illustrated the tide is incoming each unit of the invention further comprises on the main frame 25 a plurality such as four equidistantly spaced sub frames 35 each having an upper bar 36 and a lower bar or arm 37 the bars 36 and 37 are rigidly connected by a gear rack 38 and the two bars are slidably mounted by bearings 39 on a pair of parallel guide posts 40 of each main frame 25 the tops and bottoms of the posts 40 are rigidly secured to the main frame bars 22 and 23 a rotary gear 41 on a bracket 42 fixed to one post 40 of the main frame is in constant mesh with the adjacent gear rack 38 of each movable sub frame 35 the gears 41 on the main frame 25 are driven by the reciprocating linear movements of the sub frames 35 under influence of floats 43 carried by yokes 44 secured to rotatable shafts 45 journaled in bearings 46 on the arms or bars 36 and 37 the floats 43 of each unit assembly of the invention are elongated as illustrated and have rounded ends 46 and flat bottom faces 47 the attitudes of the.