There are several locks on the Douro, the largest of which has a gradient differential of 35 metres, just over 100 feet. The rate of ascent is about 1.8 metres per minute, so the trip up takes about 17 minutes. There is about 30 centimetres clearance either side of the ship and the captain negotiates the entrance to the lock manually. Although he has an iPhone on the bridge plugged into a laptop so he may just sit there while an iPhone app does the real work. Note that our ship - the Queen Isabel - has a helipad should something go terribly wrong. So far so good.