Catamaran vs Monohull

If you are thinking of building or buying a yacht, you have a significant choice to make, before you even start looking at individual boats. Do you want one hull or two?

Deciding between a catamaran and a monohull is a big decision and one worth considering well, before taking the plunge. Having sailed on both, and built then lived for 5 years on a catamaran, in this post I want to share with you, my impressions and thoughts on safety, costs, speed, stability and other advantages and disadvantages, of sailing and living aboard a catamaran compared to a keel yacht.

Discussing the pros and cons of cats vs keel yachts can be a dangerous thing to do. The topic is like talking religion, and many people stand by and defend their beliefs vigorously! So, I will tread lightly. I’m not trying to preach or convert anyone to multihulls, but I do have a bias, having spent a lot of time on a multihull.


I am no stranger to keel yachts. I crewed on many as I grew up, racing around the sticks in bay races, and offshore. And dreamed of building one for a long time, buying study plans then full plans, ready to build one myself. I’ve many friends who own monohulls, and I’ve also had some great times cruising, and short term living aboard too. 

Advantages of one hull

• Windward performance – keel yachts go to wind, in general much better than most cats, with their large keels (although not all yachts have a great keel). They point high, even at slow speed. You can feel it, before you leave the marina, how well they pivot around it maneuvering in and out of the pen. It anchors them in the water.

• Less room required in a marina – which means lower charges, and it’s simpler to find a park. Some marinas don’t have space for a full-width cat, and in Europe, most yachts berth stern-to (with the anchor or a ground line holding the bow out, and the stern (back of the yacht) tied to the dock.

• More straightforward to build – there is considerably less surface area to sand and not as much material in a monohull of the same length. While building my cat, I felt like I was making two boats (in effect I was).

• Less expensive – keel yachts are cheaper than a similar size cat. There is also a much bigger market for yachts and more competition, with a lot more scope and options to choose from. You can discover some excellent value for money in both the new and even more so in the second-hand market if you shop around.

• Smaller shed needed – with a narrow hull, makes it easier to find a place to build. Even in a suburban backyard.


• Strength (depending on the construction) – the shell of a keel yacht is similar in shape to an eggshell and has a much smaller deck area than the same size cat. So they are an inherently stronger form if they took a freak wave dumping on them for example.

It was something I often pondered, with my cat on the open ocean. Its expansive deck area and large flat aft cabin bulkhead didn’t seem that strong if a tonne of water dumped itself on me. I beefed up the deck and aft cabin bulkhead in my boat considerably, beyond what the plans called for, but the shape of a keel yacht gives it greater “survivability” on the ocean purely because of its form.

With keel yachts, building from steel is an option as these boats are anyway heavy, with the ballast they carry. So the extra weight, making the hull from steel instead of fibreglass, compared to the overall weight of the boat is not as significant a penalty as it would be for a cat. This is an often chosen material for home-built boats and makes for a sturdy, durable hull.

• Easier to haul – for road transport, being narrower they take up much less of the road. A large cat takes up both lanes. This, along with the need for a smaller shed means you could make a keel yacht in many more locations than a cat.

• Only one motor – to buy and maintain. Usually a larger one, but you just need one, reducing the expense and complexity. If you want to use a diesel motor, there is more space available for an engine in a monohull than in the cat’s slender, shallow hulls, making it more accessible and easier to work on.

• Self-righting – if they capsize they will right themselves, (as long as they don’t fill up with water). This is perhaps the main reason keel yacht owners have for not owning a cat.

• More plans available – if you are building, there are a lot more keel yacht plans to choose from, and more designers, who are often longer established than multihull designers.

• More efficient to heat (or cool) – maybe not so important, as most boats aren’t air-conditioned. Yachties usually follow the sun, but if you operate in harsh climates and need this capability, it is more economical to heat or cool a yacht being a smaller volume, and with less surface area for the same size inside.


Below is a list of some of the reasons a cat made sense for me. I try to write this from as neutral a perspective as possible, but I am biased so you can take that into account as you read this… I built a 40ft cat back in the 90’s and lived on her for 5 years. In my book Building Tokyo Express I talk in detail about the building of her and the comparison with building a monohull. 

Biased or not, below is one more opinion (mine), that you can throw into the mix to consider, to help you draw your own conclusions on what makes sense for you.

Advantages of two hulls

• Speed – possibly the biggest reason for many individuals, myself included, for wanting a multihull is the ability to go fast. The speed ability of a multi impressed me, not being a prisoner to my hull speed. It doesn’t matter what you say, “I’m just cruising,” “I have plenty of time,” “I’m not in a hurry,” nothing puts a smile on your face, (or brings on depression) like speed (or the lack of it) on the water. The ability to move even a few knots faster especially when cruising can shave hours off your day in the time taken to reach your destination. Or shave days or weeks off a more extended voyage.

Not only that, it’s FUN when you are moving fast! Something you need to experience to appreciate. When the boat begins to surf leaving rooster tails behind, and the ride suddenly becomes soft, like you are riding on a cushion of air, it’s magic. The atmosphere changes, from “when are we going to get there?” to “I don’t want this ride to end”. It is exhilarating when you really get moving…

• Stability – a cat, despite all the negative talk about the risk of capsizing, is enormously stable. This makes such a difference to life on board when you’re underway. It is a huge point, and my experience confirmed everything I had read about it. 

Even in substantial breaking seas and strong winds, I didn’t feel as if I would be turned over, and I wasn’t. But this is the extreme case. In normal operations, which is most of your time on the water, it’s just comfortable when you are sailing.

I didn’t have to walk around on a 30-degree angle holding on to everything, to stop from falling over. I could leave my coffee cup on the table in the roughest of weather, and it never moved or spilled. My dining table sat on the floor unattached, just like in your house and didn’t move. Nor did it need fiddles (the raised edging around the table’s edge).

After speed, this is the greatest thing about a multihull compared to a keel yacht. And it’s not just at sea either, stability at anchor, I would say, is just as important especially when you are living on your boat. See the section below.

• Space – cats have much more room inside and on deck, than a similar length keel yacht. The large bridge deck, the two hulls, expansive deck area and a large cockpit, all create a much bigger living space than the same length keel yacht.

• Seasickness – the movement of a cat is much less sickness inducing than the rolling of a keel yacht. Also, if you are not feeling good and you need to go below decks, cats are not so claustrophobic. Going below decks in a yacht and losing sight of the horizon, can often be enough to send you over the edge.

• Floatation – the ability to float if you damage the hull, or capsize. The materials that make up the hull, floors and bulkheads in a multihull are usually made from materials less dense than water. If you don’t add too much extra weight in the form of engines and auxiliary equipment, and with some designed in void spaces, it’s unlikely she will be going to the bottom if you put a hole in her or turn her over. A keel yacht, however, has tonnes of ballast ready to pull it there if she gets holed or capsizes. Note – if you weld up an aluminium cat, you are then more like a keel yacht, albeit without the ballast.

• Shallow draft – allowed me to cross bars and enter rivers and go places no keel yacht can go. This is a big issue on the Queensland coast where I did a lot of my sailing. My home port on the river in Noosa Heads, for example, is inaccessible to most all keel yachts. There is a shallow ever-changing sandbar with surf that even I could only cross on the high tide. My rudders were my deepest part, but they can be made “kick up” as well if you are serious about getting up creeks, or beaching your boat.

Straight tracking

• The ability to track fast and straight – when entering rivers with bars in big seas. This ability saved my butt more than once, surfing before large waves at 20+ knots. I have vivid memories of crossing the Wide Bay bar on the southern end of Fraser Island with a large crew aboard. One mile offshore, in only two metres deep water, with 30-knot winds, and a wall of breaking water approaching from behind.

It picked my stern up, and I was sure we were about to be pitch-poled and turned over end for end. But we surfed this massive wave at over 20 knots, for quite a distance keeping in front of its froth, until we were back in deeper water and it flattened out. Having two rudders, and two long slender hulls, helps cats track like they are on rails. That, along with the speed ability to surf saved the day.

• Cats don’t roll at anchor – this might sound insignificant if you have never spent time on a yacht before, but if you live aboard, this point is enormous. Recently I spent a week cruising aboard a friend’s modern 13-meter Dufour keel yacht, sailing around the Balearic Islands. Beautiful boat with a lovely big interior and we had great weather for sailing, but after that week of rolling, I was happy to arrive in a marina where it stopped moving.

This reason alone puts me off living on a keel yacht. Rolling uncontrollably at anchor with the slightest of waves or every time another vessel passes by, was enough to want to get off. Despite the stove being on gimbals, dinner almost ended up on the floor on two occasions, just from the wake of passing boats. The rolling was excessive. A heavier cruising yacht would roll less or have a slower roll, but they still roll.

And size doesn’t make life much better. On the larger superyachts and even on cargo ships, rolling at anchor can be enough to make you want to get off. With two hulls, you don’t roll, period. A cat “jiggles” then stops pretty quickly after the passing craft has gone by. Or it will keep moving about continuously if there is wave action, but it doesn’t roll. You never have to fear spilling your drink, and you don’t need a stove on gimbals.

• Lightweight – cats are light. There is no comparison between the two as the cat doesn’t carry around ballast to keep itself upright. Because of its low weight and long slender hulls, cats have the speed potential as mentioned above, that is far beyond a similar size and style of keel yacht. This also means you are not usually heading for Davy Jones’ locker (the seabed) if you capsize or hole the hull.

The disadvantage of being light is that the movement of the boat, especially in pitching can be sharp and rough with fast accelerations. It’s a movement comparable to riding on a fast train although it can get much worse in the wrong conditions. It’s not rolling, but it can get very uncomfortable. My cat pitched rather violently when going to wind, and the pitch frequency of the waves matched the boat. It didn’t happen all that often but it’s not always smooth sailing.

In summary

As you can probably tell, I’m sold on two hulls. When I build again, it will be a cat, there is no decision to be made. But that’s me.

What about you? If you have been looking around for a while, and you are still not sure, and if you don’t have friends with a multihull to get some first-hand experience, then maybe chartering one for a week or two is an excellent way to know what they are like. Get some friends together and charter a catamaran, and experience for yourself, how they compare. 

Actually, the more I thought about weight, the idea of spending large amounts of money to build a yacht with the lightest materials you can afford, then pouring tonnes of the heaviest metal you can buy into its keel just to keep it upright, doesn’t add up. But that’s another story…

The argument that is so often thrown up against multihulls by keel yacht owners is that if you turn one over you are in trouble, and they are right, you are in trouble, you need help to get a big cat or trimaran up again. But, when did you last hear about a cruising cat capsizing at sea?

Considering the amount of multihull craft on the water these days, capsize is still something I’ve only read about in books. I can’t recall ever hearing in the news about one being turned over, and there are plenty of multis in Australian waters.

I think cats and tris have proven themselves that they are seaworthy craft. For me, that argument doesn’t hold water, and my experience on the ocean has convinced me of their ability and stability. If you want to learn more, about what’s involved in building one, have a read of my book.

I hope this was of help and gives you something more to think about. 

Tim Weston