A generator for converting wave motion in a body of water to useful energy, the generator comprising: buoyancy means (1,16) which is movable in response to said wave motion; a subsurface reaction member having adjustable buoyancy and at least two buoyancy configurations, said subsurface reaction member being connected to said buoyancy means and having inertia and/or drag to resist movement of said buoyancy means caused by said wave motion; means for permitting relative movement between said subsurface reaction member and said buoyancy means; energy conversion means for converting said relative movement to said useful energy; and biasing means, such as a spring, for directionally biasing said subsurface reaction member relative to said buoyancy means, the biasing means being partially overcome by the suspended weight of the subsurface reaction member; characterised in that in a minimum buoyancy configuration, the subsurface reaction member is suspended from the buoyancy means by a flexible connecting line at a depth set by the length of the connecting line, and in a maximum buoyancy configuration the subsurface reaction member floats on the surface of said body of water, the subsurface reaction member; (i) being shaped to provide drag to movement along an axis substantially perpendicular to the surface of the body of water; (ii) having a streamlined hull to provide a stable towing arrangement in the maximum buoyancy configuration for towing the generator across the body of water; (iii) having a stable service deck which is provided with a docking arrangement for said float, the docking arrangement being configured to secure said float in a stowed position on the service deck; and (iv) having an interior space that is selectively chargeable with water or air to provide the adjustable buoyancy. buoyancy means (1,16) which is movable in response to said wave motion; a subsurface reaction member having adjustable buoyancy and at least two buoyancy configurations, said subsurface reaction member being connected to said buoyancy means and having inertia and/or drag to resist movement of said buoyancy means caused by said wave motion; means for permitting relative movement between said subsurface reaction member and said buoyancy means; energy conversion means for converting said relative movement to said useful energy; and biasing means, such as a spring, for directionally biasing said subsurface reaction member relative to said buoyancy means, the biasing means being partially overcome by the suspended weight of the subsurface reaction member; characterised in that in a minimum buoyancy configuration, the subsurface reaction member is suspended from the buoyancy means by a flexible connecting line at a depth set by the length of the connecting line, and in a maximum buoyancy configuration the subsurface reaction member floats on the surface of said body of water, the subsurface reaction member; (i) being shaped to provide drag to movement along an axis substantially perpendicular to the surface of the body of water; (ii) having a streamlined hull to provide a stable towing arrangement in the maximum buoyancy configuration for towing the generator across the body of water; (iii) having a stable service deck which is provided with a docking arrangement for said float, the docking arrangement being configured to secure said float in a stowed position on the service deck; and (iv) having an interior space that is selectively chargeable with water or air to provide the adjustable buoyancy. (i) being shaped to provide drag to movement along an axis substantially perpendicular to the surface of the body of water; (ii) having a streamlined hull to provide a stable towing arrangement in the maximum buoyancy configuration for towing the generator across the body of water; (iii) having a stable service deck which is provided with a docking arrangement for said float, the docking arrangement being configured to secure said float in a stowed position on the service deck; and (iv) having an interior space that is selectively chargeable with water or air to provide the adjustable buoyancy.