Rafael Nadal Drops Millions On Custom 79-Foot Luxury Yacht

Rafael Nadal just dropped MILLIONS on a ridiculously awesome 79-foot luxury yacht with a fold-out balcony ... and TMZ Sports has the photos.

Nadal -- one of the greatest tennis players of all time -- hit up Sunreef Yachts and ordered a customized 80 Sunreef Power ... a catamaran (a boat with 2 hulls).

SY wouldn't say exactly how much the tennis superstar spent ... but they told us a previous yacht that was used -- and had less customization -- sold for $7 mil.

So, do the math ... Nadal likely plunked down somewhere near $10 MILLION!!!

The boat is 79 feet long, 39 feet wide, and has 4 guest cabins. Nadal's master cabin has a private balcony that folds out.

In total, the yacht has nearly 4,000 square feet of livable space.

So, yeah, Rafa's boat is bigger than most homes.

Sunreef delivered the yacht to Nadal in Mallorca on his 34th birthday.