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October, 1922 from the table for the number of degrees, gives 25.2 knots that the vessel is out from her correct position. This error in position might be caused . by carelessness in. laying out the great circle course, error in getting the true azimuth, compass bearing, bad steering or a sluggish compass. The error in posi- tion has to be made good and ‘t adds to the expense of vessel operation. One error might counteract another and_ tlic position be correct but if the errors are all in the same direction they would cause an error which might prove ‘disastrous to the vessel and all on board. vessel’s Oiten it happens that a vessel such asa liner sailing over the same course finds that she is quite a distance out of her position and makes the land several miles to the right or left from the place she intended to make. The error in po- sition is usually laid to an “unknown cur- _rent as that is the most practicable reason advanced by an experienced navigator. Position From One Observation The “set of the current” covers: a multitude of navigator’s sins. The dif- ference between the position found by dead reckoning and that given by ob- servation is usually: given as the “set of the current’. That is the best the naviga- tor can do unless he has a compass which registers the yawing of the vessel over the course given, from which he can estimate the course made good or un- less he has a mechanical means by which errors can be eliminated by getting a true azimuth, the great circle course and dis- tance; and -the vessel's position with one observation without the tedius calcula- tion that has to be made by logarithms. Such an instrument has been developed and is called a spherical angle calculator. The advantage of determining a_ ves- sel’s position with one observation includes a more accurate position than can be MARINE REVIEW found by ‘the methods in practical use by all navigators who practice Marc St. ' Hilaire’s method, Johnson’s methods, con- recting longitude for an error in latitude. In all these, determining a vessel's posi- tion or fix is done by intersecting the sumner lines of position which have to be at right angles to the true azimuth of the body observed. This requires an inter- val of time between observations in or- der to get a sufficient angle to the lines of position to have them intersect as near right angles as possible. This requires a run of the vessel for two to four hours. The first line then is advanced along the true course the distance that the vessel has made in the interval. The fix is going to be in error in proportion to the errors of steering, compass, set of the current, leeway, etc. A navigator usually has to take the first observation soon after the rising of the sun and the second near meridian to get the best results from the altitudes ‘taken. ‘Being able to determine the fix with one observation will be the means of shortening the passage sufficiently to make a great saving for the company adopting the new method. the spherical, angle calculator a fix is obtained by a few movements of the in- strument. True azimuth to the nearest minute is given and the great circle course and distance is given. Fig. 1 shows the instrument as it would appear before changing any of the parts, with latitude set at zero, the hour angle set at 90 degrees and declination set at zero.. A represents the earth’s axis, securely fastened to the latitude circle G; Bis the declination circle journaled on the axis; C is the circle moving around the Jjatitude circle and to it the compass dial is attached at the ship’s meridian; D is the center of the compass rose rep- resenting the ship’s position; HE, jour- naled at the ship’s position, is the zenith By the use of © 433 distance circles; and fF represents the equator and hour angle circle. Fig. 2 shows the instrument as it would appear after making the calculation on page 81, Bowditch Epitome, requiring the great circle course and distance between 40 de- gress N. lat. 70 degrees W. long. and 30 degrees S. lat. 10 degrees *W. long. To get the zenith distance set the lati- tude on the latitude circle and clamp; set the hour angle on the hour circle and clamp; set the declination on the declination circle and clamp; the zenith distance is given on the zenith distance circle, and true azimuth on the dial at the ship’s position. To get the great circle course and distance from the _ position, set the latitude on the latitude circle and clamp; set the difference in longitude on the hour angle and clamp. Move the vernier on the declination circle to the latitude of destination. The initial great circle course is given on the dial at the ship’s position and the distance is given on the zenith distance circle. For the identification of stars, the al- titude is taken and also the compass bearing, and the compass bearing is cor- rected for the error which would give the true bearing. The corrected altitude is subtracted from 90 degrees which gives the zenith distance. Move the vernier on the zenith distance circle to the calculat- ed zenith distance and clamp; move the vernier on the declination circle until the ‘true azimuth is shown on the dial at the ship’s position. The declination of the body observed is given on the declination circle. This instrument may be adopted for use on air ships where quick calculation is necessary as the position can’ be found and the course to steer given and also the distance, without being en- cumbered with books and charts that are now required and the tedious calculation done by logarithms. Block and Tackle Need Close Attention ISCOVERY by primitive man D that fibers twisted together . formed rope probably led soon the invention of some form This first kind perhaps was nature of a fair-lead, now just. a. piece of But purchases available until after to of block. in the called a_ bullseye, wood with a hole in it. or tackle ‘were -not wheels were discovered, as with- out a sheave one would lose more by iriction than would be gained by the extra length of rope. Nowadays blocks are to be had in infinite variety, plain or patented, of wood, iron or metal, each suitable for its own pur- pose and as a rule for no other, ne- BY CAPT. E. ARMITAGE McCANN cessitating a large stock, standing and ‘spare, for the well equipped vessel. For all around work, nothing can beat the old fashioned wooden block, inside iron strapped, with lignumvitae sheave, and patent bushes where they will stand the strain, ithe more es- pecially where they are liable to be infrequently overhauled, as for in- stance for boom guy blocks and for davit tackles. For topping lifts and the like wooden blocks are not suitable; they are heavy and cumbersome in lange sizes, equal to the heavy strain imposed upon ‘them, so for this purpose, iron blocks are the best, as in fact. they always are where wire is: used. They should however, have metal bushes with holes in tthe sheaves so that the pins may be easily lubricated, making only an occasional overhauling necessary, and pins in the form of a bolt are better than those kept in position with a cotte: pin. The cargo hoisting blocks should be self-lubricating; there are many methods of achieving this, among the best being a chamber communicating with the pin which could be filled with lubricant through ‘the shell. They should have well curved edges to prevent chafe. The swivel eyes must be kept well oiled and freely working