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

x ior | MARINE REVIEW [November 9, ships of unequal size but of similar form and similarly propelled, driven at the 'same speed, the larger will have the higher co-efficient of perform- ance and for the same co-efficient her speed will be higher. Torpedo boat steam trials have proved, however, that the value of the Admiralty co- efficient does not continue diminishing indefinitely. The curve of co- =] lot OL ¥ E 2 a ° at oO Ww a nN et | 1 1 1 4 -- i -- ; 4 -- - 4 4000 8000 1RD0O +=: 16000. RO.000.-----R4.000. 28.000 Scate ror DISPLACEMENT, ee Fic 6... efficient reaches a minimum at a certain speed, which we will call the rising speed. The increase in the value of the co-efficient beyond the frising speed is due to a bodily rising of the vessel out of water and a consequent lessening of the displacement and wetted surface. The direct resistance is proportioned to Dj V® and the phenomena of rising occurs when the ratio of the direct resistance to the displacement aN ee ee DT py attains a certain value. Fig. 5 shows the Admiralty co-efficient of a modern high-speed tor- pedo boat. Mons. Normand found that in the Forban, a French torpedo boat of 125 tons displacement, the minimum value of C, occurred at a speed of about 20 knots. Above this the value of the co-efficient in- creased, and at 31 knots, 11 knots beyond the minimum, it was. still : cae V?__ 400 ay rising. Di 6 fore approximately given by the formula V=9*,/ p» --assuming 9 to be the square root of 80. ; The value of the above co-efficient will probably vary somewhat with different types and sizes of vessels, but for torpedo boats the writer has found by experience that the constant or co-efficient 9 is applicable to al- most all modern torpedo craft and small high-speed vessels. The follow- ing figures will prove interesting, as they give the speed of minimum effi- ciency and the speed at which torpedo boats and destroyers will commence to rise out of water: 80. The speed of minimum efficiency is there- Displacement. Rising Speed. 25 pb os: 50 17.3 100 19.4 150 20.7 © 200. 21.8 | 300 2237 7 400 27 500 O54 Fig. 6 shows the approximate rising speeds of ships up to 30,000 tons displacement using the same co-efficient 9 in the formula given above. weyers ' When the United States harbor defense ram Katahdin was being constructed, naval architects were almost unanimous 'in the opinion that she would rise out of water forward when driven at full power, and there- fore great speed was predicted. Actual speed tests proved that she did not 5 jon 5 20 25 30, 3s 40 45 SPEED in KNoTS. Fie change her trim at all when the false above-water bow kept the solid water from piling up on her forward deck. When the false bow was removed, the weight of water carried forward depressed the bow some- what and there was certainly not the faintest natural tendency to rise manifested. It is not surprising that the Katahdin refused to act as pre dicted, for the rising speed of a vessel of her displacement is in the vicinity of 32 knots, and the maximum speed of the vessel was only 16% knots per hour. ne 7, curve A, shows an Admiralty co-efficient curve for a 1,000- ton visionary ship continued beyond the rising speed. Curve B is the co-efficient curve for a 10,000-ton ship of similar form and proportions. V/10,000 = 2.154 and \/2.154=1.468=speed constant. Therefore the cor- #4/1,000 : eponting speed of 10 knots is 101.468=14.68 knots; 20 knots= 20 1.468--=29.36 knots; 30 knots=44.04 knots, and 40 knots=58.72 knots. -- 't will be at once noticed that beyond that speed at which the two curves A and B intersect the larger ship has a smaller co-efficient than the smaller ship at the same speed. It has always been maintained that the larger the ship the higher the Admiralty co-efficient at the same speed, but it will be seen that this assertion does not hold good beyond the vicinity of the rising speed. Of late years the size of torpedo boats and destroyers has been rapidly increasing, until at present boats of over 400 tons displacement are being built. These boats have in many cases a de- signed. speed of 28 knots per hour, and it may be well: to: note' that this speedis within three knots of 'the rising speed,' the speed' of minimum' efficiency. Aside from weight, and looking at the matter from a propul- sive standpoint only, it becomes then quite apparent that the smaller the torpedo vessel the easier it: will be to'obtain any high speed, for a 100-ton 2514-knot boat will have reached a:speed' of 6 knots beyond the point of minimum efficiency when a 500-ton, 2514-knot boat will be at the mini- mum of the Admiralty co-efficient curve. _ It follows, therefore, that the larger the boat the higher will be the Admiralty co-efficient, provided the rising speed is not reached, but if this speed be exceeded, the larger the boat the smaller will be this co-efficient. If the difference in size between two similar ships be very great, the point of intersection of the two Admiralty co-efficient curves will be at a speed a few knots beyond the rising speed. As the difference in size becomes less, the point of intersection will approach the rising speed of the smaller ship. Naval architects have not yet begun to appreciate the importance of the rising speed. The builders of a number of torpedo boat destroyers will become better acquainted with it before long, and before many years the builders of fast yachts and passenger steamers will undoubtedly feel interested in it and endeavor to keep away from its detrimental influences as much as possible. . THE NAVAL WIRELESS TELEGRAPHY TES'S. Tests which officials of the navy department are making with the Marconi system of wireless telegraphy will extend over a period of two weeks or more, and probably no definite statement as to the results will be obtainable until t'he navy board of equipment is enabled to make public the report of the special board detailed for the observation of the experi- ments. It is known, however, that the preliminary tests were highly satisfactory. The cruiser New York and the battleship Massachusetts, the two vessels fitted with the wireless apparatus, lay in the North river, New York, about 48 yards apart, or about the distance that would sepa- rate vessels steaming in squadron formation. The sending instrumen' was operated on the flagship by Signor Marconi personally, while the receiving was done on the Massachusetts, the instrument being operated by one of the inventor's assistants. The particular object of the tests was to determine the practicability of using the system for short signaling while squadrons are at sea, and its adaptability for this work was proven admirably. Six tests were made, beginning with the sending of a newspaper ar- ticle of 1,500 words, which was transmitted without a single error. The rate was eleven words per minute, a little over half the average speed maintained on the ordinary instruments, but Signor Marconi explained that this speed could be greatly increased and that the instruments had, indeed, during the yacht races, transmitted at the rate of sixteen words per minute. The speed, he said, depended simply upon the speed of the operator. The message after being sent to the Massachusetts, was re- ported back to the. New York, the words being registered on tape. which was taken by the inspectors and filed away. The second test consisted of the sending of a series of numbers of varying lengths. The third test was on the transmission of a series of letters, written and drawn at random. The fourth was.made up of the transmission of short messages, and the fifth.and sixth tests consisted of the transmission of a series of code messages. The vessels. then: proceeded to sea for further-tests. .A- feature of the tests at seawill be the firing. of the big guns of the battle- ships, while the messages. are being sent, in.order.to determine the i1se-- fulness of the system during an engagement. _In'a circular just issued relative to his Paragon 'boiler, whichiis used on several canal steamers and yachts,,.as well-as numerous. other -small vessels, Capt. M. De Puy, patentee and sole owner. quotes Manager W. x, Nourse of the Marine Iron Works, Chicago, as saying: "It is the best boiler on the market"; and Charles Riter of the Eagle Biiler Works, Buffalo: "Tt is the best plan of a boiler I ever saw. There is not a weak point in its construction; not, over expensive; can be kept clean; will be durable; and in case repairs are ever needed, every part of the boiler is get-at-able."' The Roberts Safety Water Tube Boiler Co. of New York has not fig- ured very prominently in the discussion that has been going on for a long time regarding the respective merits of cylindrical and water tube boilers for ships of war, big merchant steamers, etc., but that company keeps on turning out great numbers of boilers for vessels and paying dividends just the same. The Roberts company has just paid a ninth consecutive annual dividend of 10 per cent on its capital stock, commencing with the year of organization (1890) and continuing through all the panic years. ial iT a a