Abstract
Abstract There is an increasing interest in cultivation of seaweed, and in the process of developing a seaweed industry, new knowledge on e.g. farming methods and technology is needed to facilitate sustainable seaweed farming. Ono piece of this puzzle involves establishing knowledge on loads and movements of seaweed cultivation lines (ropes with seedlings), which is addressed in this paper. It is important to establish knowledge based on studies of kelp grown at sea. Both to learn about kelp properties and behaviour in its natural environment, and to provide data for validation of laboratory tests. A test set-up for in-field measurements and methods for data processing was established and tested. To monitor loads and movements, load shackles and depth sensors were installed on kelp cultivation lines (grow lines) at an IMTA-farm for salmon and sugar kelp farming. Registered data from these sensors and measurements of water currents have been analysed, and it was found that both grow-line positions, drag loads acting on the seaweed, and gravity loads and kelp biomass may be estimated. A maximum tensile load of 30 kg was measured for a 40 m long cultivation line, probably as a response to a current velocity between 0.1-0.2 m/s normal to the kelp line. The vertical position of the kelp lines varied significantly between a line sag of −0.5 m and 2 m. Gravity loads were found to be very low, and the material density of the cultivation line, consisting of a nylon rope and sugar kelp, were found to be close to seawater.