It could be a mismatch of expectation and reality about harbour tugs. The 50-100 tonnes of bollard pull is very small when comparing to the momentum of a moving ship at that speed. And very often, the bitts and bollards on board are not able to withstand that amount of pulls. After all, emergency anchoring is about anchoring in emergency, in areas, something somewhere somewhat unexpected.
Exactly… it may be one of the areas that Antonio is looking into. Making an angle of 30 degrees across a stream could be making as much as half of the pressure that could be generated at right angle. That is what rudder circling about, I guess. The small rudder, the anchor drag in this case, may not reduce a ship’s speed much. The ship’s hull may.
Antonio, please consider sending us a copy of your thesis when it is completed.