why was it difficult for the three friends in the boat to cover the boat with canvas?

In Chapter Ten, because they did not bring a tent, they have to pitch the canvas cover over the boat before they can sleep. This task proves more difficult than it seems, and it takes them several attempts to successfully set it up. They used the wrong hoops, were thrown into the water, injured themselves, and got themselves rolled up in the canvas. It was, for lack of a better word, a nightmare.