Monday, March 13, 2006

error analysis: weather

We knew the ice would be brittle at cold temperatures, but we didn't expect the problem to be so severe. The weather during the competition (9:00 AM Tuesday to 9:00 PM Thursday) was unusually cold. Normal high temperatures in Fairbanks in early March are 15°F or so, but, out of three days, only Thursday had a high temperature above 0°F. Working the ice that day seemed incredibly easy after our experiences the previous two days.

At 20°F, carving ice with appropriate tools is like carving a block of cheese; at -20°F, it is more like carving glass. Miniscule impacts can result in huge fissures, and contact with liquid water yields a lattice of tiny surface fractures at best, more often causing substantial cracks. If you have ever heard ice cubes crack after being dropped into a beverage, you can imagine the effect on a larger scale. We learned a fun trick: Take a fair sized (fifty pounds or more) slab of ice at -30°F and toss a bucket of warm water over it. Spectacular shattering! Unfortunately the effect meant that we were completely unable to use waterglue at the extreme temperatures. Even around 0°F we had to be very careful, making sure the water was no warmer than 32°F and spreading it thinly.

Cold temperatures are hard on tools as well. Gasoline powered chainsaws are particularly difficult to operate, but we were able to minimize the problem by constructing a small warming tent for our tools out of a blanket, a steel chest, and a small space heater.

To a certain extent, we can chalk up our temperature troubles to bad luck, but there are a few things we could do to better handle the situation. Now that we've learned which tasks can't be accomplished at extremely cold temperatures, we can plan those tasks for the warmest times of day. We can also maximize the amount of daylight work hours. Spending the entire day of Tuesday in the shop eliminated a full third of our (relatively) warm temperature hours.

We've also talked about trying a larger scale warming tent, possibly encompassing some of the pieces of ice to be worked or even ourselves. Taking the idea to the extreme, we might try warming the entire 7600 pound block of ice or even constructing a tent around the whole work site. These efforts would certainly be overkill in normal temperatures but might be worth consideration in a bad cold snap.

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