During nighttime boat unloading operations on a floating facility in marginal weather conditions, the Crane Operator made the last of several heavy lifts using the crane’s 2-part load line. The final operation was to lower a personnel basket to the boat on the crane’s fast line to retrieve a Roustabout. The Crane Operator began lowering the fast line to the pipe rack while simultaneously raising the load line. Sometime during this activity, the fast line and “headache ball” swung over and threaded itself through the two load lines but the Crane Operator was unaware of this happening. The personnel basket was picked up and lowered to the boat and the Roustabout was lifted up to the pipe rack. After storing the personnel basket back on the pipe rack, the Crane Operator realized the fast line was not recovering properly and shut down operations.