In the movie Fermat's Room / Logic Room what happended on the boat?

In the spanish movie Fermat's Room (aka Logic Room) the girl Oliva tells the story of how she met with Hilbert (the older mathematician). She describes meeting him through playing online chess and eventually meeting him in person on board of a boat.

She says that what happened on the boat would be illegal in any country. Apparently something very illegal / horrible? went on on this boat, but it is not explained what exactly happened.

I got the feeling that it somehow was apparent what happened, but I did not get it.

So my question is, what happened on the boat?

This is the conversation that takes place:

Olivia: "We played chess dozens of times and he always beat me. So I got interested in him. One day the idea came up of meeting to play face to face. He invited me to a party where there would be important people."

Galois: "In his house?"

Olivia: "No. Not in his house... on a boat.

Galois: "On a boat? Why?"

Olivia: "That's what I wondered too. Why on a boat? Then I found out. It had to be out at sea because at that party... things happened that would be illegal in any country. You want to know what things? Come on. Dare to ask."

Galois: "No, forget it."

Olivia: "At that party... things happened, and the things that happened made me go back more times."