Go under the deck of the boat and locate the area where the seat will be bolted. Do not bolt the seat to any place that is in close proximity to the boat's fuel tank.
Screw in a piece of plywood underneath the deck where the pedestal seat plate will be placed. This spreads the weight of the seat out over more surface area.
Drill out four holes that match the size of the mounting bracket's bolts. From under the deck, twist the four bolts into the holes. The bolt thread will be facing up.
Place the seat plate onto the four bolts that are sticking up. Tighten the nut for each bolt to secure the seat plate.
Place the pedestal into the large center hole on the seat plate.