4 BULLETIN 300, XL S. DEPARTMENT OF AGRICULTURE. 



A dipper dredge to withstand the severe stresses due to the con- 

 stantly changing loads must he very strongly built. If the hull is of 

 wood it is made up of a strong frame work of timbers planked on the 

 sides and bottom with 3-inch (or heavier) planks. It is always 

 strengthened with numerous cross trusses inside, to prevent buckling. 

 The front end of the hull should always be of double thickness to pre- 

 vent damage and possible sinking through the dipper striking the 

 hull. 



In the larger sizes of dredge built at the present time the common 

 practice is to make the hull of the same width, top and bottom. On 

 some of the smaller machines, especially those with steel hulls, the 

 top is made wider than the bottom. Hulls must be very carefully 

 caulked, since in operating the dredge the strain on the hull will 

 tend to loosen any poor caulking. 



It often becomes necessary to dismantle a dredge in order to move 

 it from one project to another. Wooden hulls, because of the 

 necessity of their being so strongly built, are practically destroyed 

 by being taken down, and it is in many instances cheaper to build 

 a new hull than to move and rebuild the old one. To save this 

 expense steel hulls are used to some extent on the smallest-sized 

 machines, although they have not been generally favored for the 

 larger dredges. On some of the small one-half yard or three-fourths 

 yard dredges the hull has been made in sections, which can be taken 

 apart and hauled or shipped to another project. This method, 

 however, is not adapted to the larger machines. 



The machinery of a dredge is ordinarily placed on the deck of the 

 hull. It is, however, sometimes placed below the deck in order to 

 gain head room. Sometimes the boiler and coal bins are placed on 

 a deck from 1 to 3 feet lower than the main deck. 



ENGINES AND BOILER. 



The power most commonly used on dipper dredges is steam, 

 although a number of machines are now in operation which are 

 equipped with internal-combustion engines or electric motors. 

 The majority of dredge operators are more familiar with steam plants 

 than with oil engines. Also, steam power has the advantage of 

 being good for from 50 to 100 per cent increase over its rated capacity. 



Internal-combustion engines are generally rim on either gasoline, 

 kerosene, naphtha, or distillate oil. Practically all of the dredges 

 equipped with this type of engine are of the one-half yard or 1-yard 

 size, although it has been used in at least one instance on a 3-yard 

 machine. An internal-combustion engine is usually rated at its 

 actual capacity. Therefore, when replacing a steam engine with a 

 gas engine, it is a good plan to put in a plant with from 50 to 75 per 

 cent greater power than the rating of the steam engine which it is to 

 replace. Contractors as a rulo do not consider internal-combustion 



