South African scuba supremo Nuno Gomes is the world's deepest diver. On 10 June 2005, after 12 hours and 20 minutes in the Red Sea, Gomes surfaced with a new world record under his belt. Official measurements on site revealed that he had reached a depth of 318,25m beating the record of 307,80 m, set by John Bennett in the Philippines in November 2001.

Gomes, a 52-year-old civil engineer, had reached a depth that was the equivalent of the length of the Eiffel Tower - including the aerial at the top.

It had taken Gomes about 14 minutes to reach 318,25m, and 12 hours to surface.
Gomes is one of only a handful of divers who have been below 250 m. In fact, more people have gone to the moon than have gone to that depth. He now holds the world records for the deepest sea and deepest cave dives. In 1996, Gomes descended into the inky blackness of Boesmansgat, in the Northern Cape, 282,6m under water.

The record depth achieved by Nuno is based on the tag which he removed at 318,25 m below the surface. It is hypothesized that the depth Nuno reached was in fact even deeper due to rope stretch. The tags are placed at regular intervals along the nylon rope (descent line or shot line). A weight is then placed at the end of the rope and lowered into the water. It is believed that the additional weight stretched the rope resulting in the tag retrieved by Nuno being even deeper. This hypothesis was tested by Prof W Burdzik from the Department of Civil & Biosystems Engineering at the University of Pretoria in South Africa.

Diving procedures
The dive took place in the Red Sea north of Dahab four kilometers off shore. The dive took place from the boat the NABQ Explorer. A shot-line was dropped, with additional diving cylinders for decompression deep down as deep as 180 metres and the signed tags one of which Nuno would have to retrieve and surface with to prove his record.

The dive required the finest most reliable equipment available on the market capable of functioning at such great depths. Nuno donned an Eques inner garment and Poseidon Dry Suit. The knife on Nunos arm was in place, the knife would provide a location on which to clip the tag (the handle had a perfect hole).
Nuno decided to use his Poseidon Cyclon 5000 regulators on both his main quad configuration cylinders as well as his side slungs. Special oil filled and glass toped Poseidon SPGs were used on all deep regulators. Nine different gas mixtures were used on the dive which consisted of Oxygen, Air, 3 x nitroxes, and 4 x trimixes. Nuno used nearly 90 000 litres of gas. Hit kit consisted of the following:

· 4 x 18 l cylinders (3 manifolded together and one independent) with Poseidon tank valves
· 2x 14 l side slungs
· 1 x 12 l side slung
· 28 x 12 l stages
· Old Uwatec computer
· VR3 computer
· Sabre torches
· Tektile torches
· Eques Fleece inner
· Poseidon dry suit
· Poseidon fins
· Tusa mask
· Poseidon regulators (Cyclon’s and Extreme’s)
· Poseidon SPG’s
· Casio G-shock watches
· “Nuno Gomes” wings by Triple-L

Measuring the descent
The descent was measured using electronic computers as well as placing depth tags at specified depths below the surface. During the descent the electronic computers failed when Nuno came close to the planned ultimate depth. The only reliable method to determine the actual depth was thus to measure the depth up to the tag which Nuno brought to the surface. The descent line was measured by independent persons, whom verified the depth of the tag, which Nuno retrieved, was placed at.

A weight of 21,77 kg was placed at the end of the descent line and lowered into the water. Cylinders was also placed at vital points for Nuno’s dive and the rope itself weighing 25,2 kg (with SG being 1,14) could have resulted in the descent line being stretched and subsequently resulting in the retrieved tag being even deeper. These factors were not taken into consideration during the initial determination of the depth of 318,25 m. The procedure followed to test this hypothesis was to first determine the elastic characteristics of the ropes, which he used as his descent line, in a laboratory under controlled conditions. Secondly the weight distribution along the descent line was established and used to calculate the increase in length (stretch) for the different sections (Line A and B).

Experimental investigation

At the University of Pretoria, Prof Walter Burdzik from the Department of Civil & Biosystems Engineering determined the characteristics of Line A and B (also referred to as the thin and thick lines respectively). An experimental set-up was made where a force was applied to the two lines individually to determine their elasticity.

The lines were tested dry and wet and the tests repeated for representivety. The tests indicated a near linear increase in length with increase in load (tension force). The results are summarised in the table blow.

A typical test result (in this case Line B, Test 4) is shown in the graph below.

The reduction in stretch values when looking at for instance Test 4 to 6 for Line A is due to the recovery of the rope which has not yet fully taken place before the tests were repeated. The most conservative values of Test 6 (wet tests) were used in calculation of the increase in length. Based on the weight distribution along the descent line and the characteristics of the lines as indicated above the increase in length up to the point of the retrieved tag was calculated. The experimental tests indicate a definite increase in length with increase in tension force.

Congratulations Nuno your record is actually an invincible 321,81 m. The additional weights at the end, which kept the descent line vertical, weight of the cylinders and weight of the lines itself resulted in the retrieved tag being at least 3,56 m deeper than originally determined. This value can be even deeper if the elastic characteristics as determined with Test 4 be used, resulting in an increase in length of 5,03 m.