The Cayman Islands play host to scores of friendly sea creatures, discovers Hannah Stephenson.
"If you kiss a stingray, it means seven years' good luck," our genial skipper jokes before we tentatively enter the sea amid what look like giant flat mushrooms.
We're in Stingray City, the most popular attraction of the Cayman Islands in the Caribbean, where the enormous, elegant creatures gather to be petted and fed chunks of squid by the hordes of enthusiastic tourists who come to see them every year.
It's a unique attraction, 20 minutes by boat from Grand Cayman, where vessels moor at a sandbank and invite passengers to mingle with the stingrays in the waist-high water.
It's controlled in that about 50 per cent of the rays are "clipped" (their stings removed), but uncontrolled in that it's in open water, so anything is possible.
After initial trepidation and reluctance to walk on the sandbar in case we step on one, we are stroking the smooth underbellies of these gentle, gliding fish as they suck the squid from our hands into their powerful jaws.
Fishermen used to clean their catch on the shallow sandbars here, unwittingly giving rays a five-star feast of fish guts and effectively luring them to the spot.
My 16-year-old son Will and I have come to the Cayman Islands, a trio of islands in the British West Indies - south of Cuba and west of Jamaica - to dive, and specifically to pass our Professional Association of Diving Instructors (PADI) open water certificate which, when completed, will allow us to dive to depths of about 20 metres without an instructor.
The Caymans - Grand Cayman, Cayman Brac and Little Cayman - are ideal for learners thanks to their calm, warm waters, high visibility underwater, professional dive schools and English as the first language. They're still a British territory, but most visitors are American.
Normally, this Padi course takes between five days and a week but, as we don't want to spend our holiday time in a classroom, we do a referral course, completing the theory via an e-learning course and pool work at home beforehand.
The computer-based study takes around 15 hours to complete, teaching you the basics of diving, section by section, with video illustration and multiple-choice tests, followed by several pool sessions, before completing the final four dives in the resort of your choice.
Some dive operators offer the Padi open-water diving course only to people who've already done the e-learning theory, so check before you book.
We set off from the famous Seven Mile Beach, a dazzling strip of white sand and picture-postcard azure sea, for our first dive on a boat captained by Chris "Crispy" Ploughman, an ex-nightclub owner from Middlesbrough, who gave it all up for diving. He says many of the dive-boat captains and instructors are British, because in this tax-exempt haven, the locals would rather be bankers than dive-masters. "The Caymanians don't run dive schools as they don't make enough money from it, but for me, diving gives you a passport to travel."
As we prepare for our first dive, our young Canadian instructor, Devon, tells us to look out for Kiki, a nurse shark with a scar down one side of her face, who may appear from nowhere and gently nudge up to you like a puppy, but never aggressively.
Devon says we're also likely to see turtles - they are prolific around the Cayman Islands, which was originally called Las Tortugas (Spanish for turtles) by Christopher Columbus, who came across the islands in 1503.
Right on cue, as we plunge into the tepid waters at Governor's Reef - no wetsuits needed here where the water remains between 27-29C - we encounter a large green sea turtle foraging for food. Thankfully, we don't bump into Kiki.
Shadowing the reef, we see petrol-blue parrot fish, sharp, skinny barracuda, huge, beefy grouper and shoals of tiny multi-coloured fish darting between the coral.
It's a riot of aquatic activity in a world where the only sound is your breathing, or the occasional tap on your oxygen tank when your buddy has seen something he wants to share.
Loggerhead, hawksbill and green sea turtles are common on the west side, where hotels line Seven Mile Beach, while you're more likely to spot reef sharks and nurse sharks at the choppier east end of the island.
Grand Cayman also has other attractions - a turtle farm, native blue iguanas, horseback-riding in the sea, kayaking and bioluminescence tours at quirky Rum Point.
Once certified, there are many locations to practice.
Little Cayman is the smallest of the islands and the one from which you can access Bloody Bay Wall, the most famous reef of the Caymans, which runs alongside a tremendous abyss, a seemingly bottomless blue hole.
Mixing Bowl offers coral fans and tubes, which provide fascinating nooks and crannies for a wealth of sea life, including huge lobsters and grouper, and we look beyond the reef into the deep, blue bottomless chasm.
Perhaps diving has given Crispy a passport to travel, but it has also given us a passport to a whole new world - both above and below the surface.
has a 7-night Caribbean cruise from $1129pp twin share, departing April 8 from Tampa, Florida.