Man with boat (Planet of the Spiders)

A man was securing a speedboat and chatting to Hopkins, a man piloting a hovercraft, when Lupton, who was being pursued by the Third Doctor, stunned Hopkins and stole the speedboat and pushed him into the water. He made several attempts to get back on the speedboat, but Lupton finally succeeded in pushing him off. The man eventually swam to shore. (TV: Planet of the Spiders)

Behind the scenes
The man with boat is named Bob Armitage in the novelisation.