I grew up in Richmond Hill and in the 50's and the 60's we used to go to Rockaway Beach and watch the Fourth of July fireworks show fired off of a towed barge just off the beach. Probably the best fireworks show I ever saw and ruined me I guess for future shows. One year, I can't remember when the barge blew up, scared the hell out of me but best show ever, probably the early 60's.
Maybe you're finding remnants of that barge? Maybe you're finding parts of a washed out boardwalk?