Sinkage and Resistance for Ships in Channels

by John S. McNown, (F.ASCE), Prof.; Dept of Civ. Engrg., Univ. of Kansas, Lawrence, Kans.,

Serial Information: Journal of the Waterways, Harbors and Coastal Engineering Division, 1976, Vol. 102, Issue 3, Pg. 287-300

Document Type: Journal Paper


Ships moving in restricted water as in a canal or an inlet to a harbor sink lower in the water and experience greater resistance than they do in open water. The ship settles more because the velocities induced in the water by the motion of the ship are greater and the elevation of the water surface drops correspondingly. The amount of sinkage depends upon the cross sections of the ship and the channel. The resistance also increases because of the constriction of the return flow around the ship. Two remarkably good approximations: (1)The sinkage is the change in potential energy required to produce the kinetic energy of the return flow; and (2) the extra power is that needed to pump the amount of water in the return flow from the lower level back to the original level of the quiet water.

Subject Headings: Hydro power | Flow resistance | Ship motion | Return flow | Load and resistance factor design | Ships | Potential flow | Water flow

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