These are nesting raft pots for hydroponic gardening. The irregular shape ensures that they move dynamically through the water, the integrated flotation rim provides buoyancy, and the mesh bottom is holds enough hydroton to keep your plants out of the water. 

These are part of a larger indoor aquaponic system I designed and will be posting here over time. 

To achieve long-term seaworthiness, you'll need to print with reasonably thick walls and hot, well-bonded layers.