Welsh was a journalist and a writer, and is the guy who had the idea of building a trireme. He then went on to actually do it, and built the Olympias with Morrison, the historian, and Coates, the naval architect.
This book is the history of building the ship from his perspective.
Welsh was no trireme expert at all, so this book is not extremely interesting from an historical or ingeneristic point of view. But he tells the story of how Olympias was built and of the first tests in a lively style, providing a nice insight. Plus, it includes quite a few interesting pictures.
Recommended if: either you find a cheap copy on ebay (mine was 3£!) or you are really a big Olympias fan.