The thrust developed at zero ahead speed. Bollard pull is the most commonly used measure of ship-assist tugs performance which have propellers optimized for maximum thrust at close to zero speed. Ships requiring high bollard pull can be fitted with a nozzle, which increases thrust by up to 20-40% compared to open propellers.
Rough estimation of bollard pull BP = (T x k1 x k2)/9.81, T = (D x PD )2/3
BP = bollard pull (ton), k1 = 0.9 (10% losses), k2 = 1.2-1.4 (20-40% addition depending on nozzle), T = Thrust (kN), D = propeller diameter (m), PD = delivered power (kW)
Note: When measuring bollard pull water should be deep enough, there should not be too much current or wind, the vessel should not be close to a pier and the rudder angle should be close to zero degrees.