Wi-Fi on a Boat

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Making shore-based Wi-Fi Internet work well on a boat.


Wi-Fi articles
Wi-Fi (main article)
   alt.internet.wireless (discussion group)
Fast Fixes to Wi-Fi Problems
Wi-Fi How To
Wi-Fi on a Boat
   rec.boats.electronics (discussion group)
Wi-Fi Phones

Contents

Common Problems

In locations where shore-based Wi-Fi signals are strong, using them for Internet access on a boat is comparable to using Wi-Fi hotspots on land. However, the marine environment tends to exacerbate general Wi-Fi problems and create other problems of its own:

  • Boat hulls and sailboat masts can block radio signals, reducing range.
  • Movement of other boats can cause interruptions of Wi-Fi connections.
  • Location of a Wi-Fi antenna in a cabin below deck can further reduce range.
  • It may be difficult to get close enough to the Wi-Fi access point for sufficient signal, especially when anchored.
  • Boat movement can result in aiming problems with highly directional antennas (even when tied up).
  • Moisture in the marine environment can result in electronic failures.

Improving Wi-Fi

Higher Power

American Alligator

While it may seem that higher power Wi-Fi might help to improve your range, that's not necessarily true, since higher power only helps on transmit, not receive. Thus it's only likely to help if the other end of your connection is using higher power as well, which is often not the case. In other words, what you may well wind up with is an alligator, big mouth but small ears. Also, unnecessarily high transmit power will tend to increase your interference with other Wi-Fi users, making you a bad neighbor. It's usually much better to just improve your antenna, which helps both transmit and receive.

Better Antenna

Outdoor wireless access point with high-gain omnidirectional antenna.

Usually the best way to improve range is to use a better antenna (or reflector with a standard antenna), which helps both transmit and receive.

Better antennas work by being directional:

  • concentrating radio energy/sensitivity to/from the desired direction instead of wasting it in pointless directions, and
  • reducing interference from other radio sources not in the desired direction (path).

The improvement in antenna performance is referred to as gain, where a higher number indicates the amount of performance improvement expressed in dBi. It takes an increase of 6 dB to double range; e.g., as compared to a typical 2 dBi antenna, an 8 dBi antenna has double the range.

However, a highly directional antenna can be problematic on a boat, since it must be kept aimed accurately at the remote end of the connection, which can be difficult on a boat floating in the water (even when tied up). The width (angle) of the directional pattern (both vertically and horizontally) can be used to see how accurately the antenna must be aimed.

The simplest and easiest improvement is to use a higher-gain omnidirectional antenna (4-8 dBi), thereby avoiding the need to aim the antenna horizontally (point it at the shore-based wireless access point). Such an antenna works by concentrating energy/sensitivity in the horizontal direction that would otherwise be wasted vertically (up and down). Beyond about 8 dBi the vertical beam angle becomes so narrow that vertical aiming can be problematic on a boat:

Omnidirectional
Antenna Gain
Example of
Vertical Beam Angle
  4 dBi
  6 dBi
  8 dBi
10 dBi
12 dBi
50°
28°
15°
11°
  8°
 Omni Antenna Patterns.svg.png

Antenna Location

Higher antenna locations tend to have less interference (e.g., from other boats) than lower locations, so in general it's a good idea to locate the antenna as high as is practical. On a sailboat, the ideal location is at the top of the mast.

Since signal loss in the cable between the radio unit and the antenna increases rapidly with the length of the cable, it's better to locate the radio unit next to the antenna, and use lossless cable to support the radio unit, either USB or Ethernet, both of which have advantages and disadvantages (as noted below).

Automatic Tracking

There are products than can be used to keep a directional antenna aimed at an access point as a boat swings or drifts with precision of better than one degree (e.g., Track-It-TV). However, they are relatively expensive, and they only track in the horizontal plane, so it's important that the vertical beam width take into account rolling and pitching of the boat. Usually a vertical beam angle of 10 degrees or so is adequate for all but the roughest conditions, but even beam angles of 20 degrees or more can still result in substantial improvement in gain over an omnidirectional antenna.

Temporary Setup

Setup as needed, packed away when not in use. Ideally the radio unit and antenna are located together as high as possible (e.g., outside on the top of the cabin), usually connected by cable:

USB

Hawking HWU8DD Hi-Gain USB Wireless-G Dish Adapter

Advantages:

  • Simplicity
  • Lower cost
  • Power over USB cable standard

Typical USB setup:

Caveat: Maximum length of a USB cable is 5 meters (about 16 feet), although that distance can be multiplied by means of one or more USB active extension cable(s), effectively a standard USB cable married to a one-port USB hub (e.g., StarTech USB 2.0 Active Extension Cable USB2FAAEXT15).

Note: USB Internet connection can be shared by means of Internet Connection Sharing and a separate network (e.g., Ethernet).

Ethernet

Buffalo Wireless-G High Power Ethernet Converter WLI-TX4-G54HP

Advantages:

  • Long cable (up to 100 meters)
  • No USB driver needed (universal)
  • Support multiple clients with a hub or switch

Caveat: Not all Wireless Ethernet [client] Bridges support multiple clients. Check manufacturer specs and/or Wi-Fi Wireless Ethernet Bridges.

Typical Ethernet setup:

Power: Separate power cable, or it may be possible to use Power over Ethernet. Check manufacturer specs.

Permanent Installation

SENAO Outdoor Wireless Multi-Client Bridge/Access Point/WDS SOC-3220

Will give far more range than regular Wi-Fi at deck or cabin level:

  • Install weatherized high-gain omnidirectional antenna as high as is practical (if on a sailboat, ideally at top of mast)
  • Install weatherized Ethernet client bridge (e.g., SENAO SL-2611CB5 EXT or SOC-3220) as close to antenna as possible (as in outdoor access point picture above, in order to minimize signal loss in antenna cable)
  • Run weatherized CAT5 cable from Ethernet client bridge (if on a sailboat, down/inside mast)
  • Power client bridge with Power over Ethernet
  • At cabin end of Ethernet cable, put:
    • Hub or switch (for wired network connections)
    • Wi-Fi access point (for Wi-Fi network connections)
    • Bluetooth access point (e.g., ANYCOM AP-2002) (for Bluetooth network connections)

Managing a Wireless Ethernet Bridge

Wi-Fi at top of sailboat mast

When using a wireless Ethernet [client] bridge, IP addresses of networked clients on the boat (wired or wireless) are normally assigned by a shore-based DHCP server.

The problem is that the wireless Ethernet [client] bridge will typically have a fixed IP address for management that won't necessarily be on the same subnet as IP addresses set by shore-based DHCP servers, preventing networked clients from directly managing the wireless Ethernet [client] bridge.

Two possible solutions to this problem:

  1. Use two network adapters {wired or wireless) on a given networked client:
    1. One configured by (shore-based) DHCP for Internet access
    2. The other configured manually just for managing the wireless Ethernet [client] bridge
  2. Use a multi-homed Ethernet adapter with both a static address and a DHCP address

Wired versus Wireless Clients

Boat Wi-Fi Wired vs Wireless.svg.png

Note: In order to minimize possible interference, a boat Wi-Fi access point should ideally be on a different minimally-overlapping channel (1, 6, 11 in the USA) from the shore access point.

Power

Many standalone low-end networking devices that use separate "wall wart" type power supplies are able to tolerate a relatively wide range of input voltage, and can be run directly from 12 VDC boat power with an appropriate adapter cable. Check manufacturer input voltage specs if possible.

LAN on a boat

  • When the boat has its own wireless access point (or wired hub or switch), and multiple network devices that get their IP addresses from a remote DHCP server, then all those IP addresses will be on the same subnet, and are thus part of a local area network (LAN).
  • It won't necessarily be a private LAN -- unless the remote wireless access point implements wireless-to-wireless isolation (which many do not), all boats will be on the same LAN, and should take precautions accordingly -- see Secure Internet access in a public hotspot.
  • That kind of LAN will be "up" (working) only when connected to remote Wi-Fi; otherwise it will be "down" (not working).
  • To have a private LAN, and one that works even when not connected to remote Wi-Fi, then use a local wireless router instead of a local wireless access point (or wired router instead of a wired hub or switch). That creates a "double NAT" which will usually work fine, although it can cause problems with certain older network protocols and applications. To access the LAN management port of the wireless Ethernet (client) bridge:
    • Good method: If supported by your local wireless router, configure a manual route from LAN to WAN for a (RFC 1918) private IP address on the LAN management port. (The wireless router shouldn't forward private addresses without a manual route.)
    • Crude method: Set a fake non-conflicting public IP address on the LAN management port of the wireless Ethernet (client) bridge, which your local wireless router will automatically forward to its WAN port (since it's not a local or private address).

Relaying and Mesh Networks

When some boats are too distant from a shore access point for a direct Wi-Fi connection, it may be possible to setup nearer boats to repeat or relay the Wi-Fi signal to more distant boats. See Wireless Distribution System.

International Use

Wi-Fi channels are standardized, but vary slightly in different parts of the world. Many Wi-Fi devices will work properly anywhere in the world, either by means of a configuration option (preferable), or by means of different firmware loads (clumsy). See Wi-Fi Channels.

External Links

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