Alien Contacts: Arthur C. Clarke, Dolphin Island. Gollancz, London, 1963.
Johny runs away from home, stows away on a hover craft which is then damaged in a storm. The crew, not knowing he was there, leave without him, and he jumps into the sea. He manages to get onto a packing box and is drawn to an island by dolphins where he finds a research community who are working to understand and communicate with dolphins. The sf plot is then about teaching killer whales not to eat dolphins.
But more interesting is that most of the Island is Black, and Johnny's best friend is a local boy (black). Clarke handles this incredibly well in that Mike is just Mike: clever, and bigger and stronger than Johnny so although he is "the protagonist's friend" he never feels like a sidekick. The island economy is dependent on the work of everyone and Clarke does a really suberb job of blending the different peoples (as I had just read a K. Bulmer book in which a handsome, clever man was declared "clearly not really a Negro! There had to be some other blood in him! Clarke came as a breath of fresh air.
Shame the illustrator of the puffin edition ignored Clarke's descriptions of the boys. In the picture opposite p. 39, Johnny is drawn as his age (16./17), but Mike is drawn to be about 14. Someone, somewhere, clearly couldn't handle the idea that a Black friend could be older, smarter, physically fitter and better looking than the white protagonist.