The Harry Potter star, who is a keen sailor, is currently filming scenes for BBC TV series Timothy Spall: Back At Sea, which follows the actor and his wife travelling around the coast of Britain on their barge boat.
But on Wednesday (24Aug11) Spall had to radio for help after accidentally sailing into busy shipping lanes.
A lifeboat was called out to save the star in the Medway estuary in Kent, south-east England and rescuers guided him back in to safety.
Spall tells Britain's The Sun, "I feel foolish, but it's better to feel foolish and alive than clever and dead. I was terrified and very grateful to the RNLI (Royal National Lifeboat Institution). These guys risk their lives for idiots like us."
A spokesperson for the RNLI adds, "We're pleased he called us before he got into trouble."
Scenes of the rescue will air in the U.K. next year (12).