Yeah, I think I found a partial solution at least. It would appear that two of the conditionals that would allow the return of a properly placed ship was faulty. In 'sub place_ship' there's a line that reads:

    return 0 if $x<0 or $y<0 or $x>9 or $y>9;
[download]

Changing it to:

    return 0 if $x<0 or $y<0 or $x>10 or $y>10;
[download]