“Are you looking for sex?”

This was the unexpected and unsettling first message I received from a stranger. Taken aback by the audacity of the question, I found myself surprised by the choice of platform for such an approach.

Rather than a dating app, this bold proposition arrived through the chat feature of an app designed for a family-friendly cruise line.

At the time, I was in my cabin aboard the Costa Smeralda, having just embarked on a three-night Mediterranean journey with Costa Cruises from Barcelona. Like all passengers, I had been advised to download the app, which is intended to provide helpful information on port excursions, onboard entertainment like acrobatics, teen discos, and Zumba classes. The app also serves as a convenient tool for managing expenses during the cruise.

However, I had barely unpacked my toiletries when my phone began to light up with a barrage of personal notifications from the app’s chat function.

‘Hot sex?’ my first ‘suitor’ continues in a pestering manner, after his initial advance is spurned. I don’t even know his name, but perhaps he imagines this promise will gain the green light.

Curious to know who would have the audacity to send such a salacious invitation, I ask him about himself, learning that he’s a 44-year-old accountant named Marco from Italy.

But it’s not long before small talk turns carnal (again).

‘So, do you like sex?’ he persists.

I’ve never been on a cruise before, but I’ve been told that such chat functions are meant to help passengers communicate without wifi – useful for friends and family.

However, judging by the naughty notifications popping up, this original purpose has gone severely awry. The chat function of Costa’s app – which passengers must activate, deciding whether to keep their profile public or private – appears to have mutated into a casual hook-up service.

In many cases, the devious intentions of the chat users are immediately apparent from usernames.

Passengers are not obliged to provide legal names, so many prefer anonymity, with some forgoing ‘names’ altogether, outlining sexual inclinations via carefully selected emojis.

‘French couple looking for women,’ declares one new contact. ‘Searching for a threesome with a woman,’ says another, while yet another makes use of an aubergine and rainbow emoji.

The rainbow emoji symbolises LGBTQ+ (lesbian, gay, bisexual, trans, queer and beyond) and the aubergine the male member.

It’s the sort of thing you might expect on a swingers’ site, not a liner offering discounted tickets for families and dedicated activities for youngsters and teens – all of which are also promoted via the app.

Certain crude emojis crop up regularly, including pineapples.

‘Bonsoir, c’est Jacques’, says a man whose username is ‘Jac’ followed by two pineapple emojis. I’ve heard that pineapples are associated with swinging, but given Jacques is French, I wonder whether the meaning is different – and enquire accordingly.

‘On m’a dit que c’estait pour les gens ouverts,’ he says. My French is limited, but Google translates this as: ‘I was told it was for open-minded people.’

Jacques is on the cruise with two friends to celebrate his 50th birthday. When I ask what inspired him to use the chat function, he simply replies: ‘La curiosite et le suspense’, which translates as ‘Curiosity and suspense’.

Unsatisfied with this vague response, I push further, until he eventually explains he heard about the app from other passengers. He moves on swiftly, asking whether I’m travelling alone and inviting me to go stargazing at midnight.

As romantic as this might be with someone special, Jacques is a stranger using pineapple emojis as some sort of sex beacon, whom I’m communicating with thanks to Google Translate. I decline his less-than-tempting offer and bid ‘Bonne nuit’.

Instead, I message ‘Bel singolo cerco’ (‘nice, single, looking’) Alberto, who says straight away: ‘I am a man and I am looking for a woman.’ This is his 10th cruise this year and he’s by himself.

I ask if he’s come on the cruise to meet someone, to which he replies: ‘I travel for pleasure; if you happen to meet a woman it’s nice.’ He rounds this off with a cheeky-face tongue-out emoji and then asks: ‘Do you want to see each other tonight?’

When I swerve the question, he asks again: ‘When can we meet to get to know each other?’

Given that Alberto is also relying on Google Translate to conduct this chat, I can’t imagine his idea of ‘getting to know each other’ will involve much conversation – so that won’t be happening. I promptly bid ‘Buona notte’ to him, too.

The following morning, still reeling from my exchanges the night before, I’m sampling a poached pear from the breakfast buffet when I receive a message from someone whose username is ‘#P’, followed by a smiley face emoji. The ‘P’ stands for Patrizio, a 50-year-old sales manager from Italy, cruising solo.

He checks very quickly if I’m travelling alone, and he tells me: ‘My plan for today is to know you and lose myself in your smile.’

If Patrizio had actually seen my smile, this might be flattering. But he hasn’t. It’s impossible to send photos on this app, nor can you include a user picture. For all he knows, I might not have any teeth.

But his chat-up line is innocuous and initially he seems charming. However, the plot thickens as I come to learn that, despite his romantic aspirations, Patrizio isn’t even single. He’s been in a relationship for a year. I ask how often he sleeps with other women and he replies: ‘Very few times… I take care of my health. I do not want to risk to get something just for one night.’

So when does he make an exception? ‘When I trust in the person I have in front of me.’

As precautions go, this seems somewhat shaky. I’m pretty sure ‘trust’ is not an NHS-approved method for preventing the spread of STIs, and I can’t imagine this illusory concept consoling his girlfriend if he passed something on to her.

‘Would you like to get dinner with me?’, he asks.

Funnily enough, I don’t.

Needing a break from my inbox, I head to lunch and stick my hands in one of the automatic washers at the restaurant’s entrance – during which jets of water wash over your hands. I’ve never seen anything like this before… but perhaps, if so many passengers seem to be ‘at it’ much of the time, it’s a good idea.

More app messages pop up than I can keep up with. One guy sends a message which Google translates from Italian as: ‘Hi, my name is Matteo, I’m 54 years old, male, and not a model. I’m traveling alone to relax.’

Nothing overtly sexual about this overture, but his username consists of two emojis – a lifebuoy and a zipper-mouth emoji – which I learn means essentially: ‘What happens on board stays on board.’

Another correspondent, I’m surprised to discover, is someone working on the ship. His username consists of the following emojis: an Italian flag, a purple devil and an aubergine. This basically translates as: ‘Naughty Italian man looking for devilish sex.’ He tells me he has his own cabin.

Although, after asking Costa, the firm informs me that, given the crew have a separate app and cannot contact passengers, anyone claiming to be crew is ‘not being truthful’ – so the identity of this ‘naughty’ Italian man remains a mystery.

Meanwhile, 33-year-old Spanish fund manager Carlos seems to get cold feet. When we first speak, he uses his full name. However, when I look at our chat later, I see he’s removed his surname, and added three emojis: a pineapple, a woman and a white carousel horse. Later that day, he’s only using initials.

I wish I had more anonymity myself.

Drinks are included in my package but, because they are an add-on, every time I order a drink I must hand over my Costa card for the bartender to swipe. This card has my name on it, and often when it is returned it’s with a cheerily trumpeted: ‘Miss Samantha!’

This makes me recoil, as I have an uneasy feeling that one of the chat-function sex pests is within earshot. I don’t want anyone bothering me at breakfast, stalking me – or, worse, following me to my cabin.

I begin to feel intensely uncomfortable passing almost any man, wondering if he is one of the app’s predators. When I see a man messaging on his phone, I can’t help but question if he has been sending me unsavoury propositions.

At one point, as I sit in a quiet corner of a bar, Patrizio, the 50-year-old Italian sales manager, messages me.

He simply asks: ‘What are you drinking?’

I look around, paranoid he’s watching me.

On another occasion, I ask someone in a bar to take a picture of me using my phone (potentially for use with this article). I am wearing a pretty green-and-white broderie anglaise dress and holding a martini. The man is more than happy to help, so when he asks for a selfie with me, I don’t feel I can say no.

Then he lurches towards me. At first I assume he is going to kiss me on the cheek. Instead, he’s aiming for my mouth. I rip my face away and my skin is lacerated by his stubble. He leaves. But after ten minutes he’s back, this time taking pictures of me on his phone.

I sit there awkwardly, feeling unable to object given that I’ve opened this can of worms by asking him to take a photo in the first place.

The worst thing is the prospect of him showing people these pictures, as if he knows me – perhaps even boasting I am some sort of cruise conquest. The idea makes me feel sick.

The only person I (knowingly) meet from the chat function is a 42-year-old Spanish woman named Claudia. Her username is ‘Solo Traveller’ and she says this is her first trip alone. She explains she felt emboldened after a holiday with a female friend with the Norwegian cruise line in August, during which they were welcomed into a group of solo travellers.

The group was purely platonic – a way for people to meet and make friends with others travelling alone. So Claudia has come on this Costa cruise, and joined the chat function, thinking it will be along the same lines.

She soon finds out it is not. ‘Crazy the chat! Millions of guys, crazy crazy!’, she messages me.

Hoping to recreate the friendly group feel of the Norwegian cruise line, Claudia invites several people from the chat function, including me, to meet her in the bar, writing: ‘If you would like we can meet at Ferrari bar tonight. I will be [there] from 10.30 til 11. I will be with a black dress I am blonde and 5.6 tall see u later if you feel like it.’

Feeling wary, I opt to meet in daylight the next morning instead. I can’t help suspecting that she might not be who she says she is, and am both surprised and relieved to find the real Claudia the following day.

Her friendly meet-up the evening before had not been a success.

When the first man arrived, Claudia was disgusted to discover he ‘smelt bad, like he did not have a shower’. Then three more arrived – all annoyed to find that she was already with someone. They had not understood that Claudia intended the meet-up to be platonic – and had not expected other guys to be there. Their intentions were most certainly not to make mere friends.

That evening, Claudia and I go to the ship’s nightclub. When I head back to my cabin around midnight, I notice a message from Patrizio saying he’d spotted me there: ‘Blonde holding glass?’

This is so vague I assume it’s a random guess. The ship has a 6,000-plus capacity, and I’m pretty sure just about everyone in the nightclub was holding a glass.

After falling asleep not thinking anything of it, in the morning I see that Patrizio has messaged again, this time describing my outfit: ‘You wear a dress, not short, with naked shoulders.’

The dress I had been wearing was off-the-shoulder. He had spotted me.

I feel completely creeped out.

I have no idea what he looks like, so he could have been following me around. I am so glad to be disembarking this morning – in Palermo, Sicily.

After leaving my luggage in storage, I go to eat breakfast, and soon I’m chatting to a 48-year-old British woman named Chimene, who is with her husband of 16 years. I ask what she made of the chat function on the app, but neither she nor her husband downloaded it.

She’s shocked when I show her the level of the language used on my phone. This is Chimene’s 12th cruise this year, but it’s her first with Costa, and she’s never seen anything like this chat function.

I wish I hadn’t seen it either. The cruise ship is beautiful and there’s the potential for this to be a fantastic holiday. However, as a woman by myself, bombarded with unpleasant proposals, I’ve been in a state of constant anxiety.

Did all the would-be lotharios and swingers book with Costa because the chat function facilitates hook-ups? Or is it just a coincidence that there are so many passengers looking for sexual partners, who’ve simply made use of the tech?

Only one person who messaged me admitted to knowing about the chat function being used as a hook-up aid before booking the cruise. Everyone else has swerved the question or feigned surprise. It crosses my mind that this is an attempt to appear laid-back about their intentions.

Of course, consenting adults can do what they like in their cabins. However, the chat function means that these X-rated adult activities are not kept behind closed doors.

Instead they are broadcast to everyone who’s downloaded the app. The indecent usernames outlining sexual inclinations are visible to those with it.

Anyone on the ship using the app could be inundated with notifications from people looking for casual sex… hardly family friendly.

When approached for comment, Costa Cruises stated:

•  We invite guests to use this feature responsibly, respectfully, and according to the Terms and Conditions which outline user obligations and clearly state users’ responsibilities regarding chat content.

• Additionally, if a passenger finds themselves in inappropriate situations or is a victim of any form of unwelcome or harassing contact, aggression or violence, they can report it to the ship’s staff, ensuring a swift response onboard.

• Our priority is to ensure a safe, comfortable, and serene environment for all guests and crew members. In this regard, we remain fully committed to acting promptly should any situation arise that may compromise these standards.

* Names have been changed by the Daily Mail to protect the identities of passengers.