If your having a problem mounting a seat to your boat because of too thin of aluminum in the existing seat and worried about the bolts or screw not holding, this is a idea to try.
This is a little trick I leaned a few years ago was to use a piece of ¾” plywood about 12” square and cut a hole in the middle big enough for your hand to go into and have some movement. Lay this piece on the seat where you want to mount the seat and trace the inside of the hole onto the boat seat. Then cut the same size hole on the seat. Lay the plywood on top and drill out the mounting holes around the edges with a ¼” drill bit. Use ¼” bolts long enough to go thru the plywood and the seat. Run your hand inside the seat and use big flat fender washers and lock washers and then the nuts to secure the plywood down to the boat seat. I used 3 bolts on each side spaced out properly. Then mount your seat bracket on top of the plywood by drilling the proper size pilot hole for a ¼” hex head lag bolt thru the plywood and the boat seat. The pilot hole for the lag screws should be less than the ¼” lag screw. The lag screws have a hex head for using with a socket and ratchet and are also self tapping. It worked for me.
See pics and drawing for seat bracket. Pic show the difference between a small regular size washer and a bigger fender washer and also a lag screw with the hex head.
