Niagara on Trimix
by Tim Cashman
The word âgoldâ evokes romance and adventure, and yarns of a wreck lost with a cargo of treasure are the stuff that dreams are woven around. Under our very noses, right here in the Hauraki Gulf, lies just such a ship. At 120 metres deep (390 feet), the Niagara is near the limits of technical diving. The pressure at this depth is 13 bar (190 psi), where normal air becomes toxic. Although these toxic effects cannot be eliminated, they can be controlled, utilizing customised blends of helium, nitrogen and oxygen known as trimix. On such a dive, long decompression schedules must be followed to the letter. There is no room for error, and planning and preparation must be thorough and meticulous. A support team must meet bottom divers at set points and set times during the dive.
With all the ingredients for a fantastic expedition, Keith Gordon and I agreed to initiate a diving and ROV exploration of the wreck. Gradually a team came together. Pete Mesley was the only other diver I knew of in New Zealand qualified to dive to these depths. The support team was run by Brian Oxenham, an ex-RN Submarine Diving Officer better known as Captain Nemo, and the source of much strange submariner terminology! We used Brianâs 4.5m inflatable as a chase boat and surface support boat with VHF comms to the main vessel. Skilled support divers with small boat experience and dive organization skills are essential for deep trimix support work of this nature; Brian performed his key role impeccably. My most sincere thanks for his support on and off the water.
Dave Apperley, an expert technical diver, joined us from Australia. Dave and I had dived together in the Pearse Resurgence two years previously when we recovered a body from 85m [reported in Dive New Zealand, Feb/Mar â97 issue]. He had given up smoking two years ago and was now hooked on chewing gum. This, plus the use of the rebreather, earned him the nickname âMarine Boyâ from those who remembered the old kidsâ cartoon.
We used a shot line (a grapnel and line attached to a buoy) to hook the wreck and provide divers with a guideline to and from the surface. Stage cylinders, spare dive cylinders with regulators attached, were fixed at strategic points on the shot line as reserves in case our personal supplies failed. An inflatable âchase boatâ could re-establish contact with a diver if he failed to return to the shot line for his ascent. This could be done by lowering a dropline, pre-rigged with spare stage cylinders, to the drifting diver. Two complete sets of droplines were available. The intention was quick response deployment under any circumstances.
Finally, we held more spare gases available to replenish used cylinders if necessary. Air Liquide specified and supplied the special high purity grades of helium and oxygen we used. We ed a bottom mix containing 57% helium, 34% nitrogen and 9% oxygen. We used air, Nitrox 50 and oxygen as decompression gases. The trimix blend would yield an oxygen partial pressure of 1.2 bar on the bottom, reducing the risk of oxygen toxicity, and would give us the same nitrogen narcosis level at 120m that we would experience if breathing air at 46m.
We used âZ Planâ to generate decompression tables and opted for a 15 minute bottom time so we could carry all the decompression gas we needed. A longer bottom time would mean a mandatory return to our stage cylinders, and in the open sea there is always a chance that this wonât be possible; a risk we didnât want to take. A 15 minute dive to 120 metres would require up to three hours of strictly controlled decompression stops. A large proportion of these stops would occur in shallow depths on pure oxygen, where the divers would be exposed to wave action and tidal streams which could make accurate depth control difficult. Also, the oxygen exposure at the latter end of the decompression is very high and oxygen toxicity risks increase. I believe the shallow stops are the riskiest part of the whole dive, and require the most planning. Practice makes perfect, so practise we did, time and time again.
We started our preparation in Lake Pupuke by rigging lines, practising deploying the shot line and conducting âbrown water ascentsâ between the eels! This went according to plan … until the hospital administrator threw us out because we had used the wrong access ramp. Next we chartered Phil Bendleâs boat Norseman out of Tutukaka for a weekend, and repeated the exercise at the Poor Knights with an 80 metre trimix dive off Fredâs Pinnacle, followed by a deployed shot practice the next day in 40 metres outside Rikoriko Cave. A strong wind was blowing during this exercise, which caused the inflatable to drift across the surface (or âroofâ as Brian insisted on calling it). We had been concerned that the inflatable could drag a decompressing diver on the shot line to the surface, but found that skillful boat handling could prevent this. We also decided to mark the deployed shot lines every ten metres with orange fluorescent paint. This helped the chase boat crew veer out the correct length of line before fitting stage cylinders. Little did we know what effect this would have later!
At this stage, the team was ready for a big dive, so we went on Norseman to the wreck of HMS Puriri, a coaster commandeered for use as a minesweeper following the sinking of the Niagara. The ship swept a mine with her own hull and was blown in two, killing five men and becoming the minefieldâs second victim. It had never been dived, although Keith Gordon had taken video footage with his ROV some years earlier. Pete Mesley and I completed a dive there on January 9 as a dress rehearsal for the Niagara – see page 18 in this issue.
On Wednesday, January 26, the charter boat Reel Passion anchored over the Niagara and we launched Keithâs ROV. The team was glued to the closed circuit TV monitors as Keith deftly manipulated the joystick controls. Suddenly we all saw a view of the mast and crowâs nest we will never forget. The ship lay on her port side. The mast pointed out horizontally, and the ROV was looking along its entire length! The floor of the crowâs nest had gone and we could see right through it and beyond. Black coral trees now grew on the horizontal mast and fish patrolled the site. The whole scene was backlit by a surreal blue light with silhouetted wreckage standing out.
When the video lights came close to the wreck bright colours sprang out of the gloom enhancing the scene further. We were still gasping with wonder at the mast when Keith steered the ROV towards the superstructure. The bridge had collapsed onto the seabed to the right, portholes were visible in the hull plates on the left and Georgian style window frames lay open in front. These views were reminiscent of the Titanic film. That was enough for Dave and I. We decided to go and see it for ourselves! As I was pulling on my suit, a large black fin cut the surface! No, it couldnât be, could it? Sure enough, a large hammerhead shark was patrolling the dive site. It soon caught the attention of the rest of the team. Dave and I were assured that big hammerheads wouldnât dream of hurting us. I quote Bob Ash: âTheyâre too well fed.â Thanks Bob. It hung around for a while, but eventually disappeared, so we continued to kit up.
Finally we were ready, so in we went. The visibility was excellent, over 32 metres with clear blue water. Brian logged our descent at 12:53. Dave was ahead of me initially, but I overtook him at 50m as arranged. I switched from air to trimix and was ready to continue the descent; Dave was slightly slower as he checked his rebreather oxygen setpoint frequently. At 60m a school of kingfish swept into view from the depths and circled us rapidly. I knew then that we were in for a stunning dive. At 80m we passed through a thermocline and the temperature dropped from 20ÂºC to 16ÂºC. I could see the wreck below, lying on her side. Two rows of handrails curved gently away from us. We had landed very close to the stern. There was an old trawl net snagged across the wreck, which I avoided carefully.
Dave was talking profusely into his rebreather and gesturing. I couldnât understand a word, but I knew exactly what he meant! It was a stunning sight to see a huge ocean liner lying undisturbed on the seabed. We worked our way forward a short distance, passing portholes and a ventilator shaft. The timber decking had decayed and several deck fittings had fallen onto the now horizontal superstructure. We later learned that this area was the shipâs hospital. We saw a deck light comprising three glass prisms set in a brass frame, which would have allowed daylight into the compartment below the deck while still being strong enough for passengers to walk on. An open hatch cover invited access to the inside of the wreck, but at this depth (111m) prudence prevailed and we didnât go inside this time. This was the hold beneath the stern mast, where cargo would have been loaded. I checked my depth gauges and timers and realized it was time to return to the shot line.
During the leisurely return trip along the starboard boat deck, a hemispherical light with a brass cage around it drew my attention briefly, and I pointed it out to Dave. As we worked our way back we swam under the starboard docking bridge where we knew there was a telegraph. The trawl net was above us, and time was nearly up, so I opted not to take on a challenge at this point. The ascent began with both of us looking down until the wreck faded into the depths below us. As we ascended we could see a large tuna lying dead in the trawl. This net showed on Keithâs ROV video footage in 1988, and it is still killing fish more than ten years later, long after the fishermen lost it. I have never understood why a biodegradable net material is not used to avoid this problem. Most trawls and gill nets are replaced in far less than ten years, so long life canât be necessary, can it? Any commercial fishermen out there who can put me right?
As the wreck faded into the depths, the long decompression stops began. We carefully followed our schedules and watched ourselves like hypochondriacs for symptoms of the bends. At 20m, Dave reported red spots before his eyes! This was alarming, as we still had a very long time to go. A serious problem now would mean ascent, missed decompression, a rescue helicopter flight to Devonport and emergency recompression treatment. The odds of survival would be minimal. Dave thought he only saw the red spots when he looked in one direction. I remember thinking, âHis brainâs going too. Itâs getting worse.â Suddenly I clicked … âHe thinks the fluorescent paint flakes falling off Brianâs shot line are spots in his eyes!â I laughed, mainly with relief!
It took nearly three hours of decompression interspersed with visits from Brian and support divers before we finally reached the âroofâ again. I had a metal splinter in my thumb, and Wade Doak thought it exemplary that this was the only item we had salvaged from the wreck! We deliberately visited the wreck without disturbing the environment she had woven about herself. We unanimously agreed not to salvage any artefacts unless they were to be used for a display in the National Maritime Museum. This would require just a few specific items to enhance the story and be of interest to museum visitors. The real treasure would be video footage and photographs. Keithâs ROV would provide these, so Wade had nothing to fear!
The following day the weather packed in again, and we didnât get another chance to dive the wreck. We will, though! The first visit by divers to this magnificent ship has barely scratched the surface. Most old ships are decommissioned after an uneventful life, broken up for scrap and forgotten. RMS Niagara lives on, her incredible history still unfolding. Personal thanks: at 111 metres you need people you can trust, so special thanks go to Dave Apperley (Marine Boy), Brian Oxenham (Captain Nemo) and Pete Mesley for their expertise, outstanding work throughout, and unswerving commitment to the project.