If you go into a sailor’s bar anywhere in the world you can start a fight by insisting that “My anchor is the best!”, or “Anybody who would sail with a spade rudder across an ocean is an idiot!”
Go into that same bar and try to tell people that the ONLY kind of sailboat that ANYBODY should have is a monohull (or a catamaran) and you don’t start a fight, you start a riot. People all have very strong opinions on this topic, and it seems they arrive at their choice of preferred boat using the same level of logic that people apply when they decide that they are Catholic or Jewish or Muslim.
If you ask someone if you should by a monohull or a catamaran and they give you an answer without spending at least 30 minutes asking you questions about what you want that boat to do for you, then you can ignore everything they say. They are telling you what they think the right boat is for THEM not for YOU.
The problem is there are so many different kinds of catamarans that it is really hard to generalize about them, and that goes double (at least!) for monohulls. So I am going to restrict my comments to a very specific subset of both boats, those ones suitable for long-term cruising and ocean crossing.
The Final Frontier
Space: where a cat wins–hands down. There is more space and it is more comfortable. For a family with children a cat is ideal. For a couple sailing alone, it seems a waste because so much of the space is just extra cabins. For most catamarans, living space is grand, but storage space will be limited.
Weight–The 800lb Gorilla
There are many, many catamarans out there that are awesome sailing boats. Very, very few of them are suitable for the average long range cruiser. The big reason? To be a great sailing boat catamarans need to be built light, and stay light. Moving on to a high performance catamaran with more than a ton of gear and supplies is just going to turn it into a slug. A typical cruising catamaran like a Leopard, or a Lagoon, starts out as a slug and gets worse.
To keep catamarans light, they must be built with cored hulls: thin fiberglass skins over a lightweight foam or balsa wood core. That kind of hull construction is strong, stiff and light, but it is NOT tough. Impact at sailing speeds with a hard, sharp object can puncture this kind of hull. Now, there are plenty of monohulls that use the same construction, but I don’t think they are suitable for ocean crossing either…
A monohull can be built with a solid fiberglass hull. It is heavy. It takes special design considerations to make it stiff enough for a long lasting hull. But it WILL bounce off many things that will hole a cored hull.
All catamarans that I know of use spade rudders: rotating shafts with no external support. Again, lots of monohulls are the same, and again, I don’t think that is a safe way to cross an ocean. When you are 2000 miles from help, you do not want to worry about hitting something with the rudder that can destroy the yacht’s ability to steer, or worse, hole the hull.
So you want to sail upwind?
Now, again, I am talking about a mass-market cruising catamaran here… they do not go upwind well. Trying to get them sailing with a course over ground (NOT apparent wind angle!) much closer than 60 degrees to the wind is very hard. Almost any cruising monohull can beat that by 5 to 10 degrees.
When I had sailing students ask about catamarans, I would give them the following explanation of my views:
If you are buying a cruising catamaran with the expectation that you are buying a boat that is basically a motorsailor, you will likely be happy with your boat. If you are buying a cruising catamaran with the expectation you are buying a full-on performance sailboat, you will be likely be disappointed.
That continues to be my thinking. There is nothing WRONG with a motorsailor, if that is what you want and it meets your expectations.