The moving boat has "momentum." Momentum is simply mass times velocity, or kg times meters per second. It could be expressed as pounds per miles per hour also. Momentum of a 12000 kg boat moving at 2 meters per second (4mph) is roughly 24000kg or 52800 pounds of momentum. Any 1" nylon line would have broken in an attempt to stop this vessel, assuming the piling didn't break off first.