I think the concept also works with displaced water, those hydrophobic surfaces create air containers that make the whole thing lighter. But why so complicated

I think the concept also works with displaced water, those hydrophobic surfaces create air containers that make the whole thing lighter. But why so complicated? A 10cm metal hull seems much safer than a 5mm opening with hydrophobic coating. Also with a chamber system ship's can be made pretty robust and almost unsinkable.