The lengths of the two parts from the ship to the parallel of 55°, and from 55° to Melbourne, are respectively 3146 and 2527 miles. The portion of the parallel being 1330 miles. The total distance is 7003 miles, being 400 miles longer than the direct great-circle track, and 1130 miles shorter than the rhumb track. It is not to be expected, nor indeed to be desired, that great-circle sailing should supersede the methods now in use, but it is very desirable that it should form a part of the sailor's nautical knowledge, not necessarily for him to adopt in all cases, but that he may know which is the shortest route, that he may see it on his chart, and that he may be able to follow it if his judgment tells him it is both practicable and preferable. Use of the Terrestrial Globe in Great-Circle Sailing. As has been before remarked, all questions of great-circle sailing can easily be solved by the aid of a small terrestrial globe. A piece of fine silk thread tightly stretched across the globe from port to port will show the track of the great circle between those ports. Mark the points upon the several meridians where the silk thread passes over them, and note the latitudes and longitudes of these intersections. Mark the positions thus obtained upon the Mercator's chart in use: then the track drawn from port to port through these positions will show the required great-circle track. In Composite sailing, the point of the maximum latitude having been decided upon, the operation of finding the great-circle tracks between that point and the respective ports, by first drawing the great circles upon the globe, and then transferring them to the Mercator's chart, can easily be performed as above described. PASSAGE TABLES.* THE average rate of a Sailing Vessel in making general ocean passages may be taken as 120 nautical miles a day, and of a Steam Vessel as 200 nautical miles a day. In the following tables the miles noted under the head of "Steam," show the distance to be traversed by a ship making a direct course, on the most favourable track for steam vessels, between port and port. Passages noted under the head of "Sail," show the distances that will probably have to be run by sailing vessels; the prevailing winds and currents being taken into consideration. *For a complete set of Passage Tables of the navigable mercatorial distances between most of the known ports of the globe, calculated by Commander Thomas A. Hull, R.N., see The Sailor's Handbook, published by Messrs. Griffin and Co., The Hard, Portsea. |