The steam conditions for marine engine plants using marine Scotch boilers are usually limited, in our country, to the steam pressure of 16kg/cm2 G., steam temperature of 285°C and the vacuum at the condenser top of 710mm. Now for this vessel we preferred them as 17.5kg/cm2 G., 330°C and 717mm respectively, and made some improvements in the design of machinery parts. For the main turbine, Parsons' coefficient has reached 2, 125m2/sec2.kcal, which is quite an improvement compared with the former usual value of 1, 500-1, 800.Trial trips were made on the 9th and 13th August for the first of 3 sister ships, The “Heito Maru”, on the 17th and 19th September for the second ship “Taito Maru”and on the 31st October and 2nd November for the third ship “Shoka Maru”. The results are tabulated in the attached table. The coal consumptions for all purposes were 0.466, 0.462 and 0.492kg./s.h.p./hr., respectively, and the whole plant efficiencies showed more than 17%. Particulars of machinery parts are shown in the attached table, and the general arrangement in Fig. 1.Propelling machinery consists of one set of Mitsubishi-Zoelly double reduction double helical nodal drive geared, cross compound, all impulse turbines of the latest improved type. For reduction gear, taking special consideration for smooth running and for elimination of troubles under undue stresses due to the torsional vibration of shafting and also the end play in each pinion, the second pinion shaft is flexibly driven by a long nickel steel shaft provided with a special flexible coupling between the first wheel and the flexible driving shaft. All discs of H.P. ahead and astern turbines are solid with the rotor shaft, and those of L. P. turbine, ahead and astern, are shrunk on the rotor shaft with keys.The main condenser is of Mitsubishi-Contraflo type and is located on the port side of the main turbine.Three boilers of single ended, multitubular marine type, each 4, 600mm diameter and 3, 650mm length with a total heating surface of about 232.9sq.m. and a total grate area of about 17.5sq.m. are constructed under the special survey of Teishinsho for a working pressure of 17.5kg/cm2, Fig. 2 shows the sectional arrangement. The superheaters are of a combination of smoke tube type and Mitsubishi combustion chamber type. The saturated steam is superheated primarily in the former and secondarily in the latter, up to the final steam temperature of 330°C. The construction is shown in Fig. 3. Regulating and by-path arrangements are provided, so that any required proportion of mixing saturated steam with superheated steam is easily obtained. Superheaters will be thrown out of connection quite easily whenever required. These connection diagrams are shown in Fig. 4.