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R.H. Charlier and Chr. P. De Meyer
3.1.7.1 Dredging equipment and methods
Only dredging equipment generally used for beach nourishment, thus no bucket
dredger or dustpan dredger, will be discussed here. Nevertheless under some
circumstances other equipment may be used. However, the backhoe bucket
dredger, a more recent type of dredger, will be mentioned.
3.1.7.1.1 Trailing suction hopper dredger
The trailing suction hopper dredger, or trailer dredger is a sea-going selfpropelled vessel equipped with one or two suction pipes designed to trail over the
side of the vessel (fig. 29). The suction pipe terminates, at the lower end, in a
draghead designed to draw in the maximum amount of bed material. Suction is
provided by a dredging pump, situated in the hull of the vessel, which discharges
into a hopper in the vessel, where the soil (viz. sediment) particles settle and the
water is discharged back to the sea over a weir.
Various types of draghead have their own particular advantages and
disadvantages, depending on the material to be dredged. Generally, in soft
materials the head slowly sinks forward into the sediment and highly
concentrated materials are lifted. In harder materials penetration is shallower and
a great forward speed is required to maintain output ; disintegration of the soil at
the draghead is necessary to obtain a satisfactory output. High pressure water jets
directed into the soil and the addition of teeth are used.
The trailer dredger's speed, generally slow, is varied to suit the material being
dredged. On the way to the discharge site, speeds of between 9 and 14 knots are
usual, depending on the vessel's size.
Maximum dredging depths also vary with vessel's size, usually ranging from 10
to 30 m (33 to 99 fl). To dredge at great depths some modem trailing suction
hopper dredgers have their dredging pump located on the suction pipe well below
water level, allowing to reduce the height of the suction column.
R.H. Charlier and Chr. P. De Meyer
3.1.7.1 Dredging equipment and methods
Only dredging equipment generally used for beach nourishment, thus no bucket
dredger or dustpan dredger, will be discussed here. Nevertheless under some
circumstances other equipment may be used. However, the backhoe bucket
dredger, a more recent type of dredger, will be mentioned.
3.1.7.1.1 Trailing suction hopper dredger
The trailing suction hopper dredger, or trailer dredger is a sea-going selfpropelled vessel equipped with one or two suction pipes designed to trail over the
side of the vessel (fig. 29). The suction pipe terminates, at the lower end, in a
draghead designed to draw in the maximum amount of bed material. Suction is
provided by a dredging pump, situated in the hull of the vessel, which discharges
into a hopper in the vessel, where the soil (viz. sediment) particles settle and the
water is discharged back to the sea over a weir.
Various types of draghead have their own particular advantages and
disadvantages, depending on the material to be dredged. Generally, in soft
materials the head slowly sinks forward into the sediment and highly
concentrated materials are lifted. In harder materials penetration is shallower and
a great forward speed is required to maintain output ; disintegration of the soil at
the draghead is necessary to obtain a satisfactory output. High pressure water jets
directed into the soil and the addition of teeth are used.
The trailer dredger's speed, generally slow, is varied to suit the material being
dredged. On the way to the discharge site, speeds of between 9 and 14 knots are
usual, depending on the vessel's size.
Maximum dredging depths also vary with vessel's size, usually ranging from 10
to 30 m (33 to 99 fl). To dredge at great depths some modem trailing suction
hopper dredgers have their dredging pump located on the suction pipe well below
water level, allowing to reduce the height of the suction column.