Yeah, many have tried this devious method to circumvent the limited storage available on any given boat. My friend even build a plank out over the boat, crafted a chest on the plank, then broke the plank... no dice.

There is hope for you though my friend. You can fill a cart, drag it onto the boat then break the cart. the storage containers once confined within the cart will spill out onto the deck of the boat and NOT fall through.

Unless they have recently patched this out. Best to try it with something of little value in the cart the first go as a test.

EDIT: you can also take tame animals on a boat. First hand success with Wolves and Lox. A friend said he transported a pig, but i didn't see that , and it's seems suss