Tec diving gear tryout

After coming back from our two morning dives in Amed I was having lunch with my friends Martin and Marieke and their kids at the Surya Rainbow Villas. During lunch Yvonne the shop manager and tec diving instructor at Two Fish Divers in Amed dropped by our table to ask if we were ready to ‘geek out’ in the afternoon!

Amed Bali tec diving Two Fish Divers

“Martin, you ready to geek out?”

The evening before we had a sunset drink with Yvonne. This after making her life somewhat complicated by requiring her to re-arrange her next day’s diving plan by us joining in last minute. During our drinks as usually goes with divers we talked way too much about this passion costing us all so much time and money…
I’ve always had a big interest in the gear element of diving. And with that a curiosity towards tec diving as dive equipment plays an important role in it. Actually I’ve already been flirting around the edges of tec diving, having followed the PADI Sidemount Diver instructor course, and two shallow try dives with the Poseidon MKVI rebreather at Utila Dive Center. I’m also diving a slightly ‘techy’ single tank backplate/wing and recently changed to a longhose setup and classic Jetfins.
So upon hearing all this Yvonne offered Martin and me to ‘geek out’ and play with the tec diving gear in the pool and we were eager to take up this offer!

Tec (Technical) Diving & Equipment

But let’s take a quick step back, what is tec (technical) diving and why do you need special gear for it? The definitions for tec diving vary according to who you ask. I like the following two:

1) Technical diving is any dive outside recreational diving limits; i.e. diving with a planned decompression schedule, deeper than the recreational depth limit of 40 meters, a breathing gas with more than 40{5785e09d7f157841e388556602ed452df373215bab87e1d7bcb5d74bd8927681} Oxygen content, mixed gasses, or in an overhead environment.
2) Any diving involving a ceiling (a depth you can not ascend past), either a physical ceiling (cave, wreck) or a virtual ceiling (decompression ceiling).

The fact that there is a ceiling means you cannot ascend directly to the surface in case of emergencies. That means your diving gear should provide a level of redundancy to accommodate failures. Tec divers therefore cary spares of everything (masks, torches, depth gauges, timers) and use different BCD and regulator setups compared to recreational dive equipment. Yvonne offered the chance to try these different BCD’s and regulator setups out in the pool. Yeay!

Amed Bali tec diving Two Fish Divers
Amed Bali tec diving Two Fish Divers
Amed Bali tec diving sidemount Two Fish Divers


These are the traditional and probably most common BCD and regulator setup in tec diving. It started out as due to depth and length of dives tec divers needed to carry more breathing gas. This was solved by attaching two separate tanks together. To each tank a regulator is connected. So you end up with two tanks, two tank valves, two regulators providing two separate first and second stages. That’s quite a bit of redundancy! These tanks valves are also connected together using a manifold so they basically become one big tank but can be isolated from each other by closing this manifold to avoid losing all your breathing gas if one valve or regulator fails.

The BCD’s most commonly used for twinsets is a backplate/wing combination. The backplate with harness provides a solid platform to attach your twin tanks. The wing provides the buoyancy required for your diving equipment and environment (wet- or drysuit, how many tanks). The wing can also be redundant by having two separate bladders (air cells). However views on this redundancy requirement vary per diver’s philosophy, training agency and diving environment.

Amed Bali tec diving Two Fish Divers

Putting on the twinset with Mink looking on closely.

Twinset pros and cons

The advantages of twinsets are that it closer to traditional backmounted tanks, so closer to what a lot of divers are used to. Also in theory some of the equipment (backplate and harness) can largely be used for single tank backmounted diving, although I haven’t seen this happen much in practice. Also this setup is seen by many as a more stable basis if you start adding extra tanks for deeper and more extended dives.
Disadvantages are that twinset BCD/wings are somewhat larger and you need extra pieces of equipment (tank bands, manifold) to attach the tanks together and to the BCD. Also the whole setup it quite heavy and bulky meaning it can be harder to getting in and out of the water and getting through small openings in wrecks and caves.


Sidemount diving and the equipment has its roots in cave exploration. Explorers were confronted by segments of dry cave connected by submerged sections. They needed a light and compact diving set-up to carry along and pass through small opening. This was solved by slinging a tank to their side. From this it crossed over to cave diving, technical diving and more and more into recreational diving.

In sidemount diving you wear a BCD which can be very compact and light depending on the equipment and environment you are diving in. You have two tanks which you carry on the side of your body. The bottom end of the tanks is clipped to the waist of your BCD. The tank valves are attached with elastic bungees, pulling the top of the tanks close to your armpits to make it a streamlined setup. To each tank a regulator with first and second stage is attached. So this setup provides two tanks, two tank valves, two regulators providing two separate first and second stages. Thus also providing the redundancy needed in technical diving. (you can actually use single tank sidemount for recreational diving, opinions on this differ…).

Amed Bali tec diving sidemount Two Fish Divers

Martin trying sidemount and showing nice trim!

Sidemount pros and cons

The advantages of sidemount that it is a very flexible setup for various dive environments and requirements. You can do single tank, two tanks or even more depending on your dive depth, time and decompression plan. It is also a light set-up to travel with, the BCD’s are usually very light and compact. Also you don’t need extra pieces of equipment or dedicated tanks like with twinsets as you can easily use available rental single tanks. The fact that the tanks are clipped on to the the BCD also offers advantages. While getting in or out of the water the tanks can be handed to you in the water so no need to lug  a heavy twinset around. And during the dive the tanks can be easily unclipped and held in front of you to sneak through small openings.
The main disadvantage of sidemount is that it provides less of a stable platform if you start adding many tanks and it takes a bit of training due to the differences to backmount many are used to. Also sidemount often requires a lot more tweaking to get it ‘just right’. (but for many that’s half the fun!) This to ensure it is comfortable and leading to a good trim in the water and a streamlined tank position.

Sidemount in recreational diving

The flexibility of sidemount diving means that it is also making its way into recreational diving, either in single tank or two tank configuration. It offers redundancy, and if you do a very common two-tank dive it doesn’t really matter if you do one dive and switch tanks for the second, or just take both tanks on both dives without refiling. Actually as in diving we usually surface with 40-50 bars spare you are carrying that spare from your first dive into your second dive.
However part of the popularity of sidemount is also as it has a ‘techy/cool’ image, and offers manufacturers and training agencies a new sales opportunity. I fully believe in the advantages of sidemount for both technical and recreational diving, but see that in recreational it might be driven by a bit of a trend.
For a full overview of available sidemount equipment I will refer to Andy Davis his excellent Scubatech Philippines website.

Amed Bali Indonesia tec diving sidemount Two Fish Divers
Amed Bali Indonesia tec diving sidemount Two Fish Divers

Time for the pool!

So if you’re still with me after all this talk, let’s hit the pool! Yvonne explained a lot what I wrote above, interrupted by me asking some geeky question (“So Yvonne, what is your view on bungeed wings?”).

Getting introduced to a twinset

Having previously followed the Sidemount Diver instructor course my priority was to try a twinset for the first time. It was a bit hard to get it all strapped on (also as the harness was not perfectly adjusted) and indeed a bit bulky. But once in the water I felt pretty comfortable straight away. This was probably helped by some similarities to my own single tank gear as I also have the backplate/wing and longhose setup. I mostly felt the difference when swimming inverted or sideways as that took a bit of getting used too, and when backing up using reverse frogkick.
I was surprised how easy it was to reach the valves and manifolds, and quickly asked Yvonne some skills to try out. She threw a valve drill at me which while far from perfect went quite reasonable.

Amed Bali Indonesia tec diving Two Fish Divers

Me trying a twinset.

While I was playing around with the twinset, I saw Martin cruising by with the sidemount setup. First with one tank, and then with two. What I immediately noticed was the nice trim Martin achieved with the sidemount setup. Very nicely horizontal in the water which is another advantage of this type of diving. Then Yvonne instructed Martin to unclip the tanks and hold them in front of him. That went without a hitch, he’s a natural!

Reunited with sidemount

Martin and me then switched gear. It was my first sidemount dive since 2013 and it felt like starting from zero again! I was reminded that if you have only dived backmount for a while, sidemount is a bit different. Not difficult but it needs a bit of time to get truly comfortable. So I started doing some exercises again: unclipping the tanks, inverted swimming and hover, sideways swimming and hover, reverse, inverted reverse. In all honesty I have to admit I was quite rusty and a bit disappointed how much my skills have deteriorated. I would probably need another 10 dives or so to be fully comfortable and to get to a level again to teach sidemount. So something to work on!

Amed Bali Indonesia tec diving sidemount Two Fish Divers
Amed Bali Indonesia tec diving sidemount Two Fish Divers

After playing around with two tanks I decided to try single tank sidemount as I had never really done that. I left the right tank at the edge of the pool and started playing around with just the left tank. This was for me one of the pleasant surprises of the afternoon. I actually really liked it! The unbalance in weight or drag was not very noticeable, and I loved the feeling of not having a tank on your back. You feel so much freer that way!
You loose some of the advantages of two tank sidemount (redundancy, extra gas supply). But it means with one sidemount equipment setup to buy and carry you can cover a lot of areas from single tank recreational diving to technical diving. Something to ponder on….

The dark side is calling…

Both Martin and me enjoyed our little play in the pool immensely. Many thanks to Yvonne and Two Fish Divers for the opportunity!
I already knew that diving gear interests me, and getting into tec diving has been in my mind for quite a while. The pool try-out only convinced me even more to go this direction at some point in my diving career. One of my first comments to Yvonne afterwards was “Damn, you are going to cost me a lot of money!” as getting into tec is not cheap! I’m dreading the mail she promised explaining all the tec diving and training options at Two Fish Divers….
For Martin who was unfamiliar with tec diving it opened his eyes to a new direction in diving. I think a seed might have been planted…

To be continued…..?

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