The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

10 THE MARINE RECORD. Amateur Boatbuilders. i Boats built and rigged entirely orin p stems, stern posts, keels, and frames worked to F.W. WHEELER & COMPANY, BUILDERS OF ALL KINDS OF shape in the wood for amateurs. Entire frames set fe and mark- ed and shipped “Knockdown” to any part of the world. Designs made and enlarged to full size for rowboats, sailboats, launches and yachts. Send 50 cents for 72-page “Album of Designs,” Address Station ‘‘A”’ FRED W. MARTIN, YacuTt DESIGNER, RACINE, WIS. PRON TIAR Iron, Steel, ana * Wooden Ships FOR LAKE OR OCEAN SERVICE. West Bay City, Mich. aq F. W. WHEELER, Pres. E.'T. CARRINGTON, Y. P. C. W. STIVER, Sec’y and Treas. Iron Works. MARINE ENGINES. DETROIT, MICH. WM. WILFORD’S*>— MATCHLESS WATER-PROOF CANVAS The best in the market for hatch bg covets, is stronger, lighter, and more R p9.durable than any water-proof goods Y yet produced. It is made of a twist- ed thread of pure flax, which renders it very strong. It will not crack like cotton goods, which is a great advan- tage Be ee ee ee ee Ue EDWARD A. BUNKER, Room 617 27 and 29 William St., New York. CORRESPONDENCE. __ JOTTING DOWN COURSES. The practice of jotting down courses is probably as old as navigation; it is an attempt at finding the course over the water by experiment, kept up and advocated by all pilots lacking scientific training. Jotting down courses is with them the highest perfection attainable in running a vessel from point to point and from port to port; and in testing the correctness of a compass. The corrections for variation, deviation, leeway, and current, do not bother them at all; and if their supposed test and findings do not hold good in some particular places on the coast and lakes, the compass is said to be affected by some foreign force, beyond the ken and control of man. At the beginning of this century such notions and prac- tices were excusable, because good books on navigation and good charts were rare, and the laws governing the deviations of compasses were not known. But at the close of this century after these laws have long been es- tablished, and good treatise on navigation abound, the prevalence of such notions and practices invariably proves - the low standard of pilots indulging in them. It is an established fact, that compass errors can only be ascertained, by swinging the vessel to all points and com- paring courses with well known magnetic bearings. And it is no less a fact, that the courses steered are always more or less influenced, sometimes considerably, by cur- ' rents changing. with wind and weather; so that courses jotted down one day may entirely be wrong another day. ‘The only invariable standard of courses, are true courses obtained from the chart; from which the courses to be steered are found by applying the corrections for varia- - tion, deviation, leeway and current. Each of these correc- tions has sometimes to be applied to the right, sometimes to the left of the true course, some according to their signs and some according to wind and weather. From 16-24 Woodward Ave., DETROIT, MICH. Always Tight. Pd Leaves the Stem Clean. “which follows, that ‘nobody can foretell with any degree of certainty, what the.coufse to be steered ought to be, if wind and weather and set and drift of current are not known. All that courses and return courses jotted down are good for, is to determine the error of the floating or patent log, and set and drift of current; provided the compass is correct, and no change of the current takes place during the run. Under this assumption, course and return course jotted down between any two places have the property of form- ing with the chart course the same angles. In other words, the mean of the courses jotted down, after one of them is reversed, always agrees with the chart course; which, however, is in itself no proof of the compass being correct, but only an indication that it may be correct. For, the courses jotted down may be entirely wrong and yet their mean above referred to may agree with the chart course, because of errors paralizing one another. Non-agreement with the chart course, however, always indicates that the compass is wrong, and that the courses are of no use for the purposes mentioned. The difference of the two courses jotted down, after one of them has been reversed, and the distances run by log on each course, furnish a triangle of which two sides and the intercepted angle is known; the third side represent- ing set and drift of current for both courses combined. A line bisecting the known angle divides the third side into the parts of the drift due to each course. The bi- secting line in the triangle represents the distance per log between both places, which distance divided into the distance by chart gives the log co-efficient; that is, in- dicates the number by which all distances have to be multi- plied to obtain the correct distances. For instance: A is from B, NW., magnetic, 60 miles. Courses jotted down, NNW., magnetic, 90 miles and ESE. magnetic, 61 miles. What is the log-coefficient and set and drift of current? ESE. reversed is WNW.; the mean 193=195 Bank St., CLEVELAND, O. -METALLICSToP:VALVE-PACKING PEERLESS RUBBER MFG. CO., 16 Warren St., New 202=210 S. Water St. CHICAGO, ILL. a Write us for Testimonials. OS York. of WNW. and NNW. is NW., which indicates, by com- parison. with the chart course, that the compass may be correct. The difference. between WNW. and NNW. is 4 points, which angle with the distances 90 and 61 furnish a.triangle, the third side of which equals 63 miles; its direction being S 1% W-N 1% E, magnetic. The line bi- secting the angle of 4 points is found to be ..67 miles and set and drift of curernt respectively 37-5 and 25.5 miles S by W%W., magnetic. The log-coefficient equals 60-57—= 0.9. Therefore, the corrected distances tun by log and the drift of current are respectively: 90X0.9=81 miles; 61X0.9=54.9 miles; 37.5X0.9=33.75 miles; 25.5X0.9= 22.95 miles. The preceding illustration shows what jotted down courses by a correct compass, are good for; and it also shows that such courses are good for nothing as soon as the current changes between trips. JOHN MAURICE. ee ——__.. The “Shipping World Year Book” comes to us for 1897 in its eleventh annual edition, everyone of which has been an improvement on its predecessor. Its motto is “infinite riches in a little room,” and as a desk manual in trade, commerce and navigation it is not excelled. The book contains as usual an almanac, the tariffs of all na- tions and colonies, the new regulations for preventing collisions at sea, tables of distances, trade statistics, pilot- age and towage rates, and a complete port and harbor di- rectory of the British Isles, and a directory of all the principal ports of the world, arranged in alphabetical or- der, stating accommodation, depth of water, tides, trades, and much other information. There is also to this edi- tion a commercial map of the world, which is one of the best and most informing ever issued. The book com- prises over 1,00 pages, yet is of handy size and copiously indexed, which makes it exceedingly convenient for ref- — erence. Published by the Shipipng World, Effingham House, Arundel street, London, price 6 shillings stg. Sire it atcaneas j Put up in Boxes. eee RRR ee ah, Were mio ee aN Ae Re ROE