How does a Sailboat Boom Work?
On a sailboat, the boom is attached to the lower part of the mast. It's connected using a set of links, a swivel, or a gooseneck allowing it to move freely in all directions. While under sail, the boom is rigged to move side to side.
The bottom portion of the mainsail, which is called the foot, mounts lengthwise to the boom. This allows the boom to control the lateral position of the mainsail.
What are Sailboat Booms Made Of?
Most modern fiberglass sailboat booms are made of aluminum. Hollow aluminum booms are strong, affordable, and relatively lightweight. Early sailing vessels used spruce and other strong woods. Traditional wooden booms require frequent maintenance, but they're strong and proven.
High-end vessels and racing sailboats sometimes use carbon fiber booms. Carbon fiber is strong and extremely light, and it makes an excellent boom material. Fiberglass booms are common on smaller sailboats, though aluminum is the most prevalent boom material.
Why is it called the "Boom?"
The origins of the term "boom" in the sailing world are unclear. Some people speculate that the word came from the early use of Lateen rigs in the middle east, while others attribute the term to colloquial sailor-talk.
Nonetheless, "boom" is a fitting name. An easy way to remember the boom is to picture what happens when you quickly shift heading and forget to move your head out of the way. The boom swings to the other side with the full force of the wind and gives you a nice tap on the head.
Does Every Sailboat have a Boom?
Not all sailboats use a boom. In fact, the simplest sailing craft does away with the boom entirely. One modern example of a boomless sailboat rig is the Ljungström rig, which was designed by Fredrik Ljungström around 1945.
This simple rig uses two triangular mainsails tied together at the luff and trimmed by a single piece of rope in each corner. Many ancient rigs did without the boom and relied on a single top-mounted spar instead.
Why do Most Sailboats Have Booms?
The boom greatly increases the precision with which you can trim the sail. It provides support and 'draws in' the power of the sail and makes tight windward sailing much easier. If the boom wasn't a significantly useful development, it wouldn't be so common.
Sailboat Boom Parts
The boom on a typical sailboat is a straightforward component. That said, the boom is made up of a few important parts that you'll need to know. Here are a few of the parts found on and connected to the boom.
Gooseneck
The foremost part of the boom is the gooseneck, which connects the boom to the mast. The gooseneck allows the boom to move up, down, and side to side.
Vang
Beneath the boom is the vang, which facilitates the downward force necessary to keep the sail from pulling the boom up the mast. It's a counterforce. Most sailboat boom vang systems use lines and pulleys. However, some vessels use a solid bar vang.
Mainsheet
The mainsheet and its accompanying rigging attach to the bottom of the boom forward of the vang. The mainsheet controls the lateral movement and the trim of the sail.
Reef Lines
The boom sometimes has reef lines attached to it, which allow you to tie up excess sail material after reefing. Reefing lines on older and simpler sailboats must be tied up individually after reefing.
Topping Lift
A topping lift keeps the boom level when the main halyard and the sail are loosened. Topping lifts are not found on all sailboats, but they're becoming more common each year.
Attaching the Mainsail to the Boom
A sailboat boom has hardware for attaching the foot of the mainsail. The type of hardware depends on the boat, and systems range from simple and manual to complex and automated.
Generally speaking, there are two ways to attach the mainsail to the boom. The 'loose-footed' boom design is the simplest and only ties down the sail at the corner tack and clew. The second method attaches the entire foot of the sail to the boom.
Controlling the Boom
There are two primary boom control lines on most sailboats. The first is the mainsheet, which controls how far the boom moves from side to side. The other is the outhaul, which connects to the clew, controlling the tension of the foot.
Furling Booms
Furling booms are yet another wonderful invention of the sailing community. These booms utilize an internal spindle for winding (or furling) the sail on-command.
Furling booms are useful for reefing the sail, as they eliminate the need for tying down excess material. Additionally, in-boom reefing systems offer a convenient way to stow the sail when necessary.
Electric furling booms are a new arrival to the high-end sailboat scene, but they're also available for retrofitting onto older vessels. When combined with electric winches, an electric furling boom can eliminate the need to go on deck when sailing.
These upgrades are common on large cruising vessels, as they allow you to control almost every aspect of your rigging without leaving the cockpit or interacting with any tack, cleats, winches, or lines.
Boom Maintenance
The boom is an essential part of sailboat rigging that must be properly maintained. The same goes for all the blocks, lines, winches, and cleats that work with the boom.
Aluminum Boom Maintenance
Aluminum booms require inspection and hardware maintenance. Galvanic corrosion can compromise the strength of the boom, and it's especially common in areas where hardware mounts to the metal. Aluminum booms can dent, deform, and bend under stress, so it's important to keep an eye out for kinks.
Wooden Boom Maintenance
Wooden spars require much more maintenance than aluminum, as wood is organic and sensitive to the sun, saltwater, and general weathering. Rotted spars are no good and must be replaced. Regular refinishing and coats of spar varnish can help prevent decay and keep the boom looking fantastic for decades.
Fiberglass and Carbon Fiber Boom Maintenance
Fiberglass and carbon fiber booms are low maintenance but still require inspection. Cracks, UV damage, and warping are common concerns with fiberglass booms in particular. Fiberglass is relatively easy to repair and may require gel coat touch-ups from time to time. Carbon fiber is tricky and costly, though initially stronger.
Boom Safety
Booms are one of the most common causes of injury aboard sailboats. All jokes aside, the boom can be pretty hazardous. The primary risk comes from head injuries, as the force of the wind can swing the boom with tremendous force. The boom can also shift on a dime, so it's essential to be cautious when moving around the cockpit.
In some cases, people standing on or around the boom have been knocked right off the boat by a sudden swing. The same force that causes a head injury can launch a fully grown adult right off the side and cause a perilous man overboard situation.
Keeping Passengers Safe around the Boom
Many sailing accidents occur because inexperienced passengers simply aren't aware of the boom, how it moves, and where it goes. The majority of these boom-related accidents can be avoided if everyone aboard follows a few simple rules.
First of all, ensure everyone wears a certified life jacket. Instruct passengers to always keep their heads clear of the boom and not to stand in an area where they could easily fall (or be flung) overboard. Use care when entering or exiting the cabin and when moving around the boom. Also, make sure everyone is seated and out of range of the boom when turning.
