But how does it work? Is it better than previously-employed joystick systems? And does it really save money? The following report will answer these questions.
Our test bed was a Cruisers Yachts 39 Express Coupe with twin 8.2 MerCruiser gas engines -- although the JPI system will work on any dual engine Merc-powered boat, gas or diesel. Our test boat had only a bow thruster, and that was all it needed, but the system could also incorporate a stern thruster into the equation.
The JPI system basically integrates the twin engines with the bow thruster, or bow and stern thrusters combined, to give full maneuverability. The fact that it can work with only a single thruster shows how well -- and cost effective -- this solution can be.
First, a couple of operational notes. The bow thruster on our test boat was not progressive -- it’s either on or off -- but adjustments can be made to the operation to accommodate this. Second, any electric thruster on any boat can shut down into a safe mode after heavy use until they cool. That said, during our test we pounded on the bow thruster for nearly 45 minutes and had no such problem. So we don’t feel that is a concern with this system. In any case, thrusters generally need only be used in short bursts.
When the shift controls are moved into neutral, the joystick becomes active, as seen by the green light ring around the base of the unit. As the joystick is moved, the main engines and the bow thruster (if needed) are activated to move the boat in the direction desired. As we moved the joystick, the lighted ring validated which way the thrust was being directed by turning color and lighting in the direction we moved the stick. The light will even rotate around the joystick if we rotate the stick.
The light ring is an important feature, as in many cases the boat will not respond immediately, depending on how much or how little we move the stick, and the driver might wonder if the propulsion system is properly engaged. A quick glance at the light ring will indicate both that the unit is engaged and which direction it is going to move the boat.
If the thruster, which has no variable settings remembered, pushes the bow too much to one side or the other, then the operator can rotate it in the opposite direction to take the thruster out of the equation. All electric thrusters are loud enough that we can easily judge how much or how little rotation it takes to start and stop them. In this manner, we can keep our side slip under control quite easily.
While the thruster control is not progressive, the main engines are. (“Progressive” means that the further the joystick is tilted or twisted, the more power is applied and that power is progressively increased, depending on the degree of tilt or twist of the joystick.) More stick adds more power to the mains and the boat moves faster.
Two Power Settings Feature. Mercury fine-tunes the progressive nature of the main engines with two settings -- which are essentially low power and high power -- that are selected by the push of a button. Selecting the low setting keeps a heavy-handed or novice captain from over doing it, but still allows more power when needed to fight a hard cross wind or current. Once an operator is familiar with how the boat responds in any given situation, the best power setting for the situation will be instinctive.
We think this is another important feature of the JPI. It offers captains a high level of precision.
When operating a twin-screw cruiser, turning the rudders to point in the direction that the operator wants to move will allow the prop wash to kick the stern in that direction. For that reason, we wanted to see what would happen if we turned the rudders in the wrong direction while docking. Could the joystick and the mains overcome the power of the prop wash against the rudders?
The answer was: yes, it could, but it took longer. So, when docking, it would help to have the rudders centered or set to use the prop wash to help the boat go in the direction desired.
Another important feature of this system is the ability to use only the bow thruster. By pressing the center button, the thruster system is engaged and will respond to the joystick, but the main engines will not. This feature allows an operator to drive slowly down a narrow channel or canal and use the joystick to control the thruster only, kicking the bow one way or the other with a short burst to compensate.
This means that the joystick essentially becomes a port and starboard toggle, as if there was no joystick system at all. Bow thrusters with toggles are what many boat owners have been installing the last 20 years or so, before the advent of sophisticated software that allowed joystick commands to be transmitted to pod drive and sterndrive power systems. The Mercury JPI system combines that conventional capability with the sophistication of joystick control of all of the boat’s propulsion systems.
Since the joystick software manipulates both the thrust and the direction independently for each main engine, the boat’s stern can theoretically be moved port or starboard by the thrust of these two props alone. And in most cases, that is all that is needed.
Indeed, until the use of bow thrusters in recreational boats in the late 1980s, all twin-screw boats were maneuvered through the tightest of marinas with their twin screws alone. Furthermore, most professional captains today operate large powerboats quite successfully -- and easily, because they are experienced operators -- with only twin screws. (Also, tug boat operators dock with precision with a single screw and a large rudder and no thrusters.)
So, the question begs -- is a stern thruster needed in addition to a bow thruster? The answer is: not with the JPI system.
The Mercury JPI system can handle stern thrusters, as well as those in the bow, so whichever way an owner decides to go, the system can handle the commands necessary.
Most recreational owner/operators are not professional captains and they do not spend five days a week docking their yachts in all sorts of conditions, nor have they been doing it for many years. Rather, they are generally weekend boaters who have good basic skills but find docking to be the most stressful part of their boating excursions. It is for that reason that the pod drives for express cruisers, sedans, convertibles, and motoryachts became so popular when they were introduced 10 years ago.
But at what cost? These sophisticated systems involve heavy, expensive marine gears and propulsion systems that can add $80,000 to $100,000 to the cost of a yacht, or even more.
The Unspoken Caveat of Pod Drives. All of the gears require careful monitoring of lube oil levels, something that can be costly if neglected. When pod drives are run aground, they often must be completely replaced at far greater expense than required to straighten props and shafts and re-align struts and possibly the engine mounts, then if a standard inboard-powered boat hit the same obstruction. So, pods are more costly to buy and more costly to repair in case of a serious grounding than are conventional inboard drives.
As a result of our testing of the new Mercury Marine JPI system for twin inboards, and because of the issues mentioned above, in our opinion, this new product is an important advancement in boating for inboard boats. It puts the ease of joystick docking in the hands of new boat owners for significantly less cost than previous systems.