However, the shallow Clyde was not navigable for the largest ocean-going ships, so cargo had to be transferred at Greenock or Port Glasgow to smaller ships to sail upstream into Glasgow itself.
Clyde var imidlertid så lavvandet, at den ikke var sejlbar for de største oceangående skibe, og fragten skulle derfor overdrages på Greenock eller Port Glasgow til mindre skibe, der kunne sejle opstrøms ind til selve Glasgow.