5.1.2. Boom and Tension Cable Installat ion
The installation of the tension cable and connection cables
can all be performed from deck (without requiring
the use of expensive ROVs) following these steps:
1 The underwater buoys are connected to the
mooring lines, but tension is not applied, meaning that
these buoys will be floating initially.
2 While connecting the tension cable to the underwater
buoys, the connection cables are attached and
connected to buoyancy elements, to keep these
connection cables available and prevent the tension
cable from sinking under its own weight
3 The mooring lines connected to the underwater buoy
are pulled through the buoy until the desired tension is
reached; this applied tension will position the buoys at
a depth of 30 m.
4 The boom segments are connected to the connection
cables.
Figure 5.2 gives an impression of the components, when
installed. The more detailed steps of installing the tension
cable are:
1 One side of the tension cable which is on a reel will be
connected to the mooring point.
2 While the boat sails to the next mooring point the
tension cable will be unrolled.
3 While unrolling the tension cable the connection
cables and buoyancy elements will be connected to it.
4 When the next mooring point is reached, the tension
cable will be connected to the mooring point.
5 The boom is installed to the connection cables.
Alternatively, the booms can be connected to the tension
cable onshore, creating long sections of 4 km long that
can be tugged with a transport vessel to the site.
In this case, the installation steps would be:
1 The underwater buoys are connected to the
mooring lines, but tension is not applied, meaning that
these buoys will be floating initially.
2 For each section the tension cable and boom are
connected to the underwater buoys
3 The mooring lines connected to the underwater buoy
are pulled through the buoy until the desired tension is
reached. This applied tension will position the buoys at
a depth of 30 meter.
This alternative makes installation offshore quicker, but
the transport will be less efficient if only one boom segment
can be pulled by one boat at a time (reducing the
risk of booms entangling with each other).
Challenges
• The 4 km long tension cable will be transported on a
reel. So when one side of the tension cable is
connected to the mooring point and the boat sails to
the next mooring point, the connection cables have to
be connected to the tension cable on deck while the
tension cable is unrolled from its reel. Since this has
to be done often, a quick connection process has to
be created onboard so the tension cable can be unrolled
continuously.
• When the tension cable is installed the boom has to
be installed to the connection cables. In order to do so,
first the buoyancy element at the connection cable has
to be removed which is extra work. However, the
buoyancy element can also be used by connecting the
boom to it. In this case the buoyancy element should
be provided with a connection for the boom to be
connected to, making the installation of the boom
easier and faster.
A more detailed investigation into the installation of
booms and tension cables should be done in a later
phase of the project.