Lanterna Rally

Author: Roscoe E. Perham

Publisher:

Published: 1978

Total Pages: 21

ISBN-13:

The ice booms on the St. Marys River at Sault Ste. Marie, Michigan and Ontario, were operated a second winter, 1976-77, under colder conditions, with less water flow, lower water levels, and 25% fewer ships in the river than during the previous year. The ice cover behind the booms remained frozen to shore for longer periods, and the loads registered in the booms were relatively unaffected by ship passages compared with the previous year's activity. As in the previous year, most structural load changes took place in the west ice boom and were due to movements of the ice cover immediately upstream of the boom. The cover broke free from shore on three occasions: the first and third occasions were minor events, but on the second occasion the cover cracked free, the timbers remained frozen to it, and the boom structure became damaged by the subsequent ice activity. Three anchor line assemblies broke over a period of about 4 hours; the two latter breaks occurred while a ship was operating in the ice. The first break was in an instrumented line and the measured load was unexpectedly low. The most important break was in the main shore anchor and this opened the boom. The maximum force at this anchor was estimated as less than 115 tons (1,023 kN). Some ice moved downstream without serious consequence and the boom was reconnected in two days. These events point out several factors to be considered in ice booms, such as designing the booms to withstand the action of the solid ice cover as well as the fragmented ice cover, keeping the structures and their assembly simple, and inspecting components and assemblies carefully. (Author).