Giant Kelp (Macrocystis pyrifera) is being investigated for large scale production of biomass for food, feed, fuel, and carbon sequestration. This requires a thorough understanding of the hydrodynamics, including properties of both individual kelp organisms and densely spaced groupings of organisms. T he drag (normal and tangential) and added mass of full-scale organisms was evaluated in currents ranging from 0.5 m/s to 5 m/s and oscillations with periods ranging from 3 seconds to 11 seconds. Key variables in the testing included the length of individual fronds , the number of fronds per organism , the spacing between organisms, and the orientation of the aggregate kelp with respect to the current. A full factorial experiment was performed with drag testing at the United States Naval Academy. The kelp models were constructed from synthetic materials to ensure consistency during the test runs. The models were constructed to have the same hydrodynamic properties as live kelp by ensuring that the models ’ blade geometry, net buoyancy, bending stiffness, and surface area were typical of real kelp. The characteristics of Macrocystis pyrifera vary widely between organisms in the same geographical region as well as in various locations around the planet. An extensive review of the literature was conducted to develop characteristics of a “typical” giant kelp organism. T he results are parameterized to allow applicability of these results to a wide range of realistic Macrocystis pyrifera as well as other kelp species. An important goal of this testing was to provide reliable data for representation of Macrocystis pyrifera in numerical models for the design of giant kelp cultivation systems. R esults that are presented include physical characteristics of Macrocystis pyrifera, physical characteristics of the kelp models constructed for this study, load cell data and images from the individual runs. Also presented is a detailed description of the procedures used to determine hydrodynamic characteristics of kelp from the collected data and a summary of the hydrodynamic properties.