Shipyards production rules are only needed if you are using the "shipyards" tech AND have the shipyards game option ON.
only "production" (a single production frontier) is needed for most maps. if you use ww2v2 tech then you need IndustrialTechnology production, and if you use ww2v3 tech you need Shipyards
(removes all sea units from "production" and adds "Shipyards" production rules. Only currently works when all players use a production frontier called "production"