Stopping the ferry on Colonsay

When the ferry docked at Colonsay, you could see the two hawsers in the top photograph pulling tight to stop the ship. I looked over the side and timed 60 seconds, trying to work out how far the ferry moved in that time. I'd estimate 4 metres in 60 seconds before the ropes began to tense. That's 0.07 metres per second. The mass of the ship is about 3,000,000 kg so the momentum is about 200,000 Ns. If it then takes the hawsers 60 seconds to bring the ship to a standstill then the average rate of change of momentum is of the order of 3000N so 1500N on each hawser. If the ship is moving very slowly and the time to stop if long then the forces needn't be huge. Next time I go I need to get a more accurate time to stop after the hawsers become tense and I need to find out about the hawsers to calculate their properties.