Wednesday, 1 January 2014

HOW TO: SET UP A TWINSET - PART 1: CYLINDERS

This article is designed to allow the reader to set up their twin cylinders based on a Hogarthian/DIR setup.  The information below is based on how I dive and how my equipment is configured (unless teaching where agency standards dictate otherwise), however other methods are available.

Overview
So what is an Hogarthian setup and what is DIR?

The Hogarthian setup is named after renowned cave diver William Hogarth Main.  He pioneered a simple streamlined setup, where anything that was not directly needed was left behind.  He also encouraged all divers, or team members, to use the same setup thus making emergencies such as out of gas or rescue situations easier to handle. 

So what then is DIR?  And why don’t we all dive it?  Firstly DIR stands for “Doing It Right” which can be a little confrontational, especially on online diving forums or communities, as it may suggest that everyone else is “Doing It Wrong”. Which isn’t the case as thousands of divers conduct thousands of dives every year safely.  The equipment configuration that I will discuss in the future blogs is in general, a GUE (Global Underwater Explorers) standard where as other agencies (including the ones I represent) allow different setups providing it meets their standards.  That said the majority of technical divers and instructors from around the world have generally adopted a lot of the principles.  Lastly, the equipment setup does not suit everyone and not everyone adopts all of the principles, however in my opinion what I like about this style is:
·    Flexibility.  Although one could argue it’s not the ideal setup for all diving configurations, it allows the diver to dive in the same way whether bumbling around in the shallows, exploring a cave or diving deep on trimix.  As William Hogarth Main tried to adopt, when an emergency happens and muscle memory kicks in everything is always in the same place.
·   Cost.  It is often a miss-conception that diving in this style is more expensive; initially maybe however in the long term it is much cheaper as generally other than a different size wing (the wing blog will explain why) the remainder of the equipment will go with as your diving progresses you thus making it future proof and saving you money.  What you’re not doing is buying a-clamp regulators & selling them for DINs, swapping out different hose lengths and having a variety of BCDs or wings for different setups.

Before I start properly on the article, I should point out that I haven’t always followed these principles; I had different size cylinders, bungeed wings, harnesses with a break and a bungeed long hose but as my diving has progressed and as I have learnt more my style has changed to that that you will read about in these blogs.  I only wish I had dived it this way from the start as the transition process would have been easier and certainly cheaper as my equipment wouldn’t have changed so much.

Happy reading.

Cylinders
There’s actually a lot to discuss regarding a twinset starting with what do I call them? What size do I need?  Steel or aluminum?  What Pressure rating?  What manufacturer?  What hardware (bands, manifold etc..)?

Firstly lets look at the name.  Is it a twinset, twins or doubles?  Honestly who cares but as we’re British we’ll stick with twinset. 

Now size.  In the UK there is generally twin 7’s, 8.5’s, 10’s and 12’s although larger cylinders such as twin 15’s and twin 18’s are available.  The size and pressure rating (see later) will depend on how much gas you need for the dive.  Gas planning is a whole other subject and one that I will write on at some point however for now I would suggest that twin 12’s are the primary choice for the majority of divers.  So why do I say this?  The reason is because they are larger enough to carry gas for dives up to 50m and are also tall enough to reach the valves if setup correctly.  Twin 7’s are an ideal replacement for a single cylinder if you still want the redundancy of a twinset although one may struggle to reach the valves as they are short cylinders.  8.5’s however are even better as they are the same height as 12’s.  With regards to twin 10’s the majority of people I know who have owned them have gone on to replace them with 12’s as they’re too small, both in terms of capacity and height so dive times and reaching valves become a problem.

Composition?  As we’re British steel is generally what you will find in the UK however when travelling abroad expect to find aluminum cylinders. 

232 or 300 BAR?  I’m not going to lie, I used to own 300 BAR 12’s and I thought they were great.  However in reality they were heavy, cumbersome and you could never make the most of the capacity (most dive shop’s fills would cool to around 270 BAR although there are plenty of places that can fill up to 300).  I know that I did say gas planning is a separate topic but before moving on I thought I should do a comparison:
Twin 10’s @ 300 BAR = (10 x 2) x 300 = 6000l of gas.
Twin 12’s @ 232 BAR = (12 x 2) x 232 = 5568l of gas.
So looking at that the 10’s give more gas, however based on a surface consumption rate (SCR) 20l/min at an average depth of 35m it’s only an extra 5 minutes of gas.

So what manufacturer?  There are a number of manufacturers such as Faber, Euros (Euro Cylinder) and Beaver to name a few.  The pictures on the left are 232 Faber 12’s v 232 Flat Bottomed Euro Cylinder 12's.  I’ve not used Beavers so I cannot comment however the Fabers weigh in at 38kg and the Euros at 39.9 kg.  The Fabers tend to be slightly neck heavy which may help your body position, however you may find it also pushes you too far forward.  Euros tend to be slightly longer than Fabers which helps the kitting up process and reaching the valves, however Flat Bottomed Euros are slightly bottom heavy so this may pull you out of trim.  The ideal cylinders in my opinion are the round-bottomed Euros as there are very balanced in the water.

So is there anything else that you need to know about cylinders?  As you can see boots are not fitted, as they are not required for 3 reasons.  Firstly the main reason for boots is to stand a cylinder up, and as most divers are taught to not do this it’s irrelevant.  Secondly they can become a line trap, as if any fishing line, or even guideline such as in a cave or wreck were to slide through the gap it may get trapped.  And lastly they can hide corrosion that will only be noticeable when they’re removed for a test. 

Nets are not fitted as they don’t really offer any protection and they also create a gap between the cylinders and the bands that could cause slippage. 

And finally the cylinders are fairly free of stickers.  On the other side (the side that faces away from the diver) there are none and those that are on the cylinders are mounted in such as they’re hidden under the backplate.  Why?  Well firstly you’ll look cool in photos.   But in all seriousness when it comes to the test and O2 clean stickers they’re protected to prevent any damage whilst wriggling through small spaces.   The only other stickers fitted are my identification stickers which are made by Dive Signs.

Manifolds
A Manifold is designed to connect two cylinders together to effectively make one larger cylinder, however it also gives the diver the option of isolating a single cylinder (along with the use of that regulator) in the unlikely event of a neck o-ring failure.  For all other failures such as a free flowing second stage, a ruptured hose etc… the appropriate cylinder valve can be closed (along with the use of that regulator) allowing the diver access for the remaining contents of both cylinders.  Further instruction regarding isolation procedures or valves drills can be sought from your instructor as there are a variety of methods each with their own pro’s and con’s.  

AN ISOLATOR VALVE IS NOT TO BE USED TO DIVE WITH DIFFERENT GASSES IN EACH CYLINDER. 

So what type of manifold should I go for?  There are a variety of different manufacturers to choose from and they vary in price, however it is important to make sure that the manifold has an isolating valve.  Although it may seem obvious, there are old second hand manifolds for sale online that do not.  These are NOT to be used as they offer no redundancy and in the event of a failure there is no way to preserve any gas.

The 2 main types of manifold have either a barrel o-ring or a face o-ring inside.  The majority of new have manifolds have a barrel o-ring.  The advantage of these is that if the manifold becomes loose, it allows movement in the center section without leaking.  This does not mean face o-rings are dangerous.  In fact, there are a number of people who will only use the old style MDE manifolds that use face o-rings as they are some of the easiest valves to turn during a drill. 

Lastly the isolator valve should be positioned in such a manner that it could be reached if required.  This may be straight up or at a slight angle facing the diver.  It is recommended that you try your own to find out the best position.

So is there anything else that you need to know about manifolds?  The on/off position.  A number of people open all of their valves and then close ¼, ½, or ¾ turn.  This is not advised as it could cause confusion therefore delays when trying to close a valve for real.  If it only turns one way then the decision is simple.  Remember “lefty loosey righty tighty”. 

DIN v a-clamp.  This shouldn’t be an issue on twinsets as manifolds are normally Deutsche Industrie Norm, or DIN as it’s more commonly known.  The DIN system is a much safer design as the o-ring is trapped inside the valve thus preventing a leak if knocked. 

Cylinder knobs or handwheels.  Shown in the picture are a variety of knobs that are commonly available however if not fitted, I would suggest that the larger more tactile knob as seen on the right is fitted to allow easier access to the valves. 

Lastly there’s the ‘furniture’ and by this I mean other items that divers have been known to add but are not really necessary.  These are:
·    Halos or valve protectors.  They create a guard over the valves for protection but also act as an entanglement hazard.  And similar to cylinder boots they can hide rust.
·    Lift bars.  These are fitted to prevent strain on the manifold when lifting but as above they can also hide rust.  The simplest solution is to carry a twinset by the cylinder knobs. 
·   Isolation or “slob” knobs.  These are fitted to the isolator valve and are routed around the diver to a more accessible location.  These create an extra failure point and providing a twinset is setup correctly there is no need for them.

Twinning Bands
Ideally the bands should be as thick as possible.  The Euro’s are fitted with V4TEC bands and a very robust and very well made.  The Fabers are fitted with Custom Divers bands which although do the job are much narrower and have started to bend slightly at the fixing point.  Regarding the positioning, the top band should be placed at the break of the neck and the bottom band will be placed according to the eyelets on your wing and backplate.  This is generally the industry standard.  I’ve seen lots of divers with the bands positioned much further down in order to try and reach the valves.  Like the isolation knob if your equipment is setup correctly there is no need to do this.  Firstly it will alter the weight distribution and therefore your body position.  And secondly if you travel and hire a twinset from abroad then the setup is different from your own and may not be suitable.

More information on the correct way to setup a twinset can be learnt when we some to building a harness correctly. 

Finally
Is there anything else that still hasn’t been covered?  Only really an independent twinset, ie without a manifold, or an inverted twinset.  Many people would argue there are reasons for both however in my opinion both are only really used when divers have not set up a manifolded twinset correctly and cannot manipulate their valves.  Other may disagree and by all means I am happy to discuss this, otherwise if you wish to know more about these then please ask.

My final point is cylinder matching when team diving.  Another common mistake is that people with a higher SCR get given larger cylinders so they avoid hitting their reserve first.  THIS IS A MISTAKE.  Why do I say this? 

(Ok I know I said no gas planning however) For example, there are 2 divers both on different size cylinders but both filled to 210 bar (for ease of maths and a realistic fill):
Diver 1 is diving twin 10’s @ 210 BAR = (10 x 2) x 210 = 4200l of gas.
Diver 2 is diving twin 12’s @ 210 BAR = (12 x 2) x 210 = 5040l of gas.
The majority of recreational divers would look at this and plan to thumb the dive when the first diver hits their third (140 BAR).  This works when diving the same cylinders but not when miss-matched.  For example:
Diver 1 third = 70 BAR x (10 x 2) = 1400l.
Diver 2 third = 70 BAR x (12 x 2) = 1680l.
Therefore if diver 1 thumbed the dive on thirds before diver 2 had reached their third, and then diver 2 had a catastrophic failure there would not be enough gas to get both divers out of the water.

So ideally everyone in a team should be diving the same size. 

This is not always the case as I mentioned there are a number of a different capacity cylinders available.  So what do we do if we have to dive miss-matched cylinders?  The turn pressure is worked out by capacity in litres of the smaller cylinder.  So using our same example:
Diver 1 third = 70 BAR x (10 x 2) = 1400l.
Diver 2 third = 70 BAR x (12 x 2) = 1680l.
Therefore:
Diver 1 turn pressure  = 4200l – 1400l ÷ (10 x 2) = 140 BAR.
Diver 2 turn pressure  = 5040l – 1400l ÷ (12 x 2) = 151 BAR.

I hope you enjoyed this article and if you have any questions please ask.  I would however always recommend speaking to an instructor about your own individual equipment requirements.

The boring bit!
All opinions expressed in my articles are my own and may differ to other instructor’s and agency guidelines; by no means are they wrong and I would not wish to disrepute any of them.  This article is for information only and should not replace proper training.

Safe diving!

Timothy Gort
BSAC, PADI & SDI/TDI diver training
l Mob: 07968148261 l Email: tim@rectotec.co.uk l