A computational procedure for the hydrodynamicanalysis and design of horizontal-axis tidal turbinesis presented and numerical applications are discussed. Themethodology combines an original design algorithm and aturbine hydrodynamics model valid for arbitrary 3D flows.Different from standard design methods based on bladeelement models, 3D-flow corrections are not necessary.Blade geometry parameters are determined with the objectiveto maximize power at given design Tip Speed Ratio(TSR), whereas a constraint is introduced in order to limitturbine thrust at TSR higher than the design condition.Numerical applications include the design of a laboratoryscaleturbine and a full-scale turbine for the exploitationof tidal streams in the Messina strait. Alternative designsolutions obtained by varying the design TSR are comparedin terms of energy output as well as mechanical loadstransferred to the powertrain.