Silly question .... But

[S/V Alchemy]

That is the access plate to a Whale Gusher manual bilge pump. If the diaphragm isn't completely rotted, you'll be able to put the black knobbed handle you should find in the closest locker into it, and given 20 or so pumps to prime. Then the contents of your bilge, if it's not full of paint chips, paper and hair, should spurt into the sea.

You can still buy replacement parts. And should.