Cockpit electronics

Today’s marine electronic world is a far different place from what it was only a few years ago. Individual transistors have been largely replaced by integrated circuits, and many of those have in turn been replaced by large-scale integrated circuits and microprocessors. Unfortunately, a considerable part of the value of today’s marine electronics is routinely unavailable to many shorthanded voyagers. The equipment is there, but much of it is installed at the chart table.

This type of installation is a vestige of the past, when electronics had to be carefully sheltered from the elements. Expensive electronic suites at the chart table are impressive; however, unless there is someone attending this below-decks gear and relaying the information to the helmsman this type of installation has limited real-time value.

As far as possible, all of a pleasure boat’s navigation and communication electronics should be within reach and close sight of the helm. The challenge is to place the equipment where it needs to be while respecting its environmental limits, ensuring that it does not block the helmsman’s vision or restrict access to the helm and takes into account the magnetic, electromagnetic, and radio frequency signatures and susceptibility of each unit. It won’t do much for accurate navigation if the VHF radio’s loudspeaker creates a 20° error in the steering compass or if the autopilot runs the boat in circles because its fluxgate compass has fallen in love with the magnetic field from starboard speaker for the cockpit stereo system.

The planning of the electronics installation should begin with preparation of a list of every device you now have on board or may wish to install in the next few years. From this list, select all of the devices you wish to use while at the helm. Separate this equipment list into: a) those items that do not require access to the controls during use and b) devices that require operation of controls to be effective. Examples of the former include sailing instrument installations using one indicator per function, for which there is no need to switch an indicator from one parameter to another. VHF radios, radar, chart plotters, and multi-function sailing instruments are examples of devices requiring frequent control input.

The owner’s manual for each piece of equipment will provide the environmental information required to guide the installation. For example, the manufacturer’s literature will generally indicate the degree to which the product can withstand exposure to seawater. Only devices specified as submersible should be considered truly waterproof. Many units are advertised as waterproof when mounted to a panel in a manner that shields electrical connectors from direct exposure to water. Some products are designated as splash proof, a generally imprecise term that should be viewed with suspicion when it comes to surviving direct exposure to the open cockpit environment. Devices with this designation should be installed in a manner that protects them from a direct blast of seawater. Regardless of the environmental rating of any device, electrical connectors always deserve special protection from exposure to seawater. The addition of a drop of seawater to the closely spaced power pins in a connector creates an ideal electrolytic cell, quickly destroying the conductors.Magnetic fields

When in operation, electronic devices typically produce external magnetic fields. Any device proposed for mounting closer than about one meter from the steering compass should be checked for influence on the compass in both operating and de-energized modes. When making this check be sure to evaluate the effects for all relative positions of the device and the compass. Many installation/instruction manuals specify a “compass safe distance” that is often on the order of one meter. However, a careful on-board evaluation may show that, depending on relative orientation, the device can be safely mounted significantly closer to the steering compass. An example of this effect can be seen in some CRT radar’s for which the screen can be within 12 inches of the compass without detectable effect while unacceptable compass errors were noted when the rear of the radar was less than 30 inches distant.

The passage of direct current through any power wiring can create a magnetic field capable of interfering with a compass or flux detector. Twisting the two power wires around one another, creating a twisted pair, will largely cancel this magnetic field. It is for this reason that a twisted pair of wires is used to deliver current to the compass light.

Virtually all loudspeakers and many microphones contain permanent magnets capable of producing significant external magnetic fields. A magnetic compass or flux detector up to one meter distant can be rendered inaccurate by an innocent-looking device such as a portable radio. The handheld VHF radio’s loudspeaker or the magnet in the earpiece of a cellular phone can induce large errors in the steering compass or deflect the autopilot if placed close to the flux detector. Even the headphones of a walkman can have an adverse effect at short distances.

All data displays in the cockpit must be reasonably visible under all lighting conditions. Monochrome LCDs used to display alphanumeric and digital data present the least visibility problems. Many have variable contrast controls, allowing them to be adjusted to suit the changing operating conditions. Color LCDs present significant visibility problems when used in any above-deck environment, including indirect sunlight conditions. While some displays are fully sunlight readable, others provide no useful information in direct sunlight and may be marginally readable in any daylight condition.

Manufacturers of LCDs measure screen brightness in units called nits. (A “nit” is a measure of the amount of light emanating from the screen – these are not the same nits as often accompany lice. See sidebar for more than you ever wanted to know about nits.) LCDs designated as sunlight readable usually have brightness levels of more than 1,400 nits. Screens rated as daylight viewable may have brightness ratings of 300 to 400 nits and will be very difficult to view in direct sunlight. Sunlight-readable screens are presently quite expensive.

Regardless of the type of LCD used, it is important to check its visibility when viewed through polarized sunglasses. LCD operation is based on the use of polarized light. The polarizing film in sunglasses is set at an angle defined by the natural polarization angle of sunlight. The polarizing screens in some LCDs are set at angles that make the screen appear completely blank when viewed through polarized sunglasses.Heading info is paramount

The position of cockpit-mounted navigation aids and electronic devices relative to the helm should be dictated by the role each device will play when navigating in the most challenging circumstance. The vessel’s heading is always paramount, therefore, the steering compass is placed on the binnacle immediately in front of the helmsman. The vessel’s radar, a relative-position navigation device, is usually next in importance. Absolute navigation position indicators, GPS and loran, support the function of the radar. They should be located close to the helm but do not necessarily need to be in the helmsman’s primary vision field. Unlike air navigation, in which virtually all high-altitude flight is accomplished with hardly a glance outside the cockpit, navigation on the sea is overwhelmingly visual. This is especially important for small vessels, since many large ships proceed with limited visual observation of what lies in their path. Being head-down in the cockpit, staring at a data screen, is unacceptable.

Data displays that support navigation-wind speed, direction, hull speed, water depth, and temperature-should be located where they can be seen, without interfering with clear vision of the surrounding sea area. Multi-function displays can be installed below the helmsman’s line of sight, in a position where their control keypads can be easily operated. The VHF radio can be mounted in a compartment in the side of the cockpit, readily accessible but far enough from the steering compass to prevent magnetic interference. Remember to keep the radio’s microphone at a safe distance from the compass.

Many of today’s radar systems can superimpose waypoint position information on the radar screen. Some can overlay the radar information on a chart or share the screen with a chart and other navigation data. Satisfactory performance of a radar/chart overlay display will, to a large extent, depend on the stability of the magnetic heading reference system. The additional navigation information these systems can display may include: vessel speed and course over the ground (SOG and COG), VMG, apparent and true wind velocity, set and drift of the current, and sonar data. This type of display closely resembles an aircraft multi-function display and can greatly simplify the helm electronics installation. Dedicated electronic chart plotters are best positioned alongside the helm station rather than in the primary scan area.

Regardless of the presence of a chart plotter, there must always be a convenient means for using a paper chart. While a simple, transparent plastic-covered board or the envelope sold for use with ChartKit chart books will suffice, the Yeoman Sport electronic chart board can be an ideal solution to the chart navigation requirement. This device can be connected to a GPS or loran, automating much of the routine navigation work, including on-chart position fixing, waypoint fixing and entry and calculation of ranges and bearings. The data cable from the GPS or loran to the Yeoman can be terminated both at the chart table and in the cockpit. When not required in the cockpit, the Yeoman can easily be carried below and used at the chart table or taken from the boat for use ashore. Two of the most interesting attributes of the Yeoman approach to electronic chart navigation are its ability to work with any chart, including one prepared on the spot, and the way in which it simplifies the posting of updates published in the notice to mariners. Some items best belowdecks

Some electronic devices are best placed belowdecks, where they won’t compete for prime real estate at the helm. The HF/SSB radio should be mounted below, in a location where weak signals can be heard clearly and where it can be readily connected to the computer used to capture weather maps and data. Likewise, the boat’s computer, unless it is especially designed for installation in the weather and equipped with a sunlight-readable screen, must be securely mounted below. The boat’s weatherfax receiver/printer must be sheltered from the elements. Installed below it can share the SSB radio’s antenna. A Navtex receiver belongs at the chart table. It will sound an alarm on receipt of warning or emergency messages, and routine messages can be read by the off watch at any time.

To conserve space in the cockpit, the main autopilot control can be mounted below, provided the remote control is located in easy reach of the helm. The fluxgate sensor or digital gyro for the electronic compass and autopilot benefit from being installed as low as practical, near the center of the boat where motion is at a minimum.

Entertainment systems, including the TV set, are best installed below, out of the weather. Automobile radio/CD/tape systems designed for mounting in a car’s trunk, with just the control head on the dash, can be installed so that the control head is accessible just inside the companionway. With this type of system the “front” speakers are installed in the saloon, with the “rear” speakers in the cockpit (but remember to keep all speakers at a distance from all magnetic sensors).

Using magnetic shielded loudspeakers similar to those used in color TV sets can reduce interference problems (see sidebar, “Quashing stray magnetic fields”).

Cockpit installation of electronic units can be greatly simplified with the use of commercially produced equipment mounting pods. The Edson Company, for example, offers a number of housings designed to work with their pedestal systems. Ocean Equipment, Inc., also offers a range of useful devices they call NavPods.

Today’s marine electronics provide navigation, entertainment and safety capabilities far beyond what anyone had envisioned only 25 years ago. The cost of even the most complete installation is a fraction of the investment that was required to purchase the most basic navigation/communication system in 1975.

Proper installation of this equipment will make navigation safer and more enjoyable. The small size and rugged weather tolerance of today’s equipment allows us to put things where they are of most use-in the cockpit.

Contributing editor Chuck Husick is a sailor, pilot, and Ocean Navigator staff instructor.

By Ocean Navigator