Thus a shorn camel with fur 0.5-1 centimeters long would evaporate 50 percent more water than would an animal with unshorn fur. Think about the physics and you will see why fur hinders the efficiency of sweating. Fur hinders the free flow of air. The air under the fur becomes saturated and must be replaced by dry air for heat to be removed. Water on the skin under the fur is cooler than water would be on the open skin.
Cooler temperature means slower evaporation and less heat removed per unit time.
Some of the sweat under the fur will be stuck to the hair itself. When it evaporates, it cools the hair, which does not have the same effect as cooling the skin, under which flows the blood. It is the blood which needs to be cooled so that it can cool the interior of the body. This is a size effect. African bodies, like the Watusi, are long and lean, maximizing surface area and minimizing heat retention.