Nice explanation.

A boat can start surfing once the waterline fits on one face of a wave, so <1/2 wavelength. So a 70m tug just needs a 200m long wave. Mind you, those waves could be 30m tall and breaking over you :-O. So not impossible, but I'm not eager to try it.

https://www.passagemaker.com/lifestyle/freaks-of-nature-rogu...

The wave-glider is much more practical.

https://www.liquid-robotics.com/wave-glider/how-it-works/