Ice Boat on

Published in Brain Teasers

On a hot summer day by a lake you are determined to build a boat made of ice, using a refrigeration unit and a large mold in which you can pour water. Nearby you notice an Egyptian mummy resting on a pile of wood pulp. What is the best strategy for building an ice boat that will not melt before you sail it across the lake?


Forget about the mummy. Add the wood pulp to the water and freeze the mixture. The resulting solid, called pykrete, will have incredibly useful properties. For example, several decades ago Geoffrey Nathaniel Pyke (1894-1948) showed that the frozen mixture was extremely hard to break and very slow to melt. If a ship were made of pykrete, it would be unsinkable; torpedoes could hit it and do little damage. Pykrete has a crush resistance of greater that 3,000 pounds per square inch. A 1-inch column of pykrete can support an automobile. The wood pulp also makes the pykrete extremely stable at high temperatures. If a .303 caliber bullet is fired at the pykrete, it will penetrate only 6.5 inches. The United States and Canada were so impressed with the idea of assembling pykrete warships that a 60-foot-long, 1,000-ton pykrete ship was built in one month on a Canadian lake and never melted through the hot summer.

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