Abstract: A blade of a built-up marine propeller is balanced by forming an open cavity of a predetermined size at a predetermined location proximate to the blade tip, conducting a spin-balancing test in which the blade being balanced and a calibration blade are assembled diametrically opposite each other on a dummy hub to form a simulated two-blade propeller, determining from the test the weight that must be added to the blade to balance the simulated propeller, and affixing a balance member of a predetermined weight in the blade cavity. A cover plate is secured in the cavity opening of the blade in sealed relation, and the external surface of the cover plate is ground to make it fair to the profile of the portion of the blade face adjacent the cavity opening.