This is a yawn of a slasher movie, made in 1976, although it was stuck on the shelf for five years before being released. When you see it you'll know why. The film plays like an uneasy combination of "The Texas Chainsaw Massacre", "The Phantom of the Opera", and "Pod People".
After a brief, tense, and needlessly melodramatic opening revealing conflict and parenting issues within a tedious group of people, the cast goes to a creepy old cabin for the weekend, where crazy Otis works as a boat caretaker. How do we know Otis is crazy? The heavy-handed direction and screenplay have one cast member mention to another that Otis has previously kidnapped and branded (yes, with a branding iron) a woman. But that's all in the past, and they have no reservations whatsoever about letting Otis stay on as the caretaker of their boat. It turns out that Otis is none too skilled at his craft, as they bring in an outsider to assist him, after which many bad things happen. Coincidence?
The film is mostly boring, although there is one fairly good plot twist which you can predict if you watch carefully: I was too bored to watch it all that carefully in part due to the tedious flute and banjo music. I give "Savage Weekend" two stars for throwing the curveball at the end.
As a side note, the movie is available as part of the "50 Movie Pack: Drive-In Movie Classics" collection, normally for less that you would pay for this single DVD.