THE DIVE OF TWO HALVES – Niagara revisited!
text by Pete Mesley and Dr Simon Mitchell
main photograph by Ed Jowett, Natural History, New Zealand.
This was my second expedition (first dive refer to O/N 2001 issue #66) to the HMS Niagara which sank off the east coast of New Zealandâs North Island near the Hen and Chicken Islands after striking a German mine in 1940. Her bullion room held over 7.5 tons of gold bullion!
Our crew consisted of Rex Tonks skipper and master chef of the mother ship Bluefin, Willie Heatley manned the eight metre surface support RIB and Geoff Payne was our support diver; a compact but highly efficient support team. Simon Mitchell and I were the bottom divers.
While anchored at the Hen and Chicken Islands Rex fed us like kings as we sheltered from continual frontal systems. Life was just fine! After day two a weather window opened and we headed out to the wreck site early Tuesday morning, 4 June.
The first half
Just below the surface Simon and I rechecked our gear before heading down the shot line. Descents are so important on deep dives, go too slow, you chew up all your bottom time. Descending too fast with some rebreathers doesnât allow their scrubber enough âdwell timeâ to extract the carbon dioxide out of your exhaled gas. Also your counterlung may have difficulty in equalising, making it difficult for you to take in a full breath.
Itâs hard to explain the wonderful feeling as you descend the shot line, which vanishes into 120 metres, knowing at the end, is a world-class ocean liner waiting patiently for you!
At about 80 metres the wreck, lying on her port side, came into view. There was not a breath of current, and the visibility was truly astounding! â Simon just looked at me with those eyes which said, âThis is unbelievable!â On the surface things were a little different but down here the rain had stopped, the sun was out and there were two kids rearing to play! One of the first things I noticed was the abundance of fish life. As on my previous dive to the wreck, a huge school of kingies spiralled round us, just out of reach. A fantastic experience. We swam over the hull through schools of golden snapper toward the bow until we found the infamous hole that was blasted open in 1941 when salvagers Johnson and Williams made history by recovering 555 bars of gold. During the dive there is always that niggling thought âWhat if we come across one of the five bars of gold that were not recovered?â The chances of finding a 25cm x 9cm bar amongst 14 thousand tonnes of shipwreck were a little optimistic to say the least! The holeâs walls had caved in. There were no recognisable features amongst the huge steel plates, metal girders and debris that hampered any penetration opportunities into the ripped apart bullion room area.
Just being there, swimming round the wreck was Simonâs and my âbar of goldâ.
Before the dive we both looked at the ships plans and some pictures of the internals of this magnificent ship. She was so stately and luxurious she had been labelled the âTitanic of the Pacificâ.
The details of a magnificent oval stain glass skylight drew our attention. It flooded natural light into the first class smoking room the first class accommodation block vestibule and the first class dining room. We looked at this detail and tried to imagine its beautiful elegance. We made it one of our objectives of the dive to see if it was still intact, Iâm forever the optimist!
We discovered that the skylight was gone along with the promenade deck (B deck) and the shelter deck (C deck) which is where the first class accommodation was. Simon and I swam into the first class dining room through the oval skylight hole that was now the top deck. I recognised the sculptured columns and the moulded ceiling patterns. The tabletops had long since disintegrated leaving only their legs bolted to the floors. A ceiling fan hung by a cord. The once beautifully polished floor now laid at 90 degrees covered in a thin layer of silt. All the hand made chairs, table fittings, cutlery and crockery predictably lay in a huge pile of rubble on the ocean floor covered with over 61 years of silt and wreckage. Our time was up! Even with 25 minutes of bottom time it just shot by!
At the 80m stop on the shot line the view was amazing. I could see that the two upper decks had collapsed almost three quarters of the way towards the stern. Incredible!
At our scheduled 50 metre stop I popped my deco marker buoy and our drifting shot with bailout gas was deployed by our surface support.
The Second half
We arrived at the nine metre decompression mark and after about two minutes into the stop I suddenly started to spin uncontrollably â or at least it bloody well felt like it. I immediately thought it was my rebreather and switched to bailout. No change, still spinning! I switched back to my rebreather. Signalling to Simon that something was a miss, I tried to control the increasing nausea but after about 10 minutes I had to switch to my bailout and was sick. This happened frequently throughout our two and a half-hour deco. Fun and games!
Back on the main boat we tried to piece together what happened to me. Having one of the worldâs leading hyperbaric physicians on the dive had its advantages! Simon had my diagnosis figured out well before we surfaced!
I had suffered a case of inner ear decompression illness (DCI); pure inner ear DCI to be exact, meaning that the inner ear was the only organ affected. I had none of the other more common symptoms of DCI such as pain, tingling, or weakness.
Simon explains: âPure inner ear DCI is a rare condition that is almost unheard of in air diving. It is well recognised in mixed gas diving, particularly when gas switches are made from mixes containing helium to mixes containing nitrogen and no helium (such as air or nitrox) during the ascent. Both Peter and I changed the diluent gas in our rebreathers from helium-rich trimix to air during the ascent. This practice can shorten the decompression from a deep dive quite substantially.
No one knows for sure why the helium to nitrogen gas switch precipitates inner ear DCI, but there are two prevalent theories. The first focuses on the possibility that tiny helium bubbles form in the fluids of the inner ear during the ascent. The theory holds that these bubbles are not big enough to cause any problems on their own, but that when the change to a nitrogen-rich mix takes place the higher numbers of nitrogen molecules that suddenly appear on the scene diffuse into the bubble faster than the helium molecules can diffuse out. The net effect is that the bubbles grow. The second theory focuses on the possibility that there are no initial bubbles, but that the helium molecules diffusing out of the tissue and the nitrogen molecules diffusing in have to âpass each otherâ on their journey (for want of a better way of putting it). This could cause a transient local gas supersaturation in the area, particularly if the passage of the molecules in each direction is held up somewhat by a natural diffusion barrier (for which there are several membrane candidates in the inner ear). The reason for the inner ears particular susceptibility to such events is thought to relate to its fundamentally watery nature and poor blood supply. In this setting, gas diffusion takes place over relatively long distances and unpredictable consequences of the relative diffusion properties of the gases involved can come into play.
Pure inner ear DCI in mixed gas diving appears to be a fundamentally random event, and the frightening thing is that almost all cases occur in divers who have completed (or are completing) uncomplicated dives in which there is no breach of ascent rates or table/computer decompression prescriptions. In Peteâs case he was lucky because it was only his balance organ of his ear that was affected. In some cases the hearing mechanism can also be affected. Pete was treated by Drs Alison Drewry and Des Gorman at the Auckland Navy Hospital, and made a complete recovery.â
This experience demonstrates that you can plan an expedition, be methodical in your planning, factoring in foreseeable contingencies, have back up plans and emergency procedures in place, execute the dive with precision and still have problems. This is the nature of this extreme sport.
I have to say that the deco was a challenge, probably the longest two plus hours I have ever spent underwater!
Hence, a dive of two halves. The first halve was the biggest blast a technical diver could ever wish to experience. The second was a blast of a less pleasant sort, but one that weâll just have to chalk up as experience. In closing, it must be said that the most essential component of any expedition of this type is the support team. Without these skilled people acting immediately to problems fatalities can occur. There is no room for error. Our team â Rex, Willy and Geoff were amazing in their support efforts. Thanks guys.
Until the next time! It was an amazing dive!