Adam Levine and Behati Prinsloo Can't Keep Hands Off Each Other During Yacht Day

Adam Levine and Behati Prinsloo don't need a payphone to chat ... because they're hanging all over each other during a luxury vacation -- packing on the PDA before hitting the ship's slide!

The music star and his model better half were spotted floating off the coast of Saint-Tropez Thursday ... Adam showed off his impressive body art while Behati opted for additional sun protection with a long-sleeve swimshirt and tight-fitting spandex.

AL & BH wrapped their arms around one another at one point ... soaking in the feel of the other -- before showing their kids how it's done on the slide!

Behati looked less than thrilled while streaking down the apparatus, seemingly screaming as she threw her arms over the sides of her face.

Adam seemed less concerned when jumping into the water ... kicking his legs high up in the air like only a rockstar can before landing in the deep blue sea. Adam and Behati's two kids -- Dusty and Gio -- also made appearances on the deck.

Of course, the pair have a windfall to spend on this summer vacay ... as we told you, they sold their house for $60 million in the fall -- so they can afford to treat themselves to the finest amenities of yacht life.