CONTAINMENT SPECIAL
TOP TIPS PENS: top tips By Iain Forbes Director, Fusion Marine
n recent years fish farming pens have been installed on sites with progressively higher offshore wave climates, further from land. This has been forced through saturation of sheltered inshore sites, better growth and fish health offshore, and the conflict between scenic and environmental amenity inshore. However, these advantages are attained by only the absolute necessity for much stronger engineering advancements with great focus on safety, security and containment.
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• The pen collar material: There are numerous advantages of plastic pipe construction. They do not suffer from corrosion in sea water. They are also flexible, very strong, and suffer less fatigue than steel structures. There is some evidence to suggest that plastics which have been stressed by repeated bending will, if given a period without stress, recover their original properties
• The triple ring pen collar: The main advantage of the triple ring floatation collar, as opposed to the two ring configuration, are its inherent strength and built- in redundancy. The third ring is vital to stock security and containment and is highly recommended when considering the suitability of the equipment required to withstand tough environmental conditions.
• Site choice: Fish farm companies will spend many years planning, getting concessions, environmental permissions and finance for a fish farm, thus the choice of site location is very important to optimise investment. Classification of sites is also vital during these assessments. A site should be classified according to the offshore storm wave climate, its prevailing wave climate and water depth.
• Service boats: Consideration should be given to the berthing of service boats alongside pens. with many pen sites, large boats (such as wellboats, feed barges, etc) may be brought alongside the cages for various operations. The windage and tonnage of such boats, even in relatively light weather, may overload the cages and their moorings. Operational procedures MUST be put in place, so that wellboats and other large vessels cannot berth in conditions likely to compromise the integrity of the pen system and its moorings.
• Pen nets: These generate huge loads on the cage collar during heavy wave motion. The strongest components of force are usually in the vertical direction. If the collar buoyancy causes the collar to be accelerated violently upwards, as a wave crest approaches, the vertical heave loadings on the nets and the net attachment points are very high. It is for this reason that the principle net loads must be carried on the pen collar, and not on the collar stanchions.
• Addition of retrofit components: Whenever the fish farmer adds components to a system, after installation, these components will add to the maximum design loads
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on the system. For this reason, the fish farmer must notify the supplier of the equipment, so that these extra loads can be taken into account. This may require extra moorings, or cage bridles, or some other solution, to restore the system to its original level of security.
• Operations involving nets: Whenever the fish farmer makes a temporary or permanent change to the rigging of a net - eg to shorten nets for grading - it is vital that the nets are properly re-secured, so that the loads are carried solely on the main collar pipes and not on the handrails, or any other cleats and fittings. With regard to the number of net attachments, and other rigging matters, the fish farmer should be guided by the net manufacturer’s recommendations.
• Compatibility: Moorings and nets influence loading; this is crucial when determining the compatibility of equipment. Correct information and compatibility of engineering will future proof your investment, increase lifespan and even reduce maintenance. Pen and net survival cannot be taken out of context from the environmental conditions of wind, waves and currents on specific sites.
• Maintenance records: It is important to record, log and file all maintenance records. All inspections must be recorded on suitable pre-printed forms, so that information collected can be filed sequentially, rates of deterioration can be assessed, and so that past records show which components were inspected, and what the results were. In addition these records can provide the basis for insurance and warranty, and for determining any remedial work required. It is therefore vital that all data collected be ACCURATELY reported and recorded, together with exact LOCATION IDENTIFICATION, so that future repair work can be quickly located without the need for further inspection. A general diagram of a component identification scheme is recommended.
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