he dredger being drawn
forward by the head chain, she is drawn across the river by the
starboard chains, and, having reached the extent of her work in that
direction, she is then drawn a few feet forward by the head chain, and
the bucket frame being still in motion the vessel is hauled across by
the port chains to the side whence she started. By means of this
transverse motion of the dredger a series of cross cuts is made; the
dredger takes out the whole excavation from side to side to a uniform
depth and leaves no protuberances such as are found to exist between the
furrows in longitudinal dredging, even when it is executed with great
care. The two systems will be understood by reference to fig. 1, where A
and B are the head and stern moorings, and C, D, E and F the side
moorings. The arc e f represents the course of the vessel in cross
dredging; while in longitudinal dredging, as already explained, she is
drawn forward towards A, and again dropped down to commence a new
longitudinal furrow.

[Illustration: Fig. 1.--Diagram showing Moorings for Transverse
Dredging.]

_Hopper Dredgers._--In places where barge-loading dredgers are
inconvenient, owing to confined space and interference with navigation,
and where it is necessary to curtail capital expenditure, hopper
dredgers are convenient and economical. These dredgers were first
constructed by Messrs. Wm. Simons & Co. of Renfrew, who patented and
constructed what they call the "Hopper Dredger," combining in itself the
advantages of a dredger for raising material and a scow hopper vessel
for conveying it to the place of discharge, both of which services are
performed by the same engines and the same crew.

The vessel for this type of dredger is made of sufficient length and
floating capacity to contain its own dredgings, which it carries out to
the depositing ground as soon as its hopper is full. Considerable time
is of course occupied in slipping and recovering moorings, and conveying
material to the depositing ground, but these disadvantages are in many
instances counterbalanced by the fact that less capital is required for
plant and that less room is taken up by the dredger. If the depositing
ground is far away, the time available for dredging is much curtailed,
but the four-screw hopper dredger constructed by Messrs Wm. Simons & Co.
for Bristol has done good work at the cost of 5d. per ton, including
wages, repairs, coals, grease, sundries and interest on the firs