Tables, dive computers and pre dive planning – what’s that all about? Groans and irritations from divers as they have reduced no decompression limits for their repetitive dives. Even worse than that, the terrifying conversation post dive ‘It said STOP and ASC-CEILING, but I didn’t know what that meant.’ Come on, who doesn’t understand what ‘STOP’ means?!
A new favorite course of mine to teach has been the multi-level speciality. It provides my students the opportunity to focus on their pre-dive plan much more extensively than they ever thought. It is a great way to revisit and look at all the different tools for planning that we have at our disposal. Plans, back up plans, gas management and multilevel profiles….these are things that get me excited about diving!!
Just what is a ‘decompression model’ I hear you ask. The algorithms or models used work in many different ways. Some are simply a test of pressure/time exposure with a gradient ascent from maximum depth to the surface. Others try to calculate the theoretical critical volume of bubbles or nuclei and try to prevent the generation or expansion of them. Further models combine various elements of both tables and mathematics models. Others are calculated by divers whilst they are under water using only depth and time information and a fixed ratio of exposure:ascent time, using special stringent gas rules.
So let us start by reviewing dive tables. Without going into too much history we can credit John Scott Haldane with producing the first set of decompression tables in 1907. From there they took various developments including the addition of compartments, and were utilized by various worldwide organisations. Individuals, governments and agencies where creating their own decompression tables. Some of the most commonly still in use are Bühlmann and U.S. Navy tables and of course, the DSAT Recreational Dive Planner.
From Haldane’s conception over 100 years ago research and development has gone a long way. We are still not so far removed from pigs and goats, but our approach to decompression theory is. Complex algorithms are utilized across a range of new aged technologies.
PADI provides various versions of the DSAT Recreation Dive Planner. Most notable is the DSAT PADI eRDP-ML (if not for the letters alone), an easy to use, touch button multilevel dive planner. This is also available to the PADI Professional as a digital version. Thrown together with a basic depth/timer device this is perfect for the Open Water Diver. In fact the depth/timer device will satisfy all levels of diver. I am not going to go into too much detail on the table itself, but all divers should be familiar with it. For a single dive it couldn’t be faster or easier to use. Repetitive dives require a more complex mathematical calculation – addition. Honestly, I really promise, the table is that simple to use and with a little practice incredibly quick for dive planning!
We all know about dive computers, we have all seen them and I would say a good majority of scuba divers today have at some point used them. Computers are based around using the same tables that have always been used, and newer mathematical models. They utilize extra parameters or extrapolate the algorithm to provide real time information.
So why are dive computers more ‘useful’ than tables. Well, truth be told, they aren’t. They are no more valid in reliability, planning, or risk of decompression sickness. Simply put, dive computers are just a more user friendly and interactive item. The problem is divers seem to use them ‘on the fly’. They take away an element of pre dive planning – and come on, they have a plan mode! By being able to account and manage so much data and calculate multilevel profiles seamlessly a certain level of awareness regarding what is and isn’t acceptable by divers has disappeared.
The good thing for an individual with a dive computer is how personal the data is. As a computer can track and sample both depth and time information instantly, the read out data can be the most relevant on the fly information available. Dives are logged and recorded and tissue saturation data is kept indefinitely (or at least until tissues de-saturate ). Again, this makes it much more user friendly for the owner, and having the ability to jump in to an open ocean and instantly have a device which calculates a dive plan as your go is very convenient. The issue with the ease of use for dive computers is they take away a desire to create a basic dive plan. Just how much air do you need to get back to the surface? A few specialty courses can expand your knowledge vastly and create a safer dive team!
Also available are a multitude of desktop dive planners. This combines the use of different decompression algorithms or tables to a user defined depth and time scenario. Using this information the software can apply the decompression model to the scenario and generate a profile. Again, this can be used to safely plan and execute a single dive or dive series, including the use of mixed gases, decompression stops and integrated gas management calculations. There are a variety of different software available on the market, some free and some costing in excess of one hundred dollars. Many technical divers utilize this software to generate extremely complex dive plans.
So, a dive computer or a table? Bühlmann, DSAT PADI eRDP-ML , ZHL-16C-GF, VPM+3 B/E, RGBM-DS or Ratio Deco? Which one should you choose? I really wouldn’t make such a personal recommendation but I am always happy to discuss the choices behind using each one. For me, anything that gets me out the water decompressed is a winner!
The most important thing to know is what to expect from a given model. There are a multitude of dive planners and dive computer simulators available right now. Even if you have the fanciest dive computer, you should know what to expect before getting in the water.
I agree with Tim’s sentiments in our last blog. Take an Enriched Air course and extend the multilevel profile, or take a Deep Diver course and learn about creating a gas plan. Go out with an instructor and learn something new. Put some more tools in that box, and have more fun with your diving. Get your buddies involved and become a team of divers.
An old mantra, but – ‘Plan the dive – dive the plan….’