Minecraft wiki entry for Drowned_farming, associated text: To bypass the mob cap and dramatically increase the production rate, you can have the drowned be swept into a Nether portal, so the drowned disappear from the Overworld and drop onto a killing platform in the Nether. This works fine if you are the only player in the world, but if there are other players in the Nether, they need to be within the despawning radius of the killing platform to prevent the drowned from despawning in the Nether.