The hoisting gear may be driven either from the main engine by frictional gearing or by an independent set of engines. Six anchors and chains worked by powerful steam crabs are provided for regulating the position of the dredger in regard to its work. _Barge-loading Dredgers_ used formerly to be provided with two ladders, one on each side of the vessel, or contained in wells formed in the vessel near each side. Two ladders were adopted, partly to permit the dredger to excavate the material close to a quay or wall, and partly to enable one ladder to work while the other was being repaired. Bucket ladder dredgers are now, however, generally constructed with one central ladder working in a well; frequently the bucket ladder projects at either the head or stern of the vessel, to enable it to cut its own way through a shoal or bank, a construction which has been found very useful. In one modification of this method the bucket ladder is supported upon a traversing frame which slides along the fixed framing of the dredger and moves the bucket ladder forward as soon as it has been sufficiently lowered to clear the end of the well. In places where a large quantity of dredging has to be done, a stationary dredger with three or four large hopper barges proves generally to be the most economical kind of plant. It has, however, the disadvantage of requiring large capital expenditure, while the dredger and its attendant barges take up an amount of space which is sometimes inconvenient where traffic is large and the navigable width narrow. The principal improvements made in barge-loading dredgers have been the increase in the size of the buckets and the strength of the dredging gear, the application of more economical engines for working the machinery, and the use of frictional gearing for driving the ladder-hoisting gear. It is very important that the main drive be fitted with the friction blocks or clutches before alluded to.