WENDELL ROELF FIVE youths from Cape Town's Langa township squeeze into wetsuits for a snorkelling lesson with South Africa's first Black diving coach -- turning the tide on decades of apartheid history in which water sports were reserved for wealthy whites. Zandile Ndlovu's Black Mermaid Foundation aims to introduce the ocean to the country's black youth, millions of whom live in impoverished shanty townships, where beach trips are a luxury and swimming skills in short supply. Zandile Ndlovu Sitting around Ndlovu, 33, South Africa's first Black -- and Black female -- free dive instructor, the children learn how to bite…