This happened to me when I was digging my ship out once. Didn't make sense to me how the ocean level can drop like that. I understand a lake or a pond water level dropping. Don't know if this is intentional, but I feel like the ocean level should always remain constant. But of course it's early access. Things can always change! I too dug my ship out with a spade like @Dustin Michael, barely got it out! Hope you have better luck in your future adventures but...