http://home.cogeco.ca/~tanzer-26/harvey.htm#boom

http://home.cogeco.ca/~tanzer-26/images/boom-v.gif

"Project: Boom vang plans by Martial Harvey.

I have constructed an air pressurized boom vang for my Tanzer 26, and
have had the opportunity to try it out on several occasions. The boon
vang works marvellously in all types of weather, and the material I
have selected for its construction appears to be strong enough for the
job. I have used it in light winds, average wind conditions, and
strong (25 to 30 knots) winds, and everything held up fine."