How does a boat engine work?

The trial finally took place on a loch near Dumfries on October 14, 1788. The trial was said to have been a success. Later accounts would say that the boat went at 5mph and that Robert Burns was on board. However, if Burns was present, he failed to mention it in a letter he wrote on that day or in any of his verse. Certainly, the local minister and his son were on board and the latter reported the trial to Robert Cleland of Glasgow, who wrote that the trial failed and the boat had to be helped by hand cranks. The experiment did ultimately demonstrate, however, that a steam engine would work on a boat.