Underwater navigation with a GPS

[Notso_Ken]

Any thought of a detachable antenna on a 100' line, then you can keep the actual GPS with you the whole dive? Running up the whole gps unit will require the unit to re-acquire satellites, so there will be a certain amount of time required to wait with it on the surface. If the antenna is up there the whole time, you can generate a complete track.


Ken

This author made a waterproof housing for his gps with switches on the outside. He floats it up to the surface for a gps reading, and retrieve it underwater to navigate, or assist in his navigation. Interesting read.


Here is a link for the following free book on this topic:

Underwater GPS - Captain's Blog SCUBA Blog - Dive Spots

The link below will allow you to download my book / manual-
"Underwater GPS: a practical approach"
The book is free and is not a promotion for the sale of
any product. I'm distributing this pdf document, in hopes of encouraging the use of Diver GPS by avid divers, researchers, law enforcement dive teams, and public safety divers. I would certainly like to hear feedback or questions from users.
http://wl.filegenie.com/~8675309/UW_GPS_Book.pdf

 

[ClayJar]

I have a Garmin eMap that does *not* preserve the location when it loses signal, so I had to buy a megallan unit for underwater use.

I don't recall when exactly the eMap was released, but I know the Amazon page for it shows December 1999. That puts it well before Selective Availability was turned off, which is the dividing line between old and modern. At least it's a 12-channel parallel receiver, so it's only old and decrepit and not completely obsolete. :biggrin:

Even the classic Garmin eTrex (i.e. the "yellow eTrex" as we always called it) that was released around early 2000 shows coords when it loses signal (which the eTrex line does often under wet tree cover -- the patch antenna never was great). If anyone has a handheld GPS receiver model released since 2001 (or even others) that doesn't show coords when it loses signal, I'd love to know which one and what firmware revision so I can ask around geocachingdom.

 

[Brewone0to]

Must try this next time I'm at Venice,Fl for a tooth dive.
Can never seem to find way back to the sweet spots.

 

[jbmooney]

Ken, I think separating the antenna from the GPS would create an unacceptably fragile and expensive rig. Thome does mention the possibility of towing the GPS around on the surface, pulling it down to you for momentary readings/markings, then letting it return to the surface, as a way to minimize the signal acquisition time (and let it happen on the surface, where you don't have to wait for it). That would get you the same "complete track" you're after, I would think, though it would leave the unit at risk from passing boaters all the time, which might be too much exposure.