Mounting a pedestal to Xpress floor

I need some advice on the best way to mount a dome shaped 6 hole pedestal to the floor of my 22' Xpress CC. I already tried mounting seats to each side of the captians bench on the back deck. They sat on top of the 2 compartments and were not stable. I need to be able to mount the pedestals to the floor on either side of the CC for passengers to sit going to the fishing hole. The boat came with no passenger seats. I called Xpress and a guy told me that there are ribs that run crossways across the floor but you can't tell the location of them. I figure my best bet is to center the base on a rib if I could find them. You obviously can't use bolts and nuts on the floor. I plan on using rivets but am worried the aluminum floor won't hold up. Anybody have any ideas. They sure would be appreciated.

How thick is your aluminum deck? How is it fastened to the framing? What is the finish on your deck, carpet, vinyl, paint?

The aluminum on the floor is .100". There is no carpet. I believe just some sort of non-skid paint over it. The manufacture told me the ribs that run crossways are 3" wide and welded to the bottom of the floor. After they build the floor they drill holes in it and fill it with foam. He said one concern might be over time the floor might pull away from the foam where the base is mounted and would cause it to make a cracking sound as you walk over it.

Ok, I was going to suggest a backing plate if you could get to the underside of the deck but it doesn't sound like that's going to happen.

You may want to consider Rivnuts instead of rivets, they come in a larger diameter and have more holding power.

https://www.aimfasteners.com/about_rivnut.html

Here's a vid on how they work:

https://www.youtube.com/watch?v=dkPhGIaPCVs

Where can you get the rivnuts and would anyone know of a way of finding the ribs under the floor?

thecrusher said:

Where can you get the rivnuts and would anyone know of a way of finding the ribs under the floor?

Click to expand...

I buy a lot of rivets from these folks and they sell Rivet nuts:

https://www.rivetsonline.com/rivet-nuts-and-threaded-inserts/k-series-ribbed-rivet-nuts.html

As far as finding your ribs, the ol' tapping on the deck with your knuckles to find the solid sounding spot is about the only thing I can think of right off hand... or maybe contact the manufacturer for a drawing of the framing plan for the ribs in your boat.

... but if your installation goes anything like my various projects you'll find them by accident when you drills holes for the mounting fasteners.

Have you tried using a studfinder to locate the ribs i use them daily and have had greatit success with many materials besides wood

Good idea. I will try that. I wasn't sure if the studfinder would pick up through an aluminum floor.

thecrusher said:

Good idea. I will try that. I wasn't sure if the studfinder would pick up through an aluminum floor.

Click to expand...

All the stud finders I've ever used are operated with a magnet, they don't find the wood... they find the nails in the wood.

Magnets don't work on aluminum.

I have a newer model stud finder that works on electronics rather than magnets and believe I have marked the ribs. However I think I am going to install an aluminum plate between the base and the floor and fasten through both layers. I am hoping this will provide enough support.

This is what I ended up doing. Used big rivets and first mounted a 1/4" aluminum plate with rivets to floor. Then mounted the base with rivets through the plate and floor. It is solid as a rock. Problem solved.

Nicely done. Congrats on a good installation.