The pictures below were taken of the boom  vang control used by Susie and Tim Stombaugh.

Tim and Susie have installed a 4:1 purchase system made up of a Harken double block with becket and a Harken double block, the free end is run through a cheek block mounted to the mast support.  This connects to a Harken single block that is used to double the purchase of the system.  The purchase totals 8:1 when the free line finally runs through a Harken Bullseye swivel base with a cam cleat mounted on a sloped block of wood.
	A closer look at the system that doubles the purchase and how the line is routed to the swivel.
Here is a look at the bullseye swivel and the block that supports the mechanism.
This system was checked by the Chief Measurer to make sure that it was legal.  Since the swivel can not turn a complete 360 degrees the system is considered legal.