Cave Diving, Cave Exploration and Cave Mapping in Yucatan, Mexico
CCR Diver at Chac Mool Cavern in Mexico

Surveying While Cave Diving is Difficult

Alain and I spent the day developing a protocol for team tape survey.

On Friday, Alain and I spent the day working on protocols for team tape cave survey.  It was Alain’s first attempt at underwater cave survey and it was my first attempt as part of a team.  When I took my survey class, I learned solo knotted line survey (KLS).  A knotted line survey is the process of using a knotted guideline to measure the data needed for the survey.  For those of you who haven’t surveyed before, here is the simplified process:

  1. Talk to locals and dive a lot.  Eventually a good project will come to mind.  Do some test diving to make sure it is a meaningful project, get permission, and create a plan.  If you need a team to do the work, recruit them and train with them.  And before you start, check your motives.  (This one I got from Matt at Protec).  Ask yourself if the exploration is for your ego? Does it contribute to the cave community?  Are you going to follow through and give back to the community?  How much impact will it have on the cave?  Does the data exist and can I collaborate to minimize risk and impact?  Remember, exploration and survey is a high impact activity and conservation needs to be a close second only to safety.
  2. Sitting at home or in your refrigerator box, use a knotting machine to put knots ever 10ft in some guideline.  This is the really tedious part.  Spool the knotted line onto your reel.  My exploration reel holds about 600ft and my exploration spool holds about 250ft of 18guage twisted nylon line.
  3. Make some survey slates.  A survey slate has a compass and 4 columns for data:   depth, distance, azimuth and comments.  I attached my compass directly to the survey slate.  Trident makes these great slates that are 6in x 8in and have a nice slot for a pencil.  I choose to use a Suunto M3 compass  it has +-2 degrees of accuracy which is the minimum required for the grade survey I am interested in.
  4. Put all the stuff and your teammate in your vehicle and go diving.
  5. Once on site and to the area of cave you want to explore, install some guide line.  When you lay it, make sure you have nice straight level shots and the line isn’t kissing off anything.  Also make sure it isn’t a risk to other divers.  Installing the line is critical; if you do a lousy job here the rest of the job will be very difficult.  My advice is to spend a lot of time looking at existing lines and analyze their placement and their impact on the cave and the dive.  Do they look easy to swim?  Are they safe?  Can they be surveyed?  Then practice putting line into benign situations.  A tight or pristine spot isn’t the place to learn to lay line.  Be prepared!    I have heard some funny stories from Steve about him finding reels and lines that were obviously left by someone who had gotten in over their head.  And remember, take your time and enjoy yourself.  The joy is in the journey.
  6. This is where you have a choice, conditions permitting and gas permitting you can survey the line you just put in on the way out.  Or, if you don’t have the gas or conditions are too nasty, you can exit and survey the new line on another day.  Collecting the data and staying alive are critical to the success of your project.  Drowning with a slate full of survey data is stupid and will curtail any further exploration. We witnessed this recently in Ginnie Springs and it was really sad.  It impacted me and everyone else in the cave diving community, whether they realize it or not.To collect the data you need to record the depth, distance, azimuth and notes at each station.  There is a fine balance between precision and speed and as you practice you will get faster.  I am still pretty slow and I make minor mistakes pretty regularly.  Usually those mistakes are a couple of degrees one way or another, I forget to write a number down such as 16 instead of 163, or I loose count when counting the knots.  Minimize your mistakes by taking your time.  Resurveying kind of sucks and robs you of time to make real progress.And now we have come full circle, it is called a knotted line survey, because you are counting the knots between stations.  When you get to a line segment that doesn’t span two knots you use arm spanning to estimate the remaining lengths.  I know the length of my forearm, tip of finger to tip of finger and tip of finger to the middle of my chest.  Using this method I can get 95% of my data within 1ft of accuracy.
  7. At the end of the dive, immediately record the data from the slate to a notebook.  Slates have a way of loosing data by getting erased or rubbed off.  I have already lost data to this villain, you don’t need too.
  8. When diving is done for the day, I go home and enter the data into Compass.  Compass is a cave mapping program.  If I have GPS coordinates, I place the new survey into Google maps so I can see my relative progress.
  9. Rinse and repeat as necessary.

What I just described is greatly simplified and doesn’t really capture the difficulty or investment required to do a survey project.  Please do not use my instructions to go out and start a survey project.  I suggest that you seek training or mentoring from instructors who are experts in survey/mapping and actually do it themselves.  There are MANY tricks and ways to make it more efficient and I can’t really imagine learning to do it on my own.  Survey is the essence of tasking loading and perceptual narrowing.  I think it could be described as a right brain activity and it can blot out your sense of time and reprioritize things for you.

Moving right along, I learned to do KLS solo so I didn’t really have to deal with any of the complexities of communication or team logistics while surveying.  Recently, Alain and I decided to work on a project together.  The cave has existing line and the line needs to be resurveyed so we could continue our work.  The line is not knotted.  So he and I decided to do a tape measure survey and leave the existing line.  We decided to leave the line to save the impact and time of relining.  Additionally, leaving the line in maintains some of the history of the cave.  I would be sad to see my line taken out, someone placed that line with love and care and it should be respected.  I know I enjoy looking at the arrows and seeing the names and dates.  It gives me a real sense of who was there before me.

A tape survey is when you use a tape measure to measure the line segments instead of knots.  Almost everything else I described is the same.  A tape survey is much more accurate, however it is more difficult.  It requires two people or it requires one person to swim back and fourth repeatedly.  Alain and I selected a 100ft nylon tape measure.

To begin with, Alain and I practiced our survey on dry land.  I set up a circuit and we each set about surveying it solo using KLS.  I walked Alain through the process and we each took the data down.  Then we decided to attempt a tape survey with me as diver one (D1) and Alain as diver two (D2).  We decided that D1 would swim the end of the tape out and fix the guideline as he made progress.  When he reached the next survey station he would signal diver one with a BIG X.  While D1 swam away, D2 would take the depth.  Once D2 received the X, he would take the distance and the azimuth.  After completing the circuit, we switched position and tried it again.  We neglected to create any other signals.  I bet you can foresee what is going to happen. We were happy with our progress so we entered the water.

For Friday’s surveys, Alain was D1 and I was D2.  We planned to survey into the cave and we started at the beginning of the line.  The line at this location starts in 20ft of water and then drops down to 40ft and into halocline. It runs for about 300 feet at that depth and then rises out of the halocline.

Alain and I got the first 2 stations pretty easily.  Then we got into the halocline and I realized that light signals just were not going to work.  I couldn’t tell when he was giving me an X.  And I couldn’t signal to him that I needed to repeat the distance measurement.  Work really slowed down at this point, it was a real trial by fire.  Our communication protocol was short a couple of commands.

The first dive provided many excellent lessons.  I learned that we would need to develop a protocol for communicating through the tape.  I also learned that the process was going to be pretty slow and our SAC rates would be much higher as we settled into the new level of task loading.

On the first dive we collected about 500ft of survey.  It took us 54 minutes surveying and we only penetrated about 10 minutes into the cave.   At 54 minutes we both hit our thirds and had to call the dive.  Our gas consumption was through the roof while surveying.  I can tell you that I was stiff in the water and tense all over.  I could see how I was burning through the gas.  Plus, I was paying attention to surveying and not my breathing.  Luckily, surveying in adds conservatism to gas management.  I survey much slower then I swim, therefore if I use a third surveying in, I should use a 1/6 or less to swim out.

During our surface interval we worked on our protocols for communication.  We developed a system to communicate through the tape.  I also developed signals to ask him to repeat the tape measurement.

For the second dive we swam to the end of the first survey and started surveying.  At this point the cave got much smaller and the condition and placement of the line deteriorated.  The new signals worked out great.  We were a bit more efficient but covered less ground due to the conditions.  The second survey only netted about 300 feet of data.  I was still really stiff, but at least I was aware of it.

When I got home Friday night, I fired up Compass and put the data in.  The stick map started to come together.  I spent a couple of hours and learned how to put the stick map into Google Earth which was a real thrill.  The stick map super imposed on the satellite photos really pumped me up to go back and collect more data.  Overall it was an excellent day with a great dive buddy and friend.  We laughed a lot and got to improve our skills, you really can’t beat that for a Friday.


1 Jason { 11.24.08 at 5:54 pm }

Hi guys,
nice work. seems like a long process when ‘tape’ surveying!
Where are you doing this project?

2 Alain { 11.24.08 at 11:47 pm }

can’t wait to go back bro’! but next time let’s get more sandwiches 😉

3 Hans { 11.24.08 at 11:52 pm }

I think the project will take a while. To capture a reasonably accurate survey it just takes time in the water. Which means Alain and I have to coordinate our schedules and get to the site.

The answer to your question is, “locally.” ha ha ha…..

4 Jason { 12.01.08 at 9:59 pm }

Does it mean you don’t want to share?
It would be interesting to know where surveys are taking place, not to disrupt any work…

5 Hans { 12.02.08 at 9:38 am }

I would love to share the information and the experience in its entirety. However, that would put our work at risk, and since I am collaborating I need to respect their wishes and protect the project.

Unfortunately, in many cases surveys and exploration are disrupted when it becomes public information. Exploration and survey is inherently political here with turf wars and people taking malicious action against others. To be honest, I have already said too much on the subject.

In closing, if we are executing the survey correctly and the visitors to the cave are practicing conservation, it should be just about impossible to interrupt our work. You shouldn’t be able to tell we are surveying and we shouldn’t be able to tell you were there.