you ARE navalmaxxing, right?
>harbor capacity scales up to -75% control cost reduction and you can get like 30 free harbor capacity early with wharf, dock, and protected harbor
>add in infrastructure like bridge and canal, you're probably hitting 99% cost reduction now with ruler adm and development
>all this makes moving from port to sea is literally free, the harbors are also exerting maritime presence which makes moving from ocean tile to ocean tile cheap if you build some light ships to patrol and increase maritime presence even more