Complex sentence: His uncle bought a wooden narrow fly horse boat called "Cressy" and installed first a steam engine and then (having discovered the steam made steering through tunnels impossible) a Ford Model T engine.
Split into simpler sentences: His uncle bought a wooden horse-drawn narrow flyboat called "Cressy" and fitted it with a steam engine. Then (having discovered the steam made steering through tunnels impossible) he replaced that with a Ford Model T engine.