not sure i like the whole boat scenario. its quite good for the story/plot itself, but the erotic part not so much.
sure, theres sex going on, but its not hot and exciting at all. its awkward and sterile.
the mc-christine route, i think its too soon for her to be adventurous with Mc in a boat with maniacs onboard.
christine-robert, here, i think if i where Robert i would take her in a secluded space, this because shes virgin and you can control her more. theres too many variables that can go wrong in the pool and Robert is not that stupid or is he? now, sure he got her, but in a cabin, with spycamera on, thats a better place if you ask me. maybe Christine a bit more drunk/drugged and Silver spying and waiting for his turn. this also give Mc opportunity to stop it as Christine seems out or let it happen for the ntr route.