Re: [PSUBS-MAILIST] Acoustic Triangulation

["Sean T. Stevenson" <cast55@telus.net>]

Joe - I used to work for the Canadian Coast Guard, before SA was shut 
off. (SA was turned off in 2001, correct?).  Anyway, we would do some 
minor navaids placements from small boats which were not equipped with 
differential receivers, but since GPS was deemed "not sufficiently 
accurate", we had to take horizontal sextant angles off of landmarks to 
fix station, and then stationkeep while the buoy was placed.  A royal 
PITA, but good training in seamanship.  Even now, this method is 
theoretically more accurate than GPS, but usually not worth the hassle 
except to check position after placement.

For wreck diving, I always thought it would be a good idea to enter two 
positions in the log, defining the fore and aft extents of the wreck.  
This way, if you anchor instead of live boating, regardless of the hook 
position you have a reference for the divers which hopefully will 
minimize any required search.

-Sean


Joseph Perkel wrote:

> Stephen,
>
> " Remember the old days when it was even harder because you lined up a 
> dive site with shore marks"
>
> I still would still rely on this even after the end of SA (selective 
> availability) of the GPS system to get to a spot quick, fine tune with 
> the GPS, and then spot the wreck on the sounder. My problem was always 
> anchor placement, and then how far off the rode placed the boat and in 
> what direction. It never occurred to me to learn how to use a 
> grapple...silly really.
>
> Joe





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