In functions.php use:
add_theme_support( 'post-thumbnails' );
add_image_size( 'gallery-thumb', 215, 143 );
Your default posts per page will be 10 which is why you can only see 10 images. Override this by changing your query to:
$the_query = new WP_Query( array( 'post_type' => 'flota', 'orderby' => 'title', 'order' => 'ASC', 'posts_per_page' => -1, ) );
In your query replace $thumbnail and $full with:
$thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id(), 'gallery-thumb' );
$full = wp_get_attachment_image_src( get_post_thumbnail_id(), 'full' );
Then use a plugin like http://wordpress.org/plugins/regenerate-thumbnails/ to regenerate your thumbnails.
In a loop get_post_thumbnail_id doesn't require the ID to be set but if you do decide to set it elsewhere you were looking for $post->ID rather than $the_query->ID. Set $global $post; as well when using it.