TM    55-3930-660-14 APPENDIX C ESTIMATING   TIEDOWNS The  number  of  lashings  required  to  safely  tie  down  the  VRRTFL  for  highway  transport  on  a  typical truck/semitrailer can be estimated in the following manner: STEP 1  –  Determine  the  amount  of  longitudinal  restraint  needed.  [With  this  method,  the  required vertical and lateral restraint is covered by the longitudinal factor or factors.] –The highway loading restraint factor (LRF) is 0.7 (from app B) in the forward direction: 27,100 (VRRTFL GVW) x 0.7 = 18,970 pounds –The highway LRF is 0.3 in the aft direction: 27,100 X 0.3 =  8,130  pounds STEP 2 – Determine the number of chains needed. –The angle to semitrailer deck and the angle to the side are assumed to be 45°. [cos 45 x cos 45 = 0.5] –The SWL of 3/8-in. chain (from table 2-2) is 8,250 pounds: No. of forward loading chains = 18,970 = 4.6 (rounded up to 5) 8,250 X 0.5 While  5  chains  satisfy  the  equation,  6  chains  are  needed  for  a  symmetric  (side-to-side)  tiedown arrangement.  Therefore,  use  6  chains  to  prevent  the  VRRTFL  from  moving  forward  on  the  semitrailer. No. of aft loading chains = 8,130 = 1.9 (rounded up to 2) 8,250 X 0.5 Use 2 chains to prevent the VRRTFL from moving aft on the semitrailer. NOTE: This  method  is  more  conservative  than  the  “Highway  Transport”  chapter.  Fewer  chains  are  used  in Figure  2-1,  “Tiedown  of  6K  VRRTFL  on  a  flatbed  semitrailer,”  because the figure is based on the actual tiedown-lashing angles [angle to semitrailer deck (side view) and angle to the side (top view)]. C-1