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  #1  
Old 05-14-2006, 06:10 PM
Hisham Hisham is offline
Marine engineer
 
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Box shape Barge resistance

for any type of ship total resistance = 1/2 ( density * v * A * Ct)

Ct -----> Total resistance coefficient (including wave making resistance)

the common known methods for predicting Ct can't be used for box shape barge

Ct for box shape Barges should be constant since the shape is constant

can any one give me a range for this coefficient?
or where can i fiend a good document about this?
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  #2  
Old 05-15-2006, 10:10 AM
jehardiman jehardiman is offline
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Ct is not constant for a box barge. It is a function of B and T. It can also vary by -50% depending on bilge radius. And rake adds a whole different issue.
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Old 05-15-2006, 06:38 PM
SamSam SamSam is offline
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Quote:
Originally Posted by jehardiman
Ct is not constant for a box barge. It is a function of B and T. It can also vary by -50% depending on bilge radius. And rake adds a whole different issue.
Are you talking about the chine radius? If I built a scow type hull, rounded chines would have less resistance than a 90 degree angle chine? Sam
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Old 05-16-2006, 10:49 AM
jehardiman jehardiman is offline
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Quote:
Originally Posted by SamSam
If I built a scow type hull, rounded chines would have less resistance than a 90 degree angle chine?
Yes, the radius needs to be ~ 10% or more of B to get the maximum restiance per ton reduction (after about that tonnage starts going down faster than the resistance). Noticable improvenents are seen with the radius as little as 2% of B. See Hoerner: "Fluid Dynamic Drag".
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  #5  
Old 05-16-2006, 07:37 PM
Hisham Hisham is offline
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haaaaaaaaaaaaaaay

i was asking.. how i can calculate resistance for box shape barge

need help plz
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  #6  
Old 05-17-2006, 12:37 PM
jehardiman jehardiman is offline
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Come on, Hisham, this is easy. A second year hydrodynamics question...Just figure out the pressure drag and add the surface drag. Get your pressure coefficients from Hoerner or Blevins.
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  #7  
Old 05-17-2006, 03:20 PM
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Guillermo Guillermo is offline
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Quote:
Originally Posted by Hisham
for any type of ship total resistance = 1/2 ( density * v * A * Ct)

Ct -----> Total resistance coefficient (including wave making resistance)

the common known methods for predicting Ct can't be used for box shape barge

Ct for box shape Barges should be constant since the shape is constant

can any one give me a range for this coefficient?
or where can i fiend a good document about this?
Some info at:
http://boatdesign.net/forums/showthread.php?p=12081

A computer program:
http://www.ds-t.com/software-cd/soft...0TechSheet.pdf
http://www.hydrocompinc.com/knowledg...ngPowerITB.pdf

Also a simple downloadable Propulsion Prediction Program, based in Holthrop. See if your barge is within the range of applicability.
http://www-personal.engin.umich.edu/...b/newpage1.htm
Cheers.
__________________
Guillermo Gefaell
Gestenaval S.L., Naval Architecture & Marine Engineering
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  #8  
Old 05-17-2006, 08:23 PM
Hisham Hisham is offline
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tahnks...... i am going to check them
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