plunging device and the resulting perpendicular oscillation of the paddle blade will generate wave action whereas the upstroke of the plunging device is powered the force for the downstroke is delivered by the plunger 39 s own weight plus the ballast weight and it is characteristic for the invention that the suspension means here including a wire line sling will remain in tension at all times for efficient wave generation and power use it is important that the ballast is large enough to effect a rapid down stroke and that the total weight of the plunging device including the ballast is balanced by the counterweight 32 the location of the ballast 26 well below the paddle blade tends to reduce undesirable pendulum motion of the plunging device by lowering its centre of gravity and reduced water particle motion at depth allows the ballast body to act as a stabilizing vane with several wave machines operating side by side in close proximity adjacent plungers having motions not in phase with each other would receive uneven drag forces and superimposed erratic motions by installing partition structures 56 as back board projections between plungers mutual interference between plungers can be avoided in the arrangement shown on fig2 a cutaway portion of a partition structure 56 has been shown to include a brace member 58 fig3 shows in perpendicular section the relative position of a plunging device 11 the back board structure.