American Scientist

To the Editors:

Henry Petroski’s excellent article, “Slide Rules: Gone But Not Forgotten” (Engineering, May–June) is germane to a multimillion dollar icebreaker research project that was conducted in 1970 in the Northwest Passage to determine feasibility of the Passage for shipping.

The ship was the SS Manhattan, an oil tanker more than 300 meters long, two to four times the length of a conventional icebreaker. The prow and hull had been modified and reinforced. Previously, the ship had been the luxury oil tanker of Aristotle Onassis. The bridge was amidships, which is unusual for a tanker, and some quarters still had bidets and Italian art.

In the fall of 1969, amidst a flurry of publicity, the Manhattan successfully traversed the Passage. A more focused attempt was made the following spring to relate speed to ice thickness and propeller thrust, but the ice was thicker than before, and there was not enough thrust.

A suggestion was made to apply Newton’s Second Law to each ram into the ice, even though the procedure had been tried with a Russian icebreaker and did not work. The expedition leader Stanley Haas gave the go-ahead, and six engineering college students made the measurements. This “ice-testing team” was helicoptered off to measure thickness and strength of the ice. As the professor, I managed to tag along to look out for polar bears.

An experimental global positioning system was available but only tracked one satellite; radar was not reliable; and underwater sonar signals jammed as soon as the ship plowed into ice. A well-known ice scientist, Andrew Assur, set up a simple alternative: Two boards stuck out over the side of the ship could be used to measure the time it took for a snowdrift to pass the projected distance between them. A stopwatch was used to measure this time interval. Ice thicknesses were estimated as chunks of ice were turned up on edge. Running times during a ram were measured with a tape recorder. The system was so successful that it was relied on for dead reckoning of the ship position.

Each ram gave ice resistance versus velocity, as required for application of Newton’s Law, and data were gathered even though the ship came to a stop. The onboard computer died, but fortunately a small slide rule had been taken along as a joke. A $10 slide rule thus became a primary tool for reducing data from a $300-million research program. The student group made, graphed, and interpreted the measurements, and wrote a key part of the onboard report. It was described in a 1977 paper in Arctic Systems by Fen-Dow Chu as “the most valuable full-scale ice breaking data yet available.”

Many tests have since been made with conventional icebreakers, but none with a ship the size of the Manhattan. In 1987 it ran aground during a typhoon and was cut up for scrap. Still, the data live on; I cited them in a 2013 book, and I still have the slide rule.

Richard L. Handy
Madrid, Iowa

To the Editors:

When my university discontinued slide rule instruction, a 6-foot-long teaching model was relocated to a laboratory, where it became a marker of a remarkably sharp cutoff age for understanding it, attesting to the precipitousness with which slide rules fell out of use. Visitors whose engineering education occurred before about 1975 smiled knowingly, assuring us they still had a slide rule and could use it if needed. Younger folks had no idea what it was. My own Pickett Synchro Scale model N803-ES, acquired in a Future Engineers of America contest in 1959–60, remains in my desk drawer ready to serve if the power fails.

Molly W. Williams
Western Michigan University
Kalamazoo, MI