Many skippers have dived under their boat at some point to clean the hull or to cut a line that has become entangled in the propeller. This is often done with a queasy feeling and, due to a lack of air, under time pressure. Cold water, unease, a racing heart. It’s a relief to be back on board!
Yet the underwater world is fascinating and full of secrets. Countless ships and treasures lie on the seabed, surrounded by corals and sea creatures of all sizes, shapes and colours. To humans, the wet depths may seem just as threatening as the endless expanse of space, but once you’ve experienced the joy of floating, that sensation will stay with you forever.
With the right technology and equipment, the boat is the ideal starting point for a skilful dive. Once the sometimes bulky and heavy equipment is on board, it can be easily towed to any anchorage. Especially in calm, hot weather, a dive also offers a refreshing change of perspective.
Scuba diving from a boat
In this widely practised form of diving, a compressed-air scuba tank is used to supply breathing air. This artificial air supply enables dives that can last an hour or longer. The steel cylinder attached to the diver’s back is usually filled with compressed air, although other mixtures such as nitrox are also common nowadays.
Using an air-filled buoyancy compensator, the diver can regulate their buoyancy by inflating or deflating it and position themselves in the three-dimensional space of the water. Scuba diving is practised as a hobby or professionally in various sectors.
Stowing diving cylinders safely on board
When diving from a yacht, provided you hold a qualification such as the Open Water Diver certificate from the PADI training organisation, there are a few key points to bear in mind: the heavy cylinders must be stowed securely. Ideally, they should be stored horizontally and secured with straps so that they do not roll about on the rocking boat. The storage locker and a bespoke wooden rack are ideal for this purpose. The valve on the cylinder can also be protected with a protective bracket or a homemade cap.
Getting into the water isn’t a major problem. You can roll backwards from the dinghy or take a bold step forwards from the side of the boat. Swimming ladder Don’t forget to deploy it!
It becomes more difficult to get back on board later with the heavy equipment and bulky fins on your feet. It’s best to take your fins off whilst still in the water, hang them round your wrist and then climb up the swim ladder. You may also want to take off your buoyancy compensator and tank and hand them up. As a general rule, the golden rule of diving is never to descend alone and always to stay within sight of one another.
A full set of kit, including a wetsuit, dive computer or even a compressor, can easily cost several thousand euros. Alternatively, most items of kit can be hired from diving schools, which can be found almost everywhere in the world. Scuba diving is particularly worthwhile when you’re exploring fantastic dive sites.
Free diving on a single breath
Freediving involves staying underwater for as long as possible on a single breath. The roots of freediving are deeply embedded in human history, as for a very long time it was the only way to obtain coveted shells, sponges or pearls.
Nowadays, spearfishing is the most common form of the sport, although free diving is often associated with the absurd record attempts of extreme sports enthusiasts. However, mastering this traditional diving technique also offers several advantages for boaters: You can dive anywhere at any time, for example to clear the anchor or remove unwanted by-catch from the propeller. This requires no expensive equipment, just a mask, snorkel, fins and, if necessary, weights, as well as a dive computer.
Even in emergency situations underwater, the skills acquired ensure that divers can act calmly and make well-considered decisions. In a crisis, this can be a matter of life and death. As they do not breathe compressed air, free divers do not need to worry about decompression.
Relaxation controls the breathing reflex
But who is actually suited to free diving? Diving instructor Alexis Girard believes that, without exception, every person possesses the natural ability to hold their breath for far longer than they might think. Girard: “The only reason people find it difficult is the rising stress levels underwater, which trigger the breathing reflex and prompt the diver to resurface as quickly as possible. The first technique taught, therefore, is how to relax. Everything revolves around this point, because you cannot dive whilst under stress.”
The second step involves controlling the urge to breathe. Sudden diaphragmatic contractions signal a lack of oxygen and feel like blows to the pit of the stomach. These spasms increase blood flow to the heart and are actually helpful when oxygen is low. Nevertheless, blackouts can occur, which is why you should never dive alone.
“Scuba diving is a sport where you look outwards to discover the underwater flora and fauna. In free diving, divers look more within themselves to immerse themselves fully in the moment – much like in meditation,” says Girard, describing the key difference between the two types of diving. Progress in apnoea training is usually very rapid. After just a three-day basic course, most people can hold their breath for significantly longer.
Deep-water snorkelling kit for working beneath the boat
The pioneer behind this diving system, designed specifically for boaters, is Rainer Michelbach from Swabia. In 1997, the prototype of the Freediver deep-snorkelling device was presented to Germanischer Lloyd and has been continuously refined ever since. The principle: a compressor on the surface draws in ambient air through a valve, compresses it and pumps it through a hose to the diver’s mouthpiece. This continues for as long as the compressor’s battery lasts. Depending on the diving depth and battery capacity, this is between 30 and 70 minutes.
The compressor can either be connected to an on-board battery or, running on its own battery, follow the diver whilst mounted on an inflatable lifebuoy. Crews are able to help themselves at their leisure – for example, when carrying out minor repairs. Due to its compact pack size, the system is particularly popular amongst long-distance sailors and has sold a total of around 3,000 units.
Depending on the pressure setting, diving depths of up to 14 metres are possible. As with scuba diving, this involves compressed air, so care should be taken to ascend slowly at depths of six metres or more. As a rule of thumb: do not ascend any faster than your own air bubbles rise. Or, for those who have dived with a diving watch: no more than ten metres per minute.
Mini tanks for short dives
There are several mini-tank models available on the market for short dives at shallow depths. The Mini Dive Air, for example, is a 0.5-litre aluminium cylinder rated at 200 bar, with a regulator and mouthpiece fitted directly to the cylinder. According to the manufacturer, this model allows for a dive time of five to ten minutes. The cylinder can be refilled manually using a hand pump.
However, caution is advised with these systems, as there is a high risk of overestimating one’s abilities. If an inexperienced diver finds themselves in a critical situation, they will consume far more breathing air under stress – which would immediately empty the mini-tank. The same applies if you dive too deep with it.
Decompression sickness: symptoms and safety stops
Diving sickness is caused by inadequate decompression following exposure to high ambient pressure. When diving, the body absorbs nitrogen, which is released again during ascent. If decompression is too rapid, bubbles form in the tissues, which can damage the brain, lungs and other parts of the body.
There are two types of decompression sickness: a mild form, which is usually easily treatable, and a severe form that causes long-term complications. Type 1 presents with symptoms such as itchy skin and tingling, whilst Type 2 can cause paralysis, loss of consciousness and impairment of vital brain functions. If such symptoms occur, whether mild or severe, the diver must leave the water immediately and be administered pure oxygen. Severe symptoms require treatment in a hyperbaric chamber.
Safety stops slow down the ascent to reduce nitrogen saturation in the body. The depth and duration of the stops depend on the dive depth, the bottom time (the period from descent to the start of the ascent) and residual saturation from previous dives. The figures are calculated using a decompression table or a dive computer.
Anyone who does not dive deeper than ten metres does not expose themselves to the risk of decompression sickness in the first place. Experts nevertheless advise making a safety stop at a depth of three metres when ascending. You should therefore always allow sufficient time for the ascent.
Fear of sharks
There remains the primal fear of encountering a large shark. Even though divers are attacked by these animals extremely rarely, diving expert Alexis Girard has some valuable advice on how to behave in the event of an encounter: “Always keep an eye on your surroundings, as these predators like to attack from behind. And should a shark become too curious, it is advisable to make direct eye contact and position yourself vertically in the water.”
It is no less important to stay calm, even though that is naturally difficult, explains Girard. In most cases, this is enough to signal to the shark that you do not fit the profile of its prey. If you are carrying any fish you have caught, you should discard them. Then surface slowly and keep the shark at a distance by moving your fins. Finally, the expert adds with a wink: “Don’t forget the selfie!”
Diving terminology
- Scuba diving: In this type of diving, a compressed-air scuba tank is used to provide a continuous supply of breathing air. This artificial air supply allows for dives that can last a good hour or more. The steel cylinder attached to the diver’s back usually contains compressed air, although other mixtures such as nitrox are also used.
- Free diving (apnoea): Freediving involves staying underwater for as long as possible on a single breath. The roots of freediving are deeply embedded in human history, as for a very long time it was the only way to obtain coveted shells, sponges or pearls.
- Decompression sickness (DCS): Diving sickness is caused by insufficient decompression following exposure to high ambient pressure. During a dive, the body absorbs nitrogen, which is released again during ascent. If decompression is too rapid, bubbles form in the tissues, which can damage the brain, lungs and other parts of the body.
Book recommendations
The practice of diving provides the basics and more advanced knowledge required for scuba diving. The textbook accompanies the training programme from the basic diving certificate right through to higher-level diving qualifications, and also covers orientation and diving safety. Question and answer sections help learners to test what they have learnt.
Advanced Course in Diving Safety and Rescue / Practical Medicine / Cardiopulmonary Resuscitation focuses on emergency situations. The emphasis is on preventing and identifying problems, as well as on measures to be taken in the event of diving accidents. The book accompanies the relevant advanced courses and includes assessments to check learning progress, with sample answers.
If you found a rope tangled in the propeller, would you dive down yourself, or is this generally a job for trained divers? What equipment do you use for underwater work? Please share your experiences and opinions in the comments.
Morten Strauch
Editor News & Panorama