Ship Interaction when navigating in a Narrow Channel
When navigating in narrow channels, water flow, and pressure systems increase significantly. This results in the ship pushing water ahead of her and the surface of the water rising noticeably several ship’s lengths ahead of the ship. Along the ship’s side, water will flow back with higher velocity than in open water of the same depth, and abaft of the ship, water will be pulled along in the direction the ship is sailing.
To avoid the turning effect caused by the cushion effect, the ship should sail in the center line of the channel, which should be symmetrical about her.
If the ship gets close to one side of the channel, it will turn away from the channel bank and at the same time is sucked in towards it.
To sail parallel to a channel bank, the ship must lie at a certain angle away from the channel bank, and a permanent rudder must be given towards it.
The position of equilibrium may be obtained where rudder power and repulsion at the bows neutralize the suction, and the total turning moment of the three forces about the centre of gravity of the ship is zero.
If the ship steams into a bend of a channel, the bank effect should be taken advantage of to assist the vessel’s rounding the bend. She should accordingly be placed on the outer side of the bend.