DIY GPS dive tracking

[CT-Rich]

I have been getting a steady stream of people asking how we make the maps tracking our dive paths. It is not particularly difficult or expensive, so I thought I would share what I have learned doing it over the past few years.

To start, we are not taking a GPS or similar device under water. GPS signals do not penetrate water. What we are using is a cell phone attached to the flag that we are towing. Here in New England, we are required to tow a flag while diving without a boat. So for pretty much all shore diving, we need to have the flag anyway.

What you will need:

• A cell phone- I do not take my personal phone diving. I use an old decommissioned phone instead. There are two ways a phone can track your location (I am not an expert and those that are, can feel free to add in the comments). One method is to actually acquire GPS satellites and pinpointing your location. This is the best way for this activity. The second method is to triangulate the signals between multiple cell towers. Triangulation will work, but not reliably. I tried using an iPhone Mini (circa 2016) and it didn’t work well because of blind spots. Currently I am using a Samsung\ Galaxy J3 Eclipse and it works great. It is not part of a plan, so it does not work as a phone.
• A dry box- I buy the cheap polycarbonate dry boxes from Walmart. They are normally under $10. The key features to look for are that it has some sort of gasket seal, fits the intended phone and is designed to get submerged. If you tend to pull your flag under while diving, you may want something else. I have friends that use dry bags and they haven’t had any problems. I like that I can anchor the box from between the bottom of the flag and the top of the float.
• GPS tracking software. I use one called Strava, because the free version does pretty much everything I want it to do. I can turn it on, stick it in the dry box and forget about it for the duration of the dive.

The downside of using an old phone is that after the dive, you need to pair it to another phone or device and export your path with a Google Map Image. You can look at and save the map between dives, but I wait until I am home to make the final version.

A good thing to keep in mind when doing this, is the GPS is being recorded for where the float is, not where the diver is. If you are running a really long line, your location will be off by several meters. What I do if I find something of interest on the bottom and want to mark it, I will reel in the line and let it bob directly overhead for a minute. Another thing I have done to mark a spot is to swim perpendicular to our path for a couple yards and then swim back. This will leave little “X” on your path to mark your treasures.

What I find useful about tracking is the ability to compare where I thought we had gone to where we had really been. If I thought we were following a compass heading, after the dive we will know if we were right or getting pushed by a current. Some of the dives I like are kind of sprawling and comparing what I remember with where we really went can make understanding it and locating a particular spot much easier.

 

[Johnoly]

That's exactly what I do also to zero in on a spot that I'm having trouble knowing when & where to turn. I only do it if I'm trying to zero in a path (once a year maybe). The only difference is instead of a cellphone, I use a garmin Etrex. You can find them for $40 on ebay all the time and they only cost $90 on sale. The nice thing is they easily overlay on most of NOAA's bottom charts. The GPS map has timestamps at each point so by looking at your computer you will know when a turn is coming (or compass heading you should be at.)

It's a great idea !!

 

[34109411]

I have been getting a steady stream of people asking how we make the maps tracking our dive paths. It is not particularly difficult or expensive, so I thought I would share what I have learned doing it over the past few years.

To start, we are not taking a GPS or similar device under water. GPS signals do not penetrate water. What we are using is a cell phone attached to the flag that we are towing. Here in New England, we are required to tow a flag while diving without a boat. So for pretty much all shore diving, we need to have the flag anyway.

What you will need:

• A cell phone- I do not take my personal phone diving. I use an old decommissioned phone instead. There are two ways a phone can track your location (I am not an expert and those that are, can feel free to add in the comments). One method is to actually acquire GPS satellites and pinpointing your location. This is the best way for this activity. The second method is to triangulate the signals between multiple cell towers. Triangulation will work, but not reliably. I tried using an iPhone Mini (circa 2016) and it didn’t work well because of blind spots. Currently I am using a Samsung\ Galaxy J3 Eclipse and it works great. It is not part of a plan, so it does not work as a phone.
• A dry box- I buy the cheap polycarbonate dry boxes from Walmart. They are normally under $10. The key features to look for are that it has some sort of gasket seal, fits the intended phone and is designed to get submerged. If you tend to pull your flag under while diving, you may want something else. I have friends that use dry bags and they haven’t had any problems. I like that I can anchor the box from between the bottom of the flag and the top of the float.
• GPS tracking software. I use one called Strava, because the free version does pretty much everything I want it to do. I can turn it on, stick it in the dry box and forget about it for the duration of the dive.

The downside of using an old phone is that after the dive, you need to pair it to another phone or device and export your path with a Google Map Image. You can look at and save the map between dives, but I wait until I am home to make the final version.

A good thing to keep in mind when doing this, is the GPS is being recorded for where the float is, not where the diver is. If you are running a really long line, your location will be off by several meters. What I do if I find something of interest on the bottom and want to mark it, I will reel in the line and let it bob directly overhead for a minute. Another thing I have done to mark a spot is to swim perpendicular to our path for a couple yards and then swim back. This will leave little “X” on your path to mark your treasures.

What I find useful about tracking is the ability to compare where I thought we had gone to where we had really been. If I thought we were following a compass heading, after the dive we will know if we were right or getting pushed by a current. Some of the dives I like are kind of sprawling and comparing what I remember with where we really went can make understanding it and locating a particular spot much easier.

nice

 

[gmerick]

Garmin inReach mini. Will record tracks without a subscription. Can also activate a month by month subscription and it will function as a web tracker and rescue beacon. Comes with it's own custom drybox rated for recreational scuba depths.

 

[rob.mwpropane]

@CT-Rich when you download the map via Strava can you overlay that or export that?

@Johnoly can you enlighten me on the overlay part?

I think I want to do this for my local spot. I've been wanting to do it for years, would be something new to do. I like making an X on the map, would've nice to be able to match up time stamp with depth. Does Strava do that @CT-Rich?

 

[CT-Rich]

@CT-Rich when you download the map via Strava can you overlay that or export that?

@Johnoly can you enlighten me on the overlay part?

I think I want to do this for my local spot. I've been wanting to do it for years, would be something new to do. I like making an X on the map, would've nice to be able to match up time stamp with depth. Does Strava do that @CT-Rich?

The Strava premium makes time stamps. I haven't really worried about time stamping locations (I am a cheap bastard). In the subscription version, I am pretty sure you can. I am not using it for much other than diving and the occasional bike ride.

Strava, without a cell phone connection will only have a crude low res map of the area. To save the dive, you need to synchronize the app with a server. When you do that, you can overlay a google earth image on your path. I save the dive when I come out after each dive and then either synch it using a regular cell phone acting as a hub or when I get home and use my house WIFI. I have found I can associate thing like bottom topography or changes in compass headings with the images. If you stop somewhere for a minute to dig around or look at a critter, the flag will bob around and create a little knot in the path.

 

[Jai Bar]

I have been using this method for years- before cellphones were "smartphones" I used a garmin device, then some older phone that was sitting useless in the drawer.

I started with some otterbox, then swapped it for an old olympus camera case that was quite compact but not too bulky. This is convenient because you can reel in the case to your current depth and have a look at the last recorded location, then send up the case to continue recording on the surface.

 

[rob.mwpropane]

The Strava premium makes time stamps. I haven't really worried about time stamping locations (I am a cheap bastard). In the subscription version, I am pretty sure you can. I am not using it for much other than diving and the occasional bike ride.

Strava, without a cell phone connection will only have a crude low res map of the area. To save the dive, you need to synchronize the app with a server. When you do that, you can overlay a google earth image on your path. I save the dive when I come out after each dive and then either synch it using a regular cell phone acting as a hub or when I get home and use my house WIFI. I have found I can associate thing like bottom topography or changes in compass headings with the images. If you stop somewhere for a minute to dig around or look at a critter, the flag will bob around and create a little knot in the path.

I'd like to get times stamps so I can mark depth. I will look more into Strava and the like.

I have been using this method for years- before cellphones were "smartphones" I used a garmin device, then some older phone that was sitting useless in the drawer.

I started with some otterbox, then swapped it for an old olympus camera case that was quite compact but not too bulky. This is convenient because you can reel in the case to your current depth and have a look at the last recorded location, then send up the case to continue recording on the surface.

That's a good idea, not sure any of my old phones would fit in the Olympus case I have.

 

[Johnoly]

@Johnoly can you enlighten me on the overlay part?

I like making an X on the map,

There are tons of different ways and some are really technical. But the easiest way is how this guy does it on his youtube video (although a bit slow). You can take almost picture or screen shot and overlay it.


In our Jupiter diving, 99% of divers just go straight north with the current. But the real secret-sauce is knowing when to turn and jump left or right when the reef line splits off to way more productive sections. It literally is a new completely full harvest line hidden in plain sight with just a slight jump over to it.