I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "The tide-predicting machine invented by Sir William Thomson in 1872 was of great utility to navigation in shallow waters. It used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location."? 

What time frame was it when it become easier for people to get around in water that wasn't deep?