View Full Version : Drag Forces on a Flat Face Barge

 mitch1028403-05-2013, 12:17 PMHello. I'm working on constructing an anchoring system for Barges on the MississippI River in St Louis and need to determine the force the river will impose on an anchored barge. I'm using the Drag Force Equation F = 1/2 x velocity^2 x density x Area x Cd Assumptions Drag Coefficients Cd = 1.98 for the bow Cd = .005 for bottom and sides Density = 62.4 lb/ft^3 for water Barge is 35'x195' and sits 11' in the water I've been told by a few Barge Captains the river can reach 26 ft/s during a strong flood. I'm designing for worst case so I've used this number. The problem I'm having is that the drag force numbers I'm getting seem to be way high. Bow - 16,576,329 lb Sides - 466,433 lb Bottom - 742,053 lb Hoping someone can confirm these numbers are incorrect and can help me out. Thank You Submarine Tom03-05-2013, 12:30 PMIsn't water density 1.0? Don't discount windage. mitch1028403-05-2013, 12:36 PMUsing US Customary Units and the Mississippi is fresh water in St Louis. Regards TANSL03-05-2013, 01:00 PMCan be Cd bigger than 1? DCockey03-05-2013, 01:39 PMCan be Cd bigger than 1? Yes. Nothing special about a Cd value of 1. The table in my old fluid mechanics textbook shows a drag coefficient of 2.00 for an infinitely wide flat plate normal to the flow, 1.20 for a rectangular flat plate with an aspect ratio of 5 normal to the flow, and 1.10 for a square plate normal to the flow. Those are drag coefficients for an object completely immersed in an "infinite" flow. DCockey03-05-2013, 01:44 PMHello. I'm working on constructing an anchoring system for Barges on the MississippI River in St Louis and need to determine the force the river will impose on an anchored barge. I'm using the Drag Force Equation F = 1/2 x velocity^2 x density x Area x Cd Assumptions Drag Coefficients Cd = 1.98 for the bow Cd = .005 for bottom and sides Density = 62.4 lb/ft^3 for water Barge is 35'x195' and sits 11' in the water I've been told by a few Barge Captains the river can reach 26 ft/s during a strong flood. I'm designing for worst case so I've used this number. The problem I'm having is that the drag force numbers I'm getting seem to be way high. Bow - 16,576,329 lb Sides - 466,433 lb Bottom - 742,053 lb Hoping someone can confirm these numbers are incorrect and can help me out. Thank You You need to divide by the "density" of water of 64.4 lb/ft^3 by 32.2 ft/sec^2 to obtain the mass density of 2.0 slugs/ft^3. That will reduce the drag force numbers by a factor of 32.2. View Full Version : Drag Forces on a Flat Face Barge