Sea shipping is the most fuel efficient form of transportation that we currently have. Energy-wise, land biking is more efficient, but you can only comfortably transport about 50-100 kg max per person cycling in a trailer or cargo bike.

What about pedalos hauling a cargo boat? Horses used to pull them on waterways. How energy efficient would it be? How much could you haul while maintaining the standard waterway speed of <10 km/h?