Need device locator that works in salt water

[madcrabber]

Hey guys,

I live in Seattle and just started fishing for dungeness crab. Towards the end of the season, someone started stealing the crabs from my pot and then stole the pots altogether!

The pots are easy enough to find because they all have big red and white buoys marking their location. This is so boats don't run over them and cut your buoy line. However, it also tells poachers exactly where they can find your crabs.

So what I want to do it get a much smaller buoy, paint it black and put some kind of tracking device to allow me to find it again using my cell phone. It seems like there are bluetooth and GPS devices. Do you think either of these would work in a foot or so of water?

P.S. If the buoy line does break the crabs will be fine. There is a rot cord that disintegrates and allows them to eventually escape.

 

[Born2bwire]

Salt water is too conductive. It'll kill off the signal in a matter of inches usually.

 

[madcrabber]

Salt water is too conductive. It'll kill off the signal in a matter of inches usually.

What about an inch?

 

[William Gaatjes]

Salt water is like the ultimate cage of Faraday.

https://en.wikipedia.org/wiki/Faraday_cage

You could try to use a low frequency RF transmitter, less than 100kHz to gain a few inches. But it would drain your battery because you still need a lot of energy and a large antenna. You might want to read about the difficulties submarines have communicating and what the solutions are used there.

But GHz RF signals like bluetooth and gps will not make it far as mentioned. Perhaps you could use sound as a means.
You could use a small black buoy (1 x 1 inches) with a gps antenna only, wired down towards your crab cage.
This will allow you to receive gps signals. You could use ultra sound to for example use some coded signal to relay the coordinates. For example FSK. If you let the transmitter produce these sounds one minute every 10 minutes, you will save some battery life.
If the antenna gets severed, the MCU at your crab cage will use the last known received gps location to transmit over sound.


https://en.wikipedia.org/wiki/Frequency-shift_keying

All you need than is to be in the vicinity with a directional microphone to receive the sound signals and you would need some program to decode the FSK signal to coordinates. These coordinates can then be plugged into google maps i guess by use of some android api.
As you can see, it is not as easy as it seems.

 

[MongGrel]

I saw this last week and didn't even comment.

Painting buoys black would be illegal to begin with I imagine.

I hope you aren't randomly putting them near other peoples, a line of them is pretty much usually standard.

If you're just randomly dropping them nears other people I imagine they will get scarfed up.

Would be more of a FU thing at that point.

 

[LTC8K6]

http://www.amazon.com/LugLoc-Luggag...ef=sr_1_4?s=gps&ie=UTF8&qid=1443259778&sr=1-4

That would probably work if you waterproof it/ziploc bags, and hide it in the buoy.

There are several types of these small gps locators/trackers.

http://www.amazon.com/Sourcingbay-W...=sr_1_15?s=gps&ie=UTF8&qid=1443259778&sr=1-15