The PUNAISE Dredging System

Cost

The 8-ft dredge turnkey package, which includes the dredge, trailer, and

pipeline, costs between $750,000 and $1,000,000.

Company/Organization(s): Access restricted to U.S. Army Corps of

The PUNAISE Dredging

System

Background

Pinpoint Dredging Company of The

Netherlands has constructed and success-

fully tested and operated the PUNAISE

(Dutch for "thumbtack"). The PUNAISE is

operated by the Pinpoint Dredging Com-

pany, a partnership consisting of J.G.

Melis B.V., Ballast Nedam Dredging B.V.,

and Boskalis International B.V. The PU-

NAISE is a remotely operated, watertight,

submerged pumping system (Figure 3)

that can remove bottom sediments without

impact to navigation and without being af-

fected by storms.

Figure 3. PUNAISE at dock (Pinpoint

Dredging Company 1999;

used by permission)

Technology

The PUNAISE is composed of a watertight housing containing the dredge

pump, motor, and ballast tanks (Figures 4 and 5). It is connected to the

shore station via an umbilical that consists of control connections, power

supply, and a slurry discharge line. While in operation, the PUNAISE re-

sides on the bottom of the seafloor and pumps sediment without impact

to surface vessels. Because it is located on the seafloor, it is tolerant of

adverse surface wave action. This allows it to operate in all types of

weather and sea state conditions.

Once positioned at the appropriate location for sinking to the bottom,

the ballast tanks are filled and the PUNAISE settles to the bottom. Fluidiz-

ers are then activated, which allow the vertical support to settle into the

sand bottom so the dredging process can begin. As material is removed, a

crater or pit is formed with the P UNAISE located at the lowest point. The

submerged machine excavates by means of hydraulic erosion. This cre-

ates unstable slopes down where sediment flows to the suction entrance.

There are three PUNAISE models, PN 200, PN 250, and PN 400. The

PN 200 and PN 250 and ancillary equipment can be transported within

containers, while the PN 400 must be transported through conventional ship-

ping. Cable systems and pumping operations currently limit the ideal pump-

Chapter 4

Detailed Evaluations