One advantage of a twin engine boat is great docking maneuverability by using the gearshift controls to steer the boat. By placing the shifting controls in forward or reverse, precise steering can be achieved.
Unfortunately, the rudders must be centered during these operations for maximum control. If the rudder is not centered, shift-steering, especially when backing in, becomes as difficult as a single-engine boat.
What is needed then is a rudder indicator to aid in centering the rudders prior to shift-steering.
This project is quite simple, and consists only of a gauge, sending unit, and interconnect wiring. The system I am using includes a Faria gauge at the helm, and a VDO/Faria rudder position sending unit.
If the sending unit is located in an engine compartment, it must be Ignition Proof, according to US Coast Guard Regulation 33CFR183.
When scoping out the location for the sending unit, you must determine what direction the sending unit needs to turn when steering the boat to Port. The rudder post naturally turns Clockwise when the boat turns to Port, but the particular sending unit I am using requires turning Counter-Clockwise to read correctly on the gauge. This requires a more complicated reversing assembly.
Oddly enough, the sending unit does not come with a lot of hardware to connect to the rudder, so we’ll have to fabricate a few pieces. We will be using materials such as Starboard plastic polymer that can be fabricated with simple shop tools. No need for a machine shop for this project.
When connecting the assembly, tiller-arms will be used to provide the necessary motion, as shown by the drawing below. Pay particular attention to the angles between the arms. To obtain the most linear motion on the gauge, all of the components need to be as tangent as possible when they are centered.
Use this option when the sending unit must turn Counter Clockwise to indicate a turn to Port.
Use this option when the sending unit must be turned Clockwise when turning to Port.
The items that need to be fabricated from Starboard are the Rudder Auxiliary Tiller Arm and the Starboard Base. Dimensions are not given, because the specific location and orientation of each component may differ from boat to boat.
The tiller arm has a notch in the rudder post opening to allow the sheet metal screw to tighten down over the rudder post with a clamping action. There is enough resiliency in the Starboard material for this to clamp tightly. The notch not only allows the tiller arm to clamp down tightly on the rudder post, it alleviates the need to remove any components from the rudder post when installing the arm.
Installation of the gauge at the helm is pretty straightforward, with the only requirement being to properly wire the sending unit to the gauge, along with + and – 12VDC, and instrument lighting, if desired.
The Ball-Link assembly is an item borrowed from the Radio Control Model Airplane industry, DuBro Industries item 2262. Two ball links come in the package, and you will need about 12” of 4-40 threaded rod, which you should be able to obtain from the same Hobby Shop you purchase the ball links from. The ball links were selected due to their surprisingly precision fittings, which provides very minimal backlash.
Wiring: A single station setup is shown here (a dual-helm station would have another connection on the sending unit). The sending unit is a floating-ground, which simply means its isolated from ground. However, when attaching to the gauge, the - side of the sensor is connected to the gauge GND pin, which at that point, references it to ground. Wiring is pretty simple, and you should connect the gauge power to the RUN side of the engine's power so that the gauge is only powered when the engine is in the RUN position to prevent draining the battery. The easiest thing here is to follow the power side of an adjacent gauge to see where it connects. Chances are that there will be spare power taps available. If your wire run from the gauge to the rudder is more than 20ft or so, you may wish to use a larger cable than 18AWG to minimize voltage drip across the cable. If you find you cannot center the gauge, it may perhaps be due to too much voltage loss along the wire.
For the final assembly and calibration, some experimentation is in order. You want to make sure that the sending unit’s tiller arm does not turn so far that it goes beyond its stops. This may require some adjustment of the ball link assembly, as well as distance the ball link is from the center of the tiller arms. It is very helpful at this point to have an assistant at the helm to turn the wheel and determine when the gauge is reading at the center point. Once properly adjusted, the rudder gauge is ready for use.