American Scientist

The idea of a boat made of concrete is often greeted with skepticism, if not derision, by the uninitiated, who are as likely as not to call up the gangster-movie cliché of concrete shoes fitted to murder victims. Concrete, no matter how configured, is not supposed to float. But stereotypes and false assumptions can get in the way of common sense, for who would doubt that vessels made of steel, a material with three times the specific gravity of concrete, can float? Indeed, a kind of reinforced concrete was introduced as a boat-building material more than a century and a half ago, long before steel-hulled ships became commonplace.