A Beitass, or stretching pole, is a wooden spar used on Viking ships that was fitted into a pocket at the lower corner of the sail. This innovation was used to stiffen and hold the edge of the sail when sailing close to the wind.     
- "Ship construction Topics". http://duckduckgo.com/c/Ship_construction.
- "Glossary of Viking Words". http://www.alisons-world.net/vglossary.html.
- Grambs, David (1993). Did I Say Something Wrong?. Penguin Group. pp. 75. ISBN 0-452-26831-1.
- Gedney, Elias. Ships and Navigation of the SCA Period. East Kingdom Guild of St Erasmus. pp. 11.
- Culver, Henry B (1992). The Book of Old Ships: from Egyptian Galleys to Clipper Ships. Dover Publications.