At a very popular snorkel spot called Cemetary Beach on Seven Mile Beach, there evidently was a large boat wreck a long time ago. These are pics of stuff on the bottom there.
Click pics to enlarge
A gearshaft in the lower center, and a big wheel in the upper left. Boat engine parts.
I don’t know what this is, a piston rod from a really big piston? My Navy ship had a big wrench bolted to the side on the outside, used in the drydock to take the propellers off. This doesn’t look like a wrench though.
A V-6 Engine block (This probably was dumped on purpose as somebody’s mooring anchor)