Yes, technically an RRU is required for an inboard installation. If the boat is small, nothing keeps you from lying to the system and tell it is an outboard and giving it a try, to see if you like it without. The pilot will always work better with an RRU and at speeds lower than 3 knots, because the system really needs that RRU to know where the rudder is. Unlike outboard RRU units that get broken a lot, the inboards are rock solid and add a lot to the pilot performance. If it were my inboard boat, I would get the right inboard package with the RRU.