its totally possible to build a completly safe harbor. monsters only go for boats they have a line of sight towards.

you can either dig inland to reduce the waves or find a natural inland bay to start working on for it.

https://steamuserimages-a.akamaihd.net/ugc/2023848732779197312/E5B5EDB317E9568914C7B340F1C3C2F46383E577/?imw=5000&imh=5000&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false