My dad owns a fishing boat so we used to go offshore fishing very often when I was younger, I have a few not so creepy stories.
First one was on our trip in the Florida keys, we were maybe 30 miles offshore, no land or other vessels in sight. We were hauling a** away from some a quickly approaching storm cloud when I saw a funnel cloud appear. It was kind of eerie being an 8 year old and seeing this s**t a few thousand feet behind you, knowing that if it got close enough to us and we didn't make it, no one would ever know for a long time and there's nothing we can do about it.
Another time, when I was about ten, we were trolling for fish 40miles or so off the coast of bimini (bahamas) and this large lump floated within a few feet of our boat. It was a dead sea turtle, a pretty big one too. We gaffed it, flipped it over in the water, and there was a huge baseball sized hole through its underside, and it went all the way through its body until it reached its shell area. It was like a neat cylinder had been carved out of its body, and it looked flat black. I don't know if it was just rotting, but it almost looked charred. Turtle also had numerous hooks and cut lines coming out of its mouth, which is pretty normal for dead ones. We set it loose, still no idea what happened to it.
This last story I thought I had dreamt or something until I asked my dad about it recently and he confirmed it. I was around the same age as my last two stories, and we were offshore fishing for mahi pretty much all day. I don't remember if we were on the gulf side or Atlantic side, but the water was seriously deep and blue. We must have been many miles offshore and looking at the sonar I remember it being much deeper than 2000 feet. Anyway, about midday, bored 10 year old me was sitting on the roof of our center console, and I see this dark shape about 20 feet under the surface. It was seriously huge and definitely not a whale or anything. It was man-made, a gigantic a** submarine, and it was RIGHT next to our boat. Like 20 feet away. It stayed next to us for about 60 seconds, then submerged slowly and went on its way. It was so creepy seeing it out in the middle of absolutely nowhere, and knowing that there were people right inside of it.