It is surprisingly easy to move even a relatively heavy ship just by pulling on ropes.

Distance is speed times time. Speed is acceleration times time. Acceleration is force divided by mass. A modest force (let's say 50 kg-force) applied to a large mass (let's say 100 metric tons) for a modest amount of time (let's say 20 seconds), is enough to accelerate the mass to a slow but sufficient speed - in this case, 10 centimeters per second, if you ignore all friction. Then wait a bit, and after 10 seconds, the boat/ship has moved a meter.

Of course, water is low friction, not no friction, so it'll take more force and you'll quickly reach a max speed, but it does work in practice.

This video shows a car doing that with a massive modern ship, but as you can imagine, you can do the same with a couple of strong men pulling on ropes.