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AllezCat · 05-06-2012, 13:45

just completed passage with AIS Raymarine 500 on Raymarine MFD.
AIS is extreemly useful system. It doesn't replace radar/lights, eyes, etc.
But is better than the rest combined.
However, stalkers were able to track me up the coast on internet sites. and were surprised at my early arrival time. they said my speed was in the 4 to 5 knot range.
Blasphemy!
(shtarker)Ve don't do 4 knots here.
So I am thinking it was transmitting boat speed rather than SOG.
My boat speed was not calibrated and was showing 5 - 6 knots less than SOG in the gulf stream.
So, the question is does AIS transmit boat speed/heading or SOG/COG? One is accurate - the other can be completely wrong, and misleading from the perspective of another vessel.

Also if you have receive only AIS - get transmit too - seriously you can be one of the ships or part of a ship...
cheers

DotDun · 05-06-2012, 13:52

AIS transmits SOG/COG as calculated by it's internal GPS. Yours will send heading if connected to a gyro stabilized heading source via NMEA (HDT sentence).

antondavis · 06-06-2012, 02:40

Quote:

Originally Posted by DotDun

AIS transmits SOG/COG as calculated by it's internal GPS. Yours will send heading if connected to a gyro stabilized heading source via NMEA (HDT sentence).

you'd better get to know how ais transmits

DotDun · 06-06-2012, 11:49

Quote:

Originally Posted by antondavis

you'd better get to know how ais transmits

please explain what you are trying to say?

**David M** · 06-06-2012, 11:57

An AIS transceiver broadcasts COG, SOG and other information such as the vessels name, type of vessel and status. Some information has to be broadcasted for AIS to work and some information is optional. AIS can be set up to broadcast heading from a gyro or a fluxgate. This is optional information. Some vessels broadcast heading and some do not.

An AIS receiver broadcasts nothing, by definition. It is listen only.

Anton, please describe in more detail what you meant by your snarky comment. It wasn't of any help to DotDun.

AllezCat · 06-06-2012, 12:02

Quote:

Originally Posted by DotDun

AIS transmits SOG/COG as calculated by it's internal GPS. Yours will send heading if connected to a gyro stabilized heading source via NMEA (HDT sentence).

ok that makes sense - as it should be.
not sure why others were getting such "off" readings from the base stations on the internet(which would have corresponded approximately with my un-calibrated boat speed)

DotDun · 06-06-2012, 12:15

Quote:

Originally Posted by AllezCat

ok that makes sense - as it should be.
not sure why others were getting such "off" readings from the base stations on the internet(which would have corresponded approximately with my un-calibrated boat speed)

If you have ever monitored a GPS that does not 'smooth' the SOG data, it can appear quite erratic depending on the sea condition you are in. It could be that others saw the report from your AIS when you were on the uphill side of a wave.

**Pete7** · 06-06-2012, 12:23

Quote:

Originally Posted by AllezCat

However, stalkers were able to track me up the coast on internet sites. and were surprised at my early arrival time. they said my speed was in the 4 to 5 knot range.
Blasphemy! (shtarker)Ve don't do 4 knots here.

Big brother is watching, guess you need a Klingon cloaking device so folk can't see you

Pete

**David M** · 06-06-2012, 12:34

Speed through the water to an AIS system is irrelevant. SOG is relevant.

AllezCat · 06-06-2012, 13:41

Quote:

Originally Posted by David M

Speed through the water to an AIS system is irrelevant. SOG is relevant.

i know - was just worried my AIS was transmitting spurious data

denverd0n · 07-06-2012, 05:43

Nit-picking and off topic, but that would be Siegfried saying it to Starker. I know a lot of people would disagree with me, but I think "Get Smart" may be the best sit-com ever made.

AllezCat · 07-06-2012, 07:06

Quote:

Originally Posted by denverd0n

Nit-picking and off topic, but that would be Siegfried saying it to Starker. I know a lot of people would disagree with me, but I think "Get Smart" may be the best sit-com ever made.

sure is.
would you believe? -
i haven't watched the movie - reckon it would spoil the memories of the real max...