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Care and Feeding of Autopilots

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Care and Feeding of Autopilots BOATKEEPER Care and Feeding of Autopilots From Pacific Fishing, December 1998 By Terry Johnson, University of Alaska Sea Grant, Marine Advisory Program 4014 Lake Street, Suite 201B, Homer, AK 99603, (907) 235-5643, email: [email protected] ny device that simplifies matters for work on either a wet card or fluxgate com- cal, and the whole thing must be mounted Athe vessel operator must itself be com- pass, both of which respond to the earth’s where it is out of the weather and out of the plex; so it is with autopilots. magnetic field. Naturally, they also respond way but still has correct angle and rigidity In concept, the modern autopilot is to any other magnetic field in the boat, in- to impart full torque on the steering gear. If pretty simple. A compass indicates the cluding the engine block and electrical cir- the salesman doesn’t know exactly how to boat’s actual heading, a control unit accepts cuitry. Also, they are greatly affected by calculate sprocket size and other factors, get the heading the operator wants, a micropro- motion, including rolling, pitching, and an engineer to help you work it out. Big cessor calculates the difference between the pounding. To minimize motion the compass problems result from improper sizing. On desired and actual headings, and a power must be mounted low in the boat, prefer- hydraulic units, you need to know the ram unit acts on instructions from the control ably at the waterline and slightly forward size on your steering gear to select the cor- unit to move the rudder and turn the boat of amidships, close to the centerline. To rect drive pump, but once you have it, in- so as to eliminate that difference. prevent magnetic interference, it should be stallation should be pretty straightforward. The devil is in the details. Each make placed sufficiently distant from big masses If you have power hydraulic steering and and model uses different components and of metal, circuitry, and electrical devices. need to use electric solenoid-actuated con- has different features. Nearly every mod- Be sure the arrow on the cover is exactly trol valves, and you’re not a hydraulic en- ern autopilot—correctly sized, properly in- parallel to the centerline and pointed for- gineer, you’ll probably have to hire a stalled, and kept adjusted for current ward, and never mount vertically except professional to do the job. conditions—will reliably steer a vessel on with an angle bracket which positions it on a predetermined course; but autopilot prob- the horizontal plane. Setup lems are common. Some result from error After selecting a compass location but Autopilots come in varying levels of so- at the purchase or installation stage, others before bolting it down, move the compass phistication. Take the old Wood Freeman are due to operator error or abuse. horizontally in a circle of a foot radius Model 11 (they’re still being manufac- In the highly competitive marine elec- around the chosen spot, and again verti- tured), turn on the power, point the boat in tronics market, some manufacturers engage cally; deflection should be no more than the right direction, and engage the clutch. in what one writer calls “specsmanship”— five degrees. Once it is secured, test the That’s all there is to it. Take a more mod- overrating their units to entice the buyer to compass again, and ensure that it reads cor- ern unit, like my 10-year-old Robertson, purchase theirs rather than a competitor’s. rectly. Note the exact heading, then use a and you get 50 pages of instructions (half Under ideal conditions, i.e., a well-trimmed screwdriver placed next to the card to de- in Norwegian, to be sure, but still a lot of and balanced boat operating on a calm sea, flect it one way and then the other. After stuff to digest). On a modern unit you may a small pilot will steer a large vessel. But if each deflection, it should return to within have to set rudder limit (usually 25-40 de- you want your pilot to work well and long, one degree of the original heading. You then grees), rudder turn rate (around six degrees size it for the worst conditions it will en- may need to “compensate” the compass per second for a heavy displacement boat, dure, not the best. Study the specs for mod- with adjustment screws and magnets, like up to 15 degrees on a planing boat), and off els you are considering. Unless your boat your main navigation compass. Fluxgate course alarm limit (typically 20 degrees). fits in the middle of the size category for a compasses don’t require the deflection test Usually there is a default setting for these particular model, opt for the next beefier because they must be compensated inter- factors but you may want to check and re- one. nally after installation. set them. In addition, you may have remote con- Installation Control Unit: Follow the instructions. Put trol units, portable remotes, jog sticks, a Autopilot installation consists of two the thing where it is convenient when you rudder angle indicator, and inputs from GPS phases: mechanical placement of the com- want to use it, and not in the way the rest of or loran. (If GPS or loran is connected and ponents in the boat and adjustments once the time. The trick with control units is se- the selector switched to that input, the pilot the parts are in place. Most owners hire a lecting one that has the features you need. will disregard the compass and will steer professional to install a new pilot, but it You can find lots of advertising and articles toward a waypoint rather than on a course.) pays to check that person’s work. Here are touting the features of each make and All these components may feed into a cen- a few tips on autopilot installation. model. tral junction box, which is normally mounted at a remote location, with circuitry Compass: Unless you can afford a very ex- Power Unit: On mechanical rotary (chain) to all the other parts. Installation and set- pensive gyrocompass, your autopilot will drives, the size of the helm sprocket is criti- up of some components is simple, while others like the rudder feedback unit require main circuit board. Some have self-diag- careful planning and execution; but all cir- nostic programs installed with their oper- cuitry is delicate. Again, read the instruc- ating software which provide coded clues tions. to faults. Most units have a set of controls with If your autopilot simply doesn’t work, names like “sea state,” “deadband,” “yaw,” the obvious thing to check first is the power and “rudder.” They all pertain to the way supply. Use a volt-ohm-meter to check for the control unit orders the rudder to respond power at the junction box and control unit. to the difference between desired and ac- There may be a breaker in the system, or tual courses. Rudder, or rudder gain, con- the junction box may have a fuse. But sure trols the amount of rudder movement the to determine before heading out whether the control unit orders in response to a given system has a hidden fuse, and get spares. amount of heading error. In rougher sea You may need a particular little 2-amp fuse conditions where the boat tends to swing you wouldn’t ordinarily carry in your spares off its desired course by a wider margin, kit. rudder gain can be increased to provide Conventional wisdom now holds that more immediate response; in calm condi- once electronics are turned on, they should tions, gain is reduced to smooth and mod- be left on for the season. Sure enough, my erate the response. experience is that autopilot failures most Deadband or yaw (also known as sea often occur at the moment the unit is turned state) is a control that limits the unit’s re- on. sponse to yawing or swinging from side to Poor steering can result from improper side, as in a following sea. Since the pilot adjustment of rudder gain or rudder speed, can’t eliminate yawing under some condi- or problems with the compass. If the thing tions, this control makes the unit ignore re- tries to steer but veers off wildly in un- petitive minor error to save energy and wear intended directions, check the rudder feed- on the steering gear and prevent over- back system. Some models have a little corrections. Increasing deadband allows the plastic ball joint connecting the linkage, and boat to undergo normal yaw while still put- if this comes loose, the whole pilot goes ting it back on course if it deviates more haywire. Also, the feedback potentiometer than a predetermined number of degrees. at the rudder stock can go bad and may need Reducing deadband keeps the boat from to be replaced. Momentary veering can re- making S-curves in calm weather. sult from electrical surges within the boat, Modern high-end units have learning such as keying the mike on an HF radio, or logic in their operating software that en- from passing through areas of magnetic ables them to “learn” characteristics of the anomaly. individual boat, allowing them to adjust out- If the above tips don’t solve your prob- put to the drive unit to achieve optimum lem, you probably have to send the control steering performance. This sophisticated unit in for repair. software is one of the factors that make top A final safety tip: some models are sus- units so expensive.
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