Every time I step on a cruise ship with my children, I have an irrational fear that one of them will fall overboard.
It is a split-second anxiety that dissipates almost as quickly as it surfaces, especially when I look at the reassuringly high railings on the public decks and realise how difficult it must be to accidentally fall.
But it still happens. According to website Cruise Junkie, 319 cruise and ferry passengers and crew members have gone overboard since 2000, with 2015 recording the highest total when 27 people toppled into the sea. So far this year, the count is 17. Generally, such instances tend to be down to suicide, drunkenness or foul play.
On Sunday morning, British air hostess Kay Longstaff was pulled from the Adriatic Sea having plunged from the Norwegian Star as it sailed 60 miles off the Croatian coast. The 46-year-old said her yoga fitness and singing had helped her survive 10 hours in the water.
So what are your chances of survival if you find yourself plunging off the side of a ship? The blunt answer is that the odds are stacked against you, but there are many variables that will determine your fate.
Much depends on how far you fall and the temperature and condition of the sea.
“The initial few seconds are critical,” explained Dr Simon Boxall, an oceanographer at the University of Southampton.
“If you fall from a great height, not only do you risk breaking a limb as you hit the water, but it will knock all the air out of you and you can drown very quickly.”
Upon plummeting into cold waters, victims invariably go into what is termed “Cold Shock Response” as the abrupt fall in skin temperature prompts them to take an involuntary gasp, inevitably swallowing seawater and making them susceptible to drowning.
According to Portsmouth University professor Mike Tipton, a survival expert who co-wrote the guide, Essentials of Sea Survival, 60 per cent of deaths in cold seas occur in the first few minutes of entering the water. So even if you're spotted going overboard, by the time the cruise ship turns around to retrieve you it will be too late.
A further 20 per cent of victims succumb to hypothermia, which can set in after 30 minutes, and the final 20 per cent die as they are being rescued – a surprising incidence that experts attribute to victims suddenly relaxing.
The temperature of the sea is a major key to survival and, not surprisingly, you stand a better chance of being rescued alive if you fall into the tropical Caribbean rather than the chilly waters of the North Sea.
As a rule of thumb, it is estimated that in waters of around 5°C, victims have roughly 60 minutes before hypothermia sets in; at 10°C this doubles to two hours; and at 15°C it extends to six hours.
“When the waters are above 25°C, there’s a saying that the problem goes from cold to shark,” said Professor Tipton. However, shark attacks in such circumstances are still extremely rare.
“One of the biggest issues of survival is knowing what is going to happen to you and that it is quite normal,” he stressed.
“Remember that the Cold Shock Response is normal and diminishes after a couple of minutes. Don’t thrash about as that uses heat and energy; try to stay still and float.”
As the cold moves through the victim’s body, they become more physically incapacitated and may be unable to hold on to flotation devices or use their hands.
Professor Tipton advises victims to prepare themselves before this happens by wedging or tying a flotation device to their body or swimming to a better position; but only using their legs as stretching out arms further cools the body.
Those with nothing to clutch on to are advised to curl into a foetal position to conserve as much heat as possible, using one leg to insulate the other. Likewise, keep your clothes on - they will help you float.
It’s also worth noting that in waters of less than 25°C, it is better to stay still as you will lose more body heat if you exercise to keep warm.
Floating in calm seas greatly increases your chances of being spotted by rescue crews, while choppier waters will severely diminish this.
“For rescue vessels, trying to find someone who has fallen over the side of a ship is really like tracking down a needle in a haystack,” said Dr Boxall.
In a situation where one does not need to swim a large distance, and as in this case, it is better to float around until someone finds you, women have the advantage, the professor told the BBC Radio 4 Today Programme.
This is because women have a higher level of subcutaneous body fat, which makes you more able to float. Because of this, they are less likely to suffer from exhaustion from swimming or treading water for hours.
For those who survive those first few terrifying minutes, the secret is to keep your spirits up.
“Keep a positive mental attitude and don’t give up,” advises Professor Tipton. “After all, in waters of 15°C, you may have six hours which is quite a long survival prospect. Just remember not to relax, even when you’re being rescued.”