SO now I own a Standard Horizon GX2100 (has AIS RECEIVE BUILT IN) and I have hooked it up at home to my Garmin Plotter. It all works fine. Here is the question. How come I can see AIS equipped vessels on my chartplotter (from the 2100) that do not appear on marinetraffic.com or on my Iphone app called SHIP FINDER? I see some of the traffic from thosse sites, but why aren't all of them there? Of the ones I could not see, 2 were commercial fishing boats ans one was a CG boat. I have all the ship types in Marine Traffic chosen.
AIS QUESTIONS
- Thread starter melkal
- Start date
Becausenow you have a real time, real AIS receiver, not a kluged app from the Internet. Those sites are really for entertainment value only, and carry disclaimers to match, including the fact that they tend to be an hour old at least.
It all boils down to antenna coverage. The internet AIS sites can only display data that has been received by one of their participating members. Their antennas are almost always located on the shore and can provide coverage only as far as a VHF radio will reach. You can only display AIS targets which are within range of your receiver. There should be some overlap in coverages, but you should not expect complete agreement in the ships detected.
The AIS sites often do provide data that is timely. You can check this by looking at the time of the most recent position update, which in some cases only a few minutes old.
We use an airborne AIS receiver and often receive over 500 ships from overhead the Delaware Bay. But then our antenna is 17,000 feet high.
Mike
The AIS sites often do provide data that is timely. You can check this by looking at the time of the most recent position update, which in some cases only a few minutes old.
We use an airborne AIS receiver and often receive over 500 ships from overhead the Delaware Bay. But then our antenna is 17,000 feet high.
Mike
Thanks Mike,
I guess I never considered the shore stations when thinking about AIS (is that what happened to the old LORAN stations?). So, that answers the question of why on marinetraffic.com or the like one cannot see ships very far out to sea. What a mariner has essentially is his own moving receiving (or xmit as well in the case of a transponder) station and can "see" AIS equipped vessels within the field of both antennas;(back to the curvature of the earth and the height of the antennas). Appreciate your taking the time to respond.
How does the distinction between moving and moored come about in the info, simply from stable LAT/LON?
I guess I never considered the shore stations when thinking about AIS (is that what happened to the old LORAN stations?). So, that answers the question of why on marinetraffic.com or the like one cannot see ships very far out to sea. What a mariner has essentially is his own moving receiving (or xmit as well in the case of a transponder) station and can "see" AIS equipped vessels within the field of both antennas;(back to the curvature of the earth and the height of the antennas). Appreciate your taking the time to respond.
How does the distinction between moving and moored come about in the info, simply from stable LAT/LON?
In an AIS message the distinction between moored and underway is purely an operator input, which means it can be incorrect.
You can trust only the automatic portions of the AIS messages (speed, heading, position and MMSI number). You should not blindly trust the operator input data (navigation status, IMO number, ship name). I once detected a 800 foot long ship claiming to be "Underway-Sail" and often see ships claiming to be moored which are moving at 12 knots.
Mike
You can trust only the automatic portions of the AIS messages (speed, heading, position and MMSI number). You should not blindly trust the operator input data (navigation status, IMO number, ship name). I once detected a 800 foot long ship claiming to be "Underway-Sail" and often see ships claiming to be moored which are moving at 12 knots.
Mike
Mike,
When a vessel first appears on the chartplotter it shows its mmsi # (and speed and direction) but after a short while the actual nsme of the vessel appears. But how does that work?
I can see a CG vessel which is moored nearby (it is a big boat) and it shows it's mmsi as 000000000, but again after a while it's name appears. I guess I am missing something in my understanding.
- Joined
- Apr 18, 2003
- RO Number
- 11439
- Messages
- 704
There are two different data packages that are sent via AIS.
A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes:
* MMSI number - unique referenceable identification
* Navigation status (as defined by the COLREGS - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined)
* Rate of turn - right or left, 0 to 720 degrees per minute (input from rate-of-turn indicator)
* Speed over ground - 1/10 knot resolution from 0 to 102 knots
* Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) RAIM processing is being used
* Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
* Course over ground - relative to true north to 1/10th degree
* True Heading - 0 to 359 degrees derived from gyro input
* Time stamp - The universal time to nearest second that this information was generated
In addition, the Class A AIS unit broadcasts the following information every 6 minutes:
* MMSI number - same unique identification used above, links the data above to described vessel
* IMO number - unique referenceable identification (related to ship's construction)
* Radio call sign - international call sign assigned to vessel, often used on voice radio
* Name - Name of ship, 20 characters are provided
* Type of ship/cargo - there is a table of possibilities that are available
* Dimensions of ship - to nearest meter
* Location on ship where reference point for position reports is located
* Type of position fixing device - various options from differential GPS to undefined
* Draught of ship - 1/10 meter to 25.5 meters [note air-draught is not provided]
* Destination - 20 characters are provided
* Estimated time of Arrival at destination - month, day, hour, and minute in UTC
A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes:
* MMSI number - unique referenceable identification
* Navigation status (as defined by the COLREGS - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined)
* Rate of turn - right or left, 0 to 720 degrees per minute (input from rate-of-turn indicator)
* Speed over ground - 1/10 knot resolution from 0 to 102 knots
* Position accuracy - differential GPS or other and an indication if (Receiver Autonomous Integrity Monitoring) RAIM processing is being used
* Longitude - to 1/10000 minute and Latitude - to 1/10000 minute
* Course over ground - relative to true north to 1/10th degree
* True Heading - 0 to 359 degrees derived from gyro input
* Time stamp - The universal time to nearest second that this information was generated
In addition, the Class A AIS unit broadcasts the following information every 6 minutes:
* MMSI number - same unique identification used above, links the data above to described vessel
* IMO number - unique referenceable identification (related to ship's construction)
* Radio call sign - international call sign assigned to vessel, often used on voice radio
* Name - Name of ship, 20 characters are provided
* Type of ship/cargo - there is a table of possibilities that are available
* Dimensions of ship - to nearest meter
* Location on ship where reference point for position reports is located
* Type of position fixing device - various options from differential GPS to undefined
* Draught of ship - 1/10 meter to 25.5 meters [note air-draught is not provided]
* Destination - 20 characters are provided
* Estimated time of Arrival at destination - month, day, hour, and minute in UTC
- Joined
- Apr 18, 2003
- RO Number
- 11439
- Messages
- 704
My guess would be that it is an incorrectly set up radio. CGC William Tate does not show all 0's, though the first few digits are 0.