For the combination of aquaculture fish cages and OWEC structures, the
up-scaled experimental particle velocities at the highest position of the investigated
fish cages are in the range of 1.3 m/s under prototype condition for the maximum
wave height (storm conditions). This range of velocities is potentially harmful to
species candidates to be grown in the North Sea and might negatively affect survival rates and thus reduce economic feasibility of multi-use approaches.
Alternatively, the investigated cage systems could be modified in height (decreased)
and lowered further towards the sea bottom in order to circumvent the critical
particle velocities induced by storm waves. However, volume reduction of the
actual fish cages also minimizes the economic potential of the fish cages as the
amount of fish is decreased.
This alternative design has similar potential to reduce overall forces at the
contact points with the OWEC structure. In addition, as forces grow with the degree
of marine growth, net materials with growth retarding characteristics in combination with optimized maintenance cycles might decrease overall forces as well.
However, the greatest challenge for further testing in prototype conditions are still
the restraints from owners or designers of offshore wind energy parks which reject
any additional (and yet untested) loading stemming from secondary purposes for
safety reasons. Unless legitimate doubts and technological uncertainties are alleviated through further scientific effort, it seems to date still challenging to expect
marine multi-use applications in the near future.
In conclusion, based on differently far developed examples it has been
demonstrated that open ocean aquaculture has reasonable potential for future
growth and prosperity. In future, multi-use is not only a feasible add-on to farming
in open ocean conditions whenever technological or logistical challenges are
resolved thoroughly but it might depict the key innovation towards economically
feasible offshore farming in high energy environments. For example, it might be
beneficial for the aquaculture ventures to rely on pre-existing fixed structures such
as piers, foundations amongst others to attach feeding storage, supply equipment or
instruments. Rather than constructing and installation of dead weight anchors in
rough environments, pre-existing infrastructure is seen advantageous to the
installation of various forms of aquaculture technology including fish cages, mussel
ropes or net pens. In turn, infrastructure owners would be able to generate additional income through leasing out their property to aquaculture.
However, some technological or logistical challenges which have been described
can only be addressed efficiently with the help of stakeholder dialog and proper
incorporation of end-users or operators. A chain of development steps from the very
beginning of a business idea to the final operation of this business incorporates
preliminary design, feasibility studies which involves various modelling steps, a
design phase to plan for a prototype development, and eventually an operational
farm or multi-use deployment which has undergone further optimization steps to
yield its full effectiveness under a wide range of external influences. A number of
approaches to tackle those steps of the development cycle have thus been highlighted in this paper aiming to help additional projects to be launched in the future.
92
N. Goseberg et al.
up-scaled experimental particle velocities at the highest position of the investigated
fish cages are in the range of 1.3 m/s under prototype condition for the maximum
wave height (storm conditions). This range of velocities is potentially harmful to
species candidates to be grown in the North Sea and might negatively affect survival rates and thus reduce economic feasibility of multi-use approaches.
Alternatively, the investigated cage systems could be modified in height (decreased)
and lowered further towards the sea bottom in order to circumvent the critical
particle velocities induced by storm waves. However, volume reduction of the
actual fish cages also minimizes the economic potential of the fish cages as the
amount of fish is decreased.
This alternative design has similar potential to reduce overall forces at the
contact points with the OWEC structure. In addition, as forces grow with the degree
of marine growth, net materials with growth retarding characteristics in combination with optimized maintenance cycles might decrease overall forces as well.
However, the greatest challenge for further testing in prototype conditions are still
the restraints from owners or designers of offshore wind energy parks which reject
any additional (and yet untested) loading stemming from secondary purposes for
safety reasons. Unless legitimate doubts and technological uncertainties are alleviated through further scientific effort, it seems to date still challenging to expect
marine multi-use applications in the near future.
In conclusion, based on differently far developed examples it has been
demonstrated that open ocean aquaculture has reasonable potential for future
growth and prosperity. In future, multi-use is not only a feasible add-on to farming
in open ocean conditions whenever technological or logistical challenges are
resolved thoroughly but it might depict the key innovation towards economically
feasible offshore farming in high energy environments. For example, it might be
beneficial for the aquaculture ventures to rely on pre-existing fixed structures such
as piers, foundations amongst others to attach feeding storage, supply equipment or
instruments. Rather than constructing and installation of dead weight anchors in
rough environments, pre-existing infrastructure is seen advantageous to the
installation of various forms of aquaculture technology including fish cages, mussel
ropes or net pens. In turn, infrastructure owners would be able to generate additional income through leasing out their property to aquaculture.
However, some technological or logistical challenges which have been described
can only be addressed efficiently with the help of stakeholder dialog and proper
incorporation of end-users or operators. A chain of development steps from the very
beginning of a business idea to the final operation of this business incorporates
preliminary design, feasibility studies which involves various modelling steps, a
design phase to plan for a prototype development, and eventually an operational
farm or multi-use deployment which has undergone further optimization steps to
yield its full effectiveness under a wide range of external influences. A number of
approaches to tackle those steps of the development cycle have thus been highlighted in this paper aiming to help additional projects to be launched in the future.
92
N. Goseberg et al.