[PUP] AIS pitfalls

[Truelove39@aol.com]

Hi John-
 
Yes, normally we would see that, but with a slow speed on a small-scale  
chart, the predictor is very short; thus it was missed. In thinking about  this, 
our eyes tend to give precedence to the triangle unless the  predictor is 
sufficiently long. My point is that complacency with only a cursory  look (pun 
intended), and then seeing  what you expect to see, can be  dangerous. 
 
Some forty years ago while working as engineer on a ferryboat, I had  the 
pleasure of serving under a captain whose landings were so consistent I  never 
had to look at the telegraph, although I usually did, as he always rang  the 
same exact sequence of orders. One day, he rang up something different, and  I 
gave him "the usual" instead. Fortunately, my oiler was on the ball and  noticed 
the difference in time to avoid an accident. 
 
An aside - this captain had served 35 years on a CG buoy tender and  
possessed pilotage from Calais, ME to Boston - over 1500 miles of  coastline.
 
Regards,
 
John
 

> I'm used to seeing a projected course track that extends outward  from  
the target, the distance proportional to the ship's speed. At  least  
that's how Furuno displays show it when using the Furuno AIS.  Very  
handy, as you can graphically see where the target is going to  cross  
your course line.

Not sure if all units work that way or  if that would also have been  
confused by the tug.

John  Marshall
N5520-Serendipity

On Jun 3, 2007, at 5:39 PM,  Truelove39@aol.com wrote:

> As we proceeded up the Hudson River today,  a tow hove into view   
> ahead.
> Penny, at the helm,  noted that he was upbound, too. After a few   
> minutes, I  looked
> up and observed that the tug was not only closer but behind   the  
> barge; he was
> in fact, downbound. A glance at the AIS  display (on CE)  showed the  
> triangle
> symbol facing  the wrong way! Further investigation showed  that all  
> the  data
> was correct, including course, but his heading was fixed at  17   
> degrees! So we
> learned something today,  fortunately not the hard way: a  simple  
> glance at
>  that elongated triangle may not always tell the  truth!
>
>  Regards,
>
> John
>  "Seahorse"
>




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