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

— Practical Ideas fess the Engineer A Details of Construction of Large Drydock at Boston-New American Design of Diesel Engine the largest in this country. It has been under ever since 1912, when it was. started by a legislative act of the state of Massachusetts. The construction was handled by the MHalbrook, Cabot & Rollins Corp., Boston, under the super- vision of Frank W. Hodgdon of the state department of waterways. Its construction cost has been something over $3,000,000. The dock opens directly on to the main ship channel of Boston harbor and means the beginning of a new de- velopment in the South Boston district. Close to it lie the new army _ suppiy base and the big naval loading dock. The drydock itself has been taken over since its completion by the government for naval purposes. Although the dock follows closely the lines of similar docks throughout this country, its large proportions give it an, wnustal. interest. ~~ If 1s’ 1200" feet long and has a width of 149 feet be- tween copings of the side walls. The top of the dock wall is 16 feet above mean low water and the sill at the entrance is 35 feet below mean low water. A maximum length of ship which can be placed in the dock is 1140 feet and in order to economically handle shorter vessels, an intermediate B te harbor’s new drydock is construction BY H. R. SIMONDS THE FIRST VESSEL TO ENTER THE NEW DOCK WAS THE BATTLESHIP VIRGINIA sill has been constructed as part of the dock structure, permitting a division to be made in the length of the dock used. The section is 668 feet and the outer section 520 feet long. The method of building the dock has some features of interest. Two projec- inner A 1600-TON STEEL FLOATING CAISSON IS USED 10 CLOSE THE ENTRANCE oil tions of land were built out from shore about 400 feet apart by means. of hydraulic dredges. Then a_ cofferdam structure was built between the two outer ends, after which the water in the enclosure was pumped out. Dry excavation was then carried on to bed- rock and the walls of the new dock were built up on this solid foundation. The walls are mass concrete with a lin- ing of granite on the inside. The con- crete mixture used was approximately 1-214-41%4 in the massive sections and 1-3-6 near the edges and top. To pro- vide for expansion, the walls were built in sections approximately 60 feet long, each section being poured and painted with a nonadhesive paint before the next section was started. The joints are perfectly straight, flat surfaces ex- tending through the wall, except that on the outer side indentation have been left to take concrete slabs which, under the pressure of the water tend to pre- vent leaking. As the dock when filled contains be- tween 50,000,000 and 60,000,000 gallons ef water, it is evident that a large pumping plant is necessary. This plant consists of three main units together with smaller pumps for auxiliary pur- poses. The main pumps have a 54-inch suction and discharge and are each operated by a 1250-horsepower, con-