The present invention provides a practical and economical means of growing of kelp and other types of macroalgae in large quantities on and in the ocean. Through the use of catenary principles and innovative structural designs, efficient designs emerge that translate into lightweight and low-cost components. The novel design described allows cost-efficient macroalgae farming at scales and at depths unsuitable for present macroalgae farming techniques. The device and methods described present a means of farming these seaweeds for the purpose of providing food, chemical feed stocks, and a biomass suitable for the production of biofuels.