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  • AutorenbildMichael Mutter

It's the rig balance, stupid!

With a bit of luck, summer will reach us this year as well. In our latitudes, dives in uncomplicated neoprene outfits instead of dry suits will be tempting. This article explains why it is not a good idea to test the limits of recreational diving in a wetsuit.

Image: Patrick Oswald

Or to put it another way:

Why do you need a dry suit when diving in Swiss lakes? (Several answers possible)

1) As protection against the cold

2) For buoyancy control

3) As a technical diving statement

If you (also) chose answer 2), you can skip this article. Everyone else should read on.

Diving equipment generates buoyancy on the surface of the water - despite its weight on land. Additional weight is therefore required in order to be able to descend. Lead is used for this purpose. Its quantity must be selected in a way that ensures neutral buoyancy at all times during the dive. The amount of weight a divers need corresponds to the greatest positive buoyancy they will experience during their dive. This is reached when they ascend to shallow water at the end of their dive, when most of the gas weight has been used up and, if wearing a wetsuit, there is no compression of the suit material due to the pressure at depth. Ideally, divers float neutrally in the water with zero gas in the buoyancy control device (BCD) at the last ascent stop. This prevents an uncontrolled ascent with the risk of barotrauma and decompression sickness.

A "balanced rig" ensures neutral buoyancy throughout the dive.

If the equipment is correctly balanced in terms of weight, both a smooth descent and a controlled ascent are guaranteed at all times during the dive. This concept is known as "balanced rig". It is essential to ensure that not too much weight is carried in order to ensure that an ascent is still possible even if the BCD is not working properly. The type of suit plays a decisive role here.

The following table illustrates this:

In a hypothetical standard situation with a double-twelve configuration (D12), a downforce of approx. 100 N results at the water surface. This must be compensated for under water. We assume that you are diving with a standard wing (40 lbs). This generates a maximum buoyancy of 18 l corresponding to 180 N, i.e. it even manages this when the dry suit fills up and loses its 80 N positive buoyancy.

Neoprene wetsuits lose their positive buoyancy with increasing depth.

The situation is different with a wetsuit. Its material is compressed by the increasing ambient pressure with increasing depth, which leads to a constant loss of buoyancy and a much greater downforce than with a dry suit, as the latter does not lose its positive buoyancy under water due to constant filling with gas. This is why a wetsuit results in a greater downforce at 30 m than on the surface of the water. This causes problems if the BCD were to fail. The downforce could only be counteracted with fin strokes (approx. 50 N) and to a certain extent with the lungs under maximum inhalation (approx. 20 N if at all). Dropping the lead would not help either. The diver would continue to sink and would have no chance of surfacing without help from outside.

If you consider configurations that are often seen in Swiss lakes, namely diving with more lead, the setup with a neoprene suit already reaches its limit at a depth of 30 m, as the wing has to be filled to the maximum in order to ensure neutral buoyancy (180 N buoyancy). At greater depths, the whole configuration becomes overloaded and you have to actively work with fin strokes to prevent sinking.

What about a 15-liter steel bottle? Not much better. The downforce is lower at 30 m. But here, too, the situation would become highly critical at a depth of 30 m with regard to surfacing if the wing were to fail (downforce > 100 N).

This danger does not exist with a dry suit. It serves as an additional buoyancy aid and compensates for the loss of the wing by far. If you consider that the water temperatures in Swiss lakes remain in the low figures all year round at depths of more than 30 m and that therefore effective protection against the cold is advisable anyway, there is no real reason to push the limits of recreational diving with neoprene wetsuits.

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