The Cruise of the "Esmeralda" app for iPhone and iPad

This is a splendid book, beautifully written, with a strong nautical background. The heros family, which had a very long nautical tradition, was a bit short of money. But there was a story told in the family that some centuries before an ancestor of his had found an abandoned vessel which turned out to have a huge amount of gold and jewels. He had buried this in a secret location on an island in the Far East, putting directions for finding it in cipher somewhere in his house in England. Our hero finds the paper with the cipher after a long search in the house, and sets off to find the fortune, though he had not yet deciphered the instructions.

All sorts of adventures occur, including being attacked by pirates, whom they get rid of in a most novel manner. Eventually our hero seems to work out how to read the cipher, in a dream, but when he awakes he cant remember how to do it. He does of course remember, and the cipher turns out to be easy to read, once you realise how many digits you need to get each character. They get there, and sure enough, find the treasure. But of course the troubles dont end there, because some of the seamen think it would be a good idea to kill our hero, and take the treasure for themselves. That situation gets sorted out, and after further adventures they get home. They use a novel method of getting the treasure ashore without anybody in authority noticing.