Joystick Piloting for Inboards (JPI), from Mercury Marine, makes docking easier for boats powered by single or twin inboards. JPI relies on bow and stern thrusters for yaw control and coordinates with the thrust from the prop to achieve the same 360-degree control we’ve come to expect from joystick systems connected to steerable propellers.
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.
JPI also proves helpful when loading on a trailer. Picking up a fallen rider no longer requires making a big turn and bobbing through the wake. With JPI, simply chop the throttle and execute a quick joystick 180 to head back to the swimmer. JPI will also make it easier to hold the boat in place while a boarder gets organized for takeoff.
The Skyhook station-keeping feature of other Merc joystick systems is not available with JPI because, though each thruster has its own battery, the power draw of the thrusters is much greater than the charging capacity of the alternator. Battery life and thermal protection limit thrusters to eight to 10 minutes in continuous use, not enough for practical Skyhook function.
Mercury JPI also only works with a MerCruiser engine. We think JPI adds enough value to the inboard experience that tow-sports boatbuilders aligned with other engine brands may consider either offering MerCruiser power or developing proprietary systems.
