| Show rob N on the wafer of the mode I 1 ex experiment ix efel basin at the U ashington orji advy yard ak each new vess esset elof of uncle R A sams faiq feet os ss tested 4 ogg before construction by y T weans means of toy je J reproduction e p 0 ar 4 ta kenti a P patriotic a pride lif inane ane speed performances of american tight ing ships and it i you have followed follo wedi these showings closely cly you jinye no dolbi been with the steady advance made each year haval ve vessels sels haye shown consistent improve up prove i mentIn speed eed seaworthiness and engineer lug economy put but have you ever paused to ask how these results are prIm primarily artly made possible this Is the basin the model tank i lisit aeilt I 1 la generally cal called ledfor for bp evitts brevi r tys sake Is the K in which small in models of and tried on a reduced scale AM when congress was vas asked to appropriate money tor for the plant which Is n now ow a an binter interesting and important department of the navy yard yar d at wa washington shi hiton the K proposition was looked upon n as involving an expensive toy since then i however the work i done there the re preliminary to the building ox of warships has represented a abing pt many hundreds of thousands of dollars besides fa insuring fastring the designed perform J tr amyle acce of 0 the tah s Is a another example of the old ru rule to of thumb abeln be ng 9 supplanted anted by the certainties of vi science dence Vit hout going too far into the history of things itis K s sufficient lelent to know that an englishman dr william froude discovered babkin back in the seventies heie was a comparable relation between the power required to draw a small model through the water and the motive energy needed to propel a big craft of similar form the principle which ho he later became known a as broudes Fr law or the lacot law ot comparison his studies were first made u ath miniatures ture sand and then thein verified by tie t towing owing of a large vessel formed on I 1 identical i lines WIth within Inthe the last twenty years there have been created and developed many vessels of novel types and the results obtained would have been virtually out of the question but for the in model odel tank millions of dollars would have been was wasted in blind groping instead of obtaining positive assurance of what the finished vessel would do before a single cent was waa spent in her building one illustration will suffice among the vessels in the naval review Is the gunboat munbok nashville designed in 1894 sha sh lidd had a displacement of about 1 1375 tons and wl with th 2 2500 horse bower power makes 16 15 knots last year the model tank danl dev developed eloped the hum hull form tor for the gu gunboat sacramento a vessel of tons tone more displacement b but dt of a speed of 16 knots upon a development of only 2000 horse borso power this saving of horse power calculated at 60 a horse power meant on at i economy in first cost of machinery of but it also meant th that atthe the larger gunboat could be driven at a speed equal to her smaller sister ship upon tons the bigger sacramento could carry a more powerful armament go farther upon tile the same supply of fuel and be more weatherly in stormy seas in brief b be a much better unit of the fleet and all of this R ns made certain by the expenditure pend iture of a few hundred dollars for wooden n models and their testing the lines bf the hull being altered during these tests until the b best est length and shap were obtained adlof all of the models tested at washington are arc ofa of a un uniform length of 20 feet and the purpose of making them so lar large ge Is t to 0 reduce the possible error in translating the be performance figures of the model laid into those of the full sled sized vessel asset these models ahemad are made a of wood and are f d in a machine especially designed for this work next the model Is painted andl and carefully caie fully varnished in order i to obtain a very smooth surface and with this done various arlous waterlines are are marked upon the white paint so that instantaneous ous phot photographs 0 taken during the to towing wIng tests test will show just liow how anywhere and where the waves and th the a hollows produced by the miniature aln n motion are de developed eloped when the model Is 19 read ready y it Is carried to the basin byln and alerd there loaded in the balancing tank with A bags offA of shot liot until illias it has the right weight or displacement pla cemen if and proper trim or poise upon ill alie e water 4 with this done it i Is s ready tobe attached to f the towing boeing carriage and tested bested the towing I 1 cair lage Is a s sort ort of a mobile bridge w which litch straddles e s the main tank and it Is driven by a electricity the different speeds being under r very nice control contrat upon the towing ca carriage I 1 are all of f the ahe operative sv switches Itches and measuring instruments r and also the recording mechanism which marks the spead of the ilic model and its pull or resistance wh when en drawn dran through the wat anter ei tho alm aim Is to obtain enship a ship form which will show the least pull or resI resistance siance at the desired velocity the actual speed of the model Is a mathematical ratio odthe of the relation between this miniature and the full sized ship and therefore the model does doe shot not travel fasic fast if you consider what hat the big craft will really do the towing basin beslu Is 3 ato 0 feet long fiig and and 43 feet wide nad and the maximum speed of the carriage Is relatively far in excess of the probable speeds of anything but freak crafts after a n model of satisfactory form has been developed and tested then comes the further of making the figures of the trl trials a Is applicable ta to the intended ship now there la Is just one pari par of this work which doe aloes s not follow Fron prouder dds lawdy law of comparison tills 1 is the factor of t the cp between them the fajt water and tile wetted surface of the vessels underbody der body this resistance fallo follows w a a lak law of its own and it ts is necessary to tow another model w which aich consists consist of a thin plate ejust just as long as the small craft and with a submerged surface exactly equal to that of the model prom from ali these ese two tests that thai of the plane and that of the model s the designer has the information 1 1 lie he wants wa i aits land and this information avers covers varl ous trials over a wide range of af speeds speed s so that the naval architect knows both the maximum and the cruising speeds at which the vessel can be propelled most economically the cruising speed Is un an important one because it la Is at this ratio of tra travel vel that ships of war go most of the time full speed Is really a battle reserve or something to be called for only when urgency demands in this particular fighting ships differ radically from the ocean greyhound of commerce but dont think that the naval designer has an easy task even with the model tank at ids his dis acial the speed trials of alie full sized ships aro are not less im important por to him because they give him this check is ii very model work his a ch check pek upon it it enables the designer to nee necessary as sr inasmuch as bild bridge i e over v er the gap between hla his U model lodel and the re real I 1 vessel e 1 I year b by y year with more exactness ass the builder of the hull structure tur a the naval architect pr or naval colstr constructor actor h has as only a share in the final product the naval eno engineer neer must take up the problem where his brother broth erends ends that is to say the engineer knows just what energy his bis propellers must exert effect effectively iely against iii the water in order to force the ship along at aher her several speeds i he toot must work from the outside of the ship inward up to RP a point the position of th the 6 propeller in relation io the hull slid the very form of thep the propeller must be suited to the particular craft in question these can be berried tried in ml miniature stature in association 1 with othe the model for the determination of some data but after that flie alie engineer draw upon lupori exper experience lence n and nd his bis carefully tabulated records of 0 other performances the average annual expenditures tor the maintenance tena cenance ilc 3 of the m model 0 del basin at washington are under 25 and this Is a trifling sum compared wit with h the savings which have been effe effected through careful designing tn in the cased case of 0 the three scout cruisers birmingham chester and salem by merely le lengthening their hulls etwas it was found possible to save ln those three ships a combined total of horse power over that required dorithe for the ithe original de design figured at 60 a horse power this represented sent edan an economy of machinery cost amounting to the model experimental basin Is Is no longer looked upon as an investment of doubtful value every first cla class S s naval power has bas one or of these establishments h land and like that it at washington most of thern them lend the their ir aid to the merchant marine as well such Is th the a development of private i exper experiments experiment imen ts which dr william froude began so to speak in his own backyard all of the successful ships of today are indebted to his pioneer work |
