1302 TREATIES Every vessel coming up with another vessel from any direction more than two points abaft her beam, i. e ., in such a position, with reference to the vessel which she is overtaking, that at night she would be unable to see either of that vessel's side-lights, shall be deemed to be an overtaking vessel; and no subsequent alteration of the bear- ing between the two vessels shall make the overtaking vessel a crossing vessel within the meaning of these Rules, or relieve her of the duty of keeping clear of the overtaken vessel until she is finally past and clear. As by day the overtaking vessel cannot always know with certainty whether she is forward or abaft this direction from the other vessel, she should, if in doubt, assume that she is an overtaking vessel and keep out of the way. ARTICLE 25. In narrow channels every steam vessel shall, when it is safe and practicable, keep to that side of the fairway or mid-channel which lies on the starboard side of such vessel. ARTICLE 26. Sailing vessels under way shall keep out of the way of sailing vessels or boats fishing with nets, or lines, or trawls. This Rule shall not give to any vessel or boat engaged in fishing the right of obstructing a fair-way used by vessels other than fishing-vessels or boats. ARTICLE 27. In obeying and construing these Rules, due regard shall be had to all dangers of navigation and collision, and to any special circum- stances which may render a departure from the above Rules necessary in order to avoid immediate danger. Vessels in sight of osneh, sight of SOUND-SIGNALS FOR VESSELS IN SIGHT OF ONE ANOTHER. ARTICLE 28. Sound-signals. The words "short blast" used in this Article shall mean a blast of about one second's duration. When vessels are in sight of one another, a steam vessel under way, in taking any course authorized or required by these Rules, shall indi- cate that course by the following signals on her whistle or siren, viz.: - One short blast to mean, "I am directing my course to starboard." Two short blasts to mean, "I am directing my course to port." Three short blasts to mean, "My engines are going full speed astern."