Y like yoyo

In the Virgin Islands, “yoyo” diving is the world upside down! 

Definition

The “yoyo” dive was a term in vogue before the advent of computers and which condemned the practitioners of dives with a sinusoidal profile or even frankly unmanageable as opposed to the regulatory “square” dives. It was wrong. Very bad ! This nickname, however, has nothing to do with the ancient and annoying children's toy that goes up and down (in principle) along its thread ...

Synonymes

Dive profile | Square dives | Successive dives | Full brothel | 

Starter

At the landing, off Ajaccio in Corsica. After a series of “yoyo” dives…

We have already addressed this vast topic of decompression in the article on dive computers. 

As we mentioned in the introduction, the decompression algorithms are calculated for regulatory dives with a “square profile”, namely a descent, a stay on the bottom at constant depth, an ascent and stops for decompression. Strictly speaking, a second so-called “successive” dive a few hours later. It is also in this way that the old pairs of watches / depth gauges / tables functioned which required tedious calculations on and under water and which made the heyday of “recreational diving”. 

The conditions on the ground and the practice of the priesthood called “monitorat” sometimes oblige to give serious stab wounds in the contract and to chain unorthodox dives. We now know how dangerous these so-called “yoyos” dives are. In particular during seemingly innocuous exercises, in pits or at sea, where the instructor is led to practice numerous descents and ascents to accompany the students. All the more reason to take care of this during “real” dives, even if the generalization of computers leads to transgressing this rule when exploring large wrecks for example. We go up, we go back down… Be careful, it is not because a computer takes these variations into account and calculates the decompression thanks to its mathematical algorithm that it will be the same for your body!

Main course

These small reels for the buoys have indeed a bit the shape of yoyos but that obviously has nothing to do with the subject at hand!

In Brittany, where I practiced at Middle Ages the noble activity of monitor it was not uncommon to chain dives making the calculation of “successives” more than random.

Our empirical measurement was based on the appearance or not, at the end of the day, of redness and other itching, barotrauma causing pustules and red patches that we called “fleas” and “sheep”, fortunately no longer in practice today ...

As I quickly switched to cave diving, an exploration activity straddling the diving and caving, I was very early faced with this problem of “non-square” dive profiles. Indeed, underground, it is the cave which decides, leading the diver to more or less great depth according to the profile of the gallery. It is also necessary to consider the return and the presence of numerous successive siphons and therefore as many descents and ascents, with or without necessary stops ... A puzzle that for a long time limited the speleonauts confined to calculations by tables “at maximum depth”. Then appeared the first “decompressimeters”Named in the United States“ Bendomatic's ”which, thanks to empirical, mechanical and furiously analogical methods, in principle made it possible to take into account variations in depth and to propose suitable decompression stops. Undoubtedly we placed an exaggerated confidence in these first accessories of plastica, still it is it that I owe them (I took two of them…) many of my beautiful firsts…

Dives in the Middle Ages.

Falling into the Red Sea: beware of the temptation of the “yoyo” ...

Finally came the Decobrain, a digital version that seemed to be the ultimate weapon. In order to continue exploring the Mescla cave (where I would reach the depth of -80m in siphon n ° 3) and in anticipation of the large number of “successive dives” to come, I decided to train on the land of the late Jean-Pierre Joncheray in bay of Fréjus on the classic “sea lion” site. But there is no question of practicing this foot bath in an orthodox way. If I condescended to immerse myself in salt water it was to practice this classic “caving” dive; that is to say alone, as I would be later, and equipped with a bi 2 × 20 liters to have considerable autonomy and redundancy allowing a long, very long dive, between the surface and more than 40 meters, in a recreational dive always restarted, linking dozens of descents and climbs ... I relied on the beep, beep's and flashing lights from my brand new wrist computer and everything went smoothly, as expected, as well as exploring the area. Blend. This experience is in no way proselytizing, especially in light of what we know today ...

Dessert

Paul Bert, the visionary ...

It is useful to recall how the decompression and the calculation of the stops are essentially empirical. Man in fact cannot be reduced to equations and the truth is that we do not know exactly what is happening in our body, even less perhaps during successive dives or “yoyo” or the reasons which make them more. “Accident-prone”… For example, when in 1948, the Marine Nationale equipped its divers with scuba diving equipment she used the US Navy dive tables whose ascent speed was set at 7,5 m / min. Which was considered unnecessarily slow. That's why we adopted the new tables GERS in 1959 with a faster ascent rate. But, following accidents with these tables, the ascent speed drops to 17m / min. These were the 1965 GERS tables. Unfortunately, new accidents happened and the French Navy carried out a statistical survey on 250 dives which resulted in the development of the new “MN 000” tables. Tables that have been regularly corrected and used for a long time by the FFESSM as part of the training of divers. It is also with these that I learned and practiced diving (ascent at 20m / min) before the advent of computers. As we can see, the development of these tables was in fact based on a rather sinister empiricism made “of trial and error” with a considerable number of more or less serious or disabling decompression sickness as a result ...

The famous "caisson disease" ... Various hypotheses were formulated when the origin of the disease, but it is Paul Bert who discovered the cause in 1878: the formation of nitrogen bubbles in the body. It also revealed the neurotoxic effect of oxygen (hyperoxia) and, paradoxically, the beneficial effect of pure oxygen in reducing decompression sickness. He proposed, for lack of anything better, to go up very slowly ...

John Scott Haldane, the mustache.

It was not until 1907 that the work of John scott haldane (Scottish physiologist) specializing in respiratory physiology, with the assistance of AE Boycott (also physiologist) and GCC Damant (an officer of the British Royal Navy) lead to the establishment of the first diving tables in the air up to 63 meters, after having made many animal experiments. In 1943, the US Navy published its dive tables. They will be reviewed and corrected during the XNUMXs and will become essential “US-Navy Tables”, used around the world.

In Switzerland, the table “Buhlmann”, in its first version, made up of a submersible plastic table made up of a disc with a removable strip, will appear in the early 80s. The second version, in 1986, will go around the world. It is the basis of most of the algorithms currently used in dive computers ...

See you soon for a new definition of Scuba Bécédaire. The irreverent lexicon of diving, but not only. Because sometimes ...

Francis Le Guen

Café

Haro on the professional “yoyo” of “assisted lifts”! Medieval test if there is one (well, I am not dead but that does not excuse anything) denounced here by the friend Vincent d 'Aquadomia in Marseille.

And for our sequence “gnan gnan”, imagine that there is a surgical operation to treat ear infections and which is also called “yoyo”. Yes !