Art. 20.—Nothing in these rules shall exonerate any ship, or the owner or master, or crew thereof, from the consequences of any neglect to carry lights or signals, or of any neglect to keep a proper lookout, or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
The following diagrams are designed to illustrate the use of the lights carried by vessels at sea as prescribed in the Regulations above, and the manner in which they indicate to each vessel the position and course of the other.
Fig. 1 (when the red and green lights are both seen).—A sees a red and green light ahead. A knows that a vessel is approaching him on a course directly opposite to the one he is steering, as B. If A sees a white masthead light above the red and green lights, he knows that the vessel B is a steamer. A should put his helm to port; and B, seeing the same lights on board of A, should by the same rule put his helm to port also.
Fig. 2 (when the red light only is seen).—A sees a red light ahead or on the port bow. A knows that either, first, a vessel is approaching him on his port bow, as B, or, second, a vessel is crossing his bows to port in some direction, as D D' D" (Fig. 3). If A sees a white masthead light above the red light, he knows that the vessel is a steamer, and is either approaching in the same direction as B (Fig 2), or is crossing to port in the same direction as D D' D" (Fig. 3).
In the first position (Fig. 2) A sees B a little on the port bow, B's red light exposed, and, by the diagrams, B should see A's red light as well; in which case both vessels should put their helms to port.
In the second position (Fig. 3) A sees D on his starboard bow, and, from the fact that he only sees D's red light, he knows that D must be steering in some direction, as at D D' D"; at the same time, D D' D" will see A's green light on his port bow.
In this case, A, having D clearly on his starboard bow, should put his helm to starboard to turn from D, and D, having A clearly on his port bow, should put his helm to port to turn to starboard from A.
Fig. 4 (when the green light is seen, and the red light is not seen).—A sees a green light ahead, or on his bow. A knows that either, first, a vessel is approaching him on his starboard bow, as B, or, second, that a vessel is crossing his bow in some direction to starboard, as D D' D" (Fig. 5).