The primary function of the buoyancy compensator (BC, Buoyancy Control Device or BCD) is to allow you to control your buoyancy in the water; it also allows you to easily float at the surface before and after diving.

While diving you need to be able to control your buoyancy throughout the dive. For example, you need to make a controlled descent at the beginning of the dive and a controlled ascent at the end of the dive, both of which will require you to adjust your buoyancy.

You will also want to be neutrally buoyant for most of your dive and you’ll need to make adjustments when you change depth to compensate for the buoyancy changes.

It also allows you to fine-tune your buoyancy at the bottom, so you swim slightly above the sea bed rather than touching it, which disturbs sediment and damages marine life.

Most modern BCDs used in recreational diving are jacket style and also act as the cylinder harness; many also have integrated weight pockets. All BCDs of this design are descended from the Seaquest ADV, which was introduced in 1984 and revolutionised recreational diving overnight. Other manufacturers, including Mares and Scubapro quickly launched similar designs featuring a jacket design, air bladders behind the diver and running under the arms and a cummerbund release system.

They also feature overpressure relief valves to prevent the air bladder rupturing, pockets for equipment such as dive tables, slates or lights, D-rings and a low pressure inflator.

Technical divers often use a different style of “wing” BCD with all the buoyancy located behind the diver, which leaves the front of the diver clear but are not recommended for beginners as they can push you face down at the surface.

One thing to be aware of is the different release mechanisms for BCDs with integrated weights. It is always a good idea to ask your buddy how the release system works before entering the water.

This is achieved through two regulators; the first stage regulator is attached to the top of the bottle and reduces the air to an intermediate pressure that is higher than required for breathing.

The second stage contains the mouthpiece. This stage reduces the air pressure further so it can be breathed and is designed so that it only supplies air when you need it; when you breathe in it supplies air, when you breathe out the exhaled air is dumped into the water. A safety feature of scuba regulators means that if they fail they will supply continuous air rather than cutting off.

Standard practice is to carry a spare second stage regulator (usually known as an octopus), which is often marked with yellow hose connectors to make it stand out. PADI teaches divers to carry this on the right hand side so that in the event of a failure either the diver or a buddy can find the spare second stage easily.

However, many divers carry it somewhere more convenient for them. It is good practice to check where your buddy carries his or her octopus before entering the water - it’s a good idea to find out how to jettison their weights if they wear an integrated weight system too.

Marmoler

The wreck sits upright at the bottom in 42-45 metres and is therefore only suitable for experienced divers. It remains largely intact, including the bridge, which rises to 30 metres and vast slabs of marble are that are still on board, visible in the hold due to the lack of deck.

Avvenire was built in Holland in 1930 and is 47.25 meters long and of 8.34 meters wide.

Local dive centres organise dives to the marmoler, but if you want to go independently the GPS co-ordinates I have for it are: 42°N 06′48″ 03°E11′85″ - I don’t know how accurate those figures are though.

The dive profile above is from 13th August 2005. There is a lot of red on the ascent thanks to my computer thinking I didn’t have enough air - it reckoned I had 6 minutes of air for a 12 minute deco stop but in fact there was spare air at 5 metres that I didn’t use.

Also note that on the ascent we stopped for a minute each at 20 metres, 15 metres and 12 metres. According to DAN, making short deep stops reduces the likelihood of suffering decompression sickness by a factor of 10 and while it extends the final stop at 5 metres it is something I like to practice.

Time on the wreck was relatively short at 15 minutes but we had enough time for an explore. Also, we ascended on a buoy rather than the dive boat’s anchor line, which makes it less straightforward as you need to be far more aware of your depth at all times.

Name: Avvenire
Constructed: built in 1930 by the Dutch shipyard ‘De Noord’ in Alblasserdam
Length: 47.25 meters
Width: 8.34 meters
Depth: 42 - 45 metres

Also see details of the Marmoler on ecodive.org

The Medas Islands near Estartit are well known as diving and other activities have been strictly controlled there for years. The result is an abundant and diverse ecosystem, with plenty of fish, coral and other submarine fauna and flora to see.

Much of Cap de Creus is also protected, which also provides a variety of good dive sites. The depth varies, but you can go down to 40 metres in some locations and the visibility on a good day is phenomenal.

Scuba fins are designed to propel divers to more efficiently though the water. The large surface area of the fins acts against the water to create the thrust that propels the diver; just think about Isaac Newton’s third law of motion - every action has an equal and opposite reaction.

Modern fins designed for diving typically consist of a composite construction with a neoprene foot pocket and a thermoplastic blade; in the old days they were made from moulded neoprene. The composite construction makes them lighter, more efficient and they tend to be positively buoyant, which may be an advantage if you need to put them on and remove them while in the water.

The blade may be constructed in several ways to make them more efficient; many have 2 or more ribs running the length of the blade to make them more rigid; the blade may be constructed with 2 or more flexible channels running the length; they may have vents; or they may be split fins.

Most divers on the Costa Brava wear the style of foot pocket with a neoprene strap and diving boots, but I’ve seen some people wear full foot fins in the summer. Full foot fins are fine for snorkelling, but personally I think the water tends to be too cold to wear them even in July or August.

I’ve been using Mares Avanti-3 fins for years, which I’ve been perfectly happy with. The only problem I’ve experienced was that one of the strap buckles broke just before a dive, but they are cheap to replace and these days I carry spare straps and a buckle just in case.

Scubapro, Cressi and all the other manufacturers provide various designs. If you’re just starting out I’d go for a traditional type of design, but if you’re able to try out a variety of fins you may find that one of the newer types suits you better.

Sometime when you’re on a dive you’ll find that it hasn’t sealed properly against your face, allowing water to enter. While this usually doesn’t cause any immediate risk to the diver, it is irritating and can be the simple difference between a dive and a great dive.

It is simple to clear your mask underwater and is one of the first skills your instructor will teach you when you take scuba lessons; part of the PADI Open Water certification is to remove your mask completely while underwater, replace it and clear your mask.

All you need to do is hold the top of your mask with both hands; tip your head back slightly and breathe out firmly through your nose - your mask should clear even if completely full of water.

If you do have troubles with water entering your mask while on a dive it is sometimes worthwhile settling on the bottom - if convenient to do so - and remove it completely. The usual reason I have experienced is the skirt of the mask overlapping my hood, so this is something to check, but it can also be caused if you have long hair which is stopping your mask from sealing properly.

Wetsuits insulate the diver by providing a tight fitting layer of closed cell neoprene around the diver; all this means is that the wetsuit isn’t porous so you don’t get wet because of water flowing through the material of the wetsuit.

They also provide additional insulation because they prevent the flow of water between the diver’s skin and the neoprene, which results in heat loss. Wetsuits should be snug fitting to minimise any water flow, and there are some that are marketed as “semi-dry suits” - these are wetsuits with a tight fitting seal around the neck, wrists and ankles and with a waterproof zip.

In addition to full body wetsuits, two or three piece diving suits may offer you more flexibility with your diving. Think of where you are likely to dive, typical conditions and what you are used to or prefer before deciding.

The water temperature in the Costa Brava falls throughout the winter until bottoming out at around 13 degrees C by March, but I wear a 7mm ScubaPro semi-dry that sees me throughout the year. The main trick is to have decent gloves and boots - 5mm renders your hands pretty useless but I prefer that to the pain of thawing my hands after a cold dive.

Wetsuits are commonly found in 2mm, 3mm, 5mm and 7mm thicknesses - in fact after about 8mm the neoprene simply becomes too constricting to wear - think Michelin Man rather than scuba diver - but your choice of wetsuit for the Costa Brava will mainly depend on how frequently you will dive in the off season.

The temperature starts to rise with the arrival of spring so that by summer a 5mm wetsuit will be fine - the surface temperature is usually 22 or 23 degrees C. Dive centres can provide you with a wetsuit and other equipment if necessary, although they only seem to stock men’s wetsuits.

Scuba diving equipment consists of a number of different elements to overcome the limitations of the human body underwater. In cold water we cannot retain body heat without a specially designed suit; without an air supply we cannot breathe; without a mask we cannot see; without fins our movement through the water is limited. Equipment is also required to control buoyancy and measure depth, to monitor air supply and to time the dive, all variables that can be critical to survival at depth.