I had a 14ft Grumman that the former owner used for crabbing, he had those stainless slotted holders all over the boat, some had single rod tubes, a few had triple rod tubes and there was also a buoy holder that slid into them, all with the same wedge shaped base to fit those brackets.
I removed them after the first few trips because they would get caught on things at the worst times and the rod holders were sharp and always in the way. Mine were mounted on the inside rear edge of the splash well and all around the gunwales on the sides. They weren't cheap to buy, at least not the good American made version, but having lots of sharp edged metal brackets around where you fishing was just not a good idea. I removed them from my boat and a buddy grabbed them for his 20ft fiberglass boat and thought they were great.
The round black things look like maybe a base for or mount for something, possible to hold up a tarp, or hold something in place?
They look familiar, I seem to remember one boat I had coming with a pair of those on the inner sides of the gunwales. I didn't have a use for them so I didn't put them back after rebuilding the deck and interior.
I also had a cooler that came with one boat I bought about 20 years ago, the cooler was similar to a Yeti but it had what looked like cup holders on the bottom, two rows of three, each pair equally spaced. I just figured it was part of the structure for some reason. Then I found what looked like hollow hockey pucks with a bag of screws in one of the storage compartments. Turns out the hockey pucks were supposed to be secured to the deck to locate and secure the cooler. Figuring the discs would be a trip hazard and like the last owner, never mounted them.
