Fitting a NAVTEX Receiver
Most North American (NA) sailors have never used a Navtex receiver nor seen a Navtex transmission. The main reason for this is the abundant sources of NA weather forecast and Local Notice to Mariners information that can be received on VHF. Even boats which have cruised in the Caribbean, where VHF forecasts are available rarely, will not have used Navtex because the only Caribbean station transmits out of Curacao in the Dutch Antilles, a bit off the beaten track for most boats. When you arrive in Europe, you will discover that such VHF broadcasts are also rare, and you’ll quickly find you want alternative dependable methods for receiving a weather forecast…or for that matter, picking up navigational and marine warnings in waters with which you have little familiarity. Which leads us to a discussion of Navtex.
What is Navtex? In a nutshell, it is a worldwide system broadcasting text weather information, marine warnings, navigation and other related information to mariners. Almost without exception, it is transmitted on the medium frequency (MF) band, on two discrete frequencies, up to six times per day. (The Greeks also transmit it in the HF band). The effective range is intended to be 250 miles, varies with propagation, and is sometimes received up to 500 miles from a given station. (For a fuller description, visit the ICS website (www.icselectronics.co.uk/icsnet/GMDSS/navtex.htm) and Frank Singleton’s weather website (www.franksingleton.clara.net/navtex_2.html), as both offer useful information and a more complete description of Navtex.
These text transmissions can be received in a variety of ways, including copying them directly via SSB, with or without a TNC, and receiving them using a dedicated Navtex receiver (about which I’ll say more in a moment). The transmissions are sent by a collection of stations in a given region (e.g. Northern Europe) sequentially, with each station allowed a 10 minute slice of the hourly pie, thereby avoiding cross-station interference. The two frequencies serve different purposes and contain somewhat different information:
Under the SOLAS convention, NAVTEX is compulsory for larger vessels. It’s also mandated for certain types of vessels such as training ships. Perhaps this tells us something about whether we should be using Navtex information, all by itself.
Should you install a dedicated Navtex receiver? Given a boat that is SSB equipped with a newer laptop, it is possible to copy Navtex transmissions with the right software, so why fit a dedicated receiver at additional expense? The reasons a dedicated receiver are preferable also help explain how Navtex works in the real world:
1. Dedicated Navtex receivers are programmable while Navtex transmissions contain a breadth of information far beyond what you might be interested in. Using a SSB, you copy ALL of the content of EVERY transmission your SSB rig receives. If a given station has enough time in its 10 minute slot to repeat critical warnings, you’ll get those twice. However, you can throttle down a Navtex receiver to only copy the segments of a broadcast you want to receive, to only copy the stations relevant to your location, and it will automatically avoid displaying duplicate text messages on its own. If you interface your GPS to your Navtex, some units will exclude somewhat adjacent but out of area Navtex broadcasts (which you don’t need and don’t want) automatically. All of this makes reviewing your broadcast content easier and quicker.
2. If using a SSB/Laptop combination, you will need to make sure the computer is booted up and the right software running – and don’t forget the turning on and tuning of the SSB – all before each and every broadcast in which you have an interest is transmitted. This not only requires some constant jockeying of timers, software and tuning, but it means you’ll accept whatever additional amp load your SSB and laptop system requires for these periods. E.g. if dinking over to the other boat for cocktails will occur during the next broadcast period, you’ll need to leave everything up and running in your absence. However, a dedicated receiver sips milliamps (screen displays can even be turned off) and is typically left on full-time, which means it will only miss those broadcasts that local conditions or propagation prevent it from receiving.
3. The SSB/laptop system presumes that its individual components are all working properly, and it presumes no competing activities for the crew (perhaps a sail reduction, or some anxious visual pilotage from the cockpit). A dedicated receiver offers redundancy with respect to mechanical/electrical issues and, since it operates independently and is typically left on indefinitely, avoids manning conflicts.
We left the U.S. believing that a Navtex receiver was probably a good idea, that we’d make our SSB/laptop system work in the short-term, and that we’d form a final conclusion about whether a dedicated receiver was worth its keep once we cruised here a while. In addition, we simply ran out of time when preparing WHOOSH before leaving the U.S. , and also found it difficult to become knowledgeable about Navtex receivers while preparing our boat in Florida…one reason I’m writing on this topic. At it turned out, I was wishing we had installed a dedicated receiver even before we arrived in Europe (see next topic) but, in reality, making a knowledgeable product choice would have been more difficult.
Install a Navtex receiver before leaving the States…or after arriving in Europe? It’s always a challenge to find both the time and the funds to complete all one’s pre-departure tasks, so this decision may be made for you by other circumstances. However, here are a couple of thoughts to consider:
1. If other boats are any indication, you will most likely decide, in the end, to have a dedicated Navtex receiver so you probably should consider this a question of ‘when’ more than ‘if’.
2. Having a Navtex receiver aboard would have been useful to us when still a few days out of Bermuda, again when dealing with persistent head winds as we approached the Azores, and yet again when approaching Falmouth at the same time a forecasted Low was scheduled to arrive in the Channel. You too might find it useful in supplementing other weather forecast information PLUS offering local waters navigational alerts when approaching foreign waters.
3. Depending on the product you end up choosing, you could well find a Navtex receiver at a lower price from a retailer in the States than in Europe…even though two of the three manufacturers are based in the UK. For example, the Furuno NX-300 was offered to me in Southampton (UK) at a boat show price of £300 in October, 2003 ($560 U.S. at the current exchange rate) while Defender’s everyday price was $390 U.S. in January, 2004.
4. On the other hand, waiting until you arrive in Europe will allow you to sample opinion of other cruising boats, see some of the units in operation, and perhaps this benefit will offset the higher cost you will be likely to pay.
Which receiver is the “right” choice? Like other electronics, you’ll weigh the variables uniquely, have your own reaction to the user interfaces, and pick what fits your preferences and budget. However, I was surprised that the choice of a receiver performing relatively simple tasks, offered by only three manufacturers, ended up proving relatively difficult. Here’s my subjective view of the product choices, which I would encourage you to expand on via dialogue with other users.
1. NASA Clipper, Target and Target Pro-Plus Receivers: Dual 518 & 490 kHz (but not simultaneous) receiver, offered in either bracket mount or flush mount configuration. No GPS input and so programming stations and message content is done manually. I did not find these units available in the USA in early 2003, so assume a faulty unit needs to be mailed back to the manufacturer for repair. NASA is generally viewed as the budget manufacturer and their entire range of electronics enjoys a popular following in the UK due to their relatively low pricing. I heard discouraging reports on their customer service, found them to be unresponsive to my own inquiries, and found some NASA dealers (who also carried other brands) discouraging their purchase. This latter circumstance may be driven by a lower profit margin, but their explanation was that they were tired of NASA customers coming back to dealers with complaints. Since one can buy a lower priced, higher quality product in the U.S., I could not find a reason to further consider the NASA products.
2. FURUNO NX-300 Receiver: Dual 518 & 490 kHz (but not simultaneous) receiver, which can be flush mounted or bracket mounted. GPS NMEA input is provided for, so programming stations and message content may be automatic or manual. The user interface is very simple, and the screen is small but with large characters that can be read at a wide angle (helpful if your Navtex unit gets installed off-center at the Nav Station). You will need to scroll through each broadcast message due to the small screen size. Furuno’s worldwide distributor network for repair or software upgrades (see www.furuno.co.jp/english/marine/index.html), their customer service and their build quality all are considered product assets. One main reason this was my choice is that everyone aboard should find it simple to use; ‘simple’ goes a long way when tired, half seasick and time is precious…and doubly so for those without much radio savvy.
3. ICS NAV6 Dual and Plus Receivers: Both these units offer dual, simultaneous reception on 490 and 518 kHz, which means they will provide you with both offshore and inshore forecast and navigation-related information if left in the ‘dual receive’ mode. As you might expect, the ICS products are priced the highest. I did find both these receivers available through Florida electronics dealers but it took some hunting. The ‘Dual’ unit must be manually programmed, as with the NASA products, while the ‘Plus’ product accepts a GPS input and will auto-select which stations to receive unless programmed manually by the user (altho’ message content will need to be manually selected in any case). The ‘Plus’ is actually designed to be as much a Repeater as a Navtex receiver and offers a variety of screens (user selectable) displaying GPS and other sensor data. I found the ICS display to have a narrower field of vision than the Furuno and only the larger font choice seemed easily read by my aging eyes without glasses, but with even the large font the screen displayed more message content without scrolling than Furuno’s receiver. The early ICS antennas (which is also where the processing takes place on these units) were not adequately waterproof and many had to be replaced under warranty. According to dealers, this problem seems to be resolved.
NB on Dual Simultaneous Reception: Some think that simultaneous reception on both inshore and offshore frequencies is a big selling feature, justifies the price premium of the ICS product, and means there’s only one ‘good’ product choice. I’m not persuaded by this logic for two reasons: First, you will tend to want one or the other forecast as one will be more suitable for your needs at any given point in time. More importantly, there are very few stations using 490 kHz, even after it has been authorized for some years now. If you cruise in UK waters (or perhaps Vietnam or Uruguay…), you’ll find stations offering Inshore Waters broadcast, but in all of Europe and the Med there are only 2 European stations offering Inshore broadcasts (these are broadcast in Portuguese and French). North America only offers one 490 kHz broadcast, at 65° North in Canada. Given this, dual simultaneous reception is hardly a key buying criteria in my mind at this time, altho’ perhaps things will change in the coming years.
Installation: While not an expert, I’ve heard many users comment (and also read in countless boating periodicals) that receiver performance of these Navtex receivers can vary widely. The sum of the expert opinion seems to be that the antenna installation is critical. Pay special attention to the manufacturer’s recommendations and also tie the unit’s ground lug into your SSB ground plane if you have one and the unit you have purchased allows for this.
Some will temporarily arrange the antenna in a variety of locations, trying to find the place where reception is best. (This assumes that the boat is in an area where reception is generally good, sometimes an overly optimistic assumption). Others – and that certainly includes WHOOSH – don’t really have much in the way of choices and get on with the fixing in place of the antenna pretty much where it ‘has to be’.
When I first began using our new NX-300, I was amazed at the number of broadcast messages we received; it was almost like navigational spam! This was in part because we are only a few hundred miles from a different Navtex NavArea, but it was also because the Furuno’s receiver sensitivity appears to be very good, even while we are buried deep in the heart of London. After a few days, I connected the NMEA wires from my NMEA bus to the unit and, with no programming on my part, saw a sudden drop in message traffic as the unit began filtering out messages not related to our NavArea.
As mounting spaces at the Nav Station become more difficult to find, some will find flush mounting of the unit to be necessary. For those who select the Furuno NX-300 and want to flush mount it, let me pass along a clever idea from Furuno’s Solent dealer who does all the high-end Sunseeker electronics installations. (See picture) Rather than buy one of the two optional flush mounting kits, he takes a hole saw and cuts out two 1.5” (or so) plywood disks. He then drills a second off-center hole in each disk. Putting fasteners thru the off-center hole of each disk, he now has two eccentrics, which he can then rotate when mounting the unit, pulling the face of the unit against its bulkhead, and locking things in place by tightening the two fasteners. If one can’t come up with the metric fasteners easily, you can break apart the plastic knobs intended to be used with the bracket mount and use those fasteners.
© Jack Tyler – March, 2004
WHOOSH, currently lying St. Katharine’s Haven, London