más dudas
Boaters keep on wondering what kind of data class A receivers are able to see.
Right now, most class A are only able to see mmsi and location of class B. IMO is likely to take a decision on how to solve this problem soon. They are most likely to decide that large boats should upgrade their class A equipment to make it compatible with class B in our opinion, during the next few years. It just doesn’t make sense having such a powerful navigation system, in which the two most important standards are just not compatible.
Some boaters wonder if large boats can decide whether to see class B or not. In some cases it may be possible via software to filter class B data, but why should someone decide to do so? Too much information? May be in extremely crowded waters?
We must take into consideration that there is no navigation system able to substitute the good criteria of the captain/skipper.
Nevertheless, in the future, it will be possible with the new standard for base stations to disconnect the transmission of class B when overinformation could affect navigation of large boats, or when overcapacity could affect the system. But this will only be possible in VHF coverage from the coast, never far away from it.
Capacity problems are practically impossible in class A, due to the SOTDMA (self-organizing time division multiple access) protocol that they use to organize transmissions. This protocol guarantees practically unlimited capacity to the system. Transponders communicate with each other to “decide” when to transmitt or not.
Class B uses CSTDMA (carrier sense time division multiple access) to organize them. Class B transponders “listen” during the first part of the slot, to know if somebody else is transmitting, and in negative case, transmit themselves during a therefore shorter slot (and thus smaller amount of data).
In order to have class B capacity problems, a large amount of boats should be transmitting frequently in the same area. If they are moored, transmission will be only once every 10 minutes, and thus overcapacity problems are very unlikely.
We believe that an actual problem in AIS in the future will be though, the asignation of mmsi numbers.
AIS
You can find here all the relevant information about AIS.
- How does AIS work?
- CTRX Installation
- FAQ’s about the AIS-CTRX
- AIS for sailing
- AIS on the Coast
- AIS for boat rental
- AIS for regattas
- Chart calibration
GLONASS
We just found out that the Russian Government is promoting as much as it can its GLONASS system, the equivalent to the worldwide know GPS.
Apparently, from our sources, we know that Russian Authorities are not going to certify ships without an AIS system that is fully compatible with GLONASS.
As of today, we don’t know of any company producing such equipment.
The smart move of the Russian Government has been though, to ally with the Indian one. We’ll see how the race goes on among the three main contenders: GPS-GLONASS-GALILEO.
Nothing like a little research in google to find more info about this. This article (sorry, in Spanish) in particular explains a bit more about the current situation (from April).
Guardia Civil
According to this article, Spanish Guardia Civil (a Spanish police corps) will be carrying AIS on its SVE (External Surveillance Service).
It looks clear the road that AIS is taking not only as an essential aid to navigation, but also from the security point of view.
The article states however:
“Además, el AIS cuenta con una tecnología que es capaz de hacer invisibles a las patrulleras que lo tengan instalado, es decir, que se podrá desconectar el dispositivo para no ser detectadas por buques que pudieran estar incluidos en investigaciones de narcotráfico internacional”
The translation would say that AIS has a technology that “makes boats invisible¿?”. Clearly wrong, it is only a button that once pressed shuts transmission down. A button counts as a piece of technology?
We are glad they used parts of our info pages about AIS in their article. We would have liked though a simple link too!!
Navegando en un archipiélago
#GMAP_SIT(”18.520@59.333″,”4″)#
Sailing in an archipelago like the one in Stockholm, up in the map, can be really complicated, due to the infinite amount of straits and “junctions”. We had never before seen real “driving signs” at sea, and there is no doubt that they become really necessary in this situation.
AIS seems to be the perfect tool in this environment, due to its independence from meteo conditions, and because land stations can send signals that can virtually draw on your plotter indications, signs, etc…
Besides, the VHF signal can go through obstacles such as capes, islands, which lets you detect AIS contacts before you actually see them, and thus helping you to avoid possible colisions, that with a radar would be completely impossible to prevent from happening.
Below, a sign in an island indicating where you should go through depending on the kind of boat you are piloting!
.jpg "signal")