1st: 3ds Max.
2nd: you cannot convert ships for SS
3rd: 3ds Max isn't free
4th: Read this guide that Mad Fred attached here: http://www.shipsim.com/ShipSimForum/index.php/topic,11583.0.html (http://www.shipsim.com/ShipSimForum/index.php/topic,11583.0.html)