An efficient autopilot system will transform life on board. In an ideal world you would simply press a button or two, and the boat would go in a straight line. However, different combination of wind and waves will repeatedly knock a boat off course. This means there’s a whole lot more that goes into autopilots, both in terms of how they work and how to pick the most suitable components for a specific boat.
How do autopilots work on a boat?
Before deciding which autopilot to choose it's important to understand the are six key elements in the system:
1. The drive unit that moves the rudder, either with direct connection to the rudder stock, or by turning the wheel or tiller.
2. An electronic compass or heading sensor so the system knows which direction the boat is pointing. For accurate steering a gyro or rate sensing compass, which also measures the boat's rate of turn, is essential.
3. A control head. This is the user interface, which allows automatic steering to be selected, course changes to be made and on some systems lets you change rudder gain and sea state settings. Some systems also have remote control units that allow you to change course from anywhere on board.
4. A pilot computer that analyses the inputs to the system and calculates how far and how quickly to move the helm.
5. Rudder feedback sensor. This helps the system to steer a more accurate course by comparing rate of turn with the rudder angle that has been applied.
6. Integration with other on board electronics. This can enable a boat to be steered directly to a waypoint, or in the case of sailboats to be steered on a constant wind angle, rather than compass course.
Some systems combine several of these elements into single units. This is the case both with simple tiller pilots at the lower end of the market, and with recent 9-axis sensors that combine the compass and pilot computer, along with pitch and heel sensors.
The past few years have seen significant development in this field, so if you have an elderly system, or are contemplating more serious sailing, an upgrade will be worthwhile. The best electrical systems are now capable of steering a boat across an ocean, although carrying spares of key elements of the system is a sensible precaution, and generating sufficient electrical power is a consideration that must be addressed. The latest autopilot systems have adaptive software that can even “learn” how your boat reacts to different sea conditions and speeds, through time.
Basic autopilot units
The simplest electric pilots are the basic all-in-one tiller pilots that require a only a 12 volt power feed and equivalent basic wheel pilots that are mounted externally on the wheel pedestal. If of an adequate size, these can work adequately on smallish boats, particularly in easy conditions when the pilot is a useful convenience. However, it may not work in the kind of heavy weather in which a small crew is likely to depend on the pilot.
The basic unit’s lack of both a gyro (or rate sensing) compass, and rudder angle sensor, mean they are not able to respond quickly and will struggle to keep a boat on course, especially in a quartering sea. An additional problem can also be that they may not be quick at turning the rudder. These on deck units are also vulnerable to failure as a result of water ingress. Nevertheless, they are still a useful budget starting point and can later be kept on board as a spare for use in the event of problems with a more sophisticated system.
If you’re undertaking serious sailing and opting for an electric pilot it’s important to get the best you can afford. These are invariably below-deck units, with a gyro or rate-sensing compass, a separate pilot computer and a heel sensor. Some recent models combine these functions into a single unit, usually with a nine-axis sensor.
It’s often thought that the drive unit is the most important part of the system. However, while the drive must be matched to the size and style of boat, as well as its steering arrangements, the system’s ability to hold a good course depends on the quality of the data inputs.
For basic functionality of a decent system the pilot computer needs the boat’s compass heading, rate of turn and rudder angle. True wind angle and apparent wind angle are also needed to enable a sailing boat to steer to wind angles, which is important both when close hauled and when running downwind.
Heel angle sensors further improve the accuracy of steering by moving the helm in response to changes in the boat’s angle of heel, rather than waiting for the boat to change course and then responding to that. Until recently this tended to be available on only high end systems. However, new units have been developed with combined compasses/multi-axis sensors, such as B&G’s Precision-9 compass that also provides accurate rate of turn, roll, pitch and heave data to the system. Raymarine’s Evolution autopilot and Garmin’s Reactor series go one step further in combining a 9-axis sensor with the pilot computer.
The latter two systems stand out compared to older units as the interface has deliberately been kept as simple as possible. This means there are no settings to tweak for different conditions. While those who are new to using sophisticated pilots may welcome this, old hands may rue the lack of a facility to tweak the parameters in challenging conditions.
While some of the first versions of these systems showed initial teething problems when pushed very hard while racing in boisterous reaching conditions, these issues have been solved through software updates. Users now report systems as being reliable, even when pushed far beyond what would be asked of the average cruising yacht. This gives a reassuring level of confidence to those with more modest ambitions but who understandably worry about being unexpectedly caught out in challenging conditions.
Autopilot drive units
The appropriate drive unit will vary depending on whether you have a sailboat with wheel or tiller steering, or a motor boat with shaft drive, outdrives or an outboard. The main options are a hydraulic system, a mechanical linear drive, or a rotary drive. The latter is aim at predominately older vessels with chain and sprocket type wheel steering systems.
Hydraulic and linear mechanical drives can be permanently attached to the quadrant, but allow for instant transitions between using the pilot and hand steering without disconnecting any hardware. Advantages of the hydraulic option include fast lock to lock times and incredible power, especially on larger models. They are well proven in the field, with excellent levels of intrinsic reliability, but tend to be more power hungry than mechanical drives.
Tiller steered boats are unlikely to have a quadrant below decks unless the model was also offered with wheel steering, or has twin rudders. In this case options for the drive are more limited, with the most common choices being Raymarine’s EV-100 Tiller Drive, or the Canadian manufactured Octopus drive. The latter is a mechanical system with a powerful electric motor, mounted in a dry location below deck, driving a Bowden cable connected to the tiller. A clutch releases when the system is switched to standby, allowing hand steering with almost imperceptible additional friction from the drag of the cable. The unit is also offered in a package from B&G and Simrad (as the SD10 mechanical drive) and the French marine electronics manufacturer NKE. It can also be used in conjunction with an outboard motor on RIBs and other powered craft, or attached to a conventional quadrant in installations with restricted space.
The right size unit
Manufacturers of all types of self steering gear generally quote recommendations by boat size and length. It’s worth noting that many yachts, especially older craft, were built with thicker laminates than the designer originally specified and may well be significantly heavier than the figures quoted by the boat builder. In addition, even boats of a modest size tend to collect a significant weight of additional gear, supplies and crew weight that can easily add a further 20 per cent to the total weight of the boat that must be considered when the pilot is specified.
Autopilot control unit
Pilots are controlled via a keypad and instrument display, which may be combined within a single module, as with the 70 series control heads for Raymarine autopilots, or be provide as two separate items. In addition, an increasing number of MFDs (Multifunction displays) have the facility to control a networked pilot.
Control pads need to be mounted within easy reach of the helm, when on either tack for sailboats, while flybridge powerboats will need one at each helm station. It’s also worth looking at siting controls elsewhere – being able to change course from the companionway area, for instance, can be very helpful when sailing short handed. Many manufacturers also offer remote units that enable users to change course from anywhere on board. In some cases, it also allows you to pre-program helpful directions; some units have dedicated trolling patterns for anglers, or the ability to detect (via networking) and follow specific bottom contours.
Boats whose electronics are already based on the ‘plug and play’ NMEA2000 protocol (or compatible systems such as Raymarine’s SeaTalk NG and Navico’s SimNet) have an advantage when it comes to interfacing the pilot computer with the compass and other electronics. However, those with older systems that output only NMEA0183 data are at a disadvantage as the wiring is significantly more convoluted and the protocol will only support a relatively small number of devices.
Given that a new pilot can be an expensive purchase, if your boat has older electronics it’s worth considering any future upgrades you may want to carry out before buying the pilot. Improvements to the whole system can therefore be planned in unison, even if some elements won’t be changed for a few years. Equally it’s worth bearing in mind that you may need to buy an instrument display to use with the pilot – at this point buying a couple of extra units is a quick way to upgrade to a mostly NMEA2000 system, especially if you already have a chart plotter or MFD that’s compatible.
Given the reliance on the pilot, power management on a sail boat is an important consideration for any passage of more than around 6-8 hours. This can be particularly true for lower specification units that struggle to keep the boat on course, thereby using more power than a system that will steer a better line.
A smart charging regulator, which significantly boosts the charge rate from the engine’s alternator, is almost universally seen as being essential. It’s also helpful to have a large enough domestic battery bank to run all systems for 24 hours without discharging below 50 per cent, although many boats accept the need to charge on a twice-daily basis. For long offshore voyages back-up charging options are also important to consider.
If you depend on the pilot it’s important to consider what would happen if any part of the system was to stop functioning correctly. For some crews this will be little more than an inconvenience, however, for weaker, less experienced or short handed sailors it has the potential to create significant problems, especially on long passages.
Installing a second unit that can be engaged at the flick of a switch therefore makes a lot of sense. However, even that is by no means a fail-safe panacea if it relies on the same instrument data stream and charging system as the main unit. It’s also important to ensure the back-up unit is kept dry, adequately maintained and that it’s used periodically to check it works. There are legions of boats with a second pilot drive that has sat festering in a damp locker for months, or even years, and no longer has any chance of functioning. For boats travelling very long distances with a small crew a wind pilot is therefore still a popular option that provides a completely independent back up that will work even in the event of total power failure.
Getting the best from a pilot
No pilot will work efficiently on a sailing boat if the sail plan is not well balanced. Paying careful attention to sail trim, including shortening sail in good time as the wind increases, is crucial to the ease of steering the boat and the performance of all types of self-steering systems.
Many electric pilots allow you to tweak a range of settings to enable the unit to maintain an efficient course across a wide range of conditions. In addition to the basic ‘response’ setting, the more advanced rudder gain and counter rudder controls are important (note that, although some manufacturers use slightly different terms, the principles remain the same.) Rudder gain is the ratio between the commanded angle and the heading error, while counter rudder counteracts the effect of the boat’s turn rate and inertia, with the two tending to be adjusted in tandem.
The bottom line? These units aren’t nearly as simple as you might think, and there’s actually quite a bit of confusing complexity to consider when it comes to how an autopilot works. But there’s one thing that shouldn’t be confusing at all: if you think you don’t need an autopilot, the chances are you’ve never had one.
Wind vane systems
There was a time at which any long-distance voyaging boat would sport a windvane self steering gear on the transom. They tend to be robust, often requiring servicing only after tens of thousands of miles, require no electrical input, and can often be easily fixed using locally sourced parts and labour even in remote parts of the world. These remain undeniable advantages in today's world, and many seasoned skippers swear by their wind vane gear for good reason.
On the downside, the upfront cost can be relatively expensive, and windvanes tend not to be effective sailing downwind in light airs, when the apparent wind is low, and are useless for motoring in a calm when the apparent wind is always from ahead, irrespective of your course. For this reason many yachts with a windvane system will also carry an electric pilot, although the latter does not need to be of a high specification as it will only be used in easy conditions.
After first being developed in the post-war years by the likes of Bernard Moitessier, Blondie Haslar and others, windvane design now favours servo pendulum types, which magnify the power produced by the small vane on top of the unit. A number of companies have with their own designs based on this theme, most of which work on similar principles but offer various advantages in terms of size, price or track record.
One that stands out from the rest is the Hydrovane, which has a number of devotees thanks to the auxiliary rudder it incorporates. This means that in the event of the main rudder failing, you can have a greater degree of confidence of being able to reach port, even if it’s at reduced speed. Equally, the WindPilot series is seen as well engineered precision systems that have many knowledgeable and enthusiastic followers.
Popular marine autopilot manufacturers include: