Selecting an autopilot for your boat

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Why fit an Autopilot?

Using an autopilot when on your boat has several benefits.  The main one being that a steady course can be held so that the crew can concentrate on other tasks.  In effect you have an extra pair of hands.  It can help improve fuel consumption and reduce helmiong errors.  We should add that the use of the autopilot should not be at the expense of safe navigation and seamanship!  An autopilot used correctly can make life afloat a lot more enjoyable.   In this guide we want to look at what is suitable for different types of vessel, give details of some of the issues you need to consider and explain what some of the jargon means.

What is an Autopilot?

An autopilot is not unlike cruise control in a car, except that instead of holding a steady speed it allows the vessel to hold a steady course.  This course is derived from an electronic compass or from a waypoint referenced from a chart plotter.  The vessels course is corrected by adjustment of the rudder using a steering ram that can be electrically or hydraulically driven.  As with cruise control in a car the autopilot must be supervised - it needs someone on watch.

An autopilot installation has several several components and it is critcal that they are matched to the vessel they are controlling in order to perform correctly.  The good news is that suppliers now provide autopilot kits so that where the owner has the ability, understanding and inclination to install one, they can do so.  The following diagram shows the main components of an Autopilot installation.

  Main components of the autopilot, which will also include connection to a Chartplotter.

Selecting an Autopilot

When selecting an autopilot for your vessel, you should focus initially on the selection of the steering ram that will drive the rudder rather than how sophisticated the electronics are. The autopilot is not complete, nor will it operate effectively unless the there is a device that will drive the rudder(s).  This steering ram transforms the electrical signals from the autopilot control unit into mecahnical movements that adjust the rudder, stern drive or outboard as required.  Steering rams can take up a significant amount of room, particularly where the mechanical connection is made to the rudder.  A critical parameter is the 'hard over time' which is the time it takes the steering ram to push the rudder hard over from the central position to one extremity.  This time, typically, needs to be of the order of 8 to 14 seconds.

The vessels size is rarely a critical issue when selecting a control unit, for smaller vessels where space is at a premium, it is natural to think of the available space and select an autopilot that takes up the least amount of space.  Some autopilots include a control/junction box, a compass, a rudder feedback unit and need connecting to the existing steering system.  Consideration may be needed for the location of the control unit, which should be in a relatively dry space.  The location of the electronic compass should ideally to be at the centre of gravity of the vessel to deliver optimum compass performance.  Sometimes locating these items can be a compromise.  I want to now look at some case studies with examples of what would work for different types of vessel.  This is simplifed but will give you a feel for what is practical.

  The TMQ AP47 Autopilot complete with an electronic compass.

Case Study 1- Hydraulic Steering System vessel <8mtrs LOA typical of sports boats

Using TMQ's Virtual Rudder Feedback the AP-47H makes for an easier installation on vessels with hydraulically steered outboards and stern drives.  If you already have hydraulic steering you need to fit the hydraulic pump, the compass and control head.  No need for a rudder feedback unit or steering ram.  This kit uses a reversible hydraulic pump in the steering system that is quieter and uses less power than a continuously running pump.  The TMQ AP47H is a popular autopilot for trolling fishing as it can steer the vessel accurately even at low speeds of 1 to 2 knots.

Case Study 2 - Cable Steered vessel < 8mtrs LOA

Small and medium sized motorboats whith a steering wheel that is linked by cable to the rudder, outboard or stern drive need a drive unit that complements the existing cable steering arrangement.  This arrangement means that a replacement rotary drive incorporating an electric motor is fitted at the helm position.  Setting the autopilot in it's active mode allows the vessel to be steered automatically and when the autopilot is in standby, steering is achieved manually.  Our TMQ47M is a good example of what we can offer for this situation.

Case Study 3 - Hydraulic Steered Vessel > 8 mtrs LOA

Generally all vessels over 8 mtrs need an autopilot with a rudder feedback unit (RFU).  This RFU tells the autopilot the current position of the rudder, stern drive, or outboard and provides better performance in longer vessels.  Additional installation of the RFU is required and the AP47 control head will need to be set through the on screen menu to recognise the RFU.

Case Study 4 - Dual Helm positions

In vessels with dual helm positions, such as a motorcruiser with a flybridge TMQ55 is used.  This has a central control box and two identical looking control units.  Typically this is a larger vessel so there also needs to be a RFU and since the steering is almost certainly hydraulic a small reversible hydraulic pump.  Again the hard over time needs to be calculated and where larger pumps are needed these are available.

Case Study 5 - Sailing vessels < 11.5 mtrs LOA

Yachts often have steering systems that are designed specifically for the vessel.  The TMQ AP47S is an excellent kit which uses the very popular Remote Sailboat Drive Type RS.  This is an electric drive with onboard RFU and a mechanical connection for attachment to the quadrant on the rudder stock.  This type of arrangement has many benefits including a completely separate steering system.

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