I used a chair for this example;
Here on the banks with the boat and the chair;

Now in the boat, at this point you pick up the item that is resting on the banks, just before the water;

Here's me holding the item in my hands in the water;

And some sailing around for different angles;


This looks like it's been shopped, but it's in the game, and can be used to carry anything you can carry normally. Plus, it looks really weird. I'm not sure you're supposed to be able to do this.