You need to use the ID of the image when getting the url field. You can either loop through them and get the images first or you can loop through them and get the link where you need it. This example is for getting them all first.
<?php
$images = get_field('cruise_lines', 'travel-category_74');
for ($i=0; $i<count($images); $i++) {
// the id of the image is in $images[$i]['ID']
$images[$i]['link_url'] = get_field('link_url', $images[$i]['ID']);
}
?>
