Boom vangs let you control the leech tension of your mainsail independently of the mainsheet so you can shape your mainsail for maximum efficiency. They're particularly effective off the wind, when the pull of the sheet is primarily horizontal, because they prevent the boom from lifting and spilling the wind. West Marine Rigging has created four vangs to fit most dinghies and racer-cruisers. They feature: Snap shackles on each block (not on mini) so they're suitable for both permanent and temporary mounting Kits include New England Ropes double braid and free-running Ronstan fiddle blocks If your boat doesn't currently have a vang, all you need to add are snap shackle attachment points on the boom and mast base