Connect with us

Education

Variable Gradient Model: An Approach To Create More Efficient Decompressions

British tech pioneer and inventor Kevin Gurr has been building dive computers since the early 1990s, including the world’s first mixed gas diving computer, the VR3, which he launched in 1997, through his former company VR Technology Ltd. based in Dorset, UK. He also designed and built three sport rebreathers. Now the Maritime Technology Officer at Avon Protection managing military rebreathers, Gurr discusses an innovative modification of gradient factors that he developed for use with his various devices.

Published

on

by Kevin Gurr

Header Image: by K. Davidson for Halcyon.

This article is not designed to go into the finite detail of decompression modeling; other people have achieved this far more successfully. It is intended as a snapshot view of what is currently available in Avon Protections’ MCM100 military rebreather, which I helped design, hopefully with a level of technical clarity so that the reader can evaluate for themselves the merits of the differing methods.

The human body cannot currently be mathematically modelled. Not only are individuals different because of age, fitness, pulmonary and cardiac (PFO) defects, but they also vary on a daily basis due to hydration, stress, exercise, micro-nuclei generation, and many other factors. 

So how does the diving community conduct thousands of safe dives per year? Some experimentation has historically been done to produce ‘reasonably safe’ decompression tables that ‘fit’ most people for a shallow water (primarily air diving) environment. In modern technical diving, much of the deeper diving we do is simply an extrapolation of the early shallow water research. We now know that this does not always work. 

Shallow water diving is relatively well documented and we have historical figures to work with, which  is only just starting to occur with deeper diving. Let’s review the basic decompression theory so that we may investigate possible ways to deal with the problem.

Consider the Buhlmann system of decompression: it is assumed that each of the hypothetical tissue compartments can safely experience an over-pressurization during a reduction in pressure (ascent) after a pressurized exposure (time at depth) which has allowed them to absorb gas.

The subsequent decompression profile that is generated on the ascent should not exceed the tolerated over-pressure value, or M value — a theoretical construct for the theoretical controlling tissue compartment within the body, in order to avoid decompression illness (DCI). As each compartment comes into play and the relevant M value is reached, a decompression stop profile is generated.

Figure 1 represents a very simplistic example involving just one of the fast tissues which will control the primary ascent phase. The M value for this compartment is shown as a straight line. If the diver controls the ascent, the inert gas loading in the compartment will stay on or below the M value line. If they do this, let’s assume they are using 100% of the available M value, which means there’s no extra safety margin for that dive; they are theoretically diving right on the edge of the model. 

Graph courtesy of Kevin Gurr.

For a typical bounce dive, Buhlmann standard practice has been to allow a rapid ascent to the first stop to generate a high level of off-gassing. Doing this, the gas loading in the fastest compartment will be on or near saturation at the bottom depth (the slow tissues are only partially saturated). This means that the fastest compartments will control the initial ascent since their gas loadings will be near or on the tolerated over-pressure value (M value). The first stop depth is set when the controlling (fast) compartment is nearest to the M value. The example only shows up to a point where the first stop starts and does not detail the other compartments or the remaining decompression. 

Using gradient factor terminology, the M value line is the 100/100 reference. The first 100 describes how close (in percentage) to the M value line the first stop is, and the second 100 describes how close the final stop is. Thus 100/100 has no added safety margin compared to the M value. In the complete picture, each compartments’ M value and each compartments’ internal pressure right through to the end of the dive (not just to the stop as drawn) would be displayed on the graph each with the same 100/100 gradient. The slower compartments would reach their M value during the final decompression phases while the faster compartments control the deeper decompression.

The gradient factor system modifies the M value by taking a percentage of the difference between the M value and the ambient pressure value. As a simple example to illustrate how Gradient factors work, using 80% of the M value as the controlling value (80/80 line) produces a line on the graph (figure 2) below the 100/100 line, having the effect of reducing the compartments allowed over-pressure value and generating a deeper decompression stop. 

Graph courtesy of Kevin Gurr.

Again, in the complete picture all the adjusted M values and compartment pressures would be plotted, adding safety to the whole decompression profile.

As most of these early dissolved gas based tables were formulated around relatively shallow water air range dives, they do not suit deep water dives, although historically they have often been extrapolated for use in deep-water. While these tables have a varying solution for different depths they were depth limited.

So what about Pyle stops? Technical diving pioneer, ichthyologist Richard Pyle developed a practical solution that divers could understand for modifying the decompression profile to reduce the excessive over-pressurization of the controlling compartment at the deep stops. He found that by stopping and venting a fish’s swim bladder below the first tabular stop depth, he ‘felt better’ at the end of the decompression. He was in effect allowing the faster compartments’ pressure to reduce before ascending to the tabular first stop and not reach its M value peak. 

The downside of this was that other compartments were still on-loading gas, which could generate an additional decompression obligation in shallow water. He was applying a safety factor that only had an effect on the deeper stops. This had the potential to allow the slower compartments to become closer to their M value during the shallow water decompression phase unless additional safety factors were applied.

Now we move onto bubble models (VPM etc.). Put very simply, bubble models attempt to explain the growth phases of inert gas bubbles and their subsequent effects. These models focus on the first part of the ascent where the bubbles grow, and by doing so, claim they can lead to a predicted reduction of the decompression obligation in shallow water. However, because of this decompression reduction, some dives generated decompression stress which could not be explained. In recent years, these bubble growth models have gone through several iterations as a result, and new evidence suggests that “deep stops” generated by bubble models may not be more efficient than shallower decompression.

A common (but complicated) solution to reduce the problem was to combine what was known about shallow water decompressions (Buhlmann) with the deep water bubble model. We know this is still an incomplete solution as phenomena such as arterial bubbles and other effects are not taken into account. Bubble models give an explanation and provide a working model of what Richard Pyle tried to implement practically from a technical divers standpoint. 

A recent tool, which provides a simpler solution between Buhlmann and the bubble models, has been to use gradient factors with a dissolved gas model which in turn modifies the M values of the controlling compartments (Baker). This has the effect of combining a bubble with a dissolved gas model style decompression profile.

Gradient factors can further mimic bubble models by using two different gradient factors to control the decompression: one that primarily references the deep stops, and one the shallow. 

So a 20/80 gradient factor, which has been commonly used on deeper dives, would allow an over-pressure value of 20% (instead of 100%) of the difference between the ambient pressure and the allowed M value for the controlling compartment of the first or “deep stop” and 80% (instead of 100%) of the M value for the controlling compartments’ pressure difference at the shallow stop. The stops in between are calculated by drawing an over-pressure value line between the two points and plotting the new adjusted M values for each compartment in between. It assumes a linear calculation between the adjusted first and last M values. 

In Figure 3 let’s assume that compartment 4 controls the deep stop and compartment 16 the shallow stop. Again, for clarity, the on-going compartment inert gas loading reductions are not shown past the M value point, neither are all the other compartment M values.

Graph courtesy of Kevin Gurr.

The major drawback of gradient factors is that the factors applied need to be adjusted for each depth/time exposure. For example, if you used the same 20/80 gradient factor for an 80 m dive, on a 30 m dive you might have an excess of decompression in shallow water because we know from experience that a gradient factor of close to 100/100 is reliable for this shallow water dive. 

What does this mean? First, it is not necessarily appropriate to apply one gradient factor to a range of dive depths. What works deep may not work shallow. Secondly, it means just applying gradient factors in the first place may be too coarse a solution. Just drawing a straight line between the M value points and assuming the mid-water decompression follows this linear approach may not work. So how do we generate a refinement?

Stochastic modelling has been around in diving for some time. Decompression tables are generated based on statistical dive data of incidents; basically, points are plotted on a graph and an algorithm generated. So how could we use this to improve gradient factor modelling? Assuming the 100/100 factor is OK for a certain shallow dive and the 20/80 is OK for a particular deep dive, would it not be best to have a varying gradient factor depending on depth/time exposure and other factors? If we can be fairly certain of key decompression times for a range of depth/time exposures that are ‘safe’ and generate reasonable decompressions, we could use them to generate a gradient factor that varies accordingly. My term for this approach is a Variable Gradient Model (VGM).

VGM has the ability to use stochastic data and historically ‘proven’ decompression values in an algorithm and automatically adjust it for a range of depth/time exposure scenarios. The VGM software can be embedded into the dive computer, for example, in the MCM100, and its parameters can be adjusted using the screen below. Note that I also used VGM in my previous company’s [VR Technology Ltd.] VRx computers.

The Ace, Ace Profile, VR3, VRx dive computers designed and built by Kevin Gurr, VR Technology Ltd.

In summary, a VGM profile has the effect of padding the stops at certain decompression points while reducing stop times at others for a specific exposure scenario. What’s more, it changes them again automatically for different exposure scenarios and allows varying degrees of user input dependent on the application. VGM is a useful tool based on our current culminated experience. It brings together in one approach much of what we know and may help predict some of that which we do not.

Once data is available, many other variables could be built into a VGM matrix, such that with time and information it could continuously evolve to give increasingly accurate decompression predictions. While the modelling of the human body eludes us, VGM would appear to be a good solution to the current issues.

Additional Resources:

REPROGRAMMING THE FUTURE: AN INTERVIEW WITH KEVIN GURR

 Gradient Factors in a Post-Deep Stops World by David Doolette.

DELVING DEEPER INTO DEEP STOPS By Mark Powell


Kevin Gurr has been involved with Technical Diving since its inception in Europe. As well as being the first Technical Diving instructor outside the USA, he has led and been a part of many expeditions; the first sport dives on the Britannic in 1997, treasure hunting in the Pacific (and several other locations World-wide), filmmaking, and a dive on the Titanic in the MIR submarines to name a few.

As an engineer and diver he has developed several ground breaking products for the diving industry from trimix computers to rebreathers, including the Ace Profile, VR3, VRx computers, Pro Planner desktop decompression software, and the Ouroboros, Sentinel, Explorer and the MCM100 rebreathers. He lives in Dorset, England with wife Mandy, daughters Leyla and Amberlee, Neo the black Labrador, and various motorcycles.



Cave

Zen and the Art of Mexican Cave Navigation

Do you know your arrows, cookies, REMS, TEMS, presence, personal and team markers? Singley or in combination? Jump protocols? If your answer to any of these is ‘Nada’ you may find yourself lost in a Mexican cave. Fortunately, underground explorer and instructor Natalie Gibb has agreed to provide safe navigation through the watery wilds of Riviera Maya. Grab your markers.

Published

on

By

Photos and text by Natalie Gibb

The most idiotic cave navigation mistake I ever witnessed happened on a dive in Cenote Chan Hol about eight years ago. Exiting the cave, my buddy and I approached our jump line, but were pushed out of the way by a solo diver who elbowed his way over our jump line and into the side passageway. 

I stared in disbelief: the diver had not installed his own jump spool, he had just swum over mine. Had he even noticed my jump spool? Did he realize he was swimming into a side passageway? My buddy and I both had personal markers on the main line, as well as markers on our spool. My jump spool had a neon green line, and all of our markers were clearly marked with reflective tape and our names. It was not subtle.

I signaled with my light to the solo diver, and gestured, That’s my jump! He shrugged nonchalantly, turned around, swam back over my jump spool to the main line, and trundled on down the principal cave passage. If I hadn’t had a regulator in my mouth, my jaw would have dropped open. 

Since that day, I have viewed cave navigation in Mexico as a two-part responsibility: 

  1. Don’t confuse yourself or your teammates.
  2. Don’t confuse other divers. 

As one can imagine, the latter is the more difficult to accomplish. 

Cave Training Agency Differences vs Regional Navigation Differences

This article began as a comparison between different cave training agencies’ navigational standards. Interestingly, there is not much to compare!   From my research it seems that TDI, IANTD, NSS-CDS, RAID, PSAI, and GUE agree on a basic philosophy: specific navigational markings and protocols are often region-specific and even cave-specific. Every instructor from every training agency I have spoken with has stated more or less the same thing: While agencies may have general guidelines, navigation procedures are left up to the instructor. 

As a TDI instructor, my students have mentioned that it’s frustrating not to have exact navigation protocols written out in the textbook. I can understand their annoyance, but from an instructor’s standpoint, I prefer it this way.  Not having rigid operating procedures published in training manuals allows cave instructors to teach to their local protocols. 

While GUE is perhaps the clearest of all agencies, most training agencies agree on basic best practices, including the need to use personal markers to mark the exit side of intersections, the acceptance of cookies as a navigation tool, and the need to maintain a continuous guideline to the open water by using jump spools and reels. 

If regional peculiarities, as opposed to dogmatic navigation standards, dictate protocols, the question becomes: What makes Mexico cave navigation different? How should you navigate there? 

What Makes the Caves in Mexico So Confusing?

Several factors make the navigation in Mexico challenging. I believe one of the major factors is that Mexican caves usually lack strong flow. Divers who have grown up navigating caves in other regions are often used to the orienting movement of the water, providing a physical sense of directionality; it’s unlikely to become truly confused about your direction of exit if the water is pushing you “out.” Of course, there are exceptions to this rule, but in general I find noticeable flow is an excellent, almost subconscious indicator of directionality, and it’s missing in most Mexican caves. 

Diver Stephanie Lee hovers between two massive columns at Cenote Nai Tucha. Mexican cave systems can be very complex and many cenotes cannot be used as exits.

The cave systems in Mexico are very complex, with multiple cenote entrances and exits. This may sound like a benefit, but in reality, it’s not possible to exit the water in all of the cenotes, and even if you can get out of the water, you could find yourself deep in the jungle without a road or the ability to call for help. Several years ago, a lost diver perished from exhaustion after blindly following the cave arrows to an alternate exit, then wandering lost in the strong jungle heat. 

Nicholas Wheeler inside the cave Nohoch Nah Chich. Mexican cave navigation often follows its own logic that can be confusing to divers unfamiliar with the system.

The arrows in Mexico’s caves are likely to alter directions throughout a single dive, changing to indicate whatever the person who placed the arrows felt was the nearest surface or exit. That person could have been wrong. The route to the “nearer entrances” might involve 16 jumps and a no-mount restriction. The lines could have been cut or changed since the arrows were placed. There are no warnings, and there is no system in place, although we are working on one!

Additionally, Mexican cave navigation follows its own logic, different from that of other regions. We use multiple arrows, directional changes, and pretty much zero distance markers. Areas far back in the cave, or areas that were explored in past decades, may have “reach gaps,” often unmarked jumps that end centimeters from the main line, as well as blind T’s, and other navigational monstrosities. My favorite recent bizarre navigation find was an “H” intersection. 

Don’t Depend on the Arrows! 

It’s best to view cave lines and arrows as secondary navigational tools. What’s your primary navigational tool? The cave itself. 

Joe Fellows at Cenote Nohoch Nah Chich. Instead of relying solely on the line, compare your compass with the expected general heading.

Plan this out ahead of time if you have a map, and confirm it during the dive by looking back and actually checking your compass once you have completed a jump or T. If you know your directions, you won’t have to rely on the pesky arrows. The magnetic field of the earth is unlikely to change during a single dive. In a pinch, caves north of Chan Hol Cenote are typically upstream to the northwest and downstream to the southeast. This changes a bit south of Chan Hol, due to fracture zones. 

Cave tunnels often have a general direction, even if they twist and turn a little. Carry a compass and keep track of which direction you are traveling, in many places it is more or less uniform throughout the dive. You don’t need a degree heading; northwest-ish in and southeast-ish out will be enough to determine your exit direction if you get confused. If you make a 90 degree turn, you should notice the heading change. If you make a jump off the mainline or navigate a T intersection, it’s essential to know the exit direction along the mainline once you return to that point. 

Nicholas White in a tunnel towards Cenote Coop One. Despite some twists and turns, cave passages often follow a general direction.

Natural navigation is also important. A diver can observe many key features of a cave without a doctorate in hydrogeology. Is the cave big and wide, or small and restricted? What color is the floor sediment? Are there any unusual speleothems that catch your eye? Do you feel water flow? Was there a major depth change? Maybe you swam over a collapse? If you swam into the cave through a small, restricted tunnel, and you turned around to exit but passed no restrictions, you are going the wrong way.  

This simple observation would have saved multiple dive teams who all made the same mistake. They entered Cenote Kalimba and made a jump from an arrow pointing away from their exit towards Grand Cenote. When they retrieved the jump spool, they swam toward Grand Cenote instead of Kalimba, through enormous cave passages instead of restrictions. They blindly followed the jump arrow, which was not pointing toward their exit; they did not correct themselves,  though the cave passageway they were in was very different from the cave passageway leading to their original exit. The more you can learn about geology, the easier it is to read a cave, remember it,  and notice if you are going the wrong way.

Alex Buess at Santuario de los Guerreros. Enourmous and numerous cave passages can easily be misleading.

Mexican System Markers

Of course, lines and arrows are important to understand, and they give divers information about the general layout of the cave. While there is no standardized system of marking cave lines in Mexico, most caves follow a somewhat logical method. Again, a diver should never assume that the arrows are actually correct or that exits indicated by the arrows are accessible. 

A single arrow usually indicates the presence of a jump line.

In Mexico, jump lines are usually indicated by a single arrow on the main cave line. This is different from Florida, where jumps are often marked with two arrows (a double arrow). Interestingly, double arrow jumps do exist in Mexico, but they are rare and have a special significance – they indicate a particularly important jump, such as a jump to complete a circuit or a traverse. Divers familiar with popular Mexican caves may have noticed this in the double arrow jump to the Death Arrow Passage in Cenote Maya Blue, or the double arrow jump to complete the circuit in Cenote Minotauro. 

Double arrows are less common, and indicate a significant jump.

There are also a great number of secret or hidden jumps that are not marked at all on the mainline. Examples include the jump to the Chinese Garden at Cenote Tajma Ha, or the jump to the Room of Tears in Cenote Carwash. 

From a practical standpoint, the lack of double arrow jumps means that line-to-line jump connections are generally not used in Mexico, and a better protocol is to tie into a line marker (more on this to follow.)

Opposing arrows suggest there are equidistant exits in both directions.

As mentioned above, arrows will often change directions along a single cave line. If you swim far enough into a Mexican cave, it is common to encounter a set of two arrows pointing in different directions. These are commonly referred to as a directional change or opposing arrows. The purpose of opposing arrows is to indicate that there is an exit equidistant in each direction, and to draw the diver’s attention to the fact that the line markers past the opposing arrows will point away from the diver’s original exit.

A pack of three arrows suggests exits in both directions, with the doubles arrows indicating the closer exit. 

Similarly, a set of three arrows, with two pointing in one direction and one pointing in the opposite direction is intended to indicate two exits, with one being closer in time or distance. However, keep in mind that system arrows may also flip direction without opposing arrows as a warning. It’s your job to notice this.  Common practice is to leave a line marker (cookie or REM) on your team’s exit side of the opposing arrows or first flipped arrow to confirm your direction of exit.  

T Intersections. T intersections are generally rare in Mexico. Most navigation is accomplished with jump lines or gaps. T’s are most often present at major intersections, when the cave splits into two equally sized tunnels. At a T, one or more exits are indicated by system arrows pointing away from the T toward the exit.  T’s are also common close to cenote entrances, with a double arrow indicating the presence of a cenote off the main tunnel.  As with opposing arrows,  good practice in Mexico is for the cave team to mark their exit side of the T with a personal marker. 

A T Intersection with an arrow indicating a single exit. 
A T Intersection with arrows marking two exits. The double arrows most likely indicate a nearby cenote.

At this point, an important clarification must be made: never blindly follow system arrows toward an exit that you have not personally confirmed. Cave arrows may point toward an exit that requires multiple jumps, a no-mount restriction, or that is blocked by a collapse that occurred after the original line was laid.  Sometimes line markers are simply wrong. Always return to your original proven exit regardless of the arrow direction, and you will stay safe.  

Personal Markers

Three main types of personal markers are commonly used in Mexico cave diving, and many divers now 3D print or craft their own, very unique styles.  The most common markers are Arrows, Cookies, and REMs (referencing exit markers).  It’s important to consider directionality of personal markers and where in the cave they can be used.  

Arrows. Personal arrows are commonly used to anchor jump spools. However there are a few situations in which I feel that arrows should not be used. In accordance with Rule #2: don’t confuse other divers, it’s generally frowned upon to place personal arrows directly next to system/permanent arrows. A personal arrow, no matter how nicely marked, may look like a system marker to another, less observant dive team, and placing a personal arrow very close to a system marker may lead other divers to believe a double arrow is present. Remember, double arrows have a special significance in Mexico. 

At jumps, placing a personal jump arrow within a few inches of a system arrow can make it look like a double arrow jump.  Instead, the team should separate the personal jump arrows from system arrows by 0.5m/1.6 ft (if possible) to avoid confusion. 

Placing a personal arrow next to a jump arrow may create navigation that looks like a double arrow jump.
Marking a T Intersection with a personal arrow may lead to other teams confusing the personal arrow for permanent navigation.

At T-intersections or directional changes, using a personal arrow to mark the team’s exit may confuse other teams, as it may look like a double arrow indicating a nearer exit. For these applications cookies or REMs are preferred.  

Cookies can be used to mark a team’s exit at a T Intersection.

Cookies. Cookies were a Mexican cave diving innovation invented by explorer/instructor Daniel Riorden in the late 1990s, in accordance with Rule #2.  Cookies are round, or non-directional, and are typically not used as system markers. The shape makes them clearly personal markers, which simplifies marking intersections and directional changes as all other cave teams know that a cookie indicates nothing about general cave navigation. Cookies may also be used to mark a cave team’s reels. 

Cookies may be used to mark an arrow pointing away from the team’s exit, by placing the cookie on the exit side (in this case right).

Cookies are appropriate for most uses, with the exception of anchoring jump reels or spools. It’s inappropriate to tie a reel or jump spool onto a lone cookie, as the cookie alone does not indicate a direction of exit at the intersection, a clear violation of Rule #1: Don’t Confuse Yourself or Your Team Mates. 

REMs. REMs (Referencing Exit Markers), invented by Bil Phillips, are a common sight in Mexico and uncommon in most other regions.  They are rectangular markers, with slats for line attachment closer to one end. The longer end points towards the team exit.  

REMs are rectangular personal markers. The longer end of the REM faces out.

REMs are interesting in that they are directional,  but can not be confused with arrows. They can be used for the same functions as both arrows and cookies, eliminating the need for a diver to carry a variety of personal markers. In my conversations with Bil, he told me this was not his original intention for the markers, but he liked that people were getting creative with them.

REMs have one other useful feature, which is that the exit side of the marker has enough space to write a serious note. This can be left on the line for notes to a buddy or for personal notes, in place of wetnote pages or other methods. 

Creating Your Personal Markers

No matter what style of markers a diver chooses to use, their markers should be clearly personalized. All organizations teach divers to write their names, nicknames, or an identifying word on their personal markers to indicate who the marker belongs to. This helps to fulfill both Rule #1 and Rule #2, making the markers easy to identify. 

An additional method of personalizing cave markers that I recommend is to make them touch contact identifiable. I ask my divers to modify their markers in a way to make them uniquely identifiable in zero visibility, such as cutting a corner off, punching holes in them, or adding something as simple as a cable tie in order to physically identify them if visibility is lost. 

Many divers also like to number their markers, which allows divers to account for all markers and refer to a certain navigational decision in the debriefing or in their notes – for example, “the jump where the diver put down marker number three.” 

Exploration markers are typically arrows, and may have the exploration teams info, date of exploration, and a key word or identifying number written in them.

A word of caution here – it is possible that some system or permanent markers have a diver’s or dive team’s name on it. These are exploration markers. They typically have the team’s names, the date or year of the project, and maybe even a keyword or number written on them, and are not marked with touch or physical identification cues. Exploration markers are so much fun to find! Every time I run across a historic marker with an explorer’s name on it, I feel a kinship to the original explorers and imagine what the person must have felt like, being the first human in this cave. If a diver has a question about the cave, the presence of the explorer’s name indicates who to contact with questions. 

Team vs Individual Markers

Now we are getting into the great debate! Which is better, team or individual markers? 

With the “team marker” approach, the team leader places a single cookie or REM on the exit side of a T. 

When cave divers are using the team marker approach, the diver in the front of the team places all markers for the team, marking and placing jump lines, marking T’s, and placing any other markers that are deemed necessary. Other team members carefully observe the diver in front, and confirm that the markers are correctly placed. The advantage of this style of marking lines is that there are fewer markers on the line, and that it is slightly faster than having each diver personally mark intersections. UTD’s Andrew Georgitisis rather infamously premiered a REM-style “TEM (Team Exit Marker)” in a Facebook video last year advocating the use of team markers.

With the “individual marker” approach, the each diver places a cookie or REM to mark the exit side of a T. 

If a cave team uses the individual marker approach, each diver places a personal marker to mark the team’s exit at every point of navigation, including jumps, T’s, and directional changes.  The advantages of this system are that each diver physically participates in the cave navigation, which helps to fix it in his or her memory. Additionally, more markers are easier to see, and add an additional degree of personalization to the navigation. If my team is using all REMs, and your team is using arrows and cookies, just the fact that a jump is marked with arrows and cookies means that it is not mine. 

When jumping from a team marker, the team leader places the navigation and all others confirm it is correct. 
When jumping using “individual” markers, all team members mark the exit side of the jump.

However, the most important argument for this method, is that individual markers create a level of redundancy in navigation. If a diver accidentally ties into a jump arrow that points away from the team’s exit (and no one notices), but the other divers mark the exit side of the intersection correctly with their cookies or REMs, it is clear that there is a navigational discrepancy upon exit. Divers then know to refer to their compasses and natural navigation clues to determine the correct direction to exit, instead of blindly following the arrow in the wrong direction when leaving the cave. This can be life saving. GUE uses this approach, though most training organizations do not state a preference.

Individual line marking procedures can highlight discrepancies in line marking, allowing divers to notice an error and take appropriate action.  Here, the arrow is pointing away from the team’s exit, but they marked the intersection properly.

Finally, some instructors teach that in an instance of team separation, divers leaving the cave remove their personal markers, while leaving the jump lines and other team member’s markers in place. This indicates to the team who is still in the cave, and who has made it out. This method of dealing with a team separation is debated in the cave community. 

The advantages of individual markers as far as clarity, redundancy, and problem solving make the individual marker method my choice.

Presence Markers

Presence markers are personal markers that are placed at the beginning of a cave line when the line starts in open water and no primary reel is required, or on the primary reel line when a reel is run from the open water. Presence markers can be team markers or individual markers, and indicate the presence of the team in the cave. When individual presence markers are used, they additionally indicate the number of divers in the cave. 

Individual presence markers at the beginning of a cave line.

If a team must exit in complete zero visibility all the way to the end of line in the open water, personalized presence markers allow the divers to confirm that they have navigated correctly to the open water and may safely surface. No agencies seem to have a firm stance on presence markers, nor is this an established local protocol in Mexico. However, I quite like presence markers and use them in my courses and personal diving. 

Jump Protocols

When cave divers swim from the main cave line to a secondary line (jump line) in a side passage, they have made a jump. As all modern training organizations require cave divers to maintain a continuous guideline to the open water,  the cave teams install a jump reel or spool to connect the mainline to the secondary line. This is a visual reference upon exit and allows the team to navigate out of the cave in zero visibility by touch. 

How should a team install a jump line? Good question! Once again there are many options, and again, there is no “right” answer as long as the marking is clear to other divers, the team that installed the line, and has some sort of marker indicating the direction of exit. It’s helpful to use colored line on jump spools as opposed to white line, which is typically used for permanent cave lines, as this makes the temporary nature of the line obvious to other teams.  Here is a non-exhaustive list of options. 

Line to line connection. When a team loops a jump spool directly around the cave line (as opposed to tying the spool into a line marker), the jump is a line-to-line connection. This sort of navigation is more commonly observed in Florida and other locations where jumps are indicated by two arrows. The team can tie the jump spool between the two jump arrows without risk of the jump line sliding out of position. Using this method, two arrows are present (if they are pointing in the correct direction) to indicate the team’s direction of exit. 

Line to line connections are common in regions where double arrow jumps are used.

Line to line connections are less common in Mexico, because jumps are usually indicated by single arrows. The jump line can slide around without arrows blocking it on each side.

In Mexico, where jumps are indicated by a single arrow which may be pointing away from the team’s exit, this method is generally frowned upon. Lines that are not anchored by a line marker are likely to slide out of position, particularly in zero visibility. 

Jump from a system or permanent marker.  One common method of installing a jump line in Mexico is to loop the jump spool’s line around the system arrow. This fixes the jump spool’s line in place and avoids the problems mentioned above. However, it is important that the team carefully observes the arrow’s direction. Divers should never attach a jump spool to an arrow that points away from the team’s exit. Doing so has been implicated in numerous fatalities, including several well-known accidents at Cenote Kalimba. If the team chooses to use individual markers, team members place cookies or REMs on the exit side of the intersection created by the mainline and jump line. Jumping from a system marker is not possible when the arrow has already been used by another team, or if the jump is unmarked, and it’s a terrible idea if the arrow points away from the team’s exit. Always be prepared to use the final jump method.

Jumping from a system arrow using the team marking approach.
Jumping from a system arrow using individual marking with REMS (cookies may also be used).

When jumping from a team personal marker, the leader installs his own arrow or REM on the line.

Jump from a personal marker.  To jump from a personal marker, the team leader places an arrow or REM on the line indicating the team’s exit direction, and ties into the personal marker. If individual markers are used, each member of the team places a cookie or REM on the exit side of the intersection created by the jump spool line and the main line. Again, this can be used as standard protocol, in the case where the jump arrow is pointing away from the team’s exit, in the case where the arrow is already used by another team, or in the case where the jump is not marked by a system or permanent arrow. This is my preferred method because it avoids uncertainty, and I use the same exact protocol for every jump, regardless of what is present in the cave. 

When jumping from an individual personal marker, the leader ties into his own arrow or REM, and all team members mark the exit side of the intersection with personal markers.

If a team chooses to jump from a personal marker when a system arrow is present, what side of the system arrow should the team jump from? I prefer to install my personal marker at least arm’s length away from the system arrow to differentiate my navigation from the system navigation. I like to jump from behind, or from the cave side of the direction the system arrow points, because this leaves the permanent marker on the exit side of my intersection, allowing other teams already in the cave who have noticed this arrow to have an unobstructed reference to the exit. 

Marking Reels and Spools. 

When tying into the main cave line or a jump line, many divers, myself included, like to place a marker on the reel or jump spool line. On a primary reel line, these markers serve as presence markers. The markers also help to visually and physically identify the diver’s line in zero visibility, especially in the event that there are multiple spools or reels tied into the cave line. Finally, this helps to unambiguously identify similar types of spools and reels, helping to avoid  removing a different team’s reel or spool by mistake. Not everyone does this, and some consider it redundant and unnecessary, as realistically divers should be able to identify their own reel or spool. I feel like it is extra clear, so I like to mark my spools and reels. 

A spool is marked with a team cookie.
A spool is marked with individual REMs.

Navigating Around Multiple Cave Teams

Placing a jump as the second team in the cave (yellow line with cookies and arrows).

A brief note is warranted to mention protocols for navigating when there are multiple teams in the cave.  The general rule is to attach any spools or reels cave side of another team’s spools, unless there is a very large space exit side.  The same rule applies to the placement of jump spools. When navigating a T, place your markers on the exit side of the other teams markers, so that their markers are the first encountered during the exit. 

Tying into a cave line or jump line as the second team (yellow line with cookies and arrows).

What’s the Number One Navigational Mistake I Should Avoid as a Tourist Cave Diver in Mexico?

The number one navigational mistake to avoid is to blindly follow arrows and lines to your death. Nearly every Mexican cave fatality I am aware of involves navigational errors exacerbated by camera use. Mistakes include divers jumping off system markers pointing away from their exit and subsequently going the wrong way when returning from their jump line, or teams getting turned around when taking photos.  Mark all intersections methodically with personal markers, understand the overall compass heading of your planned dive, and be aware that arrows do not always point towards your team’s exit, or even an accessible exit. Notice if arrows change directions and mark them accordingly. In the event that you become confused, use your compass heading and natural navigation in conjunction with the cave lines to find your way home. 

Mexico Cave Navigation Is an Art

Navigation in Mexican caves is subtle and often confusing. My shop teaches the system of navigation that we like the best, but there is a wide variety of protocols used in the area, and I wouldn’t say that any one way is necessarily incorrect. I am probably in the minority with this opinion, but I would say as long as you and your teammates stay oriented, and you don’t confuse other cave diving teams, have at it. No matter what you do, someone else is going to think you are wrong. Chin up. Did you confuse your team? Did you confuse other teams? No? Good enough. 

In fact, I actually think it’s great that there are slight variations in the way people mark their lines. If I use REMs, and you use arrows, then I can easily and quickly identify my markers simply because they are different from yours. Nice! 

Divers Nick, Nik, and Troy turn a corner at Cenote Nohoch Nah Chich. Always be sure to be on the same page as the rest of your team and develop a navigational strategy together.

One cannot be too strict with navigational protocols in Mexico, because while a team can have a standard way of placing and marking lines, the established lines in Mexico do not have standardized systems of marking.  Maybe you like to anchor your jumps on personal markers behind the system markers? I do. But it’s not always possible based on the layout of the cave. You must adapt your navigation to the environment, and that’s why it’s an art! As unsettling as this is to many people, there are no absolutes. 

So Many Options! What to Do?

Yes, it can be confusing, and determining your personal or team navigation style takes some thought and discussion within the dive team. There are options, and as grown up adults, you get to choose what is clearest and easiest for you. When evaluating a navigational method, just make sure it doesn’t violate the rules of safe cave navigation:

  1. Don’t confuse yourself or your team mates.
  2. Don’t confuse other divers. 

Based on the previous discussion and general cave training organization guidelines, we can add two additional points. 

  1. Maintain a continuous line to the open water using spools and reels as needed.
  2. Have a marker on the line indicating your direction of exit at key points of navigation, including jumps, T intersections, and directional changes. 

In addition, I would urge dive teams to be consistent. Come up with a protocol, whether it’s team or individual markers, anchoring your line on system markers or personal markers, and use the same protocol on every dive. This makes in-water decision making easier and helps to avoid confusion. Review your navigational protocol with new team members, and agree to a protocol before entering the water the first time. 

Diver Bre Kramer at Cenote Caterpillar. The cave line can be a good directional tool but at the end of the day the cave itself will give you the best navigational indicators.

No matter what navigational procedure your team chooses to use, keep in mind that while important, plastic markers and the cave line are secondary navigational clues. Your first source of navigation is the cave itself: directionality, formations, physical features, and flow if it exists.  Unlike lines, cave features are unlikely to be removed or changed. Learning to observe and read the cave will increase your safety and enjoyment!


Natalie L Gibb’s passion in life is underwater cave exploration and conservation. With her exploration partner Vincent Rouquette-Cathala, she has led her team to discover over 20 previously unknown cave systems in Mexico’s Yucatan Peninsula, mapping more than 80 kilometers/nearly 50 miles of cave passageways. She is a public speaker, author, photographer, and videographer, and a member of the Woman Diver’s Hall of Fame. Natalie is co-owner of Under the Jungle, a cave diver training center in Mexico, and a TDI Full Cave Instructor.

Continue Reading

Subscribe

Submerge yourself in our content by signing up for our monthly newsletters. Stay up to date and on top of your diving.

Thank You to Our Sponsors

Education