TM   9-2350-261-10 WARNING C a r r i e r    c a n    s i n k and   personnel   can be   trapped   inside and   drown   when hatches a re closed.  All  hatches must   be   in   open   position   with locking   pins   installed   during   wa- ter   operations. 21. 22. 23. Open   driver’s   hatch   and   install locking  pin  (page  2–144). Open  commander’s  cupola  cover and   install   locking   pin (page  2-148). Open  cargo  hatch  and  install locking  pin  (page  2-146). WARNING Carrier   can   sink during   water   op- e  r  a  t  i  o  n s when trim   vane   is   not extended and locked   in   place. Personnel  can  be  killed.  Extend and  lock  trim  vane  in  extended position   before   entering   water. NOTE Although   vehicles   have   the ability   to   float,   swimming   is   not allowed.   However   since   bottom beneath   surface   of   the   water may  conceal  holes,  gullies,  soft spots, and other   hazards, vehicles   must   be   prepared   to float and to move out of dangerous   areas. 24.   Extend   and   lock   trim   vane   by lifting   handle   and   pushing   trim vane   forward   until   handle catches  in  the hull. striker   on   the N O T E Freeboard   is   determined   by measuring   the   distance   from hull  top  plate  (lowest  portion)  to t h e    w a t e r    l e v e l .    F r e e b o a r d    w i l l change   when   carrier   is   traveling in   the   water. 25.   Measure   and   mark   front   and rear  freeboard  every  2  inches  on each  corner  of  carrier  with  tape. For   the   M113A2,   minimum front  freeboard  is  8  inches  and minimum   rear   freeboard   is   12 inches.   Note   that   rear   freeboard is   higher   than   front   freeboard. Note   different   rear   freeboard measurements   for   the   M577A2 and   M1068   carriers,   indicated   in the   following   table. 2-280 Change   3