A film which opens with a young man or child walking on the beach, and either seeing a box or crate on the beach, or stuck in the surf. Inside is either a skeleton or a dead body.
I could have sworn it was from a Peter Benchley film, such as THE DEEP or THE ISLAND, but no such luck. It was definitely from that time period–1975 to 1983 approximately.
The Deathmaster (1972)?
Sorry, it’s called Deathmaster. There’s no ‘the’ in front of it. It’s a vampire film and there is a scene just like this at the start of it.