The story appears to be romance miss-classified as fantasy. Readers aren't allowed to discover the world for themselves, and the world-building is inconsistent that readers go off in the weeds when attempting to engage in discovery. What is the reader to make of lighthouse so poorly located and designed that a storm will wash it away? Or an iron ladder which hasn't rusted. I can get past one or two minor oversights, but this story is weighed down with both unnecessary explanations and with errors which contradict the explanations. If a society could organize to build a lighthouse out of granite, surely they could move rip rap in place to protect the installation. If the lighthouse is hundreds of years old, why hasn't that iron ladder rusted?
If they hero observes the tides why has he never mentioned the phases of the moon? The story starts near the start of winter. Does that mean nearly solstice(December) or nearly Samhain(October)? An opportunity for showing the calendar has been misses. I suspect that a calendar for the world has never been considered. I quit reading after one chapter because I expected the remainder of the book to be as poorly thought out as the lighthouse engineering.