Is there a reason to execute the query in each individual div instead of looping the div within the query?
<?php
$my_query = new WP_Query( 'post_type=portfolio&showposts=13' );
while ( $my_query->have_posts() ) :
$my_query->the_post();
?>
<div class="port1">
<?php the_title(); ?>
</div>
<?php endwhile; ?>
If you want to number the divs sequentially, you can use a counter:
<?php
$i=0;
$my_query = new WP_Query( 'post_type=portfolio&showposts=13' );
while ( $my_query->have_posts() ) :
$my_query->the_post();
?>
<div class="port<?php echo $i++; ?>">
<?php the_title(); ?>
</div>
<?php endwhile; ?>