Found on YouTube. Created by "ISSIMS - Innovative Ship Simulation". Originally published on 2022-04-21.
Operation of ships with POD propellers during astern motion has a lot of advantages –
This movie is an introduction and explains the dynamic and typical motion elements when steering the ship moving ahead or astern. The effect of the position of applied control forces seen in the direction of motion is demonstrated – The differences are shown for the configurations when
1. acting at the aft end of the ship (e.g. rudders at the stern making headway, or stern thrusters/ pods making if the ship is making sternway) and acting to the outside of the future turning direction: This creates a drift angle, which supports turning and leads to a bigger swept path and larger speed loss and also a pivot point position to the fore end of the motion.
1. acting at the fore end of the ship seen in the direction of motion (e.g. thrusters at the bow making headway, or pods at the stern making sternway) and acting to the inside of the future turning direction: this creates no or only small drift angle, which lead to a smaller swept path and speed loss and a pivot point position to the ships centre (or even to the aft…).
THAT’S WHY THE STERN FIRST METHOD MAKES SENSE FOR POD SHIPS!
2. Generally, the steering effect of the control forces depends highly on the ships speed – if the speed drops (e.g. a pod is braking!) the hull forces decreases and the control forces effect increases!
The position of the Pivot Point (PP) is discussed here again and it is pointed out that the distance between the momentary PP position and the positions of control forces cannot be seen as “Lever” to create / explain steering moments / effects – This is wrong, because the PP changes its position immediately with the control forces!
Numerous samples of manoeuvres with one or two pods or thrusters in typical configurations will be demonstrated with the SAMMON-Planning-Tool to show the effects of the different pod and thruster strategies. Have fun – and let me know your comments / wishes!
