Big Blue Tech completed a TDI Advanced Nitrox Course yesterday with the combined afternoon of skills which embodied both TDI Decompression Procedures and TDI Advanced Nitrox.

With the flexible curriculum offered by TDI it was possible for the training team to introduce interesting and valid skills which are appropriate for the diving ahead.

The students on the course were Mark Slinn, Andy Cavell and Ash Dunn who are all working towards a future as a technical diving instructor.

One of the signature skill introduced involves using a 3m marked line on the sea bed and having the divers wearing full technical diving gear start at the 1m mark and start fining, during fining the diver must remove one decompression cylinder without loosing control, upon reaching the end of the line the diver stops and begins backwards kicking, collecting his decompression cylinder while kicking backwards and returning to the start where the diver turns 180 degrees and moves away. The goal is to not use your hands and focus on perfect trim and balance while performing these skills.

Backwards finning can be quite difficult initially, to help this process we provide Jet Fins to our students as part of the equipment they will be using during the course to enhance the ease of learning. Here is a video to help illustrate the skill:

Additional to these skills was task loading with 8 cylinders removing and replacing each one while maintaining buoyancy. The training team felt the students really excelled and didn’t see them disturb the bottom, without being told to, during both 50 minute dives.

This would be the last dive until the after christmas as the students progress on to their Gas Blender and BSAC Instructor course.

Complex navigation in the cave environment is critically important. Taught at the Apprentice Cave Diver level, it is further refined at the full Cave Diver level. At the Cavern and Basic/Intro Cave Diver levels we discourage complex navigation and train divers to stay on the main line. No jumps, no circuits, and no traverses. Cave diving fatalities have occurred when team members mismanaged complex navigation and lost their reference to the direction of the exit.

Skill Review

In the last couple of issues of the Underwater Speleology I have reviewed “How to” scenarios: How to relocate a lost buddy and how to relocate a lost guideline. I encourage you to re-read those articles with special attention paid to the primary sources of trouble: lack of awareness in the cave, failure to use a continuous guideline, and the direct link between increased task loading and decreased awareness.

The modular programs in cave training take advantage of compartmentalizing chunks of training and, by design, save complex navigation for the latter half of training. The reasoning for this is that the task loading cave students undergo at the cavern and basic cave levels (things such as how to properly deploy a reel, buddy awareness, line awareness, overall situational awareness, and dive technique) should be mastered and in muscle memory before more complex dive plans are made and students begin using one third of their gas supply for penetration.

Plan Your Dive

Once a dive plan is made that includes jumping off of the mainline onto another line, the following procedures help the team stay focused on the task of more complex navigation and helps prevent them from “going the wrong way” during their exit.

Divers should always run a reel to the main line and for all jumps. Proper directional markings are essential for safely navigating to the exit. Relying upon memory or someone else is not the safe way to do this. In low or no visibility we realize that it is very easy to become disoriented and go the wrong way.

Dive Your Plan

Once in the cave at the agreed-upon jumps, one teammate designated to install the jump reel should locate the line they are jumping to. He/she should deploy the jump reel, tying in to the other line, to make a continuous guideline back to the exit. The other teammates should wait on the mainline providing light for the teammate deploying the reel, as well as verifying that the jump is done correctly.

Most popular jumps have double line arrows indicating both that a jump exists in the vicinity and indicates the nearest exit direction. If there are no arrows on your jump, place one that can be identified as yours by sight and touch once you return to that line/jump point. Once the designated teammate installs the jump reel he or she will OK the other teammates with his or her light and only then do the other teammates cross to the new line. Once crossed the teammates should inspect the tie off also inspect the reel to ensure they can identify it as their team’s reel once they return. Reels should also be prepared in such a way that they can be identified by touch.

The team is then safe to continue into the cave until someone turns the dive and the team begins its exit. At this point the team’s approach to safely navigating out of the cave is critical, partially dependent upon how the jump line was initially installed and marked.

Safe Exit

After the team turns the dive and once the team reaches the point where the jump was made all teammates, except the team member running the reel, cross to the other line and wait for the reel person on the exit side of the jump. This helps set up the proper exit direction and the proper team order is not changed.

The person responsible for pulling the jump reel should wait at the reel and ensure his/her teammates have each made the jump and are waiting on the exit side before untying the reel from the line. Once all teammates are on the exit side the team member managing the reel can remove it.

Low- or No-Vis Exit

This method is relatively simple and works very well in good visibility. If the team is exiting in low or no visibility the reel(s) should just be left in place. These procedures help ensure that each teammate is thinking about the navigation and is not just following another teammate. Each cave diver is verifying and validating this phase of the dive, as they must also be doing during all phases and transitions during the dive. — Text by Jim Wyatt (photo by Jill Heinreth)

by Becky Kagan for DivePhotoGuide.com

“Take a deep breath” is what I told myself as I knelt down on the hard rock floor about 400 feet inside a Florida cave system. It’s been one of those days, my buddy had a few equipment problems so I was standing around in the hot sun in my drysuit, I was using a new piece of dive gear that I wasn’t comfortable with yet, my mask was leaking, and I needed to get the shots completed!  I stopped; taking a deep breath after also fighting a scooter with an over weighted video camera mounted on top of it. I had just been fighting it the whole way and the stress was starting to take over. All I needed was one more thing to go wrong and I knew it wouldn’t be a good situation. It just shouldn’t go this far, I was too task loaded and called the dive.
Task loading can come in many forms and it’s different for everyone day to day. Task loading can be anything physical to mental or a combination of both. It could be pushing an over weighted camera with lights in a strong current while trying to set up shots, positioning a model, dealing with sea sickness, a broken fin strap, and a depth and time limitation. All of these little problems can build up into one larger problem so it’s important to recognize when you’re overwhelmed and when to call the dive before it becomes dangerous.

Continue Reading Here

Twin tanks are increasingly sought after nowadays and many purchased with little or no thought. Twin-sets normally consist of two tanks, which are joined together using a manifold, which gives the user access to both tanks through a single regulator, although this isn’t always the case. There are three general ways of diving with twin tanks:

1. Diving Independents

This is where two tanks are mounted on your back but are run as separate systems. If you have a failure with one tank then you have lost that entire gas supply and cannot gain access to it but still have access to the remaining tank. Diving with independents involves additional task loading and superior gas management skills to ensure that you always have a gas supply available in the alternative tank to the one which you are breathing.

You must also be able to differentiate between which gauge and which regulator belongs to which tank. This is a less than optimal choice when compared to the third alternative.

2. Diving Twin Tanks with a non-isolating manifold

This time the two tanks are joined via a manifold which takes the form of a permanentely open connection running between the two tanks. This enables you to gain access to the contents of either tank via either pillar valve. This has the benefit of avoiding the duplication of gauges and eliminates the need to keep swapping regulators. However, your twin cylinders are now effectively just a single larger tank. This deprives you of the redundancy which can be achieved by running two separate systems, since one failure can affect your entire gas supply. Consequently, in many failure modes this arrangement is less safe than independent cylinders and cannot be advocated except when diving in less than demanding environments such as when a single cylinder would equally suffice.

3. Diving Twin Tanks with an Isolation manifold

This is without a doubt the best of the three options since it has all the benefits of both the previous systems and none of the disadvantages. It enables you to gain access to the contents of both tanks through one regulator and read the total gas supply off one gauge.

If you suffer a failure in one tank then you should normally still be able to gain access to the contents of both tanks through one pillar valve.

If there is a worst case scenario, such as the failure of a main tank O-ring (highly unlikely) then you can “isolate” one tank from the other by turning a handle, which is in the middle of the manifold, this will protect half your gas supply.

This retains the redundancy which is lost by using a non-isolating type manifold. See the section on “manifolds” below for additional considerations.

Twin tanks should always be mounted with the manifold uppermost, such that you can reach over your shoulder and turn your own valves on or off whilst in the water. This ensures that you can use the manifold’s full functionality at all times.

Sometimes you see tanks inverted, this is a distinct no-no, since you will then need a cage guard to protect the manifold. This is something which is subject to entanglement and an added unnecessary complication which makes access to the valves harder, completely defeating the idea of turning the set upside down in the first place. In addition, all hoses must be custom made.

You also occasionally see remote valve winders (known as “slob-knobs”), which consist of a handle on the end of a long hose-like type connector. These are attached to the pillar valves and isolation manifold and allow you to turn these pieces of equipment on or off without reaching behind you. Unfortunately they are subject to corrosion and, should they fail or seize, make it impossible to operate the valves either directly or remotely.

Simply owning an isolation manifold is not enough, you also need to know how to use it properly. See the “Valve Drill” link for training with an Isolation manifold. The chance of a failure is highly unlikely but the options available to resolve or minimize the impact are greater than the alternative equipment types.

Cylinder Size

Cylinders should be of the same size and dimensions if they are to be “twinned” up. Twin sets normally consist of either twin 7’s, 10’s, 12’s or 15 litre cylinders.

Twin 7’s are generally used for the types of dives, which fall within the “normal” club type diving description. i.e. under 35 metres, not involving any mandatory decompression stops. One twin set is normally only sufficient for one dive.

Twin 10’s have a greater volume and are suitable for moderate club diving, which involves some degree of decompression for a single dive. They may be unsuitable if you wish to use them without a gas fill/top-up for a full day’s normal club diving i.e. two dives under 35 metres with no stage decompression stops. This is due to their reduced volume compared to diving twin 12’s. You may have to support their weight on your back whilst sitting down and waiting to enter the water due to their reduced height.

Twin 12’s are normally suitable for a full day’s moderate club diving (two dives), which involve limited decompression stops for the first dive. They may only be sufficient for one dive if it is to a greater depth/for a greater time with a lengthy decompression. Twin 12’s seem to represent the best choice for the average diver.

Twin 15’s tend not to be used, due to their size, weight and the amount of drag that the diver has to suffer, unless he has some form of motorized propulsion available. These are only normally used for over 70 metre-ish trimix dives with multiple stages.

Alloy

The choice of tank depends on the suit you wear due to their buoyancy characteristics. If you are diving in a wetsuit then aluminium cylinders represent the best choice since they won’t cause you to be over weighted - obviously this is only the norm if you are in foreign climes. If you dive in a dry suit then steel tanks will remove some of the weight from around your waist, this is the reality for British divers.

Manifolds
As has already been discussed, using an isolating manifold is the only real choice, but there are a number of further considerations:

Barrel O-Rings Vs Facing O-Rings

This consideration is about the way in which the manifold is sealed against the two pillar valves.

Barrel O-ring systems have an O-ring(s) which seal around the exterior of the isolation manifold insert and the surrounding interior of the pillar valve. In contrast, Facing O-ring systems use an O-ring which is trapped much like a DIN fitting. That is to say, it is trapped between two parallel vertical surfaces.

Barrel O-rings are more tolerant of movement within the manifold and are less likely to be forced out of position, which would cause a gas leak. The editor was present on two occasions when a twin set fell from a great height due to a lapse of attention by the owner, landing on the manifold. On both occasions, the barrel style manifold successfully kept the gas supply intact, in spite of there being considerable mis-alignment. This testifies to the resilience of this design.

One of these examples is shown on the left (Scubapro). The arrows run straight through the middle of each pillar at a 90 degree angle to emphasize the extent of the misalignment present in the middle section. Please see the recommendation on Scubapro Manifolds below before buying this product

Ideally barrel O’ring designs should have two O’rings on each side of the isolator since this provides some degree of redundancy. The first O’ring will also prevent a build up of dirt and salt next to the second O’ring, helping to keep it in pristine condition.

Balanced Valves Vs Unbalanced Valves

If a pillar valve is balanced, then it should be just as easy to close the valve as open it. Unbalanced valves are easier to open than they are to shut and should consequently be avoided.

Valves tend to operate by screwing a widget in and out by turning the knob’s spindle. A balanced valve either has a groove cut into the the widget’s threads to allow gas to equalise quickly from one side to the other (MDE) or a small hole (Scubapro). Unbalanced valves rely an the gas equalising by migrating along the threads which is normally somewhat slower…effectively you will find that the greater pressure inside the tank will aid opening a valve (easier) and inhibit closing it (stiffer).

It may be possible to “balance” an “unbalanced” valve by using a hack-saw to cut a groove within the valve internals, this is not recommended unless you know what you are doing!

Rubber Knobs

These are more often called “tactile handles” in dive shop speak. These are far easier to grip than normal hard plastic knobs and far more resilient. The option of using solid brass handles may at first glance seem like a good option, but in fact they transfer shocks from the handle to the shaft of the valve and can cause the valve to seize preventing opening or closure; this is an additional problem of hard plastic knobs. In comparison rubber knobs will absorb a lot of the impact, resisting damage to the valve.

The rubber handle must have a metal insert to stop the thread being stripped through use.

Tank Bands

These are used to hold the two cylinders together.

Cam band (webbing) systems are suitable for independent cylinders but completely inappropriate if the tanks are manifolded in any way, since the tanks aren’t held rigid. The subsequent movement stresses the connections between the manifold itself and the pillar valves.

There are a number of stainless steel bands available. They generally look like strips of stainless steel, which have been formed in the shape of a figure eight with a bolt through the middle. This bolt is tightened to hold the tanks in place.

There are certain things to avoid:

Sharp edges on the bands, which will cut into the tanks’ paint work and encourage corrosion.

Spot welds, which are not as strong as continuous (seam) welding.

D Rings on the lower (and upper) bands which can easily become entangled during a dive, this entanglement is then difficult to clear. Band mounted D Rings offer nothing but problems to the diver since they are so difficult to reach during a dive.

Low marine-grade stainless steel.

Bands, which warp under stress.

Bands, which are too narrow and do not hold the tanks rigidly aligned

Cylinder Boots

Cylinder boots, whilst maybe offering the benefit of greater stability to the single tank diver, offer little if nothing to the twin set diver. Twin sets are inherently far more stable when stood upright, they can only move forwards or backwards. Sets can be easily rigged whilst leant against a boat side/wall etc and one hand is usually enough to stabilize it whilst putting it on.

All in all, when you consider the scope for corrosion with cylinder boots, you are really better off without them. For further information including a picture of tank corrosion, see the relevant section under Which Tanks? Single Cylinders

Buoyancy

Obviously a larger form of buoyancy is needed for a twin set due to the additional weight. A 55lb wing should be sufficient for your needs, even if you carry 2-3 decompression cylinders, provided they are of the “right” type and you are properly weighted.

A 35lb wing represents the minimum lift you should consider but future flexibility and the ability to carry stages with this sized wing would be limited.