Experimental results of tests carried out to investigate the hydrodynamics of marine current turbines are presented The objective is to build an experimental database in order to validate the numerical developments conducted to characterise the flow perturbations induced by marine current turbines For that purpose, we used a tri-bladed horizontal axis turbine The work is dedicated to measuring the behaviour of the system and to characterising the wake generated by the turbine The efficiency of the device is quantified by the measurement of the thrust and the amount of power generated by the rotor for various inflow conditions, whereas the wake is characterised by Laser Doppler Velocimetry Particular attention is paid to the flow characteristic effects on the performance of a 0 70 m diameter turbine The load predictions on the structure and the measured performance of the turbine over its working range of currents and rotational speeds are presented The results showed that this kind of turbine is sensitive to the quality of the incoming flow The turbulence intensity effects on turbine behaviour and on its wake are also characterised in order to study how the far wake decays downstream and to estimate the effect produced in downstream turbines