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.
It is easy to land much closer to other vessel than intended. Since you too are moving, all calculations become complex. Therefore there is risk of mis-judgement.
Rule 7 stresses the need to check continually that no risk of collision exists, to eliminate any doubt that it does and to guard against taking action based on inadequate information. As a result, it is implied under Rule 7 that an OOW’s responsibility is that as soon as he/she sights another vessel, the OOW must determine whether a risk of collision exists. This means every object detected is considered as risk till it is ruled out by systematic follow up. The OOW must not dismiss the other vessel as being a Give-Way because of its position relative to his/her own vessel without determining whether a risk of collision exists. Typical example of this is a crossing vessel on your starboard bow.
The normal method of assessing collision-risk on any vessel, is to take a bearing of any approaching vessel using a compass. If the bearing remains constant, there is a risk of collision and action must therefore be taken.
Rule 7 makes it compulsory to carry equipment suitable for taking compass bearings. Radar is not a requirement under the collision regulations, but all vessels fitted with a set, which is operational, should use it at long range to obtain early warning of other vessels in the area. The operator is also required to assess on screen, whether a collision risk exists. This means that you should always radar plot any detected Objects in order to determine if any risk of collision exists.