Heidi Klum & Tom Kaulitz The Never-Ending Honeymoon ... PDA-at-Sea, Topless Too!!

Heidi Klum and Tom Kaulitz can't keep their hands, or mouths, off each other on what's turned into a marathon of a honeymoon in Italy. Hey, don't let us interrupt!!!

The ex-supermodel and her new rock star hubby are STILL laying out on the high seas off Capri, where they've been enjoying the yacht life ... but, more importantly, each other ... as you can tell in these pics of them smoochin' and getting a little nakey on board.

Tom's kissing Heidi's thigh, she's kissing Tommy's abs ... and even some boring old school kisses on the lips. Like we said, lots of PDA.

BTW, Heidi has NOT been shy about losing the upper half of her outfits these past couple weeks -- besides going topless here, she also posted a kinda, sorta NSFW shot 2 days ago.

As the kids are saying these days ... #FREETHENIPPLE!!! More power to ya, Heidi.

As we reported ... Heidi and Tom got secretly hitched about 6 months ago. They had a big Italian yacht wedding a couple weeks ago with friends and fam, and have been there ever since. They're coming up on 3 weeks of honeymoonin', to which we say ... great work if you can get it!

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