I like that.
In essence you would have two different types of navigation.
If you own a chart for the area, be it bought or made by yourself, you just travel via minimap, no hassle, no need to actually produce charts for the game, no discouraging those who don't like navigation.
If you don't own any charts you travel by navigation, thereby producing a chart which means you don't have to do it the second time you travel these waters and you could sell it. Also it is a valuable ressource, so if your ship ends up as a prize it could maybe be a nice commodity for your captor. And you should not be able to sell it to other nationals. Let each nation find their own ways through the carribean.