ComNav Autopilots have gained a reputation for top performance and reliability.
ComNav Marine has a broad line of marine navigation systems for virtually any commercial marine or pleasure boat application.
- G Series GPS Satellite Compasses
- NX Series Nexus Instruments
- Autopilot Accessories
- Remote Controls
- AUTOPILOT STEERING COMPASSES
- Recreational Boating Compasses
Autopilots & Basics
These electronic marvels free up the captain and crew to concentrate on navigation, maintaining a watch and managing the vessel.
There are three main components to an autopilot; a heading sensor (usually a fluxgate compass), logic, feedback and power circuits, and a drive mechanism. Only the drive mechanism varies between the types of autopilots.
Versions of autopilots
Each of these has limitations in their use and you should be aware of these prior to purchasing your unitómost autopilots are meant for use in light to moderate wind and sea conditions.
There are three types of autopilots- tiller, wheel, and below-deck units.
For instance, light duty tiller and wheel pilots may not operate efficiently in a large seaway. Under-deck units are primarily found on larger, heavier displacement boats headed offshore.
Tiller pilots are used on tiller steered sailboats and are attached to the tiller making course corrections with a push-pull ram.
Light duty autopilots for boats with a displacement up to around 10,000 pounds are designed to have the control unit mounted to the cockpit coaming and the control buttons are on top of this unit. These units are great for the small sailboat used on lakes or inland waterways.
Heavier duty autopilots for vessels with displacements between 10,000 to 20,000 pounds have the control unit mounted in the cockpit separately from the ram. These autopilots are rated for offshore work.
Wheel pilots are available in two styles, wheel mounted belt drive or a wheel mounted drive motor. These units are primarily used with wire-and-pulley, push-pull or mechanical cable steering systems. These pilots are good for using nearshore or on inland waterways.
Belt drives use a belt that is connected directly to the wheel and the drive unit is either bulkhead, floor or pedestal-mounted. The separate control unit, which also contains the fluxgate compass, is also mounted remotely. Some motor and control units are removable allowing you to stow them when not in use.
Drive motors are attached directly to the wheel, eliminating the belt. The motor and sprocket which attaches to the wheel spokes are enclosed in a single casing making installation simple.
Under-deck pilots, also called below-decks or modular pilots, are used primarily on larger, heavy displacement vessels doing offshore work. There are five basic components; the brain box (course computer), compass, rudder reference transducer, control head and drive unit. The first four components have minimal variation other than the size required for the boat's displacement, but the variety of drive units available can make selecting an under-deck unit a confusing process.
The drive units for under-deck autopilots can be linear, hydraulic or rotary and is connected directly to the rudderstock or steering quadrant.
Linear drive autopilots
Linear drive autopilots use a push-pull ram, similar to a tiller pilot, and are either electrically/mechanically or electrically/hydraulically operated. Electrical/mechanical units are primarily found on mid-sized boats from 15,000 to 40,000 pounds displacement operating on either 12 or 24 volt systems. Hydraulic units supplement the electrical power generating more thrust and are designed for heavy displacement boatsó50,000 to 75,000 pounds.
Units are available for boats without hydraulic steering that combine a hydraulic pump and cylinder attached to the tiller arm or steering quadrant of the boat. These drive units have no hoses or external reservoirs and no oil filling or bleeding is required.
Hydraulic drive units use the hydraulic ram connected to the rudderstock on boats already having hydraulic steering systems installed. The hydraulic pump can be continuous or reverse running. The pump's flow rate should be matched with the capacity of the steering cylinder, providing a hard-over to hard-over time of between 7 seconds and 18 seconds depending on the vessel's size.
Continuous running pumps are electrical or engine drive with a solenoid valve controlled by the autopilot which in turn controls the flow of hydraulic oil into the steering cylinder. Because the motor runs continuously in one direction, wear on the motor is reduced. Another advantage to using this type of pump is that the autopilot's electronics are not switching large amounts of electrical current, increasing the reliability and life of the system as opposed to using reverse running pumps.
These pumps are primarily used by vessels where the autopilot
is in use for long periods of time.
Reverse running pumps are operated by electronic controls which reverse the motor. The pump is switched on by the autopilot and makes the steering correction left or right by changing the rotation direction of the pump motor. These are usually found on sailboats, motor cruisers and other craft less than 49 feet (15 meters) where the autopilot is not heavily used.
The ComNav Type 3 lower power consumption motor pumpset (on photo below ) is manufactured specifically for boats with steering cylinder displacements between 66 to 984cc. Available in both: 12 and 24-volt DC power systems.
Rotary drive units, also called chain drive, use an electric motor, reduction gears and chain and sprockets which attach to the steering system. The size of the sprocket is related to the number of turns of the steering system. These are found on boats up to 65 feet with mechanical steering systems (rod or chain) where the use of a ram is not possible because of location. These drive units must be lubricated and tightened regularly.
Behind-the-bulkhead rotary drive units are available for motor cruisers and power craft less than 40 feet with cable steering systems. The drive unit comes with its own stub shaft which attaches to the front of the bulkhead for the wheel and the existing cable steering shaft fits through the rotary drive.
Available accessories can enhance the operation of your autopilot, such as handheld remotes, interface "brains," joysticks and alarms.
Handheld remotes allow you to change course from anywhere
on the vessel.
Interfacing the autopilot with a GPS permits it to steer a pre-set course, allowing it to automatically account for set and drift, altering course as needed.
A steer-to-wind option uses an apparent wind direction sensor to sustain relative wind angle if the vessel is under sail.
Joysticks increase rudder response through "power-assisted" manual control.
For the shorthanded crew, alarms such as man overboard, off course, watch, and dodge capability offer electronic assistance.
Accessories that can alter the height or length of the tiller pilot location make tiller pilot installations easier.
Belts for wheel pilots are available in several lengths to accommodate different mounting locations. The belt-type drive units may require a pedestal-mounting bracket.
On comnavmarine.com you can find autopilots and accessories include motor pumpset.
This Bracket Mount compass by Com Nav offer reliability and accuracy for an economical price. include: Double gimballing and Internal lighting system
Autopilot Buying Guide
Know what the limitations are on the autopilot that you're considering purchasing.
Study the manufacturer's size recommendations carefully. If your boat falls in the upper range of the unit size to boat size/displacement recommendation, buy the next larger unit. Don't under buy an autopilot.
If you're an offshore sailor with a heavy displacement cruising boat, buy a unit that will handle the loaded displacement of your vessel and rough sea conditionsóusually an under-deck style.
When purchasing an autopilot, consider the conditions under which you may require a fast helm-response timeóhow long does it take to go hard-over to hard-over on the wheel or tiller? If you operate a powerboat or use a spinnaker in downwind conditions on a sailboat, you'll need a quick response time from your autopilot to prevent hewing and yawing, or rounding up with the spinnaker.
Check the manufacturer's degrees of course change per second. Autopilots have what is referred to as a ìdeadbandî area around the course setting. This deadband area is determined by sea state and the autopilot won't correct course unless the boat goes beyond this area. Some models have a user-adjustable deadband.
What is the force required to hold a course setting? Heavier helms will require more pressure or force to hold the course, especially in windy conditions or when operating in a heavy seaway, and for sailboats when going upwind.
How far does your helm need to be turned for course correction or course change? Some rudders are inefficient and undersized, requiring a longer throw for helm correction. The gain setting on your autopilot controls the speed and time in which the rudder responds to the helm and may be user-adjustable for the sea conditions.
Rudder position sensing feedback ensures that the rudder is deflected only far enough to make a timely correction from an off heading. Autopilots without this feature won't steer as accurately in a seaway.