Roman Polanski has a consistent thread of claustrophobia in his movies. Rosemary is slowly getting isolated from the broader world by her neighbors, and The Pianist is trapped in a room he can’t leave with a piano he can’t play. But even as narrow as the worlds in those movies are, he’s made some movies that are even smaller than that: Carnage has one location and four characters; Death and the Maiden is about a woman who has been kidnapped and most of the movie is just the two of them in one room. Knife in the Water - one of his first films - is nothing more than three people on a boat.
Compared to his other small ensemble dramas, Knife in the Water has some strengths and some weaknesses. Being set out on the sea certainly makes it more picturesque; the living room in Carnage is well decorated, but it’s still a room, while the contrast of the waves, the horizon and the people gives Knife a poetic look. Three is also a better number of characters than four or two, because it’s not enough people for cross talk (which can descend into chaos) but it is enough people for shifting alliances to have immediate effects. Also, three figures is almost ideal for shot compositions – it’s enough to create an interesting tableau, but not enough to be cluttered.
The area where Knife suffers compared to those other movies is that it doesn’t do nearly as good of a job of establishing the stakes of the story early and strongly. The fault lines between the couples in Carnage are instantly apparent, and while the symbolism of their debate is heavy handed enough that it’s slightly problematic, at least you get a sense that there’s a reason why we’re watching these people argue. Death and the Maiden’s stakes are literally life and death, so the tension is unrelenting from the get-go. But Knife is more of a slow-burn. A couple picks up a hitchhiker and invites him onto their boat, and there is some tension in their interplay - the husband and the hitchhiker are both being really territorial and trying to out-macho each other - but no one is really in any physical danger and the hitchhiker repeatedly threatens to walk away from the whole weird situation as soon as they are near shore again, undermining the claustrophobia of the set up. It isn’t until you really see more of the cracks in the husband and wife’s relationship that you realize that there’s something deeper at stake here than “are these guys going to have an awkward afternoon?” but that doesn’t happen until the halfway mark of the movie.
That said, I can see how the slowness of the first half of the film might appeal to other people. It allows these characters to slowly evolve into people, whereas the other two movies are basically about walking metaphors. This is a movie that’s more about the psychology of individuals than it is about some intangible trait of the whole human race; to that extent a more fitting comparison might not be one of Polanski’s films, but Mike Nichols’ Who’s Afraid of Virginia Woolf, which would be released four years later.
If this film had been made by a filmmaker with a less strong filmography, I would probably recommend it based on the cinematography alone, but because it’s a Roman Polanski film I have to say that you are probably better off watching one of his later films which would use a similar set up but execute it better.