Counter people who gives up land and plays sea only?

Twice now in a very short time have I met people that give up their TC and build one on the shore, and all their buildings along the shore, just to build war ships to cover them.

The first time I tried to build culverins as they have decent range and are anti-ship. He simply shot them down. So this time I thought I would try mortars and simply take down the buildings, but everytime he shot them down and I have no idea how, he said they were always in visible range, even tho I went for the buildings closest to the mortars. I even sent my army in first so that the mortars could shoot from their absolutely longest range.

It's impossible to beat their economy and the first time I also tried to destroy the buildings with cavalry. But apparently war ships + dragoons are a deadly combination. I got slaughtered.

This just feels like a cheese tactic that demands no skill from my opponent at all, and they still crush me. What can I do?