Mike and his family are members of the Tanga Yacht Club. No, it's not the aristocratic place you are picturing. Yachts do indeed moor in the nearby cove, but it's a bit more humble than what you are picturing.
There's not many familiar "western" forms of leisure in Tanga. The yacht club offers decent meals and a very tiny beach.
And yes, the commodores (club directors) go back to 1941.