Volume 8 – Mechanical and Electrical Services - Malaysia Geoportal

Chapter 8 DREDGER
In general, a trailing suction hopper dredger (TSHD) is a vessel that is suited for deep-sea
navigation with the ability to load dredged materials into its own hold, the so-called hopper, by
means of centrifugal pump(s) and suction pipe(s).TSHD's are fully maneuverable, as they are
required to sail during dredging operations. When a TSHD approaches the dredge area it will
reduce its sailing speed and lower the suction pipe(s) overboard.
The draghead(s) at the end of the suction pipe(s) will be kept above the seabed until the dredge
area has been reached. The dredge pump(s) will be started. The water that is thus taken in, prior
to the draghead(s) touching the seabed, will be pumped overboard or in some cases in the
hopper of the vessel. Upon arrival at the dredge area the draghead(s) will be lowered onto the
seabed. Due to the forward movement of the vessel the draghead(s) will loosen the seabed
material. In this way a mixture of soil and water enters
The suction pipe and loaded directly into the hopper. Water jets, which may be on the
draghead(s), can assist in loosening the soil, hence optimising the production.
Fig. 8.3 Trailing Suction Hopper Dragger
While dredging, the TSHD will sail at a speed of 1 to 3 knots, dependant on the dredge location,
surrounding marine activities, sea condition and soil parameters.
The actual position of the draghead(s) and the suction pipe(s) in relation to the position of the
vessel can be checked through the following measurements:
By measuring the angle of the vessel in combination with the draught and trim of the vessel and
combining these measurements with those of the draghead(s) and the suction pipe(s), the latter
can be determined through measurement devices mounted on the draghead(s) and the suction
pipe(s), which indicate the angles of the different parts of the suction pipe(s).
The depths of the different parts of the draghead(s) and the suction pipe(s) can be determined by
using pressure readings from specially installed sensors on the draghead(s) and the suction
pipe(s).
March 2009 8-3