An automatic direction finder (ADF) has a motor that rotates the loop antenna, keeping the loop alwAY in the null position. The motor also actuates a needle, similar in appearance to a compass needle, that indicates the position of the loop. This so-called radio compass points not toward north, but toward whichever station is tuned in on the loop antenna. Such direction finders can operate on any radio station broadcasting a continuous carrier on a frequency that the radio set can receive. Virtually all aircraft and ships were equipped with D/F equipment. Radio D/F equipment is also used in police work and counterespionage to locate hidden radio stations.

PCs

First the Apple then the generic IBM PC style of machine, and more recently the Notebook computer have appeared on chart tables. Until recently most computers were used on board for weatherfax reception, charting display, plotting positions and word processing. The usefulness of e-mail to folk who only occasionally touch base with civilization has brought new converts to computing, and further electronic developments are set to do the same.

The main attractions of PCs compared with Notebooks are their relative cheapness to buy. repair, anti upgrade and the relative ease with which functions can be added simply by installing the appropriate "board" in an expansion slot. PCs also have a large display screen with good resolution, good daylight or nighttime viewing, a full size keyboard, and a proper mouse.

A PC's main disadvantages are bulk, need for a desk surface, lack of portability, and, above all - large power drain. The lack of portability rules PCs out for a few applications such as C-mail communications via an audio coupler at public 'phone booths – and at around 25kg (the weight of a typical PC, monitor, and printer) will be a negative factor on racing yachts, compared with around 6kg for a Notebook and compact bubble-jet printer. If these factors are not overriding considerations the common PC can be about as convenient to use below decks as it is in the office.

Compared with PCs the advantages of Notebooks are in their size, weight. portability, significantly lower power requirements and ability to run for some hours on internal rechargeable batteries. Most but not all programs that run on PCs will also run on equivalently powerful Notebooks. Disadvantages such as their smaller screens and compact keyboards are not a serious drawback for most uses, but the various substitutes for the mouse (track balls, joy sticks and touch pads) are often fiddly so the ability to connect a conventional external mouse is worth looking for.

A major drawback to Notebook's of course is their price, which range from nearly double to around four times the price of a similarly powerful PC. Notebooks rely on expensive CMOS components to achieve their low power requirements, but screen differences and general reliability and workmanship (reflected in warranty periods) are other significant factors in the price.

The portability of a Notebook allows it to be taken to a public phone to send and receive e-mail and faxes, but also opens up numerous other possibilities, including idyllic word processing in the shade of a palm tree. More practically perhaps, allows the one computer to be used at home, in the office, and on board - spreading the investment and avoiding the need to transfer and update files between to or three separate machines.

Notebooks run, or can run, from rechargeable battery packs. Older machines use NiCad (Nickel Cadmium) batteries although many now use Ni-MH (Nickel Metal Hydride). Ni-MH batteries are supposed to have less of a "memory" problem, but full discharge before recharging is still recommended.

Even better performance should be expected from Lithium Ion batteries although these are generally only found in the more expensive models. Duration under battery power varies depending on the processor and application, but can be less than an hour with some models, so in practice one will usually want to power them from the yacht's DC supply.

An AC charging/running adapter is supplied as standard, so Notebooks can be powered through quite small inverters, and DC adapters with "cigarette lighter" plugs are available for some models. AC adapters for powerful Notebooks may carry ratings of over 100 Watts to allow for simultaneous use and fast recharging of the battery, but the actual power consumption of the Notebook is far less. For example a modern Pentium 133 Notebook with 32 MB RAM, a CD ROM, and a dual scan color display draws about 2.5 Amps (30 Watts) from the yacht's batteries - similar to running navigation lights - and supportable by a single 40 Watt solar panel. An "active matrix" display needs a further Amp. Notebooks of course are easily accommodated on board. Waterproof carry cases are available and might be a good investment, especially if the computer is routinely transferred in a dinghy.

On some yachts computers are already far more than just a convenience. Large Motor Yachts and fishing craft began using raster and vector type chart navigation several years before the advent of ARCS, and in one-off situations such as the BOC and Whitbread races, individual competitors go to considerable trouble to seal displAY and keyboards for computers used for weather satellite reception and communications. The BOC boats used Notebooks, and the fishermen (for whom power is not a problem) generally use PCs, but in either case the computer cannot be mollycoddled, and must be as reliable as possible. The interface with the operator has to be waterproof, robust, and convenient to use with cold wet hands. One solution is to use waterproof touch screens, where the human finger chooses alternatives or points to places on the screen directly (as is done to interface with some bank teller machines). These were originally based on CRT monitors sealed into bulky GRP fairings, but splash proof color LCD touch screens are now available and able to display chartware and tactical data to the deck crew right in the cockpit.

Firms specializing in such things also extend marinisation to the computer itself, with the electronics and board drives in sealed cases, and cable entries through grommets or sockets. Floppy or CD-ROM drives may lie mounted separately in protected locations. Waterproof keyboards and mice, and wireless remote mice are available. Specialized systems tend to be quite expensive but with an appropriate power source can provide relatively reliable on-board computing. Options and economies will no doubt improve in the next few years as commercial shipping switches to Raster and Ecdis charting systems.

A development with perhaps more relevance to ordinary yachts is the ruggedised waterproof Notebook computer. Such things were originally pioneered for military applications but civilian equivalents that can withstand severe shocks and inundation if not actual submersion are now available for field workers, traveling salesmen etc. Prices are in the mid to high range for Notebooks depending on the screen, microprocessor, and drive options chosen, and they're even available in conspicuous colors to match your rubberized binoculars.

The Future