What is a Monohull?

Lori Kilchermann

A monohull boat is the typical design that most people imagine when thinking of a boat. The single-hull boat is called a monohull, while boats with two hulls are known as catamarans, and three-hulled or tri-hulled boats are known as a trimaran. The monohull or single-hull boat is perhaps the most common boat design in use today. Used in every type of boat design from small sailing boats to the super tankers and freighters on the open ocean, the monohull design is a tested and very successful boat type.

Monohull boats cut through waves easily.
Monohull boats cut through waves easily.

The advantages of a monohull is that the boat is able to cut through heavy waves with ease. By slicing through the waves as opposed to running on top of the waves, the boat is able to ride much more smoothly through the water. Having a single hull in which to load freight allows the monohull to distribute the weight where it will provide the most stable ballast while en route to the ship's destination. Most monohull ships have segregated cargo holds within the ships hull which can be loaded and closed off from the rest of the ship by the use of heavy locking doors.

Monohulled vessels usually dig in to the water as they sail into a crosswind.
Monohulled vessels usually dig in to the water as they sail into a crosswind.

One of the disadvantages of the monohull design is that it must use ballast for stability. The ballast can be made up of virtually anything that might weigh the vessel down and offset any wind or wave that might attempt to capsize the boat. The downside, however, lies in the fact that unless the ballast is made up of a product that will float, the boat is liable to sink if it happens to take on too much water.

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In contrast to monohulls, multi-hulls such as trimarans have smaller outrigger hulls that are separate from the main hull.
In contrast to monohulls, multi-hulls such as trimarans have smaller outrigger hulls that are separate from the main hull.

Some monohull designs actually have two hulls. Ships such as tankers which carry oil and liquid cargo often have a dual hull design. This design consists of a hull inside of a hull that allows a hollow space to exist between the two hulls. This helps protect the ship from punctures if it should encounter an object, thus preventing dangerous and expensive leaks.

Most large warships, including the US navy's Zumwalt class destroyers, are built with a monohull.
Most large warships, including the US navy's Zumwalt class destroyers, are built with a monohull.

While not as stable as a multi-hulled boat, the single hull design has stood the test of time in relation to being a safe, sturdy and efficient design. Used in racing as well as pleasure boating, the single hull design is fairly easy to operate and is the traditional design used to teach a novice to sail. While some seamen move onto multi-hulled boats to practice their craft, most will return to a single hull design to enjoy the sport in its most pure and traditional form.

A boat with a single hull is classified as a "monohull".
A boat with a single hull is classified as a "monohull".

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