What is an Autopilot?
Using an Autopilot when trolling has several benefits – the main one being that a steady course can be held at slow speed so that the crew can concentrate on fishing – we should add that this should not be at the expense of safe navigation and seamanship! An Autopilot when used correctly can make life a whole lot more enjoyable.
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 either from an electronic compass (e.g. fluxgate, Transmitting Magnetic Compass, satellite or gyro compass) or from a waypoint referenced from a chart plotter. The vessels course is corrected by movements to the rudder and this can be done either through a hydraulic or electrically operated steering ram. Just like cruise control in a car the autopilot still needs to be supervised – it needs someone on watch!.
The Autopilot installation has several components and it is important that they are matched to the vessel which they are controlling. However the good news is that suppliers are now providing autopilot kits so that where the owner has the ability and understanding to install, they can do so.
Selecting an Autopilot
There are many autopilots to choose from. However, when selecting an autopilot for your boat, there are important factors to consider. Surprisingly it’s not so much the sophisticated electronics and display that are critical but the selection of a suitable unit to drive the rudder.
The most important decision concerns the boat’s steering system. The autopilot is not a complete system until the drive unit has been chosen. The drive unit transforms the electrical signals from the autopilot into mechanical movements which turn the boat’s rudder, stern drive or outboard motor. The existing type of steering system decides what kind of drive unit the autopilot needs to complement it. Drive units can take up a fair amount of space particularly at the mechanical connection to the rudder. The critical parameter is known as the ‘hard-over time’ which is the time it takes the rudder drive to push the rudder hard over to one extremity. This needs time needs to generally be in the region of 8 to 14 sec.
The boat’s size is rarely a critical issue in the choice of autopilot controller. However for smaller boats, it is natural to think of available space and select an autopilot that occupies the least space. The display is the visible part and often the smallest part. Autopilots may also include a control/junction box, a compass, rudder feedback unit and need connecting to the existing steering system.
The control/junction box may need to be installed in a protected space away from the elements. The TMQ AP47 has a major advantage here in that it does not have a control/junction box and is ideally suited when space is at a premium. The compass will need fixing in a suitable location so that it can provide it’s optimum performance.
The following sections give a simplified method of selecting an autopilot for your boat. This is a generalised solution and if you need assistance please contact us at NavigateByUs for assistance.
Hydraulic steering system < 8 Mtr LOA
With it’s virtual rudder feed-back the AP47 makes for an easy installation on boats under 8 mtrs with outboards and stern drives.
Where your boat already has hydraulic steering fitted then you only need to install a hydraulic drive unit such as a reversible electric pump which is connected to the existing hydraulic hoses. Chosing the right size of the pump is dependant on the volume of the existing hydraulic ram that moves the rudder. Most kinds of autopilots need a “hard over” time between 8 to 14 seconds which in turn specifies the pump flow rate. Reversible hydraulic pumps are smaller and use less power than continuously running pumps.
The TMQ AP47 is a popular autopilot for trolling fishing as it can steer the boat accurately, particularly at very low speeds of around 1-2 knots.
Cable steering < 8 Mtr LOA
Small and medium-sized motorboats with a steering wheel frequently have a rotary drive with a cable attached to the outboard motor or stern-drive. Drive units are available that complement existing cable systems. The most common solution for cable steering is to replace the rotary drive behind the steering wheel with an electric motor. Setting the autopilot in it’s active mode allows the boat to be steered automatically. When the autopilot is in standby mode the boat is manually steered by the wheel.
Hydraulic steering system > 8 Mtr LOA
Boats longer then 8 meters need an autopilot with a rudder feed-back unit like the AP47R. Most of them have hydraulic steering systems and the autopilot can be complemented with a reversible pump.
Choosing the right size of pump is dependent on the volume of the existing hydraulic ram that moves the rudder. Most kinds of autopilots need a “hard over” time between 8 to 14 seconds which in turn specifies the pump flow rate.
Dual helm positions
Where a boat has two steering positions,one on the fly-bridge and one internally for example, an autopilot such as the AP55 should be choosen. Most boats of this size would have hydraulic steering systems and the autopilot should be fitted with a reversible pump.
To chose the right size of the pump is dependant on the volume of the existing hydraulic ram that moves the rudder. Most kinds of autopilots need a “hard over” time between 8 to 14 seconds which in turn specifies the pumps flow rate.
How does an autopilot work?
An autopilot is maybe one of the most advanced and technically sophisticated instruments you can have in your boat. It has all the intelligence needed to automatically steer your boat once you have told it the direction to steer or where you want to go. Once installed it’s quite easy to use it, but it is important to understand how it functions and why it behaves in the way it does This ensures you get the maximum benefit from the equipment and knowing your equipment is important for safety at sea. All autopilots on the market work in much the same way so what’s explained below is more or less the same for any brand of autopilots.
When the boat turns off course or the reference course is changed, the autopilot should apply helm in a way which brings the boat quickly back onto course without overshooting the reference course. The correct rudder angle depends on the amount of the error, the speed of the boat, its size and the effectiveness of its rudder. In order to customize the autopilot and adapt it to the surroundings there are control settings that need to be tuned. Normally you don’t need to modify these settings, the factory settings are usually good for most types of boats and weather conditions. If you need to optimise the settings it’s important to know what you are doing.
The two most important settings are Sensitivity and Rudder factor.
Sensitivity (Also known as Yaw, Weather etc)
The main task of an autopilot is to lock the heading of the boat to a predefined reference course. This is the course the boat has when you press the auto button. In the auto mode the autopilot constantly compares the boats true heading given by the compass with the reference course in the same way that any control system does. If there is deviation,the autopilot applies power to the steering system and the rudder turns the boat to get it back on track. The rudder angle is feed back to the system. There is a trade off between the accuracy of holding the reference course and the activity of the rudder movements. The more accurate you want to hold the course the more the drive unit has to work. Changing the Sensitivity parameter lets the user calibrate and fine tune the autopilot to a balance between these two factors and adapt to changing circumstances during cruising such as changing weather conditions, heavy weight etc.
The sensitivity control governs the sensitivity and is used to determine the amount of “wander” in the boat steering. A high value for the sensitivity will allow the vessel to drift off course before correcting. A low value for sensitivity will attempt to keep the vessel more precisely on course. If you want to change the factory setting of this parameter set the lowest sensitivity value that you can, without having the steering motor continuously “hunting” from side to side. This minimum setting depends upon the amount of slack in your steering, vibration around the rudder feedback mounting position, characteristics of the steering drive system and the weather conditions. The sensitivity setting is remembered when the unit is turned off and on. Lower numbers are most sensitive and will give a straighter course steered. Do not set this so low that your steering equipment is continually working or “hunting”, as this will cause premature wear on your system and, in severe cases, may cause malfunction. In heavy weather you can increase the value to let the boat follow the waves without correcting the course all the time.
The Rudder Factor is a tool to adapt the autopilot to the steering system of the boat. Depending on the rudder size etc. the amount of force needed to turn the boat can be adjusted using this parameter. This function makes it possible to tune the amplifier to the rudder angle and how many degrees of helm that are applied for a given course error. In large or slow boats it would be more and in light, fast boats it may be less. Setting the rudder factor too high causes over steering. Too low a setting causes under-steer and a slow response.
In the picture to the right it’s shown what happens when the rudder factor is to high (at the top) and when it’s to low (at the bottom). The movement of the boat is of course exaggerated for illustration purpose only. In real life and when correctly tuned the boat should move in a straight line. The adjustment of this parameter should be done on a calm sea.
Modes of Operation (with reference to the TMQ range)
An autopilot can work in one of several modes dependent on what you want to do with it. At start up it will always go in to manual or stand-by mode. The different modes are explained below:
Manual Mode, the autopilot is standby and the boat is under manual steering. The display shows the actual heading course.
Auto Mode, the autopilot is activated and steers the boat to the reference course which is then shown on the display. The reference course will be the course the boat has when auto mode is selected. You can change this desired reference course by pressing the arrow buttons on AP47 and AP55.
GPS Mode. In this mode the autopilot gets steering information from a separate GPS unit. All Autopilots with GPS connected for navigation can follow a track to a distant bearing and can follow a route of multiple way points and automatically turn to a new reference course when switching to next way point. In the picture at right you can see how it looks on a GPS plotter. Note that the boat will not cross the waypoint, when it’s close enough to the waypoint the autopilot will automatically turn to the next waypoint.
Power Steering Mode. In this mode the boats helm system is controlled by the helmsman with buttons on the Display unit. Since the autopilot is in command of the helm system through its drive unit, this is a convenient way to steer the boat and to get power steering. This can also be done by a remote device on a cable or a second steering station mounted away from the main steering wheel. Since the autopilot controls a power steering system, options are available to use this to steer the vessel by hand while away from the main wheel. This can be done by a hand-held device on a cable or a permanently mounted second steering station.
We can supply a wide range of kits that are tailored to your specific needs. Some of the more popular ones are available in our store now. Please feel free to contact us for more details.
Web site www.navigatebyus.com
Contact is Chris Cole +44(0)1494677751