"When naval ship propulsion gear teeth break@ the affected teeth are ""field dressed""@ so that the units can be put back into service. Then the gears are rerated to a lower rating and used reliably@ at least until replacement elements become available. Using sketches or computers@ an estimate is made of the instantaneous total length of contact as the damaged sections go through mesh with the results being used as a basis of rerating the unit. Consideration is given to end reliefs@ the location of the damage on the helix and the nature of the field dressing@ and actual material properties. The results of this analysis@ together with analysis of the causes of the original failure@ provide limits within which the unit can be operated with the same reliability as new."