I've had the nautical navigation work fine when canoeing on rivers and streams where you're following linear features on the map. What it lacks is the ability to plot a sensible course across a polygon of open water.

Rumor has it that routers have the same issue with highway areas so best practice is to add a "spine" to them

https://wiki.openstreetmap.org/wiki/Key:area:highway#Routers

https://wiki.openstreetmap.org/wiki/Proposal:Area_highway/ma...