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Tim Cashman interview


By Dave Moran


On 27 January 1999 Tim Cashman and Dave Apperley did what many divers had fantasized about for years. They dived to 121 metres and swam around the remains of Ocean Liner RMS Niagara which lies off the Hen and Chicken Islands off New Zealand’s North Island’s East Coast. The Niagara was a victim of WWII when on 19 June 1940 she struck a mine laid by the German auxiliary cruiser Orion. She took 590 bars, of gold to the bottom of the Hauraki Gulf. I caught up with Tim when he returned to further explore the wreck. (See June/July 2007 Issue # 100 for the full story of this latest Niagara expedition and Issue February/March 2008 Issue #104 for the RMS Carpathia at 150m)


Dave Moran (DM): Tim, welcome back to Tutukaka New Zealand for another adventure diving the wreck of Niagara. I guess there is still some unfinished business after your dive in 2003?

Tim Cashman (TC): In 2003, we dived it several times but hadn’t explored very much. This is an opportunity to further our knowledge of this wreck.

DM: Tim, you have dived many major shipwrecks around the world, how do you rate the Niagara?

TC: She’s is definitely one of the best wreck dives in the world. I haven’t dived any that are better but I’ve done one or two that are just as good. It was a huge personal achievement for me to dive her in 1999 so she has a special place in my heart. She’s as good as it gets.

DM: What makes it stand out?

TC: She’s a top quality ocean liner in clear water with beautiful marine life growing over her. The story of the gold salvage and difficulties that United Salvage Pty Ltd out of Melbourne Australia and their head diver Johno Johnstone had to overcome was phenomenal. When you dive her you become, in a small way part of the on going history of the wreck.

DM: The diving equipment you’re using now, how different is it from what you used when you first dived the wreck in 1999.

TC: On that first dive I used open circuit. In 2000 I switched to using an Inspiration Rebreather. I’ve been using the same unit ever since, it suits the type of diving I do.

DM: In 1999 I noticed everyone was using different decompression tables on their laptops. Is there now a dominant table that most divers use?

TC: More and more people are using trimix computers such as the VR3. The Inspiration now has Vision Decompression software built in. Currently divers are using a range of decompression tables.

There isn’t a consensus as to which ones are the best. The more radical ones that get you out of the water quickly seem to have been dropped. Now extra-conservatism has been added and there’s less variation between tables.

DM: What depths can the tables take you?

TC: That’s an unknown. They are mathematical formulae that you can put any number in and they’ll spit out an answer. But whether that will work to safeguard a diver’s physiology is, I believe, unknown.

DM: Who developed the tables?

TC: Mathematicians. Many are based on the old Buhlman algorithms. Most of Buhlman’s work was done on nitrogen and many years of air diving experience. His algorithms have been transferred to calculate diving tables using helium but there is far less experience of helium based diving. I think these tables seem to penalize the use of helium too heavily. As new mathematical versions are developed, divers try them. Some have a reasonable dive and others not. It’s really guinea pig territory!

DM: When diving the Niagara at just over 120m and staying at that depth for 30 minutes how do you mentally prepare for such a dive and the decompression penalty of up to five hours?

TC: I try not to change my diving equipment or its configuration from one dive to the next. I get everything on and relax, sitting quietly as I mentally go through an equipment check list, making sure everything is right where my hand expects it to be. It’s the same routine every time, it becomes second nature. When I’m ready the skipper brings me near the buoy/shotline. I jump in and drift over to the buoy and hang onto the line and get comfortable and recheck my gear, making sure it’s all hanging in the right place and nothing’s tangled. I’m also breathing from the rebreather and checking that it’s functioning correctly. Then I usually drop down to four metres and recheck everything again. Once I’m sure everything is functioning correctly I swim down – but not hard – trying not to waste too much time getting to the bottom but without exerting myself.

DM: For these deep dives what is your normal planned bottom time?

TC: Normally 25-30 minutes. It’s difficult to get to these wrecks so we try to make the most of every dive. If it’s really nice I may extend it to 35-40 minutes but those extra minutes add a lot of extra decompression time.

DM: The shotline is your guide to the surface. What precautions do you take to ensure you can always return to it when you’re ready to return to the surface, especially if visibility is bad?

TC: The visibility on the Niagara is usually good, especially by UK standards. Normally I clip a strobe onto the shotline because I can see it from a reasonable distance.

I start at the shotline noting some of the wreck’s features in that area. Then I swim for approximately five metres and make a note of another landmark and quietly hop along the wreck keeping track of where I’ve been. Then on my return I can tick off all these points.

When visibility is limited I clip my safety reel’s line to the shotline and spool off. When I’ve finished exploring I just reel back. If I think there could be a problem locating the shot line I use the reel, if not I just do it by navigation. It’s common sense really.

DM: If you didn’t find the downline you use plan B to complete your decompression, correct?

TC: Correct. There’s really no difference because plan B is to send up a yellow Surface Marker Buoy (SMB). This would tell the surface support team I’m off the shotline and I want help. They would send down a drop line attached to a buoy. This line carries some spare cylinders, so I would basically end up drifting on a one man decompression station.

DM: Besides the rebreather you carry spare gas as well?

TC: Yes, I take two open circuit cylinders, one for the bottom – a minimum 12 litre cylinders with 250 atmospheres. That gives me about 10 minutes. So if I have rebreather problems at the bottom I’ve got enough gas/time to organize myself and begin my ascent. The second cylinder provides enough gas for me to reach the intermediate depth range where the support divers can reach me. There are two of them so you’re not just relying on one. So you have three levels of redundancy. Touch wood!

I’ve never had a dive where I’ve had to do the above and sometimes I start wondering why I’m dragging all the excess cylinders around. But on the other hand, if I did incur problems I sure would need those two extra cylinders of gas!

DM: So having good surface support is critical to your safety due to you not carrying all the gas required to complete the dive.

TC: Absolutely! In 1999 I was on open circuit. I took all the gas I needed to complete the entire dive. I had two cylinders of bottom mix gas and three cylinders of decompression gas; a total of five cylinders for a 15 minute bottom time.

Dave had an Inspiration, but also carried a complete set of open circuit bail out gas. We had support divers, who could assist us, but we were completely self sufficient. As we dived deeper and for longer we realized we couldn’t carry enough bail-out gas to fully decompress. The rebreather would provide as much gas as we needed for the entire dive, but if it failed we needed a back up system to guarantee the support team could reach us with spare gas. I’d say that’s critical!

DM: Many scuba divers look at all this gear and the up to five hours of decompression for a 25 minute bottom dive and wonder is it worth the pain? Plus for some, the organization required to have their equipment sent half way around the world.

TC: It’s only worth it if you have a really good dive. When it’s a bad dive – missed the wreck or you dive in bad conditions then it’s definitely not worth it. This time on my first dive the visibility wasn’t very good and the tide was running so I aborted my dive after five minutes on the bottom. I was back on the boat within three hours. Later in the week we had superb conditions, Craig found the ship’s bell, and a telegraph and we all decompressed in azure blue with sunbeams piercing the water. When it’s good it’s well worth the pain!

DM: Rebreather technology has opened up another layer of deeper wrecks worldwide for divers.

TC: Exactly. I think the closed-circuit rebreather has done for diving what the aqualung did in the 1950s. It’s enabled divers to dive in a new layer of water which was previously impossible for us to explore. There are two main benefits when using a rebreather: It constantly optimizes your gas mixture so that on the ascent you’re getting the best possible decompression mix and you never run out of gas.

DM: In the UK is diving with rebreathers becoming more commonplace.

TC: The bulk of divers still use open-circuit scuba but there’s a very large minority using trimix rebreathers. I don’t know the percentage but there are a lot of rebreathers around.

DM: I understand some dive charter boats are set up for rebreather diving?

TC: Yes. Most of the dive charter operators on the south coast of England are familiar with divers using closed-circuit rebreathers and trimix. They have fast boats to access deeper offshore wrecks and many have diver lifts. You swim onto the lift’s underwater platform and hold onto the handrail and it lifts you level with the deck and you just shuffle forward and sit on a bench – great!

Elsewhere around the UK coast it varies because they don’t specialize in technical diving so you have to make do with a slow fishing boat and a ladder, like the old days, so it varies quite a lot.

DM: A few years ago the percentage of rebreather divers to the percentage dying was really unacceptable. How is it perceived now?

TC: When rebreathers were new to the market I think people didn’t really understand them properly and mistakes were made. I think most of those mistakes aren’t being repeated but rebreathers still demand respect. You have to be very aware all of the time, that the rebreather is constantly mixing your gas. They’re very reliable but if they do stop working and you don’t notice, it’s curtains!

DM: Do divers factor in their own personal fitness when doing these deep dives?

TC: Not really, A lot of water gets drunk before a dive these days and being fitter has to be better but it’s not taken all that seriously by divers in the UK. A lot of them are pretty unfit, including me. But I’m working on it!

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