Maintaining Electronic Shift and Throttle Controls
Do electronic engine shift and throttle controls fail? Absolutely. I’ve had four failures in 20 years. But mechanical systems, be they cable, hydraulic or pneumatic, have failed me half a dozen times. Mechanical controls require diligent maintenance — tending to small leaks or stiff cables promptly. If they fail, it will likely be in gear. Electronic shifts and throttles, on the other hand, self-monitor to offer warnings before they finally give up and return to neutral and idle. Just like mechanical shifts and throttles, however, electronic controls require maintenance, particularly as boats age.
“There are no moving parts, so no wear and tear, but you have to have good power,” says John Skvarla, ZF Marine’s training supervisor (www.zf.com). Once they start, most mechanically governed diesels run without electricity. But engine computers and electronic controls require constant DC power. It’s now critical to test batteries regularly. One quick way is to shut down all chargers and let batteries sit overnight, and then make sure batteries can crank engines and power controls in the morning.
Check charging systems too. Dead alternators often go undetected because they are backed up by generators and battery chargers — until the generator overheats and the boat is left without DC power. Again the test is simple. Turn off the chargers, check the battery voltage for each bank, and then start each engine, making sure the voltage increases to prove alternator output from each engine.
Electronic-control manufacturers prefer independent start batteries for each engine plus a house bank. They also like short runs between batteries and controls on both positive and negative wires, with no other equipment attached. This helps ensure adequate voltage and guards against interference from other systems. Short, direct runs also protect against physical damage — say a fire in the main electrical panel. “If some other system fails, we want to avoid placing the control system at risk,” says Tyson Schey, who co-leads Cummins MerCruiser Diesel’s controls group.
As engines crank, DC battery voltage drops, which could affect controls. Manufacturers handle this differently. Twin Disc (www.twindisc.com), for example, recommends separate power feeds from two battery banks — when voltage drops on one, the controls grab power from the other. These aren’t always installed, though. “We like to see three [DC power] wires, negative and positive from the primary starting battery and then another positive wire from the opposite engine bank,” says Bob Bertolasi, Twin Disc’s marine electronic controls manager. Check installation manuals and ensure such redundancy before needing it while under way.
Moisture is an obvious problem. Older control heads “are protected from spray from the top but not underneath,” Skvarla says. “Check underneath. Make sure there is no sign of corrosion or water.” He also says connections should easily withstand a firm tug using just a thumb and forefinger, and warns to replace mounting gaskets whenever removing control heads. New controls are well-sealed, but physical damage — let’s say the canvas installer dropped a drill and cracked a control head — can leak water into any head.
Relying on electricity around water has its shortcomings, but electronics bring the advantage of redundancy. On mechanical systems one leak or stuck cable could kill the entire system. With electronics, “every single station is completely isolated. If there is a failure in any control head, it isn’t going to affect any other,” Skvarla says. “That’s why I like to see at least two stations aboard.”
DC-powered computer chips make electronic controls self-monitoring. “We have multiple systems cross-checking each other — multiple CAN [controller area network] busses, separate control stations that are completely independent,” Schey says. But this relies on skippers to heed warning lights and alarm beeps that typically precede outright control failure. “The reason we put those warnings and alarms in place is that something has got to be attended to,” says Robert Mirman, product manager for Cummins MerCruiser Diesel (www.cmdmarine.com) pod systems. Older systems rely on decoding flashing lights while newer systems display the problem in text.
With Murphy’s Law in mind, both ZF and Twin Disc offer completely independent backup systems — bypassing all control heads and system circuit boards. The backup systems won’t have the same silky-smooth shift or advanced docking modes of primary systems, though. Try them out while in open water, before needed.
Over the years I’ve noticed that the infamous Murphy errs on the side of optimism. A lightning strike or fire can take out control systems but leave engines running. The same is true of mechanical shifts and throttles, but these can be operated directly on the transmissions and engines. Electronic transmissions actuate solenoids — the only moving part on many systems and the one part that can’t be made redundant. Fortunately these solenoids can be operated manually as well. On most Twin Disc transmissions this is done by removing a safety pin and then pushing or pulling a red knob. ZF gears differ by model, but most have a knob that is turned and then pushed or pulled. Be warned, though: What puts one engine in forward likely puts the other into reverse. Learn to use these backups before an emergency, and label them for forward and reverse. Many electronic controls will operate throttles with transmissions engaged manually, but check engine original-equipment-manufacturer information to learn how to bypass throttles as well.
Fly-by-wire steering is finding its way aboard many boats in pod-drive systems and is now even being connected to conventional rudders. Going electronic offers proportional steering — smoother at high speed but quicker at slow speed. Split rudder or pod angles enhance joystick maneuvering, and an actuator on each rudder provides redundancy over typical single hydraulic systems tied to both rudders. Electronic steering carries the same problems as electronic shifts and throttles but benefits similarly from self-monitoring.
Electronic controls have been around for more than two decades, so those earliest versions have probably been aboard through one or two complete electronics refits. Is it fair to expect more from critical engine controls than, say, a GPS or radar? The newest systems carry many advantages — they are fully waterproof, offer better redundancy and utilize more sophisticated monitoring. Aging controls can typically be replaced with new ones using existing wiring. ZF even offers a credit toward new controls for boats replacing older ZF or Mathers systems.
Outright replacement might not be practical, but don’t take for granted that those electronic shifts and throttles will work flawlessly forever. They deserve maintenance just like mechanical systems do.
What About Pods?
Pods bring aboard both electronic shift and throttle and fly-by-wire steering. Like conventional transmissions, pod systems can be locked in gear manually. Electric motors turn ZF pods to steer, so if necessary, turn the permanently installed hand-crank knob to center the pods and steer by varying port and starboard throttles. Volvo IPS also uses electric steering motors. Center drives with the supplied brake release and crank. CMD Zeus drives use a hydraulic steering pump integral to the pod. If the engine works, so does the pump. Actuate hydraulic solenoids on the pod manually to center drives. Pods also carry duplicate systems on port and starboard, and with the inoperative pod centered, boats are much more maneuverable on one pod than with just one engine turning a conventional shaft.
