catamaran hull

The 8 Main Characteristics of a Catamaran Hull

Posted on May 28, 2022

Ever wonder why your catamaran ride is so much smoother than other boats, including yachts? Why don’t I get as oozy as when I’m on other vessels, even when the water is choppy?

It’s all about the hull, my fellow water enthusiasts. Not just one but two hulls, positioned in such a way as to give us the most perfect ride we can get on the ocean, without us having to grow fins.

Catamarans have a wide beam, instead of a ballasted keel like a monohull vessel, which provides its steadiness. It has a more shallow draft and smaller displacement than a monohull with a similar length. Its hull offers stability, more space, privacy, no heeling, lower hydrodynamic resistance, and more.

Now that you’ve gotten the gist of it, let’s look in-depth at the hull characteristics.

1. Lower Hydrodynamic Resistance

Hydrodynamic resistance of the combined two hulls is usually lower than equivalent monohulls, needing less power from the sails or the engines. A catamaran’s broader posture on the water can decrease the feeling. 

It also lessens the motions caused by waves, which can also produce smaller wakes than on a single-hulled vessel. 

A cat’s hulls have a less wetted surface area, which means they burn less fuel. The boat may be propelled by one engine in mild winds.

2. Reduced Heeling

The term “heeling” refers to the tendency of a sailboat to lean to one side due to the force of the wind on its sails. The boat is oriented so that the wind hits the sails at an angle and pushes them to one side of the boat, propelling the boat.

Catamarans are the safest way to navigate the oceans because they have no heel angle. Cruising catamarans are safer than monohulls for their crew because they offer better protection and a no-heel environment. 

As a result, the crew will be less exposed, make fewer mistakes due to exhaustion, and arrive at their destination more rested.

3. Less Displacement

Boats that employ buoyancy to support their weight are referred to as displacement hulls. To provide its name, it is partially immersed and moves by causing water to be dislodged. 

Its weight is equal to the amount of water it dispenses. In stormy water, it maintains its sturdiness. As a result, cruisers and sailboats alike frequently make use of this design.

4. Stability 

In place to evade capsizing as well as heeling, the catamaran depends on hull stability, while hull stability depends on buoyancy and beam. About half of a typical cruising catamaran’s length is its beam. 

Say, for example, that the boat was 50 feet in length, the beam might be about 25 feet broad so that you could maintain the balance between heel and righting moment.

On a cat, passengers who are prone to motion sickness will be far less affected by the impacts of motion than they would be on a monohull. The cook’s task is made much easier while traveling and at anchor because of the cat’s extra stability. When compared to monohulls, catamarans have less rock and roll.

Once you’ve decided to sail, you won’t have to worry about scrambling to stow things or securing them with bungee cords. Relatively rough seas have little effect on most of the ship’s equipment.

5. A Bridgedeck Connects Them

You can’t ignore this reality! Bridgedeck clearance, or the gap between the water and the bridge deck, is an important factor in a catamaran’s safety and reliability. Ocean waves have room to flow between the hulls thanks to the bridge deck clearance. 

Our catamaran’s hulls create waves that converge underneath the bridge deck, requiring a larger buffer for the bridge.

If you don’t have enough clearance, your catamaran will be pounded by the waves. 

In addition to slowing your catamaran down by 3 to 4 knots, rough seas can also put your guests’ health and safety at risk, as well as inflict significant damage to your boat and rigging.

6. Can Maneuver Shallow Water

A boat’s draft is the distance from the water’s edge to the hull’s center of gravity. It is important to know the depth of a boat’s draft since it determines the quantity of water that can be displaced for safe passage. As a result of their parallel hulls’ buoyancy, catamaran vessels can have fewer drafts without affecting their stability or their ability to maneuver. 

When it comes to hull stability and handling, monohull vessels are built with a deeper draft to protect against capsizing as well as heeling. Because of this, the catamaran was deemed suitable for use in shallow waters. 

Boating activities such as swimming and fishing aren’t the only ones that benefit from being able to dock in shallow water. A boat with a shallow draft will be more maneuverable in areas where you may have to sail through a variety of shallow areas, some more than others. 

Monohull boats with deeper drafts may be unable to access shores, intertidal zones, coral reefs, or even sandbars because of their shallower depths. Also, shallow-water swimming and snorkeling are two of the most popular pastimes for sailors plus their families. To ensure a smooth experience, you’ll need secure access to shallow waters.

There are several types of fishing that require a catamaran’s dependability and readiness, and these include trout, oystering, and clamming. These activities become much easier when you can navigate shallow waters without worrying about running aground or striking underwater objects.

7. Allows Cat to Have More Space

It certainly does. Eating and preparing food can be done side by side. One hull is used as a big cabin in the “owner versions,” which are fantastic for parties.

Most comparable-priced monohulls lack the amount of interior room seen on catamarans, especially in the primary salon, galley, plus cockpit. As a result, their cabins tend to be larger, and now even the tiniest cat in the group has a stand-up headroom in each one.

8. Offer More Privacy

The distance between the two hulls allows for greater privacy than on monohull yachts, which tend to be closer together. 

Because of the configuration, a cat offers more solitude than monohulls, and the increased separation between the main living area and the cabins makes it simpler for children to go off to sleep at a normal hour when aboard.

What Are the Differences Between Catamaran and Monohull Sailing?

Most characteristics of sailing a catamaran resemble those of sailing a monohull. In most Catamaran Sailing Boats, the abilities you acquire on a monohull, you can transfer to a cat. A few minor distinctions must be made though, including these.

Keep a steady speed during the tack to avoid “winning,” which can occur if you relax the mainsheet too much. Winning occurs when a catamaran’s larger mainsail tries to direct the boat towards the direction of the wind.

Gybing on the monohull necessitates much more caution, therefore you have to slow down your gybe considerably. Travelers on catamaran boats have an advantage since they can sustain a pace while gybing to depower the main.

You can tell when you’ve got too much sail on a monohull by the way the boat is heeling, which tells you it’s time to reef. Since catamarans don’t heel, we have to be super cautious when reefing the enormous mainsail because it’s so heavy. 

In most cases, the first reef will be thrown in between wind speeds of 18 and 20 knots (determined by the size of our yacht) and the second reef will be thrown in as the wind speeds reach up to 25 knots.

Many elements of sailing a catamaran are fairly similar to those of a monohull, so making the switch should not be too difficult.

Are Catamarans Safer Than Monohulls?

Exactly what I was looking for! People are less likely to drown when sailing on a catamaran than on a monohull, thanks to the boat’s greater stability. They are bigger, more steady vessels. In most cases, this makes cats “safer” than a monohull of the same size.

Having two engines makes catamarans “safer” in the event of an engine breakdown. Sailing is the sole alternative on a monohull boat if the motor is out of commission. In the event of an emergency, the second engine on a catamaran is always ready to assist!

Is Sailing A Catamaran Easier Than Sailing A Monohull?

It is more difficult to sail a monohull because of heeling and the constrained space it has to offer. In greater gusts, monohulls heel, making it harder to accomplish most activities. 

Sailing aboard a heeling vessel is more difficult for a variety of reasons, including heading forward to a reef, having to haul in a sail, or just moving around the boat. 

The greater stability and space provided by catamarans, on the other hand, make moving around the boat easier than on other types of boats. The fact that catamarans are typically referred to as “easier” to sail is due to this.

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Catamaran Design Formulas

• Post author By Rick
• Post date June 29, 2010
• 10 Comments on Catamaran Design Formulas

Part 2: W ith permission from Terho Halme – Naval Architect

While Part 1 showcased design comments from Richard Woods , this second webpage on catamaran design is from a paper on “How to dimension a sailing catamaran”, written by the Finnish boat designer, Terho Halme. I found his paper easy to follow and all the Catamaran hull design equations were in one place.  Terho was kind enough to grant permission to reproduce his work here.

Below are basic equations and parameters of catamaran design, courtesy of Terho Halme. There are also a few references from ISO boat standards. The first step of catamaran design is to decide the length of the boat and her purpose. Then we’ll try to optimize other dimensions, to give her decent performance. All dimensions on this page are metric, linear dimensions are in meters (m), areas are in square meters (m2), displacement volumes in cubic meters (m3), masses (displacement, weight) are in kilograms (kg), forces in Newton’s (N), powers in kilowatts (kW) and speeds in knots. 

Please see our catamarans for sale by owner page if you are looking for great deals on affordable catamarans sold directly by their owners.

Length, Draft and Beam

There are two major dimensions of a boat hull: The length of the hull L H  and length of waterline L WL  . The following consist of arbitrary values to illustrate a calculated example. 

L H  = 12.20      L WL  = 12.00

After deciding how big a boat we want we next enter the length/beam ratio of each hull, L BR . Heavy boats have low value and light racers high value. L BR  below “8” leads to increased wave making and this should be avoided. Lower values increase loading capacity. Normal L BR  for a cruiser is somewhere between 9 and 12. L BR  has a definitive effect on boat displacement estimate.  

• Tags Buying Advice , Catamaran Designers

Owner of a Catalac 8M and Catamaransite webmaster.

10 replies on “Catamaran Design Formulas”

Im working though these formuals to help in the conversion of a cat from diesel to electric. Range, Speed, effect of extra weight on the boat….. Im having a bit of trouble with the B_TR. First off what is it? You don’t call it out as to what it is anywhere that i could find. Second its listed as B TR = B WL / T c but then directly after that you have T c = B WL / B TR. these two equasion are circular….

Yes, I noted the same thing. I guess that TR means resistance.

I am new here and very intetested to continue the discussion! I believe that TR had to be looked at as in Btr (small letter = underscore). B = beam, t= draft and r (I believe) = ratio! As in Lbr, here it is Btr = Beam to draft ratio! This goes along with the further elaboration on the subject! Let me know if I am wrong! Regards PETER

I posted the author’s contact info. You have to contact him as he’s not going to answer here. – Rick

Thank you these formulas as I am planning a catamaran hull/ house boat. The planned length will be about thirty six ft. In length. This will help me in this new venture.

You have to ask the author. His link was above. https://www.facebook.com/terho.halme

I understood everything, accept nothing makes sense from Cm=Am/Tc*Bwl. Almost all equations from here on after is basically the answer to the dividend being divided into itself, which gives a constant answer of “1”. What am I missing? I contacted the original author on Facebook, but due to Facebook regulations, he’s bound never to receive it.

Hi Brian, B WL is the maximum hull breadth at the waterline and Tc is the maximum draft.

The equation B TW = B WL/Tc can be rearranged by multiplying both sides of the equation by Tc:

B TW * Tc = Tc * B WL / Tc

On the right hand side the Tc on the top is divided by the Tc on the bottom so the equal 1 and can both be crossed out.

Then divide both sides by B TW:

Cross out that B TW when it is on the top and the bottom and you get the new equation:

Tc = B WL/ B TW

Thank you all for this very useful article

Parfait j aimerais participer à une formation en ligne (perfect I would like to participate in an online training)

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What Is A Catamaran Sailboat? (And What It Looks Like)

Last Updated by

Daniel Wade

August 30, 2022

Catamarans are increasingly popular for sailing and commercial use, but what sets them apart from monohulls and other multihulls?

A catamaran is a twin-hull boat with two equally-sized hulls placed side by side. They’re powered by engines, sails, or both—and they’re known for efficiency and speed. Catamarans are the most common kind of multihull boat.

In this article, we’ll go over the characteristics of catamarans and how to differentiate them from other types of boats. Additionally, we’ll cover the advantages and disadvantages of catamarans and compare them to trimarans and monohulls. We’ll also go over the most common types of catamarans and their uses.

We sourced the information in this article from marine design guides, boat identification resources, and the online boating community.

Table of contents

‍ How to Spot a Catamaran

Spotting a catamaran is easy. Simply look at the hulls and count them. Catamarans have two hulls side by side and a relatively large gap between them where you can see light on the other end. Catamarans are distinct from trimarans, which have an additional hull between the two outer hulls.

How do Catamarans Work?

The principle behind the catamaran is simple. You can think of catamarans like cars and monohulls like motorcycles. Catamarans distribute their weight between hulls on either side, whereas monohulls utilize only one hull.

Evidently, cars are much more difficult to tip over and can hold much more weight. Additionally, cars are wider, as they have much more contact with the road. Catamarans work in a similar way, as they have a wide stance and contact with the surface on both sides.

Obviously, that isn’t the most precise comparison. But the basic principle is the same, and catamarans have a few notable benefits over monohulls.

Catamaran Vs Monohull

Catamarans are easy to distinguish from monohulls. A monohull is just a regular old boat with a single hull. The vast majority of boats and ships are monohulls. Catamarans have two hulls, which are usually sleek and narrow.

Here are some comparisons of catamarans and monohulls, along with the advantages twin-hull designs have over most single hull types.

Benefits of Catamarans

Catamarans have numerous benefits. The first is speed. Catamarans produce less drag than monohulls and thus can achieve excessive speeds both under sail and power. They don’t need to plane like monohulls to achieve these high speeds, and they use less fuel.

Catamarans are also much more stable than monohulls. They have a wide stance and shallow draft, and many waves and swells can travel between the hulls instead of below them. This effectively reduces an entire axis of movement and prevents catamarans from rolling excessively.

Drawbacks of Catamarans

Catamarans aren’t advantageous in every way, or else we wouldn’t bother building monohulls. The disadvantages of catamarans limit their use to niche commercial applications and high-end yachts. But what are the drawbacks of a twin-hull design?

Sailing catamarans don’t follow many of the traditional boat handling rules and characteristics that sailors pass down for generations. Some, such as hull speed limitations, are good to do away with—while others, such as responsiveness, are not.

Catamarans aren’t as quick to the helm or responsive as monohulls. There are some exceptions to this rule, but for the most part, you’ll get a lot more feedback from a single-hull vessel. Additionally, the large section of deck between the hulls of a catamaran is prone to pounding in rough seas, which is loud and uncomfortable.

Catamarans can sometimes be twice the width of an equivalent monohull sailboat, which can increase mooring fees and limit docking options.

The final major drawback of catamarans is a consequence of their stability. Traditional full-keel monohull sailboats have a very low center of gravity, which makes them roll in heavy seas but ensures a recovery.

Catamarans have a higher center of gravity, and they can’t right themselves after a knockdown. And though catamarans are less likely to roll, a severe list on a multihull is a much more serious concern than on a ballasted monohull.

Catamaran Vs Trimaran

Catamarans and trimarans are often lumped together, but they have very different design and performance specifications. Trimarans have three hulls, whereas catamarans have two.

Trimarans look a lot like catamarans from the side, but a quick glance at the bow or stern can set them apart. Trimarans are faster than catamarans, as they distribute their weight across three hulls instead of two. This helps them stay centered and reduces interference from pitching and rolling.

Catamarans are fast, but they lose out to trimarans when going head to head. However, catamarans are much less expensive to build and maintain and often have roomier cabins due to their larger hulls.

Types of Catamarans

There are numerous types of catamarans, and their uses vary widely. The catamaran is one of the oldest and most useful hull types, and some variants have been used for thousands of years. Here are the most common kinds of catamaran boats and their uses.

Sailing Catamaran

Sailing catamarans are probably what you think of when you hear the name. Sailing catamarans are sailboats with two identical hulls connected by a center deck. The largest sailing catamarans are spacious and stable vessels that are capable of serious offshore sailing.

Sailing catamarans have a number of notable advantages over monohulls. Monohulls, which are traditional sailboats with a single hull, are limited by a simple concept called hull speed. As the bow and stern wave of a monohull intersect, they cause drag which limits the top speed of the boat.

Catamarans are not bound by hull speed limitations, as they have two hulls. Catamarans can go twice or even three times as fast as similar monohulls and achieve excellent travel times.

Catamarans are also more stable than monohulls, as their wide stance and shallow draft reduce the effect of rough water. They don’t heel, as the force of the wind is counteracted by the double hulls. Additionally, modern sailing catamarans can ‘wave pierce’ by cutting through swells instead of riding over them.

Sailing catamarans come in many shapes and sizes. Small sailing catamarans, such as those used in races and regattas, are known for their speed and relative stability compared to light racing monohulls. Sometimes, they feature a smaller second hull for stability—these are called outriggers.

Sailing catamarans have spacious interiors thanks to the large cockpit between the hulls. This cockpit usually contains cooking and eating spaces, a place to sit, and a hallway between the hulls. The hulls usually contain living quarters and often mirror each other.

Power Catamarans

Power catamarans have an even greater variety than sailing catamarans. These vessels are used for everything from party platforms to ferries and patrol boats.

Power catamarans are a recent development, as engineers and marine architects now realize they have numerous hydrodynamic advantages over other hull types.

Catamarans are much more efficient than other hull types, as they have less drag relative to their size. Additionally, you can build a much larger catamaran with less material. This makes them popular for car and rail ferries, as builders can construct a very wide vessel with two small hulls rather than a narrower vessel with a large single hull.

Military and Commercial Catamarans

Even the military has found a use for the catamaran hull shape. The Spearhead class EPF is an expeditionary fast transport vessel designed for carrying capacity and speed. It has two sharp hulls and a huge cargo capacity.

The Spearhead class EPF is 337 feet long, which is about the same length as a WW2 escort destroyer. Yet despite having a similar length and displacement, these catamarans can travel more than twice as fast—43 knots, or nearly 50 miles per hour. Their great speed is a direct consequence of their catamaran hull type.

Power catamarans are also used as patrol and utility boats on a much smaller scale, with either outboard or inboard motors. The State of Texas uses catamarans to patrol shallow rivers and lakes. Texas Game Wardens utilize state-of-the-art aluminum catamaran patrol boats, which are fast enough to outrun most fishing boats.

There’s another form of power catamaran that you may not have considered. Pontoon boats are technically catamarans, and they’re enormously popular on lakes and rivers throughout the country. Pontoon boats aren’t known for speed, but they’re a great platform for a fun and comfortable outing.

Catamaran Houseboats

The final common type of power catamaran is the two-hulled houseboat. Houseboats don’t always use the catamaran hull type, but it’s common enough that most major manufacturers offer it as an option.

Catamaran houseboats have a few notable advantages over monohull designs. For one, they’re easier to build—especially when pontoons are chosen. Additionally, they’re better suited for navigating shallow water. These vessels can support more weight across their two hulls, offer increased stability, and they’re also efficient.

Why Aren’t Catamarans More Common?

With all the advantages listed in this article to consider, it may seem strange that the use of catamarans is still somewhat limited. At the end of the day, it comes down to economics—as monohull boats and ships are simply cheaper to build.

Additionally, catamarans have some distinct limitations. Monohulls have lots of storage space in their hulls and can carry thousands of tons of cargo safely in all weather conditions. Catamarans lack this space and low center of gravity, so they’re not ideal for transporting cargo past a certain point.

Additionally, monohulls work, and many people are reluctant to experiment with new designs when old designs work just fine. This rule applies to both large and small boats.

A large monohull sailboat can be constructed at low cost from stock plans and reliably sail almost anywhere. Very little complex structural engineering is involved, and looser tolerances reduce cost and maintenance requirements.

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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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