The human body is an incredible machine, capable of maintaining an astonishingly constant temperature of approximately 37° C throughout our entire life time, regardless of whether we are exposed to excessive heat or cold. To compensate for excessive heat, the body uses mechanisms like evaporative cooling via perspiration.
To compensate for cold, aside from the obvious option of adding more layers of clothing, the body can at first initiate shivering (involuntary muscle contractions which produce a fair amount of energy) or also implemente vasoconstriction: meaning that body parts that are “expendable”, like the arms and legs, will receive less blood in order to preserve body heat at the core (torso and head) as much as possible.
When diving in cold waters, the extremities are the first to get cold. When this happens, the brain has already reduced blood flow to these regions, in order to protect the core. Reduced blood flow plays a role in on-gassing and off-gassing and hence needs to be taken into account in a decompression algorithm. One of the Adaptive parameters in our ZH-L8 ADT algorithm is in fact the ambient temperature and the changes it causes on the diver's physiology. In some cases simply recording and factoring the temperature in the decompression calculations is not enough, and UWATEC's core technology provides the right answer for some special situations.
Let’s consider the normal evolution of a dive in cold water:
Let’s now consider the special situation presented by fresh water lakes in the summer. This is a perfect example of the same effect occurring at sea, but it’s easier to understand thanks to the larger temperature change.
Water temperature from the surface down to 10-15m is warm, however, past a certain depth the water will have the same temperature as in winter (approx 4-6 °C, see the dive profile graph below, the thin brown line shows the temperature). The diver that starts to feel cold during the dive should not be penalized by vasoconstriction, because most of the off-gassing will take place at 6m and above, and there the diver will be warm again due to the higher temperature at that level.
An UWATEC dive computer can handle such a situation without penalizing the diver.
In order to do this, the temperature measurement needs to be fast enough to detect the actual temperature of the water at the surface and down to 6-7m during the descent.
UWATEC Galileo and Smart computers do just that: during descent, the temperature above 7,5m is measured and stored in memory and this value is applied for all decompression at the 3m and 6m levels. As a result, if there is a strong temperature transient, the diver with an UWATEC computer will not be penalized by the cold water encountered during the deeper parts of the dive.
To ensure that this is done correctly, Galileo and Smart have a temperature acceleration algorithm, which predicts actual temperature based on an initial cooling rate. (In Smart COM this is not necessary because the temperature sensor is attached to a metal component exposed to the water, so that temperature equilibration takes place almost instantly).
Aladin computers (ONE, PRIME, TEC and TEC2G) also have an exclusive temperature accelerating algorithm. However, the Aladin line comes in a range of versions: wrist mount, slate or consoles. Computers in consoles are insulated from the outside temperature and this causes a non-negligible delay in temperature equalization.
It could happen that during a warm early spring day, the computer that has been in the sun for a while and registers a temperature of 25° C, will still display that temperature when going through the first 10m of the water column even if the actual water temperature is only 4° C. This would work against the diver by not offering the proper degree of protection against vasoconstriction (just as any other computer would not). For this reason, Aladin computers do not remember the temperature measured at 7,5m, but calculate decompression obligations based on the actual water temperature as measured by the accelerating algorithm.
The result is that during dives with strong temperature gradients an Aladin will show a higher decompression obligation at the beginning of the dive compared to that displayed by a Smart or Galileo. Once the diver is at the deco depth, the Aladin will warm up and start applying the correct perfusion parameters based on the warmer water temperature, so it will tick off decompression minutes faster than a Galileo or Smart, eventually reaching almost the same - shorter and correct - deco time.
Let’s use an actual dive as an example.
We dove in a Swiss lake with a 16° C temperature difference between the shallow and deep parts of the dive. We brought along 4 dive computers:
The table below list the Total Ascent Time (i.e. the time needed to reach the surface ascending at the correct rate and doing all the required stops) at four differents moments of the dive for the 4 test computers.
| Dive Time | Aladin 2°C | Aladin 25°C | Smart Z | Aladin TEC |
| 30 min | 37 | 24 | 27 | 37 |
| 35 min | 39 | 24 | 28 | 36 |
| 40 min | 34 | 19 | 23 | 25 |
| 45 min | 30 | 15 | 18 | 21 |
The difference in decompression times between the PRIME set to 2° C and the one set to 25° C (chart below) shows the overall effect of the vasoconstriction on the Total Ascent Time calculation, in the worst case.
The Smart Z example shows that, through the intelligent implementation of a temperature memory above 7.5m, the effect of vasoconstriction across a steep thermocline can be minimized and result in deco times that are very close to those calculated by the Aladin PRIME set to 25° C.
The normal PRIME shows how the decompression times at first are similar to the PRIME set to 2° C, but eventually, once in the warmer water closer to the surface, the minutes tick off faster until they are almost the same as the Smart Z. The chart on the right shows how the difference in decompression time is big at first but the two computer converge towards a very close outcome.
Other manufacturers either offer no protection against cold, or protect the diver simply by offering shortened no stop times. Still, it is up to the diver to set the computer into “cold” mode. At UWATEC, we utilize technology to do the work for you.
Through smart engineering and sound product development, we offer the diver a tool that analyzes the real conditions and finds the solution that best fits the situation. When there is an inherent limitation in what we can do, as in the case of the Aladin consoles, we still find a way to maximize the protection of the diver while also maximizing how we handle the limited (delayed) temperature data set we have at our disposal.
