I was a bit intrigued by the tower, and wondered if it had ever been a lighthouse, so looked it up when I got home. It was an observation tower for the former bombing range at Rosehearty. It was apparently operational as a RAF bombing range from the 1950s until 2000, when the buildings were sold off.
Apparently the tower has bomb-proof and bullet-proof windows and cost £750,000 to build. It was sold for a mere tenth of that and is now a private house, with, I'd imagine, a great view.
The real lighthouse in Rosehearty is a beacon on the end of the pier. I'm not sure whether it's operational or not.
The fishing boats were all ashore, presumably for shelter from the winter storms.