MODERN DREDGES.

Hauraki Plains Gazette, Volume XXXV, Issue 4678, 24 March 1924, Page 4

MODERN DREDGES.

ALL-ELECTRIC VESSELS. DESCRIPTION OF AMERICAN TYPE In order to carry on more rapidly and at reduced cost the important work of keeping channels of American harbours at the required depth the corps of engineers o£ the United States Army, which is responsible for this service, has designed four sea-i going dredges of a radically new type. Two of these dredges, the A. McKenzie and W. L, Marshall, have just been landed at the yards of the Sun Shipbuilding and Dry Dock Company, Chester, Pa.,, and two more, the Dan C. Kingman and the William T. Rossell, will be completed at the same yards in the near future. These dredges are the first all-electric ships ever built. Electricity is used on them for every possible purpose : for propulsion, for operating all auxiliary machincry., and for cooking, heating, ventilating, and lighting. ’ Their power is not generated by steam engines in the usual manner but by internal combustion oil engines resembling automobile engines on a big scale. Every movement of each ship is controlled from the pilot house, where the navigating officer personally starts, stops, changes the speed, and reverses the ship, without signalling to the engine room. Each of these features is a new development in marine engineering, and never before have all of them been combined on a large vessel. Hence these dredges represent a retinite advance in naval architecture.

The duty of these dredges will be to clean channels through the sand bars that are always forming at ths entrances of seaports. They remove the accumulated .silt by means of powerful suction pumps, collect it in capacious hoppers, and, when loaded, run out to sea and dump their loads in deep water. All harbours, if left to themselves, would in a short time become blocked to all but the smallest steamers. Hence it is due to the never-ceasing dredging operations of the United States engineer corps that foreign commerce is maintained and that the products of factories, forests, mines, and farms can be sold to world markets.

Because these dredges must be thoroughly seaworthy, they outwardly resemble ordinary commercial steamers, but when a visitor boards one of them he finds that the entire amidship section is taken up With two rows of yawning hoppers with a long, narrow well, open to the sea, between them.

Withijn this well the actual dredging mechanism is located. This consists of a 26-inch pipe, 45 feet long, supported in a frame of steel lattice work. One end of the pipe is connected through a flexible joint to the suction end of an 800-hbrse power centrifugal pump, and the other end carries a heavy steel casting which resembles a huge gridiron in shape and is called a "drag.”

VZhen dredging is- to be done, the drag is lowered to the bottom, the pump is started, and the vessel is run slowly along the course to be dredged out. The drag, acting like a great claw, loosens the sand, which is sucked up by the dredge pump and discharged through suitable piping into the hoppers. Where the bottom i,s too hard to be loosened by, the drag, jets of water, powerful enougn to cut into almost any material except rock; are forced out through the drag. When the hoppers are full, the dredge goes well out to sea and deposits her load by opening doors at the bottom of the hoppers. The overall length of each dredge is 268 feet 5 inches; beam, 46 feet.; depth, 2 feet 6 inches, and capacity of hoppers 1,250 cubic yards. Nowhere else, afloat or ashore, can so many different applications of electricity be found in so small a space. Electricity drives the propellers, operates the dredge mechanism, opens and shuts the hopper doors, pumps water and fuel oil, compresses air for* blowing the whistle, makes ice and maintains cold storage, heats all holds and living quarters, keeps the fuel oil at the proper temperature, ventilates every part of the vessel, runs the machine shop tools, raises arid lowers the anchors, operates all wenches and capstans, heats the water, does the steering, cooks the meals, and lights the cigars, cigarettes and pipes. There are. on each dredge 56 electric motors, 100 electric heaters, 25 electric fans, and two electric ranges. These dredges are perhaps the first habitations of man where fire in some form or other is not needed. Electric power for all this apparatus is produced by three 1,000, horse

power Mclntosh-Seymour oil (or Diesel) engines, each of which drives a 700 kilowatt Westinghouse generatoi, in addition to which there are several auxiliary generating units. Two 800 'horse-power Westinghouse motors, each connected directly to a propeller, form the actual propelling machinery of the dredge. The control of each of these motors is cen-> tmd in a hand-wheel in the pilot house. To start the propeller motors, and therefore to get the ship underway, the navigating officer merely turns these two wheels. As the wheels turn, the .speed of the motors increas-. es until they come up to full speed at the extreme limit of the wheels’ motion. Turning the wheels in the reverse direction reduces the motors speed until they come to rest; then further rotation starts the motors in reverse, thus backing the ship.

The navigating officer is .therefore, in direct control of the ship and can put her through manoeuvres without losing time or risking errors through signals to the engine room. This provides a highly facile control which is of .special advantage to these dredges because their forces when at work must be extremely accurate in spite of constantly changing winds, tides, and waves.

Engineers of the Westinghouse Company co-operated with the Unite ! States Engineer Corps in selecting and designing practically all of the electrval equipment for these dredges. The drive used in these dredges is known as the Diesel electric system and was recently perfected by American engineers. Many engineers believe it to be the drive of the future for all vessels except the very largest because it combines high •fuel economy, reliability, and a high degree of manoeuvring'power. So far, it has been used only on a few fishing steamers, yachts, and ferry boats, and the new United States dredges arc the first of their size t<a employ it.

All shipping men are greatly interested in the Diesel electrie drive and are anxious to obtain reliable performance data. The United States Engineer Corps will make careful tests of tlfe equipment of these dredges under all conditions of operation, and will publish the results, thus greatly assisting marine engineers in determining the desirability of similar equipment for merchant ships.

The new all-electric dredges will, it is believed by their designers, give better service than the older steam types, and will therefore directly assist in improving the nation’s foreign trade. At the same time they are also expected to reduce the cost of dredging, and this will help to reduce the cost of government.