Using Nimble with AIS

Avoiding a collision with a single ship on the open ocean in good weather is usually pretty easy. But when at night you're closing on Cape St. Vincent in 30 knots of wind driving a hard rain that limits visibility to 500 meters, and crossing the shipping lanes blind is just a gamble, or even daylight sailing the English Channel in a light fog, a little help is good. And the best tool for collision avoidance with ships is an AIS system. The requirements for a usable AIS system include: an AIS receiver/transceiver, an antenna, and a display device. Here are some of the different options.

  • First, the display device options:
    • A computer, with AIS display software such as Nimble Navigator, is one of the displays most widely used. A disadvantage of the computer is the power consumption. Still, a small modern netbook computer consumes less than a chart plotter, somewhere around 1 amp.
    • Many chart plotters (RayMarine, Garmin, etc) can display AIS, although not all brands and models have that capability, so it is important to check the documentation of the plotter. Cost is high. Power consumption is high, up around 3 amps. But most boats that have a chart plotter keep it running all the time anyway.
    • Separate dedicated displays for AIS equipment are available. Power consumption of these units is very low. But prices for these displays can be twice that of a nice netbook computer.
    • Built-in displays come with some AIS and combination AIS/VHF systems and are becoming more common. Power consumption of these units is normally very low. But often, the usability of these systems is limited because of the software built into them.

  • AIS antenna options:
    • A VHF antenna is the requirement. And a separate antenna dedicated to the AIS can be the least costly solution. An antenna that is connected to anything else can not be shared with the AIS without a switching device. Equipment will be destroyed if you violate this rule. Manual switches are the least costly, but automatic switches can cost over 200 euros. The combination AIS/VHF radios have an automatic switch built into them.

  • The AIS hardware options:
    • Black Box AIS Receiver: up till lately, the most common and probably best solution. This low power AIS requires only a VHF antenna and a display device. The unit's AIS output can be connected to most display devices. A disadvantage using this type is the need to keep a display device running to use it.
    • Combination AIS/VHF radio: another low power solution. Because these units have a built-in automatic antenna switch, only one antenna is required and shared between the AIS and VHF. And with most having a built-in display, some minimal AIS functionality can be had without another display device. The VHF part of the unit is normally a fully functional all channel VHF with DSC capabilities. These units need to be connected to the NMEA output of a GPS and the radio's AIS output can be connected to most display devices.
    • Black Box AIS Transceiver: one of the more expensive options, but for those who want to transmit and be visible to receivers, this is the solution. A GPS is built into transceivers, and the units require both a dedicated VHF antenna as well as a GPS antenna. The unit's AIS and GPS output can be connected to most display devices.
    • Stand-alone AIS Receiver ('AIS Radar'): also an expensive option for the functionality, but requires little power. These units need to be connected to the NMEA output of a GPS, as well as a VHF antenna. These units normally have no AIS output and can not be connected to any outside display devices without electronic modifications.

  • Best Bet:
  • Unless you want a transceiver, I like the combination AIS/VHF radio connected to a netbook computer. I'm using a Standard Horizon GX2100. When I'm offshore, and I don't want my netbook on using power, I can use the GX2100's stand-alone AIS alarm capabilities to warn me if I need to startup my netbook with Nimble Navigator for a more detailed view. And, when close to traffic areas, I just keep the netbook and Nimble Navigator running, with the GX2100 AIS updating the detail constantly. Single antenna, and low power.

  • Installation:
  • Can be tricky. Because interconnections between AIS/GPS/Displays can involve both SERIAL/COM 9 pin as well as USB between multiple devices, mostly with cables having different color coding, installation can get a little strange. Maybe qualified help will be important here. Most likely, a USB to Serial Adapter will have to be used.