Starting from rest when going ahead. The transverse thrust effect will tend to swing the stern to starboard and the bow to port. The engines working ahead cause the propeller to drive a spiral flow of water towards the rudder (screw race) so the helm can be used to counteract the effect of transverse thrust. Moving at steady speed ahead. The transverse thrust of the propeller will tend to swing the ships head to port. The wake current reduces the steering power but the helm can be used very effectively to counteract the effect of transverse thrust as there is a strong flow of water against the rudder due to the screw race and the vessels headway. Moving ahead with engines stopped. Starting from rest when going astern. The transverse thrust effect of the propeller and the effect of the propeller slipstream on the hull causes the stern to swing to port. The helm cannot be used effectively to counteract the swing as there is no flow of water against the rudder from the propeller, or from the movement of the ship. Moving at steady speed astern. |