Raymarine AIS250 User Manual download pdf (Page 2)

Practical Boat Owner 517 January 2010 • www.pbo.co.uk 47

ais units on test

➜

ASA have pared down functionality on

the AIS Engine 2 to produce a budget-

priced unit. The device receives message

types 1-5, 11, 18, 21 and 24, so receives all

the messages likely to be of interest to leisure

yachtsmen including SAR aircraft and aids to

navigation. AIS is expected to be used

increasingly on buoys, weather stations and

tide gauges. The NASA unit also has the

ability to pass GPS RMC messages.

Single Channel Receivers

GPS and NMEA interfaces

Some AIS units can output GPS data with the

AIS information, particularly useful if you have

a plotter without its own GPS. However, bear

in mind that AIS data is output at 38,400bps

(bits per second), so you will need an

additional, lower speed (4,800bps) port to

accept NMEA data from other instruments.

Some AIS units solve this problem by

including an NMEA input, which will combine

the AIS and input data into a single output. All

transponders and some receivers have a port

for a GPS active antenna.

The Raymarine AIS500 is unique in having a

SeaTalk

interface. Obviously this allows

connection to other SeaTalk

instruments,

but as it is essentially the same as NMEA2000,

this should allow display of AIS data on any

NMEA2000 device that supports it. If you have

Furuno Navnet instruments, then the Furuno

receiver offers a Navnet interface.

The ﬁnal point to check is whether the

outputs are NMEA (for a chart plotter) or

RS232 (serial) or USB (for a PC). Although

NMEA output can generally be plugged into a

PC’s serial port, and vice versa, this is not

good practice, and problems may arise

unless a NMEA/RS232 converter is used.

Software

Many of the devices tested come with a

software package. For the transponders, this

is necessary for entering the MMSI number

and other vessel details. In general, the

software offers diagnostic tools, and also

displays AIS data. Some supplied software,

such as SeaClear and the SOB demo, can be

downloaded for free from the internet.

How we tested them

We used each device connected to a laptop,

tested live with the same antenna from the

waterfront at the entrance to Southampton

Water. We looked at the data interfaces and

speciﬁcations. The software packages used for

testing were AIS Analyser (www.kagstrom.no)

and Ship Plotter (www.coaa.co.uk).

We logged data from each receiver to

measure maximum range and sensitivity,

using the same VHF and GPS antennas. Our

antenna height was low, so the ranges we

logged will be lower than for a masthead

antenna, but similar to the popular pushpit-

mounted antennas. During the tests we used

the Comar AIS-2-USB as a reference model,

giving a known performance level against

which to measure the other units.

AIS can transmit 26 different message types,

which allows differentiation between sources

such as ships, class B transmitters and SAR

aircraft. We monitored Type 1 messages,

which are received by all our test units. To

check sensitivity we counted the number of

messages/minute, which we then divided by

the number of vessels within range to give an

average rate of reception. It should be borne

in mind that our results are only approximate,

and will be skewed by factors such as vessel

speed and rate of turn: ships send more

messages when changing speed or course.

We checked the transponders’ broadcast

range by driving away from a ﬁxed receiver.

The range for all units was between 4

⁄2-5 miles.

NASA AIS Engine 2

PRICE: £110

Contact: www.nasamarine.com

AIS250

receiver

offers good

interfacing: the antenna has a splitter with

outputs for both your VHF and FM radios, and

there are NMEA inputs and outputs at both

4,800bps and 38,400bps. All inputs are

multiplexed to the outputs, with AIS data

being on the 38,400bps output only. Also, if

installed by a Raymarine dealer, there is the

beneﬁt of on-site warranty. However, it is

expensive for a single channel receiver.

Raymarine AIS250

PRICE: £450

Contact: www.raymarine.co.uk

well engineered but basic receiver with an

RS232 output (not NMEA, so it may not

work with some electronic plotters), the True

Heading SR161 is a rebadged unit from Smart

Radio, a Chinese manufacturer who sell AIS

and other equipment for rebranding in much

the same way as many laptops are rebadged

units from third-party manufacturers.

True Heading SR161

PRICE: £215

Contact: www.trueheading.se

his receiver uses

WeatherDock’s S2C

(Simultaneously Two

Channels) technology

that scans both channels

simultaneously, quickly

switching to the channel with a transmission

on it, which makes performance better than

other single channel receivers. It also has the

advantage of having a built-in multiplexer that

takes in NMEA data at 4,800bps, and outputs

it at 38,400bps with the AIS data.

WeatherDock EasyAIS

PRICE: £255

Contact: www.easyais.com

Basic connections

for power, GPS

and an RS232

serial cable

1 2 3 4 5

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