A lift for a watercraft has plastic reinforcing brackets which engage in pockets in the thin-walled plastic floatation tanks of the lift and which provide mounting flanges at the top surfaces of the floatation tanks for abutment with mounting pads which connect to the watercraft support frame. The brackets are engaged on the floatation tanks and the pads overlap and are bolted to the plastic brackets, so that the pads are locked against but not bolted to the floatation tanks. Thus, the integrity of the tanks is not compromised by assembly-associated openings through the tank walls. Furthermore, the bolts are above the tank waterlines so that no corrosive material is disposed below the waterlines.