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1901.] MARINE REVIEW. 19 water lines 'an equivalent triangle may be constructed which will have the same area and center of gravity. NO be ee ge Let Fig. 4 represent a portion of some curved section, To construct an approximately equivalent triangle which will represent this section, c and d are connected and a tangent drawn to the curve parallel to cd. .At two-thirds of the distance from cd to the tangent the parallel line mn is drawn, which completes the required triangle Smn. Bisect mn at e, then g, the center of gravity of the triangle, is on the line connect- ing S and e, two-thirds of the. length from S. A similar construction will give g', the center of gravity of the area in its new position. Then from the vertical projection of g and g' upon WL, the .lever, hh', for the horizontal moment is taken, and this lever into the area of Smn is the moment of the area, transferred by the heeling, This moment is an element of the integration to. be made by the Simpson's rule for the moment of the transferred volume. The work can conveniently be ar- ranged in the following tabular form: SECTION AREA LEVER PRODUCr MULT. FUNCTION 1 a, hh, a,.hh, 1 a,.hh, 2 Ag. hh, a,. hh, 4 4.a,.hh, 3 ae hh, | a,.hh, 2 2.a,.hh, Etc. ; Etc. = a.hh 2a.hhx % longitudinal interval--=moment of volume. Then dividing this moment by the volume of the total displacement gives the horizontal distance the center'of buoyancy has moved. This new horizontal position of B is then plotted in Fig. 3 at R, a vertical line is drawn through R and the righting arm for this angle, Gz, is the hori- zontal distance from G to this vertical through R. Turning again to Fig. 1: The arm Gz is set up from O X at the point representing the "deck edge" angle of inclination, say 40°. Now the slope of the curve at the initial point, the arm and slope at 90° and the arm at 40°, are known, and therefore with a light true batten placed tangent to O M at O, passing through z, and tangent to the line of slope 'at Z, the curve of stability may be: drawn. Experience has shown that for a normal form a curve thus found may be taken as fairly accurate and dependence placed on it in actual work. : Modifications in the text and application of the method quickly sug- gest themselves. The most prominent is perhaps that in the last con- dition where accuracy can be gained by calculating the true position of the water line, which will lead to the true position of R, by the difference of the volumes of the wedges, as in the Barnes' method, or by setting up a displacement curve from T, Fig. 3, as in the second condition. Another step leading to greater accuracy would be the introduction of more than one intermediate point. say two, one at 30° and also at 60°. Then in the opposite direction a slight loss in accuracy may be conceded with a con- siderable saving in labor. In the second condition, for instance, the position of the water line may be determined by. the eye and should it be near the center line plane, the center of gravity of the plane may be taken as that of the layer A W L K, and also its inertia used as.that of the water line in the calculation for B' M'.. Then too, some approximate method, as that given in White's "Naval Architecture,' may be used for estimating the initial B M. These approximate methods have, of course, their chief value in the facility with which a result can be obtained that will give a fair and reliable check on the qualities. of a preliminary de- sign, so that the trouble and expense of altering more complete and de- tailed plans may be avoided. It is the earnest desire of the writer.to eliminate all error and mis- understanding from this article and to extend his knowledge of the matter under discussion, and he will therefore be pleased to receive and 'will endeavor to answer criticisms and questions concerning the matter. Address in care of the Marine Review Pub. Co., Cleveland. KRUPP ARMOR PLATE THAT FAILED. An examination of the Krupp armor plate, representing 300 tons of armor for the battleship Maine, which failed to fulfill the requirements in the official test at the Indian Head proving grounds last week, shows that cracks in the plate existed prior to the test. The specifications per- mit another test} and if this is successful the government will have the option of testing a third plate to determine whether the group of armor represented comes up to the requirements. Should the second test prove unsuccessful the entire group of armor would be rejected. The official report -has not been received at the navy department and decision as to 'whether there will be a second test will be reserved until it has been received by the naval ordnance ofncials. Thomas McCosker & Co., Baltimore, Md., launched last week a wooden tug boat 112 ft. in length, 25% ft. beam and 10% ft. deep, for the National Dredging Co. She will be put in service in Mobile, Ala: tinually foul condition." THE QUESTION OF COPPER SHEATHING. The following article in the Naval Military Record, questioning the propriety, of sheathing the British Royal yacht, will be read with. interest in the United States where sheathing is an unsettled question: "To sheath a ship with copper for its anti-fouling properties alone is not only not worth the initial outlay, but really results in a great waste of money for the extra coal burnt, and also a great loss in efficiency. On stations where there are docks, it is the custom for sheathed, ships to be docked once a year. At the end of the year, however, the bottom of such a ship will be found to be in a worse state than the bottom of an unsheathed ship which is docked every six months, in spite of the anti- fouling properties of copper. Where there is only a little weed on the latter ship, the former will be found covered with minute shells of animal organisms and embryo barnacles. Consult the log of the sheathed ship and the engine room register, and compare the vessel's speed at the beginning and the end of the year, and the result is startling. Again compare these results with the performances of a sister vessel which (being unsheathed) is docked every six months, and the result is still more startling. "The anti-fouling qualities of copper presuppose that it is originally clean and smooth on leaving dock. This may be true on first leaving the dock yard, but unfortunately it is not always the case during the periodical dockings of a ship's commission. We have reason to believe that the admiralty are beginning to doubt, or are not satisfied with, the superior anti-fouling qualities of copper, because at the present time, and for the past two or thrée years, they have been experimenting with a composition for coating copper-bottomed ships. Why should it*be necessary to go to the expense of coating sheathed ships with anti-foul- ing composition if copper is really so effective as it is believed? As a matter of fact, we are of opinion that the necessity for coating sheathed 'Ships does not arise from a mistaken idea of the merits of copper, but the reason may probably be traced to the cleaning of ship's bottoms when in commission. The usual plan is to scrub down as the water is pumped out of the dock, and this is probably good enough for a six months' docking of unsheathed ships, when there is little more than weed upon the ship. The scrubbing is done by the ship's crew, and when, later on, the dockyard painters come along to put the composition on, they remove any roughness that mav be left before applying it. With a sheathed ship, however, that is not to be painted, the scrubbing as the water is pumped out, as a general rule, has to be sufficient. As there is no composition to be applied, the immediate necessity for making the ship's bottom absolutely smooth is probably not taken into account, and the consequence is that a rough surface is formed by myriads of minute shells, which remain as a nucleus for future growth. Cleaning a ship's bottom ought not to be treated as an evolution to be performed as quickly as possible, but the chances are that the work being altogether outside the commanding officer's usual routine, the time for cleaning the ship's bottom is cut down to the shortest possible limits. This is shown by the following illustration: - "Two or three years ago, two sister ships, both sheathed, were docked at the same time side by side. Both had the usual scrub down as the water was being pumped out of the dock, the operation being apparently completed at the same time.. The dock yard officials, how- ever, thought that one of the ships on docking had a much larger growth than she ought to have had since the previous docking. The.con- Sequence was that they applied for and received permission to try the effect of a special coating of anti-fouling composition for copper-bot- tomed ships. In order to watch the effect properly, only one side of the ship was to be coated; the other side was to be left. bare. When the painters arrived to apply the composition, they found that it was abso- lutely useless to attempt to apply the paint to the so-called clean bottom, and a squad of men were specially applied for days in scraping off the minute shells that still adhered after the ship had been scrubbed down. This having been done, and the paint applied, the other side of the ship had also to be scraped and cleaned with similar care, in order to make a fair comparison. Whether the coated side or bare copper side proved the superior history does not relate, but the same green composition is still being applied to sheathed ships, and it may be presumed that it is still under trial, or its superiority over: bare copper has been proved. Shortly after the two ships in question were completed both were sent on a voyage, practically in company, going the same distance, in the same time, and experiencing the same weather. The speed was 11 knots, and both ships started with four boilers alight; but, whereas the ship which had been properly cleaned maintained its speed with perfect ease and comfort in the stokehold, the other ship, after struggling hard to maintain the same speed, eventually had to light another boiler. Com- parisons at the end of the trip showed that one ship had averaged eight or nine revolutions more than the other for the same speed, and with an ee coal consumption of 10 to 12 tons a day. Comment is super- uous. "This illustration may not form a conclusive argument against the sheathing of ships, but it must be remembered that this was a case of a fair comparison between two ships which were supposed to leave the dock both in the same clean condition. It is not the theoretical value of sheathing that has to be considered, but the result of working under gen- eral service conditions. No unsheathed ship would have been allowed to leave dock in the rough state of one of the ships mentioned above, 'and it must be remembered that the other would have left in a similar 'state but for the fact of trying an experimental coating of paint. The case of these two ships is probably not an isolated one, and, if sought for, many more examples could be found where the sheathing of ships has, perhaps indirectly, been the méans of keeping the bottoms in a con- Preparations have been made for the launching today (Thursday) of 'the steamer Mary C. Elphicke at. the Chicago works of the 'American Ship Building Co. This is the second steel freighter launched this season at the Chicago works for Mr.»C. W. Elphi¢ke and* others of 'Chicago. The other vessel, the Wm. L. Brown, was launched a few weeks ago. Dimensions are 450 ft. over-all, '480°ft/ keel, 50 ft. beam and 28% ft. depth of hold. Engines are triple expansion with cylinders of 23, 38 and 64 in. diameter and 40 ft. stroke. Scotch boilers furnish steam at 180 Ibs, pres- sure. The capacity of the'ship'is- abott '6,300 gross tons. ©