In the donner party, why was the blue rover built?

The Blue Rover was built to help get the Donner Party and their wagons safely across the river. The craft was finished on May 30th by volunteer boat builders. It was not made to be pretty, but of necessity. The wagons were put on the Blue Rover one at a time, and took until nightfall until the mission was completed. A total of 9 wagons were taken across using the Blue Rover. After everyone was safely across, the Blue Rover had its ropes detached and was left to drift away. 

Ithink it would be d