IMO needing a rudder up to 17ft isn't about length it's about volume and rail shape. There is no problem steering a board without a rudder if you can carve. But most current UL boards have rails that are so chunky that this is not possible. You are just a passenger on a boat. So a rudder is of benefit - at least in some conditions. There are some DW conditions (big, steep, messy short period) where you'll be always right on the tail when on a bump so a rudder isn't much help: it's either foot steer or not steer. But I realise that you guys probably won't accept this, because you've only ever tried thick-railed high-volume UL boards so you know no different, and you DW in conditions where you can steer on a bump from towards the middle of the board without pearling.