I remember 30ish years ago seeing a design for a boat powered by wave action.
It was a trimaran, and the amas (outriggers) were not mounted solidly to the center hull. Instead there was a pivot that allowed some flex, and a "shock absorber" that was actually a hydraulic pump piston.
The wave action "flexed" the line through the three hulls, pumping hydraulic fluid, which then powered a hydraulic motor driving the prop.
You can transfer a hysterical amount of power through a tiny hydraulic pump/motor system, and there is enormous energy in the waves.
Seems to me a raft built on the same principles, anchored just offshore, could both pull most of the power from the waves and attenuate the waves to create a calmer area between it and shore. Something like a seawall outside an inland passage, but doubling as an alternative energy source and thus twice as useful.