Why You Need One
Revised by BoatUS editors in April 2012
Boom vangs, or kicking straps, are essential on any sailboat. Ultimately, they are the fundamental boom control, preventing it from "skying". Technically, this means they eliminate twist in the mainsail by controlling the leech tension. The vang, by flattening the sail, makes the boat easier to control, increases boat speed and sailing efficiency, and allows it to sail closer to the wind.
When running and reaching, the mainsheet traveler is all the way out. Without a vang, the sail will twist, causing the upper part of the mainsail to luff. In an effort to prevent this, the helmsman's natural reaction is to sheet in. However, this results in the sail being sheeted in too tight, which will produce excessive weather helm. In stronger winds, the effect is more dangerous. Constant attempts at correcting the luffing by sheeting in and then releasing the main sheet as the boat becomes overpowered can cause a rocking motion. Without an efficient boom vang, this can develop into a "death roll", ultimately leading to a broach.
A vang also helps you to control your jibing. By using a snap shackle as the lower attachment, the vang can quickly be moved to another point as a preventer. Favorite locations are the toe rails and the headsail sheet tracks. This allows for controlled jibes by the crew. Accidental jibes cause injury and gear failure on large yachts and result in capsizes on dinghies.