1. In reduced visibility, vessels and convoys not navigating by radar shall immediately proceed to the nearest safe berthing or anchoring areas. The following provisions shall apply during the voyage to this berth:
(a) As far as possible they shall proceed on the navigable side of the fairway.
(b) Any vessel proceeding alone and any vessel carrying the boatmaster of a convoy shall sound one long blast; this signal shall be repeated at intervals of not more than one minute. Such vessels shall have a lookout forward; in the case of convoys, however, a lookout is required on the leading vessel only. The lookout shall be within sight or hearing or in communication through a voice link with the boatmaster of the vessel or convoy.
(c) When a vessel is called by radiotelephone from another vessel it shall reply by radiotelephone, giving its category (for example, convoy, high-speed vessel, small craft), name, direction and position. It shall also state that it is not navigating by radar and that it is making for a berthing area. It shall then agree on a passing procedure with this vessel.
(d) As soon as a vessel hears the sound signal from another vessel with which it has not been possible to establish contact by radiotelephone, it shall:
- if it is near to a bank: keep close to that bank and, if necessary, stop there until this vessel has passed;
- if it is not near to a bank and especially if it is crossing from one bank to another: clear the fairway as fully and as quickly as possible.
2. Ferry boats not navigating by radar shall, instead of the signal prescribed in paragraph 1 above, give as a fog-signal one long blast followed by four short blasts; this signal shall be repeated at intervals of not more than one minute.