More and more powerboats are sold today with joystick control systems incorporating bow and stern thrusters. Imtra systems expert Peter Nolet explains how and why the integration works so well.
The introduction of joystick control for motor vessels has appealed to boaters for many of the same reasons that bow and stern thrusters have become standard equipment on many boats—increased maneuverability for close-quarters situations, especially when approaching or leaving the dock.
Thrusters of almost any kind can be used on a joystick-controlled boat without being integrated into the same control system, but they end up opposing some of the engine forces and therefore generally must be sized up significantly to do their job. And traditional on/off-style thrusters including Side-Power models have been integrated with joystick systems, but the operation is often rough, with excessive vibration, noise and turbulence.
A key innovation that has allowed Side-Power thrusters to work much better with joysticks occurred in 2011, when Side-Power developed DC-powered variable-speed thrusters. Let’s review why this was an important development.
Joystick control systems for pods and outboards function by using opposing forces from multiple engines. These work effectively in many scenarios, but create more turbulence and use more energy, and for larger boats or boats with extra windage they may not provide enough control of the bow. The integration of thrusters creates a much smoother, more efficient operation and generally better control of the bow because the thrusters move the boat side to side and the engines move fore and aft. This also allows thrusters to be sized normally; they don’t need to be oversized to oppose engine forces.
To enable this integration, Side-Power began early on to license the blueprint of their Gateway interface to its S-link system—the proprietary Controller Area Network (CAN) that signals to the thrusters how much output is required. Side-Power decided to make its intellectual property available and made agreements with major joystick builders, starting with JMS, which is produced by ZF. Now, virtually all joystick manufacturers have signed on with Side-Power, including Twin Disc, MTU, CAT, Cummins, Xenta “Smartstick” and Volvo (with straight-shaft propulsion only).
When docking, any captain needs graduated throttle control for the engines—not simply having full power on or off. Having bow and stern thrusters with similar speed controls rather than simple on/off functionality has proved equally valuable. Joystick controls can be configured to work with on/off thrusters but results in rougher operation and shorter run times.
In fact, smooth and efficient joystick integration with a reasonable run time is seriously compromised if the amount of thrust can’t be controlled. Integrated thrusters provide the best operation for a joystick system, as there are no opposing forces and wasted horsepower (see diagram above). Thrusters and engines can work in concert, and systems run more smoothly and quietly.
As importantly, the introduction of joysticks has changed handling expectations and usage of boats carrying this equipment. Most have “hold” functions to keep a boat against a dock temporarily. Some have “station holding” capability to essentially park the boat while waiting for a bridge to open or while leaving the helm to get fenders and dock lines prepared. This has expanded user expectation for run time with thrusters operating, a requirement that is greatly enhanced by the efficiency of proportional control use as opposed to the full-power of an on/off thruster.
In recent years, station-holding capability has become popular among builders of sportfishing boats, whose captains prefer to avoid dropping 1000 feet of anchor line to hold position when bottom fishing. While DC thruster systems by Side-Power can run upwards of 10 minutes, the desire for unlimited run time while fishing has in some cases required the shift to hydraulic power, which utilizes the engine(s) to maintain system pressure.
Normally, the expense and space requirements of hydraulic systems limit their use to boats 60 feet and up, but Imtra has recently helped spec out systems on Viking 48s and 52s, and is currently working with OBX, a custom sportfish builder, on a 38-footer. Sportfish builders have a space advantage and can more easily accommodate extra systems than motor yachts. The latter are apt to have more trouble fitting them into engine rooms that are often smaller and already crowded with extra generators, AC units, water-makers and other amenities. Fortunately, DC-powered thruster systems, integrated with joystick controllers, are typically more than adequate to the needs of smaller motor yachts that don’t require the unlimited run time of hydraulic thruster systems.
For more information on variable-speed thrusters, check out our article: 5 Common Questions About Proportional Speed Control Bow & Stern Thrusters