SEA Explorers Club

When making decompression dives we need to ensure we have gas available to complete our required decompression stops. More commonly than not, we use different gasses, with a higher percentage of Oxygen to “accelerate” our deco. When selecting our deco gasses we have to take a f

ew things into consideration. We need to keep our oxygen partial pressure at between 1.4 and 1.6 to really get the benefits and speed our decompression stops, therefore if we have many stops at different depths it is a good idea to carry more than one deco gas. When we are planning a dive as a team it is important that we all plan our gasses together and everyone uses the same gasses. This reduces confusion while gas blending, and also helps keep the team together while completing deco stops (as opposed to one person gas switching on to 80% at 9m and one person switching on pure oxygen at 6m) so if there are any problems your team mates can help out. We at Davy Jones Tech use a set of standard gasses while diving, to make dive planning easier and to ensure if we overstay our time we can have contingencies already written out in our wetnotes. As you progress through the tec courses not only will you progressively go deeper, you will also start increasing the oxygen concentration and eventually the amount of deco gasses you will carry.

At Davy Jones’ Tech we like to get out to some of the local wrecks to go for a tech fun dive. Later this month we are planning a trip to the infamous Tottori Maru, A Japanese prisoner of war ship more commonly referred to as a “Hell Ship”. The Hellship Tottori Maru and its sister ship, Tokushima Maru were built in Glasgow, Scotland in 1913 – 1914. These 6,057 Gross Ton ships were 423 feet long, 56 feet in breadth and capable of speeds of 10 knots.

When fate finally caught up with the Tottori Maru, she was en route to Singapore in convoy with the Hatsutaka running escort. She was not carrying any POW’s at the time of her sinking.

The Tottori Maru now lies in 75m of water on her port side, bow twisted and nearly broken off, facing the surface.

In the next few weeks Davy Jones’ Tech are planning a trip to Song Hong sinkhole in the south of Thailand. Led by head Technical Instructor David, we are planning a Trimix dive to 100m in the sink hole, accompanied by 3 other divers who are Trimix and Full Cave certified. Song Hong lake is the gateway to a huge underground river, which is believed to flow all the way to the sea which is over 60km away, where it flows to and from is unknown due to its depth and sheer size. The deepest dive made in the cave was 140m and over a kilometer in, and this barley scratches the surface. The purpose of this trip is to try to explore more parts of the cave and have some fun at the same time! The roof of the cave starts at 40m and wen you are on the main line you cannot see the bottom or any other walls, despite the water being crystal clear below 30m. It is a great dive, especially if you are interested in cave diving and the possibilities exploration that it offers.

If you are new to Technical diving, or looking at getting into it, then there is a word that you would have heard getting thrown around quite a lot. Trimix, and if you have already started your technical diving career then you probably have some basic understanding of what it is, but may be unsure of why it is used, and it’s advantages and disadvantages.

To put it basically Trimix is a breathing gas with 3 main gasses in it, Nitrogen and Oxygen (standard breathing air) and Helium. Trimix comes in endless different blends, all of which have their own use in technical diving. The main reason Trimix is used is to extend your depth. Using air the deepest that you can go is around 60M (however most training agencies say 50m or 55m). This is because as you go deeper the partial pressure of Oxygen gets too high and it would be unsafe to go any deeper. So to go deeper we must get rid of some of the Oxygen from the breathing gas, and this is where Helium comes into the mix. Once we start to add some Helium the percentage of the other gasses begin dropping and now we can start to go down further. This is the main advantage of Trimix, it allows us to go to places where we cannot go using air, and however there is one other major advantage. As you are probably aware of, when we start to go deeper than around 30m we begin to feel the effects of ‘Gas Narcosis’ kicking in. Helium however is non-narcotic so when we start to add the Helium we reduce those narcotic effects, which is great if you are doing anything that is more complicated than just swimming around a wreck i.e. penetration or complicated navigation. So some training agencies will start to use it for going deeper than 30m, so narcosis doesn’t even become an issue. There are however some disadvantages to Trimix, the main one is the price, Helium is not a cheap gas, and this is why rebreathers are becoming more and more popular, as you can use trimix in a rebreather and because your body doesn’t use the helium it just gets recycled, and this cave save considerable amounts of money!

If you are interested in extending your bottom depth then we can teach PADI Trimix 65 and Full Trimix (which maximum depth is 90m) or TDI Advanced trimix (which maximum depth is 100m). It is great training even is depth isn’t your thing, as you will learn to deal with many problems all at once (with the surface not being an option)