Wave energy conversion systems (WECS) with internal power take-off mechanisms using internal inertias as well as WECS using a submerged water head for driving a turbine at a steady rate. The WECS involving internal inertias is effected through relative oscillation between masses inside the hull of watercraft excited by wave motion and whereby the masses' oscillations are captured by actuators (e.g., hydraulic) that pressurize a fluid or generate electricity. Different relative oscillation mechanisms are disclosed herein. The WECS involving a submerged water head involve the use of asymmetric floats, arranged in a circular orientation for omni-directional wave energy capturing, that drive respective pistons that pressurize the water head and drive the turbine. Alternatively, the use of articulating raft/barges or floats coupled via a lever arm can be used instead of the asymmetric floats for pressurizing the water head.