According to British scientist, historian and sinologistJoseph Needham, the dimensions of the largest of these ships were 135 metres (440 ft) by 55 metres (180 ft).Historians such as Edward L. Dreyer are in broad agreement with Needham's views. However other historians have expressed doubts over the dimensions of these treasure ships. Xin Yuan'ou, a shipbuilding engineer and professor of the history of science at ShanghaiJiao Tong University, argues on engineering grounds that it is highly unlikely that Zheng He's treasure ships were 450 ft long, and suggests that they were probably closer to 200–250 ft (61–76 m) in length