with the slightest swell or chop, some people cannot sleep on a moving boat and rough seas can be frightening. Live-aboards appear expensive, but you get more dives for your money and all food is included. You need to pack warmer clothing for the cooler conditions at sea.
While live-aboards may offer five dives per day, divers also have to think about tides, currents, personal nitrogen-loading, and the visibility on ebb tides can be poor. It is better to take fewer (quality) dives each day than five dives, of which some may be mediocre.
Most divers do not like to have large numbers of people in the water at the same time. Larger live-aboard boats should either have two tenders serving two separate dive sites, or have a rota system whereby only half of their clients are in the water at any one time.
There have been cases of live-aboard boats leaving divers in the water and sailing off without them, so make sure that the boat you use has a foolproof diver check-in and check-out system.
REEF DIVING, DROP-OFFS AND WALLS
Reefs may have several distinct profiles. The top of the reef is likely to be a coral garden with smaller species of fish and crustaceans. Slopes or drop-offs have larger gorgonias and larger fish in shoals. Walls combine the above and have larger pelagic species, especially when over deep water. A wall is near-vertical and may be overhanging or undercut, while drop-offs are steep slopes of 60–85°.
Inshore fringing reefs tend to have poor visibility due to pollution from construction, domestic or industrial waste or mud carried down rivers, but they are good study areas as they harbour immature species.
Where offshore reefs have lagoons, these are convenient for safe anchorage, muck diving and snorkelling, but many prefer the better diving outside the reef. Channels into lagoons are good places to dive when the current is running, because the nutrients it carries attract smaller fish, which in turn attract larger predators. Where one side of a reef is longer or more contorted than the other side, the current is slowed down more on that side. When the currents meet again at points on the lee end of the reef they are travelling at different speeds, producing whirlpools and upwellings full of nutrients that attract large shoals of fish. In turn these fish attract sharks and other predators. If you can find shelter from the current, these points are great places to dive.
DIVING IN FRESHWATER
The main difference between diving in seawater and diving in freshwater is that freshwater is less buoyant and there are few freshwater sites that are charted. Some freshwater sites will be at a high enough altitude to require the use of special dive tables and corrections to the measured depths. Heavy rain can reduce freshwater visibility to zero.
In some areas lakes are fed by hot springs and can get very hot!
Diving in lakes or flooded quarries is relatively easy, but diving in rivers can be difficult if they are fast flowing. In general the current will be slower near the riverbank due to the friction of the water against the bank, but you must always consider where you can exit the river before you enter it. Hooks can be used to pull yourself along the river bottom against the current.
Freshwater and brackish-water sites, particularly lakes, quarries, dams, canals and slow-flowing rivers, often carry infections such as Weil’s disease (Leptospirosis) and, in countries where it is endemic, Bilharzia (Schistosomiasis).
Some reefs are submerged and can only be found by a knowledgeable boat skipper or Global Positioning System. Divers have to descend quickly to the lee of the reef for shelter from the current before they get swept off. However, such reefs usually have top diving and pelagics.
DRIFT-DIVING
Drift-diving can vary from pleasantly drifting in a gentle current to high-voltage rushes as divers are swept along walls and gullies. The main concerns are good boat cover and becoming separated from div ing buddies. Divers not using surface marker buoys should carry a delayed deployment surface marker buoy or, better still, a high-visibility rescue tube or collapsible flag, which can be raised above the swell.
Insist that the chase-boat crew follow the surface marker buoy or divers’ bubbles and do not go to sleep or have loud music preventing them from hearing divers’ whistles when they surface. Power whistles are better at attracting the boat cover than manual whistles and an old CD can be used as a heliograph.
Buddies, and preferably the whole group, should enter the water together so that they do not get separated on the surface and they should try to keep together underwater. If divers do get separated from their boat cover, it is wise to tie a buddy line between each other, inflate the BCDs (Buoyancy Compensator Device) and conserve air. It is usually best to retain weight belts unless buoyancy is a problem; in certain circumstances it may be better to jettison the scuba cylinders.
Divers wanting to fin ashore while wearing a normal BCD rather than wings will find it less tiring to fin on their backs. At the shore, untie the buddy line before trying to swim through surf or breakers.
WRECK AND CAVE DIVING
When diving in enclosed overhead environments, it is not easy to reach the surface in the event of equipment failure.
Any level of diver can enjoy diving around a wreck, but penetrating large wrecks is advanced diving and novice divers should only attempt it when accompanied by an instructor. Plan dives to coincide with slack water and wear gloves for protection from sharp metal. Carry a sharp knife and a suitable monofilament line cutter or shears for cutting fishing line and nets. Have a good dive-light and carry another as backup. Make sure that equipment is streamlined against the diver’s body where it cannot snag.
Divers should tie off a guideline before penetration and feed it out as they go, tie back any doors or hatches, so that they cannot close in a current. Remember that exhaust bubbles disturb sediment, as do fins and hands. Leave plenty of air to get out of the wreck and back to the surface.
Cavern diving, where divers are always within sight of daylight, is not difficult. However, cave diving, beyond any source of daylight, requires a safety guideline so that the divers can find their way back to safety in zero visibility. They will also need separate backup sources of light and breathing-gasses. Most important is the rule of thirds: divers turn around when one-third of their breathing gas is used up, leaving one-third to find their way out and one-third for emergencies. Apart from exhaust bubbles disturbing sediment as they strike the roof, divers can minimize the disturbance of sediment by learning to use gentle, shallow fin-strokes.
NIGHT DIVING
For night dives, divers should choose a shallow dive with easy marks for navigation, with which they have already familiarized themselves in daylight. The easiest night dives are along reef edges, where divers can swim out along the face at one depth and return along it at a shallower depth. If there is a current divers should set out against it and return with it.
Avoid dive lights that are too powerful and carry a spare as a backup, but spend some time with your lights switched off. When your eyes are accustomed to the dark, wave your arms about and you will notice phosphorescent plankton and, in caves, you may spot the bioluminescence of flashlightfish.
TEMPERATE WATERS VERSUS TROPICAL WATERS
Many divers do most of their diving in temperate waters. Shipwrecks are the most popular sites, but the marine life can be just as interesting as in
