Ski Boats Take Control

Inboard ski boats are easier to dock than ever, thanks to new rudder and joystick systems.

 MasterCraft DockStar

MasterCraft DockStar

For the uninitiated, docking a direct-drive ski boat can be a humbling experience. What makes it different from sterndrive- or outboard-powered boats is that the prop stays fixed in one direction and relies on a rudder — positioned behind the prop — for directional control. Sterndrives and outboards allow drivers to move the direction of thrust, which allows them far greater flexibility in docking situations.

Virtually all inboard ski boats have a left-hand prop, so in reverse their prop torque will pull to starboard, which is great for pulling up to a dock on the right side of the boat. Just approach the dock at a 45-degree angle and when the bow gets close to the dock, put the boat in neutral, spin the wheel to the right and gently engage reverse, which will suck the stern against the dock and straighten the boat to parallel … if it’s done exactly right. Forget backing in a straight line or pulling up to a portside dock with any semblance of grace.

That has changed. At the 2017 Miami International Boat Show in February, boat builders and an engine manufacturer introduced two new systems that make docking a direct-drive ski boat really easy, even for rookies.

Joystick Piloting for Inboards (JPI)

Mercury has had a decade of joystick experience, starting in 2007 with the Zeus diesel/pod system, followed by Axius for gas sterndrives in 2008. But never has this technology extended to single primary engine operation, until the unveiling of the JPI system. It was first seen on a Sea Ray 230 SLX-W, a wakesurfing-capable watersports boat powered by a MerCruiser 370 hp 6.2L with a V-drive propulsion system. What makes JPI work is a computer system that coordinates the MerCruiser engine with bow and stern thrusters, making virtually any desired maneuver achievable, even walking the boat directly sideways.

The JPI system activates when the boat is put in neutral. A green ring of lights around the joystick activates, to let the driver know the system is engaged. The light show continues when the driver presses the joystick in a direction and the color on that side turns to amber. Twisting it spins the boat in its own length, and the lights rotate in that direction. To switch control back to the boat’s standard control system, put the boat in gear and the lights go off.

Interestingly, the JPI system can use bow and stern thrusters built by Vetus or Side-Power to help it maneuver. While the force provided by the main engine is in proportion to how far one tilts or twists the joystick, the thrusters are on/off only, which makes fine adjustments slightly more difficult. But it works as advertised and has a very short learning curve. Five minutes of practice will have any driver feeling confident making any maneuver, including easing over to downed skiers. One of the only downsides is the $12,500 price tag, which on a smaller boat is proportionally quite a bit.

DockStar

MasterCraft attacked direct-drive boats’ steering problem in a totally different fashion. In forward, the static runner/rudder system on a ski boat works like a champ, as wash from the prop blasts the rudder and provides plenty of force to effect turns. Add tracking fins to eliminate slide, and most ski boats can generate some serious Gs while being cranked hard over. But in reverse, the thrust pushes away from the rudder, making it more of an ornament than a steering device. MasterCraft designers placed two smaller rudders in front of the prop and, voila, drivers now have directional control when the boat’s in reverse. The extra rudders are an adaptation of tugboats’ flanking rudders, which have a similar configuration and have been in use for years, so it’s surprising this clever idea took so long to appear on recreational boats. Even paddleboats in Mark Twain’s era had rudders in front of the wheel for use when reversing course.

Mercury Joystick Piloting for inboards

Mercury Joystick Piloting for inboards

There is, however, a big difference between the old school flanking rudders and DockStar’s setup. On tugboats, the aft rudder(s) and fore rudders don’t act at the same time, but MasterCraft’s designers found a way for all three rudders to act in concert to enhance steering in all maneuvers. The builder has applied for a patent for the system.

So how well does it work? The first test was trying to back it in a straight line — an impossible maneuver on a standard direct-drive ski boat, due to prop torque. I put the drive-by-wire shift on the XT-23 in reverse and promptly oversteered it, which most drivers will do, until I learned to make small corrections. But in just a few minutes I was able to make it back up in a perfectly straight line — and even to port. So no longer will drivers have to bail on a dock because it’s on the “wrong” side. The Boating Writers International judges gave this one the Innovation Award in the Tow Boat category for its effectiveness. DockStar will be available on most of MasterCraft’s 2017 lineup, and the fact it only costs around $1,500 makes it a no-brainer option.


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