92 LAUNCHING DATA FOR A BATTLESHIP. 



It is interesting to note the development of fore-poppet arrangements, from 

 that for the small vessel with fore-foot resting on a cross log and no arrangement 

 for distributing the pressure to the arrangement of suspending lashings, two or 

 more of chain or wire rope with little stretch, and forward of these two or more of 

 rope with considerable stretch that tends to equalize the pressure as the vessel lifts, 

 an arrangement that has served well even for quite large vessels; and, finally, to 

 the arrangements now used successfully for the largest vessels, either that used for 

 the Oklahoma or the crushing-chocks or gratings with the area in contact pro- 

 portioned so that where the pressure would reach a dangerous maximum the wood 

 crushes and compresses, and by yielding throws a part of the pressure further aft 

 and thus effects the necessary distribution. Large metal trunnions, with cast steel 

 and built-up saddles of extent sufficient to distribute the pressure, have also been 

 used. Crushing-chocks are described in Mr. James Dickie's paper on the "Launch 

 of a Cruiser and a Battleship," Volume VIII of the Society's transactions. 



The depth and breadth of channel opposite the Oklahoma building slip are such 

 that no checking arrangement was required. Efficient checking arrangements are 

 described in the different papers on launching. Manila cables, attached to anchors 

 or other fasts on shore, are sometimes used for checking and to have the stretch of 

 the cable stop the ship gradually. Manila cables appear unnecessary, as it is generally 

 practicable, and more economical, to use the vessel's chain cables. The chain cables, 

 if attached at some height above the ground, will bring the strain up gradually, in 

 the same way that the strains are eased for a ship at anchor by paying out a good 

 scope of chain. An error is sometimes made in estimating the checking effect in 

 breaking rope stops by assuming that it is the same as the work done to stretch the 

 rope stop to the breaking point. That is correct if both chains are stretched out 

 along the slip and the one attached to the ship secured, say at the fore- foot. Ordi- 

 nary practice is to attach it high up on the vessel ; when the strain first comes on 

 the stops the chain will hang in the curve of a catenary from the point of attach- 

 ment on the ship to some point where it touches the ground and extends along the 

 slip to the stop. As the vessel continues to move and the strain increases and 

 the stop stretches, the part of the chain in contact with the slip decreases, the part 

 hanging in a catenary lengthens and becomes flatter, and it will be found that 

 the ship moves through an appreciably greater distance than the stretch of the 

 stop, and that the work done in checking the ship is proportionately greater than 

 that in stretching the stop. The chain cannot push the ship, and no part of the 

 work done in lifting the chain is restored to the ship when the stop parts and the 

 chain surges and falls as the next stop begins to stretch. 



The launching curves, Plate 37, are of the usual type. The curve of way-end 

 pressures, now generally used, is worthy of note, as it is a criterion relative to 

 internal shoring as well as for needed support at the ends of the ground ways. 

 The curve of way-end pressure is considered in Mr. Everett P. Lesley's paper on 

 "Launching Practice on the Pacific Coast," Volume 12 of the Society's Transactions. 



The curve of launching velocity and derived curves, Plate 38, are based on 



