while (<$CSV>) {
  chomp;
  # assume csv is SHIP1,DATETIME,LATITUDE,LONGITUDE.
  # modify accordingly..
  my ($shipname, $datetime, $latitude, $longitude) = split(/\,/$_);
  my %today_details = (datetime => $datetime, latitude => $latitude, longitude => $longitude); # this is what will get pushed on the arrayref
  my @arr = @{$SHIPS{$shipname} || []}; # get curr contents
  push (@arr, \%today_details); # push today's data
  $SHIPS{$shipname} = \@arr; # push back
}
# that's you done with the merge