[asheshouse]

It would also be cool to be able to get river boats and patrol boats up river but i think this might be something to do with the maps???

This is controlled by a combination of ed_map_t.tga and map_c
The edge of water areas on map_c normally has a greyscale transition from black to white.
Somewhere in the greyscale range you create a barrier to ship movement.
I have not experimented much with this so am not sure where the limit is.

ed_map_t.tga also segregates ship and vehicle movement, useful for preventing vehicles crossing shallow water (greyscale) areas.

If a river is wide enough ships can navigate it but on narrow (normal width) rivers it seems to be not possible because the shallow water margins meet in the middle.

I improved the extent of navigation in the Scheldt Estuary by introducing ed_map_t.tga