Final answer:
Boats inside the harbor are most protected against wave action at angles where the waves have spread out post-diffraction, but specific protection angles cannot be provided without more data.
Step-by-step explanation:
Understanding the relationship between wave action and harbor safety involves applying principles of wave diffraction, which is part of physics. When ocean waves of a 20.0-meter wavelength approach a 50.0-meter-wide opening in a rock barrier straight on, diffraction occurs. Diffraction is the bending of waves around the edges of an obstacle or through an opening, which causes the waves to spread out. The boats inside the harbor are most protected from wave action at angles where the waves have spread out and reduced in intensity due to diffraction.
However, the question seems to be missing the necessary data to provide a specific angle of protection. Without details on the angles at which the boats are positioned relative to the incoming waves, or additional data pertaining to the geometry of the harbor, it is not possible to give an exact answer. In a general sense, boats would be most protected in locations where the diffracted waves have the least direct impact.
For example, on a moderately steep beach slope, when a wave approaches the shore, it will curl over and spill onto the beach instead of crashing forcefully. This type of breaker is common on beaches with gentle slopes, such as many beaches in the Caribbean.