Archive: Onboard Computers

Onboard Computers
UNDER CONSTRUCTION:-- TerryKing 10:10, September 24, 2007 (EDT)

NOTE: Please see the discussion on Onboard Computers at: Discussion- Multi-purpose Onboard Computers - Boat Design Forums http://www.boatdesign.net/forums/onboard-electronics-controls/discussion-multi-purpose-onboard-computers-19458.html

NOTE: This will (real soon, now) also include a discussion of onboard instruments, gauges and monitoring systems. NMEA-0183 will probably be a main protocol and method of interfacing these devices.

NETWORKS: Like NMEA etc. are in section 7, below.

NOTE: Please look for "#TODO#" notes in this item and contribute if you can. Click the (discussion) tab at the top to add comments and suggestions.

An excellent detailed article titled "Choosing an Onboard Computer" was written by Daniel Piltch, of Marine Computer Systems, and originally published in Ocean Navigator Issue #96. This is an overview of off-the-shelf "Marine" computers. Here's a link to Choosing an Onboard Computer

NOTE: Detailed information on more-complex subjects like network protocols etc. have been well-defined by other sources. When you see a LINK like THIS it will open an external like to Wikipedia or another source of information. Click the BACK arrow or button on your browser to get back here.

General Discussion
Computers on "Pleasure" boats are relatively recent, compared to Military ships, supertankers etc. Why would a "Pleasure" boater or "Cruiser" want or need a computer onboard? Let's look at a possible classification of computers that may be found on a 60 foot Yacht today:

Types of Onboard Computers

Embedded / Special-Purpose Computers
- We now expect our cars, microwaves and even refrigerators to "have a computer inside". These "embedded systems" perform a specific function that cannot normally be changed by the user. If we dig a little, we will find that our Garmin GPS, our Fishfinder and our Ipod Nano all have microcontrollers inside, and are running firmware that some guys sat at their desk and wrote months ago. We expect these little devices to just do their job. We can't usually fix or modify them ourselves, although sometimes we may perform a "Firmware Update", especially on a GPS. We can expect any complex onboard device like an Autopilot, Radar, or DVD player to have an embedded computer.

Laptop, Notebook, "PDA" type Computers
Small portable multi-purpose computers may be brought onboard either as the only computer on a smaller boat, or as a useful tool on a larger craft.

• Laptop and Notebook computers are similar in function. They typically run operating systems that are similar to desktop computers and run similar software. Some boaters use these computers for navigation by connecting a GPS unit to them and running navigation software such as OziExplorer or an Electronic Chart Display and Information Systems (ECDIS) that uses free electronic navigation charts (ENC) from NOAA. Boaters also use them for the same things they do at home: writing letters/emails, viewing/editing photos, listening to music, playing games, viewing DVD Movies etc.
• PDA (Personal Digital Assistant) devices and "Handheld PC's" are smaller, and less powerful than laptops, but may be more robust and take less power. Some small devices that run PocketPC and Windows CE operating systems can run navigation software such as OziExplorerCE or NavPac among others.

These computers have batteries to run for a few hours at most. Often boaters power or recharge them with the usual 115-230 Volt chargers, or available 12 to 24 volt chargers.

The primary problem with these computers is their sensitivity to damage in the marine environment. It is quite difficult to view the display or interact with these computers from the helm position without endangering them, especially in ocean environments.

There are specially-Marinized laptops beginning to appear. The Argonaut Ranger 1400T (1400TXL) is an example, with sunlight-readable display and Marinized protection.

Multi-purpose Onboard Computers
The powerful desktop and server computer systems we are used to in office and home environments are the basis for powerful Multi-Purpose Onboard systems. The ability to run more than one software product at the same time, communicate easily with other computers, interface to a wide variety of peripheral devices and store large amounts of data, including maps and graphics is a big advantage in an onboard computer. The marine environment poses the biggest challenge in using computers of this type. Powering and protecting these computers onboard will be covered in following sections. Fortunately, many of the things that were difficult one-off solutions a few years ago are more easily solved today.

Onboard Computer Applications
Lets take a look at the kinds of things we might use an onboard computer for.

Navigation Systems

• Map-based Navigation/Plotter software and systems such as OziExplorer, Winchart Nexus, Fugawi, Transas etc.
• GPS / Compass interface: up/download waypoints, maps, tracks
• Chart/Recorders
• Depth Sensors/Recorders
• Radar/AIS/Collision Avoidance/Docking Video Cameras

Onboard Systems Monitoring and Control
This would include the Monitoring (and Control where applicable) of shipboard systems. This is not unlike a modern automobile where many systems are monitored and alarms are sounded/flashed if something goes wrong. It is an extension of the "Dashboard" instruments we are familiar with, but there is the possibility of integrating them so they are all being "watched" while we pay attention to the helm. They also can be logged, so that trends and history can be shown. Systems that can be monitored include:

• Propulsion systems
• Onboard power systems
• Heating/cooling
• Lighting
• Water/sanitation systems
• Environmental and weather instruments
• Safety/Security Monitoring: Intrusion, Bilge Flooding, Heat/Fire, Dangerous Gases, Anchor Drag

Leisure Time and At-Anchor Activities

• MultiMedia: Audio/Music(MP3), DVD/Movie playback
• Writing, Photo/Video viewing and editing, Log-Keeping
• Communications thru Email and WWW
• Other typical personal-computer activities

Powering Onboard Computers
This used to be difficult to do well, but today there are several good solutions. Let's look at powering the 3 classes of computers we saw above:

Embedded / Special-Purpose Computers
In most cases these devices, such as a GPS, have a built-in power supply that is designed to run from vehicle DC power systems. Typical Garmin GPS units will operate on 10 to 36 Volts DC available on almost any boat. What is needed is the correct power cable to match the device, and these are available from the manufacturers and many aftermarket suppliers. Most other onboard systems run from 12VDC, and in some cases allow higher voltages up to 48 volts. Many GPS units also will run from internal batteries that may be rechargeable / removeable.

Many boaters have a 12VDC powered multipurpose charger onboard, used to recharge small NiCd or NiMh batteries of various sizes that may be used in GPS, flashlights, digital cameras etc.

Laptop, Notebook, "PDA" type Computers
These computers usually have internal rechargeable batteries that will run them for a few hours. They come with a shore-power charger that typically is multivoltage 110-230 Volts AC. A larger boat with an inverter that supplies 115 or 220 volts AC can power these original-equipment chargers and the computer can operate continuously. A few computers can be run directly from 12 VDC, but most require a higher voltage of 14 to 20 VDC from their "charger". There are several available types of aftermarket chargers that are intended to power these types of computers from vehicle DC power systems. This is the typical solution for a boat which has 12V or 24V DC power onboard.

Multi-purpose Onboard Computers
Desktop computers typically have a shore-power power supply built into the case. All of these are either switchable 115-220V AC powered. A larger boat with an inverter that supplies 115 or 220 VAC can run these computers directly. But we also need a solution for smaller boats and 12 V DC supplies.

Let's look at what these computers actually need for power. Their internal power supply provides several voltages that are needed for the various subsystems inside. For discussion, we'll look at the values for a typical 300 watt "ATX" type power supply:

+3.3V@21A +5V@12A +12V1@15A +12V2@15A +12V3@15A -12V@.8A +5Vsb@2.5A

Wow! That's a lot of power. And why do that need all those voltages? Rather than get too deeply into that here, take a look here at: ATX systems and power supplies

If you want to lug your high-end desktop/tower computer with you, you'll need a big boat with an inverter that can power it.

Low-Power Multi-purpose Onboard Computers
There is another attractive possibility for multi-purpose computers onboard smaller boats and cruising sailboats that have limited 24-hour power. Several manufacturers have developed low-power versions of desktop systems. Typically they are also smaller in size. See Mini-ATX Systems for more information. These small computer system boards are only 170 mm (6.7 inches) square but provide almost all the features of larger desktop systems, including Video MP4 acceleration which allows them to display commercial DVD movies at full speed. These system boards, in a small configuration, consume only about 25 watts. Along with an efficient LCD display they total about 30 watts, which means 2.5 Amps on a 12V system, which is probably workable for many cruising applications.

Along with the small low-power system board, there are several available cases and 12V DC power supplies to make up a system. #TODO# Examples here.

A critical problem with running ANY computer system in a marine environment is the corrosive effect of "salt Air" #TODO# (Better definitions). (Help me here!) I believe that salt is present in tiny particles that float in the air in marine environments. Even deep inside a larger boat, salt may be deposited on a surface and accelerate corrosion. This problem is accelerated by cooling fans that constantly draw air over internal parts. The best solutions will have NO fans and no air flowing thru the computer case at all, and will allow actual sealing of the case if desired. Some of the recent Mini-ATX boards use a low-power microprocessor chip that can run with no fan. There are also chip-cooler technologies such as "heat Pipes" and peltier element (electronic cooling) devices. But current systems can run with no fan, and the heat from the microprocessor goes Chip->Finned Heatsink->Air inside case->case walls->outside air.

See "DIY Approaches to "Marinizing" Computers" (below) for a more detailled discussion of how we can build effective low-power onboard computer systems.

Multi-Purpose Onboard Computers and Interfaces
There are no recognized industry standards regarding "Marinized" computers. We'll have to look in more detail at what each manufacturer says.

Commercially Available "Marinized" Computers
NOTE: Many of the descriptions here are from the manufacturer's literature and have not been verified.

• cruisingpc islandhopper With special emphasis placed on low power consumption, the IslandHopper PC is perfect for use on board, where power is at a premium!(Mfg Info) About $895

• Little PC Fanless A Box-level system designed without cooling fans. The rugged extruded aluminum chassis acts as a heat sink to dissipate internal heat and provide noise free operation. Stealth's new Model LPC-301FS Fanless LittlePC is a small footprint PC that features the Intel ULV Celeron 650Mhz processor that offers optimal heat dissipation and power consumption. No Operating system or software included. About $1220

• TinyByte A box-level system running WIN-XP Home. About EUR 1679 ($2250)

• SeaPC A complete system with integral LCD display / Touchscreen. About $4500

• Maptech i3 Basically, the i3 is a sophisticated chartplotter that can handle a lot of add-on options, including Skymate’s Internet Communications with alarm, position and weather link. It has an advanced TouchScreen that can be mounted at the Helm. It can also work with Maptech’s new line of radars.The base price of the i3 is $12,500, including computer, chartplotter, monitor and GPS, but not electronic charts. Radar options, depending on output power and antenna size, start at $3,900. The Skymate option is $1,500, plus service fees. The Weather Channel Marine option costs $2,200, plus service fees.

• Micro Captain PC No price available

• IslandTime PC "IslandTime PC's are 12 volt, power efficient computers for cruisers or voyagers. Each computer is custom built to your needs. We use Intel Core Duo and Pentium M CPU's or VIA C7 and C3 CPU's to provide you with a wide range of computing power that can be efficiently run from a vessels 12 volt system." $950 to $1750

• NautilusTek Marine PCs A system to fit the needs of every boater, from the weekender to the bluewater cruiser. All our units are hand treated to resist corrosion. Monitor and keyboard & mouse are also included in each package $950 to $2495

• Big Bay Technologies Has several computer systems and displays in the lineup. Examples:
  • The PC-RUG is a full-featured industrial wall mount computer that is ruggedized for the marine environment. It’s small form factor ensures that it will fit easily on your boat, while it’s powerful architecture still holds strong against the most intensive navigation software. Also, it’s fanless operation provides added protection against the elements. About $3230
  • The Mini PC is a Micro Form Factor PC where all exterior dimensions have been reduced to a bare minimum without the loss of performance or inputs. About $1795

• Argonaut Computer Has computer displays and the Merlin MX4 computer, billed as: Compact, Powerful, Shock Mounted! World's Smallest Pentium 4 CPU. About $1895

DIY Approaches to "Marinized" Computers
OK, let's try to define the problems we need to solve and the areas we need to find approaches or solutions for, to build an effective and reliable multi-purpose computer system for use on our boat. Then we'll start tackling them. The Problems and Considerations:#TODO# (ask for reviews)

• Marine Environment
  • Corrosion problems
  • Moisture protection
  • Shock and Vibration / Mounting / Location
• Power
  • Power Consumption
  • Power from onboard DC system
  • Cooling
• Interfaces:
  • Humans
  • Computer Peripherals
  • Onboard Instruments and Systems
  • Networks
• Software
  • Operating Systems
  • Applications

OK, let's try to tackle some of these problems:

[edit]
Marine Environment
A critical problem with running ANY computer system in a marine environment is the corrosive effect of "salt Air" #TODO# (Better definitions). (Help me here!) I believe that salt is present in tiny particles that float in the air in marine environments. Even deep inside a larger boat, salt may be deposited on a surface and accelerate corrosion. This problem is accelerated by cooling fans that constantly draw air over internal parts. The best solutions will have NO fans and no air flowing thru the computer case at all, and will allow actual sealing of the case if desired. Some of the recent Mini-ATX boards use a low-power microprocessor chip that can run with no fan. There are also chip-cooler technologies such as "heat Pipes" and peltier element (electronic cooling) devices. But current systems can run with no fan, and the heat from the microprocessor goes Chip->Finned Heatsink->Air inside case->case walls->outside air. In some cases a small thermostatically-controlled fan may be used inside the sealed case to improve the heat transfer compared to convection alone.

Mini-ATX based Systems
A quick pointer to a Mini-ITX system board: This item is no longer available. http://www.mini-box.com/VIA-EPIA-EN12000EG?sc=8&category=99

PC/104 based Systems
There are two basic approaches to on-board computers. The most common, and cheapest in terns of initial cost, is to use a general purpose computer, generally a laptop, that is carried aboard and set-up on an available horizontal surface. These laptops slide around and maybe drop on the deck until someone decides to tie them down. Then they get shook and exposed to salt air until components start to come loose and/or contacts corrode and reliability becomes unacceptable. At this point, most people go out and purchase a new laptop, probably changing brands thinking that will help. The real problem is consumer grade computers are not designed for the marine operating environment. The best long term solution is to replace the general purpose PC with a rugged PC that is designed for harsh environments and also more expensive but lower cost in the long term. The second approach is a computer that is integrated with the vessel (I'll call it a vessel integrated computer or VIC for short) and protected from the environment. This protection generally includes shock isolation, especially for high speed boats, and sealing it from the corrosive effects of the salt air. It may also include remotely locating the computer to reduce its exposure to temperature extremes, such as mounting it below deck instead of on the fly bridge. In general the VIC will be lower cost than a rugged laptop and easier to isolate from the environment.

Embedded PC's are much more common than you realize. Everything from arcade games to vending machines have an embedded PC in them of some form or another. This production volume helps keep cost down. There are many commonly available form factors such as;

Little Board - 5.75 x 8.0 in. single board computer,

ISA "slot boards" - full-length, 13.8 x 4.8 in. and half-length, 7.1 x 4.8 in.,

PC/104 - stacking 3.6 x 3.8 in. single board computers and expansion modules,

PC/104-Plus - PCI bus added to PC/104,

PCI-104 -PC/104+ without the ISA bus connector,

EBX - (Embedded Board eXpandable) PC/104-Plus added to Little Board,

EPIC - shrunken EBX,

EPIC Express - EPIC with PCI-express.

However, no format is more widely supported or has more interchangeable expansion modules than the PC/104, PC/104+ and PCI-104 family. The EBX and Epic options have PC/104 expansion and more board area than a PC/104 SBC, so more features can be accommodated on the main board (fewer expansion modules required) and they support PC/104(+) expansion modules. However, the larger main board of EBX and EPIC means the is many expansion modules are required then the enclosure will have a lower volumetric efficiency. In general little board is used for applications that do not need expansion modules. EBX and EPIC are used mainly when one or two expansion modules are required. If more than two expansion modules are required, then PC/104 is probably the best option. BTW: All generalizations are false including this one.

One of the main adantages of using a PC/104 card stack is the expansion capability, such as a CAN bus expansion module to support NMEA-2000, the ability to seal the entire stack into a weather tight or even air tight enclosure (example) and a small, compact form factor that is easy to mount of shock isolators and compatible with small boats.

PC/104 Cards
The PC/104 standard was developed by Ampro and the specification was initially released in 1992 to provide a compact, high reliability form factor for embedded computer systems. For additional resources on PC/104 hardware and sofyware see pc104.org. The PC/104 standard features 90 by 96 mm (3.550 by 3.775 inches) boards with 104 (64 pins on P1, plus 40 pins on P2) stacking through connectors for an ISA bus. The stack through connectors allow the boards to be stacked in parallel layers instead of at right angles, using 15 mm (.6") spacers to form a very small and compact package.

PC/104+ Cards
The PC/104+ specification was initially released in February 1997 and it adds a stack though connector for the higher speed PCI bus. For additional PC/104+ see the following link at plus_info. The PC/104+ cards are fully compatible with PC/104 cards so PC/104+ and PC/104 cards can be combined in a single stack provided the PC/104+ cards are all at one end of the stack. However, you can only use 5 PC/104+ cards in a stack, the host plus 4 PC/104+ expansion modules.

PCI-104 Cards
PCI-104 cards are similar to PC/104+ cards except the stack through ISA bus commentor is removed to provide more usable space on the circuit card. PCI-104 cards can utilize PC/104+ expansion modules using the PCI bus and by adding a PCI to ISA bridge card they can also utilize PC/104 cards.

Processor Boards
PC/104 (et. al.) processor boards range in performance from 386 and Z80 processors to Pentium M and Celeron M processors. Since the primary application for a VIC is to run an Electronic Chart Display and Information System (ECDIS) application which generally require a minimum of a 500 MHz Pentium III, therefore this discussion will focus on processors that meet or exceed this requirement. Additionally, since Pentium III processors consume more power and therefore produce more heat than Pentium M processors this discussion will focus on Pentium M and Celeron M processors.

There are a few things to watch for or consider when selecting a Processor board. Many processor cards ar PC/104 compatible but not PC/104 compliant, which means that they will function is a stack with other PC/104 cards but they do not comply with all the requirements of the PC/104 Specification such as height per card or connector area. Some processor boards have an integral fan and can only be located at the top of the card stack. Some high performance processors are a two card assembly and they require the height of two or more cards, however they only count as a single card on the PCI bus.

Pentium M class processor boards

Onboard Computer Human Interfaces
If a computer system will be used totally inside a larger boat for conventional computing purposes, the original display / mouse / keyboard system is adequate.

But there's a big challenge if the computer system is to be used actively at the Helm, for Navigation, and possibly for overall boat systems monitoring. And if the desire is to build most of a boats active "Control Panel" based on a computer solution, there are many more challenges. That said, there are a lot of interesting possibilities that are not necessarily expensive to implement, once a marinized multipurpose computer is onboard.

Hopefully the BoatDesign.Net community will get involved in a collaborative project to
show how this can be done. ( Editorial by--TerryKing 10:25, March 18, 2007 (EDT)) !

Click on the discussion tab above if you're interested in this.

Computer Displays
LCD displays are typically used onboard due to their low power requirements, light weight and ease of mounting. Visibility in direct sunlight is unuseable, unless a special (expensive) trans-reflective display is used. The alternative is to mount and shield the display so that it is visible underway on a sunny day. The brightness and contrast available from active LCD monitors is improving; the best way to know for sure if a particular unit is visible in the sun is to have the dealer plug it in outside the store on a sunny day.

There are expensive ($1000 to $5000) LCD monitors that are readable in daylight and waterproof that can be used at the helm.

[Information Page on LCD Displays from IslandTimePC]

The conventional cathode-ray tube (CRT) display is, in many cases, daylight-visible and far cheaper than the LCD option. CRTs are, however, bulky and power-hungry. Due to their power draw they are probably not a good choice on sailing craft, but may be suitable for motor yachts. The bulkiness and associated aesthetic concerns can be remedied by embedding the monitor in a console if there is room.

Plasma TV screens are generally daylight-visible. They tend to be too large for the purposes of an onboard computer, though. They lack the resolution for comfortable close-up viewing, being optimized for home theatre seating arrangements. Plasma units are also very power-hungry. They are most commonly seen as the entertainment display on larger motoryachts.

New research into organic LED technology has yielded cheap, low-power displays that are daylight visible, at least in small sizes. None large enough to be comfortable for computer work are commercially available yet.

Hands-On Interfaces
At the Helm, the primary hands-on human interface is one or two hands on the wheel! When docking, one hand on the wheel and the other on both throttles and direction is barely enough. And if you've tried to click thru a couple screens on the GPS with one hand on the wheel in rough weather, you know even a button-press can be difficult to control. Land and Air vehicles expect you to use both feet too, so maybe we could learn something there.

Conventional (or wireless) Mouse and Keyboard on the dashboard don't work well underway!

Commercial systems (such as SeaPC, above) mostly use TouchScreen technology. This works fairly well if the "hot spots" are large enough to hit in rough weather.

There are a few interesting salt-spray resistant possibilities that will bear further investigation:

• small dash-mounted "graphics tablets" that work like a mouse
• individual large, robust pushbutton, toggle or rotary switches that send keystrokes to the computer
• infrared-beam "touch" screens and "Touch-Switches"
• laser-projected "Keyboards" or "Control-Panels" that appear on the flat dashboard and use infrared technology to find out where the finger "push" was.

Although expensive, there are Industrial / Waterproof Mice and Trackballs available.Stealth Computer has some examples. Trackballs are commonly used for radars and integrated computer systems on commercial craft, as well as critical land and air applications such as air traffic control systems. The Raymarine H6 system is among the first fully integrated pleasure-craft systems to be controlled this way. Trackballs are not affected by the boat's motion and take up little space, making them generally superior to mice for onboard use.

Onboard Computer Sensor and Control Interfaces
This section will discuss ways of connecting a computer to real-world onboard devices. Such devices usually fall into one of the following categories:

Inputs and Sensors
Switches, temperature or pressure sensors, pitch/roll sensors etc

Outputs and Actuators
Relays, motors, servo systems, lights etc.

NMEA-based sensors
Many available marine sensors such as engine pressure/temperature sensors are available with NMEA network interfaces. These are more complete packages, and often easier to use, but more expensive than a 'raw' sensor. But for a few sensors, there may be savings because usually no additional interface system is required.

Onboard Computer Networks

Local-Area-Networks (LANs)

NMEA 0183

NMEA 0183 is a combined electrical and data specification for communication between marine electronic devices such as depth finders, navigation instruments, and GPS receivers. It is also commonly used for GPS receivers in cars, etc. The NMEA Standard has been defined by, and is controlled by, the US-based National Marine Electronics Association, which does not make the specification freely available. Much information has been figured out by end users and DIY boat builders.

The NMEA 0183 standard uses a simple ASCII, serial communications protocol (usually at 4800 Baud) that defines how data is transmitted in a "sentence" from one "talker" to one or more "listeners". The standard also defines the contents of each sentence (message) type so that all listeners can parse messages accurately. A high-speed (38,400 Baud) NMEA0183-HS version is sometimes used, with identical data.

Some more NMEA information and software is available HERE

NMEA 2000

NMEA2000 can be considered a successor to the NMEA 0183 standard. It is based on the CAN (Controller Area Network) network used in larger trucks, industrial systems etc. It has a significantly higher data rate (250k bits/second vs. 4.8k bits/second for NMEA 0183). It also uses a compact binary message format as opposed to the ASCII serial communications protocol used by NMEA 0183. Another distinction between the two protocols is that NMEA 2000® is a multiple-talker, multiple-listener data network whereas NMEA 0183 is a single-talker, multiple-listener serial communications protocol

The NMEA Website: NMEA 2000

Also see Nigel Calder's three articles in Professional Boat Builder:

http://www.proboat-digital.com/proboat/200510/ Networking http://www.proboat-digital.com/proboat/200512/ Networking II http://www.proboat-digital.com/proboat/200602/ See Shakeout

Lowrance has a good manual on NMEA2000 cabling and connections at: http://www.lowrance.com/manuals/Files/NMEA2000NetworksGeneralInfo_0154-173_112006.pdf

Ethernet

Ethernet has been standardized as IEEE 802.3. Its star-topology, twisted pair wiring form became the most widespread LAN technology in use from the 1990s to the present. It is used on many larger yachts to interconnect several subsystems. It is used on smaller boats to interconnect an onboard multi-purpose computer, laptop computers and WiFi Internet connections thru an inexpensive WiFi Wireless Router for in-port access to the WWW. Out of port, it still connects wireless laptops etc. to the main onboard computer. So the Helmsman can email his lunch request to the cook

Manufacturer's Proprietary Networks

[SeaTalk] is a simple interface for networking Raymarine/Autohelm marine equipment so that all devices of a ship can exchange and share their data. SeaTalk is a proprietary solution of Autohelm and not compatible with NMEA or CAN. An independently-created [Sea Talk Reference] is available.

Wide-Area-Networks

WiFi
The term "WiFi", or "wireless fidelity", encompasses a number of wireless digital protocols collectively known as IEEE 802.11. Operation is on the 2.4 GHz or 5 GHz band, depending on the equipment and protocol used. An elaborate and regularly updated description of the technology is maintained on Wikipedia.

This class of communication is a short-range technology, typically limited to less than a hundred metres from the access hub. It is generally used as a replacement for wired Ethernet connections between computers in areas where wires would be too expensive or cumbersome.

Virtually all modern laptop computers are equipped with transceivers for 802.11b and 802.11g, the most common standards. The "g" protocol is faster (54 Mbps max) than the "b" (11 Mbps) but has shorter range. The 802.11a standard is rarely encountered. A new but as yet unofficial protocol, 802.11n, can in ideal conditions give ten times the speed of 802.11g at double the range (up to around 125 m).

A WiFi hub costs as little as $25 and can be used aboard a boat to distribute a network connection to computers throughout the yacht without cables. In addition, many marinas offer WiFi access to their slipowners and guests, either free or for a small price. Some cities, such as Toronto, are using the same technology to set up wide-area networks across a downtown in which a user's computer can seamlessly jump between access hubs, much the way a cellphone does. With modifications to the antennae and hub software (easy for the moderately handy to do with some appropriate Web hunting) the signal from the hub can be concentrated into a focussed beam with up to a few kilometres of over-water range, with the caveat that the signal is negligible outside of that beam.

WiFi is inexpensive and offers the promise of easy freedom from connection cables. It does have its drawbacks, however. Data security can be a major concern on older hubs that do not support WPA encryption; never access your bank account or other secure site through an unencrypted WiFi link. The less computer-literate may also encounter major difficulties troubleshooting the wireless connection if the computers are unable to form the link on their own. WiFi is generally less reliable than hard-wired Ethernet, and the signal is prone to interference from substantial metal or concrete structures. However, it remains the cheapest, easiest and most popular solution for wireless Internet access when within range of a hub.

Satellite

"Short Wave" SSB PACTOR / Email

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