Hi CoastGuarder,
If you have not yet done so, I suggest downloading the Mission Editor Notes:
http://80.95.161.114/shipsim/forum/index.php/topic,19793.0.html (http://80.95.161.114/shipsim/forum/index.php/topic,19793.0.html)
As Angus said, barges are static ships, and are found by clicking the Static tab in the Entity creation panel.
Information on connecting barges in the editor is found in the section titled “Barges — Herkules Atlas†on page 18.
Regards,
Marty