Possibly the most interesting concept from this whole thing that I never grasped.
The reason waves like Padang/Restaurants etc only work on long period swells is due to the depth of the circles of energy (eg 17s swell reaches down ~250m/1000ft in image below), and it is some combination of swell direction and that depth that starts to drag on the bottom, slowing that part of the wave down and bending it in and around the sheltered Padang headland. If the swell doesn’t have the “depth” then it will not start the bend early enough wrap the corner, and run straight past. This is somewhat obvious but I have not found a satisfying image that demonstrates this 3d interaction! Surfline has excellent stuff here:
Surfline explanation and the very detailed explanation:
Now, let’s take a closer look. Raised off the seafloor is an even shallower seamount located about four-five miles to the southwest of the peninsula, with a depth of roughly 130 feet. This will focus swells as they near the peninsula, and the longer the period, the greater the focusing affect will be. Moving closer to shore, the waves turn further to the east and ultimately converge in the area near the end of the peninsula.
Two other links (this forming a working note-pad)
Good explanation of different wave period swells interacting
Explanation on why bathymetry matters for wave energy
