Appeared in DIVER July 2006

Night dive or NIGHTMARE
Divernet
Night-diving can be a lot of fun, but a boatload of divers on an unfamiliar site with over-bright torches, assorted location gizmos and too many pet ideas about how best to signal is a recipe for trouble. Why not try it the John Liddiard way

I REMEMBER MY FIRST NIGHT DIVE with the sort of fondness one attaches to an experience so unpleasant that I would never, ever do it again.
I look back on the memory with the satisfaction of a challenge overcome.
It was in March, in the UK. I was wearing a wetsuit. It was on the reef beneath the range building at Porthkerris in Cornwall, and it snowed the next day.
About the only positive factor was Porthkerris Reef. It would be hard to come up with a better location for a beginners night dive in England. But if the experience was not that pleasurable, why did I ever night-dive again
Masochism was the theme on that first night dive, and it was curiosity that kept me going for a few more, along the lines of: I wonder if it can be less unpleasant Then it was sadism that became my big motivation.
A year later, on the same Porthkerris club training trip, I was one of the more experienced divers (I did a lot of diving that year, as I do now). I had a drysuit, was well on my way to becoming a BSAC Advanced Diver, and was dive marshal in charge of the night dive.
hspace=5 Ideally, everyone night-diving for the first time should be accompanied by an experienced diver who has done a night dive before. Failing that, on a well-known site, our club would let a couple of experienced divers who had not previously done a night dive do so together. X and Y were experienced divers but neither had done a night dive. In any club there are divers who are best buddies, divers who are indifferent to each other, and divers who just dont get along. X and Y were both nice guys but they were in the latter category.
Neither was well known for navigation skills. Naturally, I paired them up for the night dive.
They surfaced in the middle of the main bay, well away from the reef, having a vocal exchange all the way back in about whose fault the navigation had been. Standing comfortably on the beach, the sadist in me relished their dive. As did the other spectators, who greeted them back to dry land with a round of applause.
With all that in mind, why on earth would anyone do a night dive, especially in the UK
Firstly, being trained, experienced and capable at night-diving is something any well-rounded diver should achieve.
Even if its something you dont enjoy, the skills involved in being able to do it competently will serve you well through many other aspects of diving.
But sado-masochistic thrills aside, aspects of night-diving can simply be really enjoyable. Sometimes it is just the Zen-like experience. Sometimes it is the pure satisfaction of being able to do it. And sometimes we see things we would never see in daylight.
Crabs and lobsters come out of their holes to hunt and scavenge. Some fish settle down for the night and are easier to approach.
Others come out for the night and can be seen in full rather than just as faces in hole. Some kinds of anemones and tubeworms fully extend in the dark, while others curl into a ball.
On a coral reef, coral polyps extend and the corals take on completely different outlines. At full moon, you may even be lucky enough to see the coral spawning.
Basket-stars unwrap from tight balls to sprawling lace. Squid and cuttlefish are attracted to lights from divers and the boat. In locations with frequent night divers, predatory fish such as barracuda have learned to hunt by the divers lights.
They hang just outside the cone of the light, then, as the beam dazzles a small fish, dart in to grab an easy snack.
In Hawaii, manta rays have learned to feed off the plankton attracted by lights, swooping between divers in a nocturnal ballet.
Finally, there is the phosphorescence. Plankton reacts to being agitated by emitting a spark of light. Cover or turn off your light, wave your arms, and you are the centre of a sparkling light show.

Selecting a dive site
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Finding somewhere light enough to kit up.
The hazard that is greatly increased at night is to become lost on the surface. This means, on a shore dive, surfacing beyond help from, or out of sight of, the beach.
On a boat dive, it means surfacing too far from the boat. You could come up in a current and be unable to swim back, or beyond a headland, out of sight and hearing. Divers lost on the surface at night are potentially much harder to find.
So the main consideration when selecting a site is that divers can navigate it reliably, and that there are no currents to catch out those who habitually make navigation errors.
Ideally the site should already have been dived during the day, so that divers are familiar with the location. Failing that, it should be localised - inside a sheltered bay, or on a small reef, where divers cant stray too far.
Entry and exit is a consideration when selecting any dive site, even in daylight. But hazards such as sharp or slippery rocks can be greatly magnified at night.
The danger from nets or lines is also greatly increased in the dark, so anywhere with known entanglement risks should be avoided.
Night dives are best saved for calm sea conditions. Surf makes entry and exit difficult. In addition, the noise of crashing surf reduces the effectiveness of a shout or whistle for attracting attention on the surface.
In all cases, the site should be somewhere very familiar to the dive marshal or dive guide.

Conflicting signals
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A sharpnosed pufferfish sleeps wedged into a sponge.
Signalling to buddies is both easier and more difficult in darkness. Its easy to get their attention by flicking your light back and forth across whatever they are looking at. Having got their attention, they wont see the usual hand signal until it is illuminated.
For close-range signals, you get your buddys attention by flicking your light, then shining it at your hand to illuminate whatever signal you are making.
Shining a light in your buddys face would blind them, so divers need to resist the temptation to read their buddys eyes or facial expression to see that they have understood.
While returning a signal in daylight may be a good habit about which many divers get a bit sloppy, returning a signal at night or in darkness is essential.
In good visibility and at greater separation, another method is to paint the signal with a dive light - a circle for OK, side to side for trouble, up or down for up or down. Signals such as out of air dont work at night. Just use your light to find your buddys octopus and grab it!
Back on the surface, there is no single system for signalling to the boat or shore. One convention is that any light shown above the water is a distress signal, and that surfacing divers should keep their lights on, but just below the water.
Another convention is that any moving light indicates distress, and that shining your light downwards on to your own head means OK.
Yet another convention is for an up-down movement of the light to mean OK, and side-to-side distress.
You can see the potential conflicts. Night-diving signals are nowhere near as standardised as those used in daylight, so the part of a dive briefing that summarises signals, the bit that we all usually ignore, becomes quite important on a night dive.

Switch lights round
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A snack before bedtime - a lizardfish munches on a smaller fish.
Given a choice of lights for a night dive, many divers instinctively go for the biggest and brightest they can find - a 100W HID umbilical canister light that can fry any fish that gets within a metre, and bring daylight to the underwater world.
Such a light would be an excellent choice for exploring a clearwater cave in Florida or Mexico. It may also be a good choice for a deep wreck dive, in reasonable visibility but with little natural light.
But to take the a big bright light on a night dive is to miss the point. If everything is as bright as daylight, why bother to dive at night
A better choice is a small hand-light with a tight central beam and a diffuse side beam. It will be just bright enough for your buddy to see where you are and to make signals.
To spot creatures of the night, the central beam can be scanned about, flickering across the marine life without coming to rest. Then the diffuse part of the beam can be used to hold steady illumination without scaring the subject away.
The ideal light for a night dive is what owners of a monster HID would carry as a back-up. At the same time, if anything does go wrong, a big HID is a very useful tool. So use your back-up light for the dive, but carry your primary light as a back-up!

Location gadgets
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Enjoy the tropical sunset while waiting for it to get dark enough to dive.
A host of light-like gadgets are designed more for location on a night dive than for seeing by.
Cylumes are chemical light sticks. Bend the stick to activate it, shake it about and it will glow until the chemicals inside are exhausted.
Glosticks are a similar idea, powered by an LED or small bulb inside a coloured diffusing light shade. Strobes are flashing lights that use a small battery to charge up the system, then let it all go in one bright flash, repeating every second or so.
Carried by a diver, these are a useful backup location device should dive lights fail.
Some divers will activate such a gadget at the start of the dive and leave it on, a practice of which I am not too fond. Thats because a 12-diver boatload with their location lights glowing or flashing throughout the dive is both distracting and confusing.
More practical is to save such gadgets for specific situations: placed on the beach to mark the safe exit point; tied to the railings at the steps in the harbour wall; tied to a shotline to aid divers return; tied to a delayed SMB so that a boat can see it before the divers surface; when buddy-separation has gone on for longer than it should; when the surface cover has not noticed a surfacing diver; when both primary and backup dive lights have failed; or when divers are in trouble.
The important thing is to analyse the risks of a particular dive, to agree a protocol on how the gadgets will be used, and to make sure all divers fully understand that protocol before diving.

Its cold at night
Psychologically, most divers feel colder on a night dive, even though the water is obviously at the same temperature as in daylight. The real temperature drop is above the water, where a comfortably warm and sunny day can turn into a bitingly chilly night, especially in desert locations such as the Red Sea.
The plan for a night dive has to include how the divers will stay warm before the dive and, more importantly, how they will stay warm afterwards.

If you lose your buddy
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These divers are raring to go.
Separation is the diving hazard that escalates most rapidly at night. Yet used sensibly, we also have the tools to aid relocation, both from buddy separation under water and when lost on the surface.
In the case of separation, you should rise a little from the seabed to be clear of any obstruction, and circle with your light shining horizontally.
If both divers are doing this, they could both go round and round without seeing each other, so the circling should be alternated with shining the dive light straight up, to illuminate the water above the diver as a beacon.
If this doesnt work, location gadgets can be switched on as a last effort at buddy relocation before aborting a dive.
On the surface, a similar procedure can be followed. In addition, sound carries well over the sea at night, so divers should not forget to try shouting, and to use their whistles.
For those on a boat or shore, engines should be occasionally stopped and other noises hushed to listen for divers.

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Its easier to creep up on an open oyster at night, but one flash and it closes.
Dinner and sex
In many ways, fish are just like divers. Their idea of a good night out is dinner (in a divers case, followed by a few drinks), then sex. The time that all this happens is at dusk, just as the light is fading, especially on a coral reef.
As daylight gives way to darkness, activity on the reef suddenly picks up to a frenzied pace of hunting, eating and mating.