Jiaji Li has succeeded in building a prototype Robotic Rowboat. I have used 3D printing technology ever since it was introduced decades ago to build spatial mechanisms and routinely failed, which is why this is a particularly satisfying outcome.
He convinced me to buy an inexpensive 3D printer and said he was sure PLA (poly lactic acid) would provide a strong but light-weight product. So I gave it a chance and find the result to be very nice.
Please take a look: Robotic Rowboat