“Veja Mata”. This model was scaled down to a size of 1:40 and was used to
integrate the new cage designs. After the first experiments were conducted in the
wave flume of the Ludwig-Franzius-Institute for Hydraulic, Estuarine and Coastal
Engineering we identified that the piles could under extreme conditions tend to
local vibrations (Fig. 11.37a). This effect was even intensified on the foundation
piles when integrating the cage models (Fig. 11.37b–d). Additionally, we found
that rigid constructions would lead to a static fatigue of the connection devices
between the cage and the piles due to the constraining force resulting from the
differential deformation of the piles of the tripile. A solution would be a more
flexible coupling element (e.g. spring bars) as well as a certain clearance between
the different installations to avoid that all three piles at the same time transfer the
forces through their vibration on the cage (Figs. 11.37e–g and 11.38c, d).
11.4.4 Supporting Devices
11.4.4.1 Offshore Seed Collector and Grow-Out Devices
In order to find suitable offshore locations, where the biological background conditions were suitable for both wind and aquaculture farms, in Project No. 2 “Open
Ocean Aquaculture” and 3 “Roter Sand” a number of offshore wind farm sites
within the German Bight were surveyed in 2002. Subsequently, nine locations
10–40 nautical miles off the German North Sea coast were selected for further
investigation (Fig. 11.7a). Site criteria for this survey were the vicinity to a planned
wind farm, the distance from the coast, the water depth, the water quality, and the
substratum. In January 2003, the selected offshore locations were equipped with test
moorings to investigate the potential of offshore seaweed, mussel and oyster
farming. For this purpose an offshore seed collector as well as grow out device for
extractive species was developed (Fig. 11.39a, b).
The mooring’s marker buoy had a buoyancy of 300 kg and was connected to a 2
ton concrete block with a 22 mm steel wire and a heavy buoy chain (Fig. 11.39a).
At 3 m below the surface a 1 x 1 m metal frame was fixed to the wire, providing a
holding unit for two spat collectors clamped into the frame. The depth was chosen
because of multi-annual data (Walter and Liebezeit 2001; Joschko et al. 2008) indicating little settlement in depths < 4 m. Each collector consisted of a polypropylene
carrier rope (10 mm) with four inserted transverse elements to enlarge the surface
area. The elements were made of 15 cm long pieces of the same polypropylene rope,
which were frayed manually in 1100 single fibres to produce a bow-tie-like bundle.
This type of collector is equivalent to the type used by Tortell (1976) and Dare et al.
(1983) and has proven successful in its ability to attract mussel spat in tens of thousands of individuals per meter (Walter and Liebezeit 2003). Once a month if possible
(February, March, April, May, July, September), samples were collected on a 5-day
cruise using the research vessels RV Heincke, RV Uthörn, and RB Remzy. All
11 The German Case Study: Pioneer Projects of Aquaculture …
317
integrate the new cage designs. After the first experiments were conducted in the
wave flume of the Ludwig-Franzius-Institute for Hydraulic, Estuarine and Coastal
Engineering we identified that the piles could under extreme conditions tend to
local vibrations (Fig. 11.37a). This effect was even intensified on the foundation
piles when integrating the cage models (Fig. 11.37b–d). Additionally, we found
that rigid constructions would lead to a static fatigue of the connection devices
between the cage and the piles due to the constraining force resulting from the
differential deformation of the piles of the tripile. A solution would be a more
flexible coupling element (e.g. spring bars) as well as a certain clearance between
the different installations to avoid that all three piles at the same time transfer the
forces through their vibration on the cage (Figs. 11.37e–g and 11.38c, d).
11.4.4 Supporting Devices
11.4.4.1 Offshore Seed Collector and Grow-Out Devices
In order to find suitable offshore locations, where the biological background conditions were suitable for both wind and aquaculture farms, in Project No. 2 “Open
Ocean Aquaculture” and 3 “Roter Sand” a number of offshore wind farm sites
within the German Bight were surveyed in 2002. Subsequently, nine locations
10–40 nautical miles off the German North Sea coast were selected for further
investigation (Fig. 11.7a). Site criteria for this survey were the vicinity to a planned
wind farm, the distance from the coast, the water depth, the water quality, and the
substratum. In January 2003, the selected offshore locations were equipped with test
moorings to investigate the potential of offshore seaweed, mussel and oyster
farming. For this purpose an offshore seed collector as well as grow out device for
extractive species was developed (Fig. 11.39a, b).
The mooring’s marker buoy had a buoyancy of 300 kg and was connected to a 2
ton concrete block with a 22 mm steel wire and a heavy buoy chain (Fig. 11.39a).
At 3 m below the surface a 1 x 1 m metal frame was fixed to the wire, providing a
holding unit for two spat collectors clamped into the frame. The depth was chosen
because of multi-annual data (Walter and Liebezeit 2001; Joschko et al. 2008) indicating little settlement in depths < 4 m. Each collector consisted of a polypropylene
carrier rope (10 mm) with four inserted transverse elements to enlarge the surface
area. The elements were made of 15 cm long pieces of the same polypropylene rope,
which were frayed manually in 1100 single fibres to produce a bow-tie-like bundle.
This type of collector is equivalent to the type used by Tortell (1976) and Dare et al.
(1983) and has proven successful in its ability to attract mussel spat in tens of thousands of individuals per meter (Walter and Liebezeit 2003). Once a month if possible
(February, March, April, May, July, September), samples were collected on a 5-day
cruise using the research vessels RV Heincke, RV Uthörn, and RB Remzy. All
11 The German Case Study: Pioneer Projects of Aquaculture …
317