Powerboating - Part Thirteen

Last month we opened the door into the world of modern electronics, with a close look at chartplotters and depthsounders/fishfinders. Electronics is such an enormous field that in this month's article I will continue to look at specific technology available for installation on the modern powercruiser, this time focusing on autopilots and radars.

Once again I am indebted to Errol Cain of Cain Marine for his time and patience, this time in explaining the modern autopilot to me.

AUTOPILOTS
The introduction of electronics to autopilots has made them almost as good as a human on the helm, and in some cases a whole lot better. What comprises a modern autopilot system?

Most autopilots comprise the drive unit (operates the rudder), a compass (determines the course), a rudder feedback unit (tells the system where the rudder is at any particular time) and a display unit. Expect to find a computer box as well.

When contemplating fitting an autopilot, the first consideration is what size will best suit your boat. I urge you to get good professional advice and, if possible, an inspection of your vessel to determine the best unit for your circumstances.

If your boat has hydraulic steering, and most modern powerboats do, then you will need to have a hydraulic pump fitted into the lines. This pump will operate the rudder according to the commands of the autopilot's computer. It must be capable of continuous operation over many days if the passage is a long one. That is why it is important that it is the right size for the job.

The installation of the hydraulic pump is generally straight forward. Most units use plastic hydraulic lines that allow easy line placement and have a neat appearance. Copper lines will be necessary for all craft in survey.

Some boats will have mechanical steering - either cable, chain or shaft, or a combination of all three. In these cases, a mechanical drive is used instead of a hydraulic pump. The drive unit is generally a small electric motor driving through a gearbox and clutch to the rudder.

Installation of this type of drive unit is seldom easy or cheap and must be done by a competent engineer, as the unit will work ceaselessly and exert a lot of force. If the installation is shoddy - and believe me, I have seen some shockers - then the system will not operate correctly. An unreliable autopilot can be, quite literally, deadly. Other steering systems can almost always be fitted with a driving unit, but if you are having difficulty seek expert advice.

The location of the compass is important; it should be as close to the waterline and centreline of the boat as possible and at least two metres from any large iron mass, such as engines, etc. Errol Cain recommends the checking of the anticipated location with a hand bearing compass to be absolutely sure there is nothing that will cause erratic compass behaviour.

THE FLUXGATE COMPASS
Most autopilot compasses these days are of the fluxgate type. Basically, this is an energised coil that detects the earth's magnetic field. As the boat turns, the coil detects a variation almost instantly and relays this information to the system.

A rudder feedback unit is generally necessary on all autopilots. Its purpose is to feed information on the position of the rudder to the system. Installation of this item should be done with care, as its purpose is to mirror the turning of the rudder shaft. Any slop or play in the linkage connecting to the rudder will introduce errors and lead to erratic steering.

The last piece of equipment in the system is the display unit. Almost always located at the helm, it supplies information to the watchkeeper such as compass heading and rudder angle. The latter is displayed even when the unit is on standby, and can be used when manoeuvring the boat in tight situations. Owners of twin screw vessels would not bother with this, but for single screw boats this information makes life a lot easier.

One final item is generally found on the modern system: the central computer. All the equipment is connected to this 'black box', which, like a master of ceremonies, orchestrates the system to control the boat through the water. Let's have a quick look at this in operation.

During the commissioning of the system the installer will program the latitude, hemisphere and magnetic variation into the computer. This will allow the software to adjust for these parameters for optimum performance. Although different manufacturers have different solutions to the problems of correct course steering, the results are generally pretty much the same.

The state of the sea is monitored and the amount of course error permitted before corrective action taken is factored in during the commissioning stage. Powercraft typically have a course error of around 2%, sailing boats have a much wider tolerance, which results in reduced power consumption.

HOW IT WORKS
In operation, the driver selects the desired heading and initiates the unit at the display centre. The fluxgate compass will detect a change in this selected heading and refer this to the central computer.

In turn, the computer orders the hydraulic pump to apply pressure to one side of the steering ram or the other, depending on whether the boat is turning to port or starboard, to correct the course error. The amount of rudder angle applied is relayed to the computer and a comparison to the signal from the compass will determine if more or less rudder is required.

As the boat settles back on the selected course, the pump ceases to operate until the computer instructs it that another correction is necessary. Under average conditions the pump, or whatever drive unit is fitted, will operate about 50% of the time. Power requirements will depend on the size of the drive unit.

ELECTRONIC INTERACTION
I mentioned last month the necessity of careful planning when considering electronics and associated equipment, as compatibility is a big consideration. In years past it didn't really matter what the brand of each piece was, as most items were stand alone and did not integrate with each other in any way. This is no longer the case. Although most pieces of equipment from different manufacturers can be made to talk to each other, it is a darn sight easier if they are from the same 'family', so to speak. This can allow you to connect the autopilot to the chartplotter with a simple cable between the display units.

Now the power of modern electronics comes to the fore. By pressing the correct buttons, the autopilot will follow any course plotted on the plotter (or GPS if a plotter is not fitted). When the first waypoint is reached, an alarm is activated to alert the driver to press the arrival button. This done, the boat will settle down and steer for the next waypoint.

Although it would be a simple matter for the pilot to do this automatically, this is not permitted under international marine conventions.

RADAR
So here I am motoring down the coast, the boat is steering itself, I know exactly where I am and how much water is under the keel, surely there isn't a toy I lack? What about a radar? With all the modern navigational aids I've just mentioned, surely radar is redundant on today's powercruiser?

I used to think so. But, after talking to the boys at Cain Marine, I have to admit radars are still necessary. The main reason for this is that a radar will show you exactly what is out there, while a plotter will show you what the chartmaker thinks is out there. A plotter cannot detect hazards such as an unlit ship on a dark night, nor a storm cell during bad weather.

For these reasons, the radar remains one of the most vital pieces of equipment for a boatie who wants to do a little cruising.

Once again, consult the experts, have an overall electronic plan and have the equipment correctly installed. Radar configurations are numerous to say the least, so it helps if someone knowledgeable guides you through this minefield.

You can select a mono screen, colour screen or cathode ray tube. Ranges vary from 24 miles to over 70, and the dome can be either closed or open. As you can see, there are a lot of options.

Radar systems consist of a dome or antenna and a display unit. Installation is usually simple, just make sure the dome has a clear range all around it and that it is mounted well above the operator's head, as radars emit high-power microwave pulses that can damage human tissue. For planing boats, there are radar dome bases that compensate for the change in the boat's attitude when up on the plane.

After installation and commissioning, radar units are generally simple to operate. Range rings can be toggled for screen display and alarms set to alert the driver to whatever conditions have been configured.

ARMCHAIR ADMIRALS?
Some of the most sophisticated equipment on the market will allow you to display radar information on other screens, for example on the fishfinder/plotter, and vice versa. The radar can even overlay the plotter, which allows boats targeted by the radar to be displayed on the plotting chart. Features such as these can provide great comfort on a squally night with a rising sea.

There are many other electronic instruments that can be fitted. In fact, the list is nearly endless, including wind instruments, sea temperature probes, satellite communication and weatherfax, to name a few.

To purists, boating 'by the instruments' may seem too complicated and too reminiscent of 'armchair admirals' for their liking. But, to me, everything that helps is welcome. Forget about swinging the lead to read the depth, casting the log for speed or even dragging out the old sextant for a sun shot. Try doing those things on today's crowded waterways and you're just as likely to run aground or have a collision.

People who love oil lamps and sight reduction tables should not look down at people who love beeping alarms and active matrix screens. As the old saying says, different strokes for different folks.

See you next month. I'm off to read the 200-page instruction book on my plotter!