Zac Efron Enjoys Yacht Trip With Nina Dobrev After Her Shaun White Split

Zac Efron and Nina Dobrev are sparking romance rumors ... joining two famous couples on a yacht trip after her split from Shaun White.

Check out these photos of Zac and Nina onboard a floating paradise off the coast of Italy ... they're yachting with Miles Teller and his model wife Keleigh Sperry, plus Chace Crawford and his model girlfriend Kelsey Merritt.

Nina's newly single after her engagement to Shaun was called off ... so it's interesting she's traveling with an eligible bachelor in Zac and two other couples.

Zac's rocking some platinum blonde hair and looking jacked ... dude's a stud.

Nina's a dime herself ... showing off her curves in some revealing black swimwear. The "Vampire Diaries" star is giving us the textbook definition of post-breakup hotness here.

Zac and Nina seemed flirty ... at one point, Zac had a phone in hand, snapping photos of Nina as she played in the water.

The yacht trip was packed with fun activities ... snorkeling, swimming, jet skiing, paddle boarding, tanning ... and the fellas even climbed to the top deck and jumped overboard.

A source familiar with the situation tells TMZ ... most of the group is in Italy for Ripple Labs CEO Brad Garlinghouse's upcoming wedding.