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Speed of Ships in Restricted Navigation Channels

1974; American Society of Civil Engineers; Volume: 100; Issue: 2 Linguagem: Inglês

10.1061/awhcar.0000231

2690-4055

R. Schofield,

Maritime Navigation and Safety

Ship model experiments confirm that orthodox screw-driven craft attain an apparent maximum or barrier speed in navigation channels of restricted width and depth, irrespective of available engine power. This speed is primarily a function of blockage ratio (the relationship between cross-sectional area of the ship to that of the channel). It occurs when conditions alongside become critical at the maximum section; discharge onto the screw is thereby controlled and ship speed becomes limiting. A direct hydraulic jump develops near the stern. A bow-screw arrangement permits acceleration beyond the limiting speed since free flow onto the screw is no longer prevented by critical conditions which now occur downstream. Factors studied during experimentation include ship squat, thrust, power, screw revolutions, water-surface profiles, and water velocities. A two-dimensional theory demonstrates the development of critical conditions around the ship.