SHALLOW WATER HYDRODYNAMICS

Shallow water effects on the resistance of ships are well documented. What is perhaps not so well documented is a phenomenon often referred to as "squat". When a ship advances into still water of any depth, the pressure forces over the hull are modified hydrodynamically, the water surface is deflected, and the familiar train of transverse and diverging waves is set up. These hydrodynamic pressures apply a vertical force and trimming moment to the vessel which adjusts its position relative to the still-water surface to maintain equilibrium. For tankers, this squat is manifest as a trim by the head and bodily sinkage which reduces the underkeel clearance, particularly at the bow. In deep water, this effect, although present, is of little importance to ship operators. In shallow water, however, trim by the head and bodily sinkage increase, with the result that underkeel clearance may be reduced dramatically. Furthermore, theoretical and experimental work on models has shown that squat is roughly proportional to the square of the speed of the vessel so that if the speed is doubled, squat is quadrupled.

• Corporate Authors:

  Transport and Technical Publications Limited

  161-166 Fleet Street
  London,   England 
• Authors:
  • Dand, I W
• Publication Date: 1971-1-29

Media Info

• Pagination: 2 p.
• Serial:
  • Shipbuilding and Shipping Record
  • Volume: 117
  • Issue Number: 5-6
  • Publisher: Transport and Technical Publications Limited

Subject/Index Terms

• TRT Terms: Force; Hulls; Keels; Navigation; Ship motion
• Uncontrolled Terms: Squat
• Old TRIS Terms: Hull forces; Shallow water effects; Underkeel clearance
• Subject Areas: Marine Transportation; Vehicles and Equipment;

Filing Info

• Accession Number: 00032159
• Record Type: Publication
• Source Agency: Engineering Index
• Files: TRIS
• Created Date: Apr 21 1972 12:00AM