a plastic rotationally molded polyethylene buoyancy tank for boat lifts allows connection of steel to lengthwise grooves molded into each side of the buoyancy tank . preferably , a plastic bulkhead is formed within the tank during its molding process . a segment of framing steel is bracketed between a pair of inwardly tapered compressible opposed grips . the compressible grips each have outwardly tapered slots with mating tapered rigid inserts . with the inserts partially seated on the grips , the grips are slipped lengthwise or pressed laterally into their respective grooves . bolts extending through the grips into threaded holes in the inserts are tightened to pull the grips over their tapered inserts . this spreads and compresses the grips in their respective grooves , locking the brackets and connecting steel in place on top of the tanks .