This article was originally published on SailNet January, 2001.
An autopilot creates the ultimate in sailing freedom—the freedom to do something else, like update the charts, eat a sandwich, trim the sails, get an anchor ready, use the head, read a book, or just enjoy the scenery going by. For long-distance sailors, especially those single-handed or cruising couples who are short on crew, the autopilot makes life on board truly bearable.
The good news is that choosing an autopilot has never been easier. There are specific models for nearly every vessel afloat. But before you charge off to buy one for your pride-and-joy, take a minute to look at the types available and the installations that are possible.
It is imperative that you use your boat's loaded displacement measurement as the main basis for choosing the correct size autopilot. Every manufacturer states the maximum size vessel each model can steer in its literature—so don’t buy one size too small to save a few dollars or you will be disappointed in the performance. In fact, if your boat is pushing the maximum displacement for one pilot, you might consider stepping up to the next size. This will avoid disappointment with performance in heavy weather when the smaller unit may not have the strength to handle the boat.
Tiller Pilots As the name would imply, tiller pilots are designed for boats with tillers instead of wheel steering. The most common tiller pilots are all fabricated with one-piece construction for smaller boats with the control buttons on the top of the pilot housing itself, and these units can control most boats up to about 10,000 pounds displacement. Units for bigger boats often have an independent ram mounted on the tiller with a separate control head mounted in the cockpit. These more powerful units can handle boats up to 20,000 pounds displacement.
Installation of most tiller pilots involves mounting an optional waterproof electrical socket in the cockpit and insuring that the pilot itself is level when the boat is at rest. The instructions will provide a distance forward along the tiller from the rudder shaft where the tiller pilot ball pin is designed to be mounted. This dimension is critical because the lever arm force and push-pull length of the pilot’s arm will be affected if the instructions are not heeded. Too far forward on the tiller, the autopilot will be powerful but slow—too far aft, it will steer the boat very quickly, but it might be overwhelmed by too much force. And the pilot needs to be square to the centerline of the boat. Most newer tiller pilots may be installed on either the port or starboard side, since they have a 180-degree reversing adjustment. On many tiller pilots, a few optional installation parts may be necessary. Since individual boats vary widely, I normally recommend that most owners buy the pilot well in advance, allowing a weekend to sit in the cockpit with a tape measure, the instructions, and all the parts. This way, if optional installation parts are required, they can be ordered for the following weekend.
Because the fluxgate compass inside the self-contained smaller units must be kept level, a pedestal mounting socket on the coaming may be necessary to lift the outboard end of the pilot higher. Or a tiller bracket might be required on the tiller, in some cases on top to raise the inboard end of the pilot and in some cases slung under the tiller to lower it. An installation on a boat with a very wide cockpit will demand pushrod extensions to make the pilot’s arm long enough to reach from the coaming to the tiller or a cantilever bracket to extend the whole pilot out from the coaming. None of this is difficult or expensive, but it is hard to see what is necessary until the whole thing is in the cockpit and the mounting point on the tiller is identified.
Wheel Pilots Most sailors are familiar with these units, which are popular on boats up to about 15,000 pounds displacement. The older type with an open belt has been around for many years and is well proven, while the newer integrated models are rapidly gaining popularity. Most will operate well on boats with wire-and-pulley, mechanical, or push-pull cable systems, but only the type with the open belt will work on a worm gear steering system with a reversed wheel shaft facing forward.
The open-belt type is less expensive and there are a variety of models with differing approaches to control head and compass mounting. Basically, the installation involves mounting a belt sprocket to the spokes of the wheel and centering it so that it revolves symmetrically. This is only difficult on a wooden-spoked wheel. Next, the motor is mounted to the cockpit floor, the face of a cockpit seat, or to the pedestal at a position that properly tensions the toothed belt around the wheel sprocket. An optional mounting kit for the standard round pedestal may be required here, and an extra-long or extra-short belt may also be necessary. Once the compass and control head are mounted and wired to the motor, the boat is ready to run on autopilot. One note with the open-belt style autopilots: they are designed to be easily removable by pulling one pin and the waterproof electrical socket, and thus make for a high-theft item. If you don’t take yours off when you’re not using the boat, some envious sailor may take it off for you.
The newer enclosed-drive cockpit pilots operate in much the same way, but don’t have an open belt to clutter up the cockpit. The motor and wheel sprocket are all one piece for easier installation. In fact, installation on the newest models is so easy that several sailors have told me they installed their very first autopilot in less than an hour (I’m not sure I believe this boast since it generally takes me an hour to find my wire stripper). The mounting ring on these units attaches directly to the spokes of the steering wheel, and one model simply grips one spoke and has the control head as an integral part of the motor casing—very neat. Mounting to a standard round pedestal is the norm.
Under-Deck Pilots For bigger boats or those with hydraulic steering, under-deck autopilots are more powerful, more expensive, and much more involved to specify and install. All models, whether provided in a kit form or chosen as a modular set of individual parts, have the same basic components:
- A course computer or "brain box"
- A compass
- A rudder reference, or feedback, transducer
- A control head
- A drive unit
Most of the components are the same, although larger and more powerful sizes of computers, rudder- reference transducers, and control heads are available as the boats become larger. Where the widest variations in the type of installation occur is with the plethora of drive units available. Once the drive unit type and size are identified, the other parts will be easy to choose. Let’s start with an easy one:
Hydraulic reversing pump drives are meant for boats with hydraulic steering systems—this one’s easy to choose. The pumps are three-hose types meant to plumb directly into the boat’s main steering lines, so other than purging and refilling the hydraulic lines, this is the easiest of all installations. There are pump sizes for ram capacities from six cubic inches that use two amps at 12 volts, up to units that will handle a 36-cubic-inch ram that swallow five amps of power at 24 volts. Bigger sizes are available if you own a megayacht.
Linear drives are the most commonly found on mid-sized sailboats from 15,000 up to about 40,000 pounds displacement. A bracket is made on a bulkhead or the hull to handle the outboard end of the electric ram and a lever arm or quadrant added to the rudder shaft takes the inboard end. The rudder shaft lever is generally a stock item (bored to the right shaft size and keyway), but the bracket often has to be custom- made to suit the boat. Linear drives are available in both 12 and 24-volt applications, and because they offer various lengths, thrust, torque, and speed, these need to be matched to your boat by a knowledgeable technical representative. A typical small 12-volt linear drive will generate about 700 pounds of thrust, steer hard-over to hard-over in little over 10 seconds, and consume 2.5 amp-hours in the process.
Hydraulic linear drives are the big cousins to the straight electric linear drives. By amplifying the electrical impulses with hydraulic power, these units can generate up to 2,700 pounds of thrust. They install much like a linear drive to a rudder lever arm, but with the additional step of putting in a small hydraulic pump and plumbing it to the arm. You don't need to worry about these unless you have a seriously big boat because these units are designed for boats from 50,000 to 75,000 pounds of displacement.
Rotary drives are the least popular even though they will handle the same size boats as a linear drive at the same power consumption and a little less initial cost. Partially this is because a chain sprocket must be added to the rudder shaft and to the drive shaft, a circular length of chain (like very heavy bicycle chain) tensioned between them, and a bracket made for the drive. The installation is unfamiliar to many sailors and they do consume more space than a linear drive.
Options are available for almost every autopilot that make it even more useful or fun to have on board. A remote control is nice to have, especially in congested waters. An interface to wind instruments allows the electric helmsman to steer to the wind. An interface to GPS allows the autopilot to steer to a waypoint—great on a long-distance haul.
Given a little research, a decent toolbox, and some mechanical aptitude, every sailor is capable of outfitting his or her boat with a new autopilot. Once you have that extra hand on board, freeing you to enjoy something other than the feel of the wheel, you’ll probably wonder what took you so long to install your autopilot.
Steering System Spring Check Up by Tom Wood
SailNet Store Section: Autopilots
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