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1. the original, authentic version of 瀛涯勝覽 does not mention the dimensions of the ship. The copy which added the "450 ft" (44 zhang) description was the 澹生堂刻本, which was produced in the 1580s-1620s. Whether it is earlier than the novel is debatable, but in either case, it is clear that the "450 ft" characterization is a late-16th century invention, created nearly 200 years after the original voyage. There is no intermediate work that supports this description.
2. The 5000 liao record is consistent with the Western 200 ft (61 m) estimate, not the 450 ft (137 m) claim which is the fantasy that is often taught in Chinese textbooks
This is very simple math. "liao" is a unit of volume describing the cargo volume. The cargo volume is proportional to the displacement of the ship. Thus, just like the displacement, a ship's liao is proportional to the *cube* of the length of a ship
Let x be the liao capacity of the ship
Let y be the length in meters
x = k(y^3) where k is a constant
We know that a Song-era Quanzhou trading ship excavated was measured at 34.6 meters and recorded at 1000 liao
Hence we can arrive at an estimate of k:
1000 = k(34.6^3)
k ≈ 0.024
If a treasure ship is 450 ft (137 m),
x ≈ 0.024(137^3) ≈ 61712 liao
If a treasure ship is 200 ft (61 m)
x ≈ 0.024(61^3) ≈ 5448 liao
Hence, the "5000 liao" description actually implies a ship slightly smaller than the Western historical consensus, a "200 ft" ship.
Meanwhile, the "450 ft" ship would imply a cargo volume that is more than 12 times larger than the recorded "5000 liao".
