Fire in the Mooring Ropes Due to SOOT From Economizer

The ship was in US port and expected to sail out in the evening. 2/E planned for economizer cleaning. Economiser was cleaned and secured by 1430 hrs. Ship finished cargo by 1630 hrs and sailed out by 1730 hrs. around 1900 hrs, bridge informed ER that fire had taken place near the mooring winch in the aft. On inspection, found the nylon mooring ropes had caught fire. The fire was brought under control.
It was decided later that fire patrol should be kept for few hours after cleaning the economizer.