Mercury - Pitot/Speed Sensor Kit 100 PSI SmartCraft Speed Input 881879A2. Overview. A steady, accurate water-pressure speed signal makes your SmartCraft display far more reliable at lower and midrange speeds. The Mercury 881879A2 Pitot/Speed Sensor Kit is built for boats that run under 80 mph and need a clean SmartCraft speed input without depending on paddle wheels or GPS. It mounts either on the MerCruiser sterndrive transom bracket or directly on the hull near the engine, giving you flexibili