel is to use a handheld compass. This eliminates our movement and gives a relative bearing on the other vessel.

Of course, we can have a constant bearing to another vessel moving away from us, so we’re only on a collision course if the other vessel is getting larger.

Rule 6: Safe speed Rule 8: Action to avoid collision

Key Point:
When on a collision course with another vessel, the relative bearing between them and us will remain constant. Checking and monitoring bearings to other vessels is part of our obligation under the rules.