Mercury debuted JPI aboard Sea Ray's SLX-W 230, and I trialed the system recently at DuSable Harbor on the Chicago lakefront. Sea Ray pitches the SLX-W to families anxious to join the wakesurfing craze. Its inboard prop is buried safely under the hull, but the nonsteerable prop also makes it less agile at low speeds than the same boat with a sterndrive. For $10,000 added to the boat's $107,000 base price, the issue is solved by JPI. My demo boat was powered by a 370 hp MerCruiser 6.2L ECT TowSport engine, but JPI can be rigged with any MerCruiser gas or diesel inboard that is equipped with DTS (Digital Throttle and Shift). Vetus 25-kilogram-force thrusters were mounted at the bow and transom, but a boatbuilder could also opt for Side-Power thrusters. Everything is tied together with the brainpower of Mercury SmartCraft, which coordinates controls through a joystick mounted on the Sea Ray above the throttle. Dockside, I was able to rotate the boat within its length, draw straight abeam to the dock, or crab the boat on any heading. The thrusters proved typically noisy, and there is also no modulation of the thrusters' power; they are either on or off. This requires anticipation in close maneuvers, but I quickly got the hang of it.