Re: Mounting a pedestal seat on aluminum floor
The specifics depend on your particular aluminum floor. But the issues remain the same for installing something like a seat pedestal that is going to exert a lot of force on the floor. Most AL floor sections are hollow. The sheets that comprise the floor top and bottom are thin. Countersinking into thin sheets is going to leave little support under the cap screw head. Also, bolting a seat base to the middle of the floor section is going to flex that section under side loads. It is possible to have cap screws and washers under the floor that are covered so they don't wear the underlying material, but I tried something a little different.
On my Zodiac I removed the side caps from the flooring and accessed the hollow floor sections. On some boats these are much smaller sections, but it is still possible to install backing plates. The backing plates only go a few inches in. As you can see in my examples I used a top plate to span the floor for attaching my ski pole. The top plate bolts to the backing plates, which extend all of the way out to the edge of the floor under the cap rails. This effectively extends the assembly so it is captured by the side rails, transferring the stress to the strongest part of the floor.
For my seat bench I skipped the cross top plate and just bolted right into the backing plates in the floor. How crazy you have to get depends on how much you blast around. My rail mounted zodiac bench seats rocked and wore the track. The backing plate installs have been abused for years and haven't moved or deformed the AL floor. The pole mount is very secure and I now have my custom gas tank and battery installed on a top plate installed under my front console bench. Rock solid. Just one way of doing it.
Don't underestimate the leverage a pedestal seat exerts! Good luck.
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