If one of the hulls on the catamaran had a keel and the other didnt it would be very hard to control.

Does a catamaran have a keel. Daggerboard catamarans have several advantages over their keel counterparts some of which are well known and others that are more subtle and sometimes only recognized by people who have used them. A sailboat needs a keel to avoid capsizing when the sails fill with wind. Catamarans can be designed as sailboats or motorboats.

For some catamaran buyers this is a big thing for others not so much. Upwind catamarans do not usually have the same ability to point into the wind as they have shorter stubbier keels and do not travel as quickly. On daggerboarded cats the rudder tip usually represents her deepest draft.

Active safety aspects are advantages created by speed and the ability to retract underwater appendages. Especially as it would need two. A catamaran stays stable since it has a wide base it does not have a deep keel as on a monohull.

In the case of these boats it comes back to daggerboards. Catana 39 Underbody No keel but daggerboards. You could essentially say that a catamaran with keels is a bit like a long-keel monohull and the daggerboard catamaran is a fin keel monohull in more terms.

A catamaran does not get the same benefit from having a keel. A keel also makes it possible to steer without sliding to the side especially when going upwind. Hull does not require the deep-running keel of a standard monohull sailboat.

If you are looking for a rule of thumb the shallower the keel the more area it needs to compensate for the reduced effectiveness So if the designer cant go down he must go long. Less hull drag in the water than a monohull. Furthermore I am one of the few designers who has fitted LAR keels and boards to the same hull on Strider Sagitta and Banshee and then sailed them against each other.