What is a Sailboat Boom Vang?

What is a Sailboat Boom Vang? | Life of Sailing

Last Updated by

Daniel Wade

June 15, 2022

A boom vang is a set of blocks and lines or an adjustable pole used to pull the boom down and shape the sail.

The boom vang (or “kicking strap”) is a system used to control the shape of the sail. It counteracts the upward force of the boom jack and the mainsail by pulling the boom downward. This results in the ability to control the shape of the sail.


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Boom Vang vs. Mainsheet 

What's the difference between the boom vang and the mainsheet? On many sailboats, the boom vang and the mainsheet look similar, as both use a set of blocks to control the motion of the boom.

The easiest way to tell the difference between the boom vang and the mainsheet is location. The boom vang typically begins close to the base of the mast and connects to the base of the boom at about a 45-degree angle.

The mainsheet is much further back and generally vertically-oriented. Sometimes, the mainsheet is located far at the end of the mast and connected to the stern of the vessel. Just remember boom vang forward, mainsheet aft.

What Does a Boom Vang Do?

A boom vang is a simple device consisting of a pole or a set of blocks and lines. The primary purpose of the boom vang is to control the vertical orientation of the boom and to exert a downward force on it.

Without the boom vang, the wind would blow the sail uncontrollably and make it difficult to maneuver efficiently. The mainsheet, which appears to exert downward pressure on the boom, wouldn't be able to adjust the sail effectively without a separate system like a boom vang.

Importance of the Boom Vang

A properly-adjusted boom vang becomes more important as you let out the mainsheet. The further from the centerline the boom travels, the less downward force the mainsheet provides.

This means that you'd lose a tremendous amount of control without a boom vang, especially as you loosen the sheet. A boom vang exerts a constant downward force on the sail regardless of what position the boom is in. This keeps the sail shape consistent in all conditions.

Boom Vang Types

There are two primary types of boom vangs used on sailboats today. The first and most common type is the standard boom vang. Standard boom vangs consist of a block and tackle arrangement that mounts to the base of the mast and bottom of the boom.

The second type is the hydraulic boom vang, which is more advanced and offers unique benefits. The hydraulic boom vang uses a hydraulic piston that looks like an oversized automobile shock or door opener.

The benefit of a hydraulic boom vang is that it holds the vertical position of the boom without assistance. It's rigid in both directions and doesn't require upward force to keep the boom in place.

Hydraulic boom vangs are costlier than traditional block-and-tackle setups. That said, they're easy to install and generally simple to operate. Hydraulic boom vangs are common on newer sailboats, especially those that exceed 30 feet in length.

What is a Boom Gnav?

A boom gnav is one of the most intuitive pieces of sailboat equipment. The word "gnav" is "vang" spelled backward, and it performs the exact same task on the opposite end of the boom.

A boom gnav exerts a downward force on the boom to counteract the upward force of the wind or rigging. A boom gnav pushes the boom down, whereas a boom vang pulls it down. Not all sailboats have a boom gnav, and those that do often use it as a substitute for a boom vang.

Boom gnav systems are most common on small sailboats, where the added lower triangle of a boom vang gets in the way. A boom gnav takes up no extra cockpit space as it mounts atop the boom and to a higher point on the mast.

In other words, the boom gnav operates within the sail area, which is a part of the boat that's already unusable due to the sail. A boom gnav is usually a pole that adjusts by sliding forward and aft on the boom, which changes the angle and downward force.

Boom Vang Maintenance 

Maintenance is essential to keep your sailboat in safe and working condition, and the boom vang is no exception. There are a few boom vang parts you should inspect and maintain regularly.

Check the Mounting Points

The mounting points of the boom vang are subjected to a considerable amount of force, and they should be inspected regularly. Look for signs of corrosion (galvanic or otherwise) and bending.

If you notice any deformation, replace the mounting points and hardware with marine-grade hardware. Make sure the aluminum mast is solid, as corrosion can weaken the areas around the mounting holes.

Inspect Blocks and Tackle 

For traditional boom vangs, regularly inspecting the blocks and lines can prevent problems down the road. Over time, nylon lines become salt and sun-damaged and begin to fray. If the lines are brittle and leave excessive dust on your hands, it may be time to replace them.

Blocks are generally reliable and don't require a significant amount of maintenance. That said, you should inspect your blocks and make sure they spin freely. If they don't (or they become too loose), they could be failing and should be replaced with high-quality marine blocks.

Hydraulic Boom Vang Maintenance

Hydraulic boom vangs are simpler than traditional block and tackle setups, but they still require regular inspection. A hydraulic boom vang uses a piston and a working fluid instead of lines and pulleys.

On hydraulic boom vangs, the primary failure points are the seals and the mounting points. If your boom vang begins to leak, you'll notice a decrease in stability, and the vang won't hold tension.

Another common failure point is the spring, which can weaken or break and make the vang almost unusable. In most cases, the best option when your hydraulic boom vang fails is to replace it entirely.

What is a Boom Jack?

A boom jack (also known as a lazy jack) is the rigging that exerts an upward force that the boom vang or boom gnav counteracts. The boom jack begins at the boom and reaches up to the top of the mast.

Boom jacks resemble any other rigging on a sailboat. They roughly form the triangular shape of the sail and usually mount to the boom at multiple points.

A typical boom jack begins as a single line at the top of the mast. About 1/4 of the way down the mast, it splits into two lines. At the halfway point, each end of the two lines splits again into four. These four lines run down to the boom and mount evenly-spaced apart.

The purpose of the boom jack is to exert even upward force on the boom. The tension of the boom jack is set as to counteract the tension of the boom vang, which holds the boom at a steady 90 degrees. The boom jack line runs down from the top of the mast to a block or cleat on the opposite end of the boom vang.

Adjusting the Vang

Generally speaking, the boom vang isn't as important when traveling upwind as it is when traveling downwind. This is especially true once you've maxed-out your mainsheet traveler.

At this point, the vang controls the twist of the mainsail. With an improperly-adjusted vang (or lack thereof), you could experience a lot of up-and-down play of the boom. This can cause you to lose control of the mainsail.

A properly-adjusted boom vang can help you keep your mainsail shaped correctly and keep your boom in the proper position. It also gives you precise control of your speed when traveling downwind.

What is a Sailboat Boom Vang?
Daniel Wade

Daniel Wade

I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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