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24 PECULIARITIES OF LAKE STEAMERS. BY THEODORE LUCAS, Natural conditions have exercised a very pronounced influence upon the design and the operation of steamers navigating the great lakes. Lim- ited draught of channels has been of most importance. It has made shal- low depth a logical consequence in the ships, particularly as lake waves are not so formidable as to require a very high free-board. This small depth in turn limits, to some extent, the length and somewhat the breadth also. Lately through greater attention to good distribution of materia} M @- Metacesree FZ Cor Buovaucy anove Ken = 44.0 FF. Metaceuter Aa. Cor Buor.= 27.3 - |/ C.Buoy. 8 Kee * “Bo Ft M. AoC. Bu. = 6.8 * ped M. aw Keee ee = METACENTER. a \ C.. Suie as IN B. at» 40% oF BALLAST Appen Free in How. in the section of the ship, ratios in length to depth of about 16 to 1 have proved quite successful. . : Such proportions can be adopted safely, as lake waves, while quite often steep, have not time to grow very long, and the present long ships seem to rest therefore on several waves with a fairly well distributed support. An improvement:is possible, however, in the distribution of the strains, which are still quite severe on the upper works with their enor- mous deck openings. The neutral axis is only about one-third of the total | Ie Macn. Space —I | I; C.Gray. im TRIM oF es TT, C.B. ano C. Gr. FALL TOGETHER For Lever Reet see nae ee OcEAN | BIEAMER 7% 6> OUSa GO ee _ ee beer een ae oer neree ed a i he ri f LEVEL Keet , SHIFTS ‘ATT 3 §= To depth above the keel, throwing nearly twice the strain on the upper fiber than on the lower fiber. The absolute amount of strain cannot be deter- mined with certainty, but even with only four tons strain on the bottom, ° the top may get eight tons, which, as it is about one-half the average elas- tic limit, may, under alternate tension and compression, prove rather severe for the material. The initial stability of lake steamers is usually quite high, where breadth is the one nearly unrestricted dimension. We find: proportions” LAKE ¢ a A MARINE REVIEW. For LAKE STEAMER » QCEAN [January $1! of successful sailing ships like 50 ft. beam by 28% ft. depth or 52 ft. beam by 30 ft. depth, proportions which without any top weights give on an average metacentric heights of from 4 to 6 ft. in loaded condition, while in light condition, with water ballast, they largely exceed these values. Different methods and devices are employed to ease the vessels, one of which is that of admitting loose water into the open cargo holds, a rather dangerous practice, even on the lakes. The accompanying four sections illustrate an average modern case. A shows: light condition without ballast; B shows inner bottom full; C C. or Buoy. de. Kee. = 6.3 Fr. Mera. 05. Cor B. = 16.7 « D. SHie wi Loapen Conpition.. shows condition with about 1,000 tons free water in cargo holds, under such distribution that the moment of inertia of the water plane is reduced - to one-half; D shows loaded condition. More desirable but less effective for reduction of metacentric heights are the raising of the boilers and coal bunkers on platforms as well as securing, through a very high water bottom. a higher position of the center of gravity of the cargo.. Such a high initial metacentric height and 8 to 12 ft. free-board above nearly 18 ft. draught, are a combination highly conducive to wide range of sta-~ bility under inclination. A= Pata of C.Buoy For ier. Drarts (tever : B- r) “ C. Grav. « « “ Lake vessels, however, have their reserve stability and reserve buoy- ancy so little called upon, that they could easily get along with a great deal less. As said before, depth is adopted more for strength considera- tions than anything else. se “4 Trim, perhaps, is of the highest importance for lake vessels. Where the ships load to the maximum of their draught allowance, often keeping only a few inches from the bottom of the channels, a level keel in deep- load condition becomes, for the commercial success of the ship, an im-