COST ACCOUNTING AND ESTIMATING. 251 



of material, actual casting weights being used for gross weights and scale or calculated 

 weiglits for net weights. 



The principal weight factors for propellers are the diameter of the tail shaft, diame- 

 ter of propeller, and area of developed surface. In determining the developed surface, the 

 indicated thrust-per-square-inch method was adopted, using the information as published 

 by Admiral Dyson, together with the actual practice used on merchant ships. 



Similar methods can be applied to nearly all other jobs, such as forced draft systems, 

 boilers, stacl<s, uptakes, lagging, shafting, auxiliary condensers, feed water heaters, refriger- 

 ating plants, and even tools, instruments and spares. 



While the machinery jobs lend themselves better to standardization, similar methods 

 may be applied to the hull jobs, and a few of these will be described. 



The determination of the weight of the structural hull resolves itself into two opera- 

 tions : First, the determination of surfaces and lengths according to the dimensions and 

 model ; second, the determination of unit weights for those surfaces and lengths. The sur- 

 faces and lineal dimensions can be determined directly from a series of standardized lines 

 somewhat similar to those described in the very instructive paper by Mr. A. J. C. Robertson, 

 appearing in the Transactions of 1920. These standardized lines were developed by making 

 use of the experiments of Naval Constructor McEntee appearing in the Transactions for 

 1919, and also from the various other model experiments. Investigations were also made re- 

 garding wetted surface formulae in order that the wetted surface for any particular model 

 could be quickly and accurately determined. Taylor's formula was adopted as being the 

 simplest formula, the accuracy being dependent only upon the accuracy of the coefificient. 

 A series of curves of coefficients has been developed so that for any length, for any breadth, 

 for any draught, and for any block coefificient, the surface coefficient could be obtained within 

 the desired degree of accuracy. 



The results of the standardization of lines have been incorporated in a folder with t3^e- 

 written instructions so that a complete set of lines can be at once drawn up for any condi- 

 tion without fairing, or that a particular cross-section can be obtained without the use of a 

 set of lines ; also, that the areas of any particular cross-section to any height and the girths 

 of any cross-section to any height can be obtained without the necessity of drawing lines or 

 that the entire surface can be obtained by a simple calculation. 



The unit weights are established by the classification society under which the vessel is 

 constructed, and tables of coefficients have been established for laps, butts, straps, rivets, etc. 



In joiner work standard drawings are made for the various items of portable furniture, 

 such as berths, lockers, transoms, etc., and the number of board feet of lumber of various 

 kinds, together with the amount of hardware for each of these items, have been tabulated. 

 The various kinds of bulkheads and joiner decks have been standardized for dimensions and 

 the quantities reduced to lineal or square-foot basis. The quantities for complete pilot houses 

 and rooms for the various officers have been tabulated, so that it is unnecessary to make 

 these detailed calculations for each estimate. 



The work of standardization is performed during the intervals between estimates, and, 

 when once started, the time saved on jobs already standardized can be utilized for further 

 standardization. It is believed that the time-saving element and the uniformity and accu- 

 racy of results well warrant the labor expended ; certainly, after the standardization is com- 

 plete, the time required to prepare an accurate estimate is very much reduced. 



