What is a Catamaran?
Catamarans are a kind of multi-hull sailboat with two hulls joined together. They are often short and wide, resembling a square or rectangle from above.
Catamarans are colloquially distinct from outriggers, which are double-hulled vessels with one large primary hull and a small outboard stabilizing hull.
Catamarans usually have hulls that mirror each other, both in size and arrangement. Sometimes, the interior layouts are mirrored, too—but this varies between designs and manufacturers. Catamaran hulls are narrower and taller than most monohull designs of equal lengths.
Catamarans have limited commercial and military utility, as these applications favor space and ease-of-construction over handling characteristics. That said, there are some commercial uses for catamaran designs—most commonly passenger and car ferries.
What is a Monohull Sailboat?
A monohull is probably what you traditionally think of as a boat. Monohulls are longer than they are wide. It features a single hull—it’s that simple. Sailing monohull designs have evolved over the centuries into many distinct types, usually distinguished by keel type.
Monohulls come in many shapes and sizes. For example, sailing monohulls designed for offshore use have long keels that sometimes extend much further below the waterline than the freeboard and cabin extend above it.
Monohull sailboats are also designed for other purposes, such as inland sailing and racing. These vessels have more contemporary characteristics, such as rounded shallow ‘canoe’ bottoms, V-bottoms, and fin keels.
Monohulls aren’t just sailboats. Virtually every cargo and container ship, warship, and many passenger ships are monohulls due to their strength, ease of construction, and high cargo capacity.
Are Monohull Sailboats More Common?
Monohulls are more common in every application, though multi-hulls are becoming more common for ferries. Monohulls have numerous benefits over multi-hulls, and these benefits only increase with scale.
Monohulls are easy to construct. They’re also cheap. Large monohull ships, such as container ships, can be built with very little material and effort. This is because the vast majority of the length of a monohull is just a box, with a bow and stern welded onto the end.
Sailboat construction is more intricate, but the costs are still lower. Plus, monohull designs are robust, and cabin space is plentiful. There’s a lot more study in the field of monohull design, which was the universal truth until somewhat recently.
But all in all, the reason why monohull sailboats are more common is that they work just fine. Most sailboat owners aren’t interested in breaking speed records or hosting dozens of people aboard their boats. As a result, a standard, simple, and easy-to-control monohull are more than sufficient.
Are Catamarans Faster than Monohulls?
Catamarans are most certainly faster than monohulls. This is almost always the case. Even the fastest production monohulls can’t hold a candle to the average cruising catamaran.
But why is this the case? Aren’t catamarans restricted by the same hydrodynamic forces as monohulls? As it turns out, they aren’t. This has to do with the unusual way hull waves impact speed.
Hull Speed Limitations
Monohull speed is limited by something called hull speed. Hull speed is determined using a formula that calculates the maximum speed a displacement hull can travel under normal power and conditions.
When a displacement hull moves through the water, it kicks up a set of waves at the bow and stern. These waves travel along the side of the vessel and create drag, which slows down the boat. Normally, the power of the wind can overcome this drag—but only to a point.
At a certain speed, the waves kicked up by the bow will sync with the waves kicked up at the stern and begin ‘working together’ against the boat. The speed at which this occurs is the hull speed, which is calculated from the length of the boat.
Hull speed limitations for monohulls aren’t universally true all the time. Some vessels exceed it, and some don’t—but the number is a useful estimate of the limitations of monohull designs. Modern monohulls with clever hull shapes can defeat hull speed calculations.
Do Hull Speed Limitations Apply to Catamarans?
Surprisingly no—hull speed calculations don’t work for catamarans. This is because, for one, the hulls are shaped differently. Alone, catamaran hulls wouldn’t float correctly. But together, they create different hydrodynamic effects and cancel out the effects of hull speed.
This means that catamarans can easily exceed the speeds of even the fastest monohulls of equal length—and sometimes beat them by a margin of 50% or more. It’s not unheard of for 40-foot catamarans to exceed 20 knots, whereas 40-foot monohulls rarely get past 10.
Are Catamarans More Comfortable than Monohulls?
Catamarans can be much more comfortable than equivalently-sized monohulls—up to a point. This is because catamarans engage in ‘wave piercing’ and have a wider and more stable footprint on the water.
Catamaran hulls, when properly designed, can slice through parts of a wave instead of riding over every peak and trough. This effectively reduces the height of the weight, which reduces the amount the boat rolls.
Additionally, the wide footprint of a catamaran allows some waves to simply pass right under it, keeping the boat level for longer durations. Catamarans also don’t heel under sail—instead, they plane slightly, raising the bows out of the water and reducing bumps.
Monohull Benefits
Monohulls are proven in all conditions. A well-designed displacement monohull sailboat can ride out the strongest storms, and monohull workboats can support enormous loads and move them efficiently. They can be fast, comfortable, and also easy to sail (even for beginners).
Monohulls are cheap to build and forgiving, as precision doesn’t have to be microscopic to get them to sail right. They’re robust and strong, featuring a naturally stress-resistant hull shape. They’re also easy to modify and aren’t required to meet as strict of dimensional ratios to operate.
With a monohull sailboat, you have a lot of interior room to work with. This means that monohulls are available in numerous cabin layouts and are just as easy to modify as they are to build. Monohulls often have a center of gravity at or below the waterline, which enhances stability at steep heel angles.
On the water, displacement monohulls can weather extreme conditions with ease. They lack the initial stability of multi-hulls, but they can recover from knockdowns on their own, and they’re very difficult to push past their rollover point.
Why do Catamarans Cost More than Monohulls?
Catamarans cost more than monohulls because they’re more expensive to build, more complex to engineer, and require more material. This isn’t always the case, but the design of catamarans requires much more careful engineering and strength-of-materials analysis than comparatively simple monohulls.
There are several critical structural points on catamarans that monohulls lack. In fact, the very shape of a monohull is physically strong—so it has inherent durability. Catamaran hulls must be joined in the middle, and the mast must have a strong point far from the inherently sturdy hulls.
This requires stronger materials and more care during design or construction. This is why catamarans remain a premium part of the sailboat market and why they still aren’t the most popular sailboats despite their numerous performance and comfort benefits.
Catamaran Cabin Layout
Catamaran cabins are split between the two hulls, and there’s usually a large pilothouse in the center. Pilothouse catamarans can be quite spacious, primarily due to the large space between the hulls.
The pilothouse is usually where kitchen and sitting areas are located, along with cockpit access and the controls of the sailboat. The mast is also located in this area.
Catamaran cabins sometimes mirror each other. For example, each hull may contain two identical bedroom/bathroom combos, while the center console area contains the kitchen and living spaces.
The two identical hulls sometimes make for unusual design decisions (such as small catamarans with four master bedrooms), but owners say this gives their passengers a much better experience than a monohull cabin.
Monohull Cabin Layout
Monohull cabins, with the exception of split-cabin sailboats with a center cockpit, have only one large interior space to work with. It’s usually much wider than catamarans of equal length.
Monohull cabins are usually accessible from the bow (via a flush deck hatch) and the stern via a traditional companionway. They run the span of the hull between the bow and the cockpit and sometimes include spare berths under the cockpit seats.
These spare berths are often used as convenient sea cabins, as they offer quick access to controls in case of an emergency. Catamarans often have convertible berths in the center console for the same reason.
Monohull cabins are traditional and include everything that catamaran cabins do—albeit with slightly less room overall. That said, individual spaces are often much wider, and facilities are more appropriate.
