[PUP] AIS pitfalls

[John Marshall]

The Furuno FA-150 on my boat includes a 12 channel DGPS receiver to  
ensure it always has correct internally-generated COG, SOG and  
location data. It does not need any external heading input as it  
computes it all from its GPS.

I'm not sure about other brands, but given how cheap GPS receivers  
are now (even most new cellphones have them for E911 service), I  
would be surprised if all currently-sold units don't have an embedded  
GPS.

Out of curiosity, I read the manuals on my boat to look for embedded  
GPS receivers in various equipment, and found 8 of them. They are  
becoming ubiquitous.

If the constellation went dark, we'd have trouble making toast. <grin>

John Marshall
N5520 - Serendipity



s of heading data.
On Jun 4, 2007, at 6:05 AM, Dave Cooper wrote:

> <John wrote: I'm used to seeing a projected course track that extends
> outward from  the target, the distance proportional to the ship's  
> speed.>
>
> I believe that the projected arrow is from the course info and the  
> ship's
> symbol is from the heading info. So if they are not in "approximate"
> agreement then you can have two conflicting pieces of information  
> display.
> Then it becomes as matter of "which is correct?"
>
> If the ships gyro aka heading input to the AIS box is in error due  
> to being
> wired incorrectly or some other issue then they won't even closely  
> agree.
> The AIS GPS gives the course, the gyro or whatever is used gives the
> heading. A boat making with a heading of 90 degrees with show the ship
> oriented in this direction from the heading input however if it is  
> drifting
> south then the projection line will be in this direction from the GPS.
>
> So the installation and the frequent check on the transmitted data is
> required. I would think that the system would be required to show  
> on another
> display your transmitted information....easy cross check and would  
> help to
> insure that you have inputted the correct data and that the black  
> boxes
> feeding the AIS are doing so correctly. Without this what do you  
> have??
>
> As always YMMV
>
> Cheers
> Dave & Nancy
> Swan Song
> Roughwater 58
> Caribbean Cruise '07
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