century steamers with iron hulls. Many scholars consider it unlikely that any of Zheng He's ships were in length and have proposed much shorter lengths, as low as . Zhao Zhigang claimed that he has solved the debate of the size difference, and stated that Zheng He's largest ship was about in length. Disputes of historical records of length Edward L. Dreyer claims that Luo Maodeng's novel is unsuitable as historical evidence. The novel contains a number of fantasy element; for example the ships were "constructed with divine help by the immortal Lu Ban". One explanation for the seemingly-inefficient size of the colossal ships was that the 44 zhang treasure ships were used only by the Emperor and imperial bureaucrats to travel along the Yangtze for court business, including reviewing Zheng He's expedition fleet. The Yangtze river, with its calmer waters, may have been navigable by these treasure ships. Zheng He, a court eunuch, would not have had the privilege in rank to command the largest of the ships, seaworthy or not. The main ships of Zheng He's fleet were instead six-masted 2000-liao ships. That would give burthen of 500 tons and a displacement tonnage of about 800 tons. Traditional and popular accounts of Zheng He's voyages have described a great fleet of gigantic ships far larger than any other wooden ships in history. The most grandiose claims for Zheng He's 1405 fleet are entirely based on a calculation derived from an account that was written three centuries later and was accepted as fact by one modern writer; rejected by numerous naval experts. There are even some sources that claim some of the treasure ships might have been as long as . The claims that the Chinese treasure ships reached such size is disputed because other 17th century Ming records stated that European East Indiamen and galleons were 30, 40, 50, and 60 zhang (90, 120, 150, and 180 m) in length. It is also possible that the measure of zhang (丈) used in the conversions was mistaken. The length of a Dutch ship recorded in the History of Ming was 30 zhang. If the zhang is taken to be 3.2 m, the Dutch ship would be 96 m long. Also the Dutch Hongyi cannon is recorded to be more than 2 zhang (6.4 m) long. Comparative study by Hu Xiaowei (2018) concluded that 1 zhang would be equal to