The usage of anchorage in your example is incorrect. My parents are not interchangeable between anchorage and anchoring. Is the word anchorage acceptable? One is action, the other a place.

anchorage aNGk()rij noun

1. an area suitable for a ship to anchor in.
2. ( historical ) an anchorite’s dwelling place ( reprinted ; this time referenced somewhere between 400 and 500 bc)

If a boat becomes anchored under a harbor, how

: Local waves within the harbor make the area difficult, if not impossible.

What is incomplete sentence on Wikipedia?

Local waves within the harbor make anchoring|fishing|swimming difficult, if not impossible.

An action can be made harder, but not a place/location.