A Treatise On The Principles And Practice Of Harbour Engineering

HARBOUR ENGINEERING. 256 buoys. There are some few examples which exceed these figures—for instance, on the river Mersey,—but they are of local interest only. Buoy Dimensions. Type. First Class. Second Class. Diameter. Height. Diameter. Height. ft. ft. ft. ft. Conical . 8 10 6 71 Can 8 8 6 8 Spherical 8 7 6 5i Pillar . . .. 10 15 8 12 The material used is steel plating about J inch thick. There should be two water-tight compartments in each buoy, so that in the event of collision with a passing vessel, the risk of foundering may be diminished. Mooring- chains for first-class buoys are about 1| inch diameter, and they are attached to sinkers weighing about 25 cwts. For second-class buoys, the chains are usually 1 inch diameter, and the sinkers weigh 15 cwts. Mooring - Buoys constitute a special class of buoys with functions quite outside the sphere of the present chapter. Such brief reference to them as is necessary is to be found in Chapter VIII. Channel Lighting. —Having dealt with those features of channel demarcation which are available for use in the daytime, we now turn our attention to means adopted for guidance when such signals are no longer naturally visible. Recourse has then to be had to some artificial source of light. Of the value of luminous signals to the mariner there can be no question. He approaches his destination without reference to day or night, and during the hours of darkness, while in close proximity to land, he is often without any other reliable indication of his position, or trustworthy guidance in his course. At the same time, it must be avowed that in many respects artificial lights, as they exist at present, are far from constituting an ideal system of localisation. The range of visibility is extremely variable under different atmospheric conditions, and in times of dense fog, and even in squally weather, may become of no appréciable value whatever. Then, again, a very powerful light, while serving admirably as a beacon to shipping at a great distance, is a source of some perplexity and confusion at close quarters, dazzling the sight, projecting deep and dark shadows, and obscuring the position of objects which lie outside the illuminated zone, and especially those immedi- ately beneath the source of light. Thus, lighthouses which act as landfaU or advance lights, giving the mariner timely warning of his approach to the coast-line, form a different class from those which are used to indicate navigable channels. In the former case, striking brilliance and extensive