Welcome to the spreadsheet for Towing Bridle Force Calculation

Transcription

1 Welcome to the spreadsheet for Towing Bridle Force Calculation What does this Excel Sheet do? This Excel sheet helps you calculate the force in each bridle line when the towed object is rotated at an angle It can be used for a standard case of single towline and a towing bridle comprised of tow lines (see figure on right) How to use this Excel Sheet The user is asked for inputs related to towline, towed object and towing bridle. The Input cells are highlighted in blue. The user has to provide all the inputs highlighted in blue. Once all inputs are provided, the spreadsheet will calculate the force in each bridle line The Forces can then be checked against the MBL of the bridle lines Limitations The rotation angle of the tow should not be more than 10 degrees. References 1. DNV RP-H-103 Sec For feedbacks, write to thenavalarch@gmail.com OR info@thenavalarch.com

2 Welcome to the spreadsheet for Towing Bridle Force Calculation Port bridle line α(angle of rotation of towed object) Towing Line

3 TOWING BRIDLE FORCE CALCULATOR Parameter Length of Towline (measured from Bridle Apex) Towline Tension SECTION A - INPUTS (See Fig 1 & Fig 2 on right) TOWLINE PROPERTIES Symbol Value Unit L 50 m T 0 50 kn BRIDLE PROPERTIES Distance between fairleads of Port and Stbd Bridle lines d 10 m Length of each Bridle Line s 20 m TOWED OBJECT PROPERTIES Distance of COG of towed object from Bridle fairlead (See Fig 1) X 40 m Angle of Rotation of * α 6.1 degress *Angle of rotation is positive for rotation towards port, negative for rotation towards stbd

4 X (distance of COG from COG of Towed Object d Towing Line L (length of towing line from Bridle Apex) Figure 1 - in line with the Towing Line Port bridle line α(angle of rotation of towed object) Towing Line Figure 2 - rotated at an angle α

5 Parameter Length of Towline from Bridle Apex Distance between fairleads of Port and Stbd Bridle lines Length of each Bridle Line Distance of COG of towed object from Bridle fairlead Angle of Rotation of Half Bridle Apex Angle (See Fig on right) Distance of bridle apex from Towed object COG Angle of towline with horizontal Angle at which Stbd line goes slack Check if Stbd Line is Slack Tension of Towing Line Parameter Applicable effect of slack bridle line Tension in Port Bridle Line Tension in Stbd Bridle Line Moment of Towing Force around the Rotation Center of towed structure TOWING BRIDLE FORCE CALCULATOR SECTION B - OUTPUTS CALCULATIONS Symbol Formula Value Unit L 50 m d 10 m s 20 m X 40 m α 6.1 degrees β sin -1 (d/2s) degrees R (X + s * cosβ) m γ R/L*α 7.24 degrees OUTPUTS - CHECK IF ONE BRIDLE LINE IS SLACK Symbol Formula Value Unit α SLACK Lβ/(L + R) degrees if α > α SLACK, then line is slack Not Slack OUTPUTS - TENSION IN BRIDLE LINES T 0 50 kn If Port line is slack, Stbd line takes the full Stbd line is slack, Port load. If Stbd line is slack, Port line takes line takes all load the full load T PORT T 0 * sin(β + α + γ)/sin(2β) kn T STBD T 0 * sin(β - α - γ)/sin(2β) 2.05 kn OUTPUTS - MOMENT AND ROTATIONAL STIFFNESS M G T 0 * R * (1 + R/L)*α kn-m Rotational Stiffness due to Towing Force around the Rotation Center of towed structure C 66 T 0 * R * (1 + R/L) kn-m/rad

6 β α β γ

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