"What are these blue, large (about 2m), heavy steel objects with chains and ropes attached that look as if they’re put under water (seen in a harbor)?"
A: "Those look like trawl doors aka otter boards. There’s 2 of them attached to the opening of a large fishing net to hold it open while it trawls."
They found many new uses.
#10 at first glance they looked like vacuum packed bats!
Shark eggs look similar to this as well.
This photo is taken in Hvide Sande (white sands) in Denmark
don't care, would have done her upside down, backwards, standing on my head, one arm tied behind my back, fact might have given my left nut for a run at her.