By Jack Hornor
Revised by BoatUS editors in October 2012
With each passing boat show season, it seems as though the number and size of multihulls on display increases. So, it seems appropriate we take a look at a catamaran that&s growing in popularity.
The Catana 431 was designed by Christophe Barreau and is built by Catana S.A. of Cedex, France. It was introduced in 1998 and is currently marketed as the Catana 43 Ocean Class. The model has been popular in Europe and the Caribbean since its introduction but more are coming into the U.S. each year. Her accommodations quite clearly put her in a class of cruising catamarans but her design and construction would suggest her designers are more focused on performance than some catamarans in this genre.
The first thing likely to strike most people about this design is her considerable, six-foot freeboard to the deck edge and more than 10 feet to the top of the cabin. To my eye, the result is a rather ungainly looking vessel, but owners are likely to quickly appreciate the look when some of the design considerations are considered.
First, there is well over 6 feet of headroom everywhere throughout the boat and no banging your head each time you step down into the cabin. Second, and more important, is that the bridgedeck clearance off the water is more than two and a half feet. To avoid excessive pounding in a seaway, and that annoying slapping of waves against the bottom of the bridgedeck at anchor, the bridgedeck clearance of a well designed cruising catamaran should be greater than 5.5% of the waterline length. A higher percentage is generally better and the clearance of the Catana 431 is a very satisfactory 6.25%.
Photo by Ensign Ship Brokers
Unlike monohull sailboats, most catamarans are not ballasted and rely, to a larger degree, on beam for stability. A number of factors including overall length, hull shape and volume will determine a designer&s beam to length ratio, but a good target, for boats under 50 feet long, is 50%. Lighter boats, with less volume, tend to have slightly higher ratios and heavier boats lower ratios. The Catana 431 is relatively light, with narrower hulls, and has a good beam to length ratio of 56%.
Catana uses daggerboards rather than the fixed keels which have several advantages. In severe weather, daggerboards can be raised so boat will slide down large waves rather than &trip& over a fixed keel and are considered less likely to be overturned by waves. Daggerboard designs tend to be more weatherly and boards can be raised to reduce drag and resistance when not needed. On the negative side, they are more vulnerable to damage, more costly to construct, and leave underwater running gear and rudders more exposed to damage.
The Catana 431 is built entirely of vacuum-bagged sandwich construction with PVC foam core; Twaron (Kevlar) fabric and vinylester resin. There are 21 full or partial structural bulkheads in each hull & also foam cored & and reinforced with carbon fiber for very light, strong and rigid hulls. For safety there are watertight bulkheads aft of the forepeak and forward of the engine room and the vessel will remain afloat even if totally filled with water, according to the manufacturer.
There are four large (48& X 16&) opening hatches in the outboard hull sides which provide great visibility and ventilation but on two models I have seen in the last several months, several of the hatches did not seal securely and the hinges suffered from salt corrosion. Another caution is that these boats are designed and built in Europe where electrical systems, particularly AC electrical systems, are quite different. Wire sizes and systems may not be suited to U.S. hookups.
One of the major attractions of catamarans is the impressive accommodations they offer when compared to monohull models of the same length. The Catana 431 offered two arrangement plans, one which dedicates the entire starboard hull to an owner's suite with king-sized berth aft and a very large head and shower forward separated by storage lockers, washer/dryer and a small desk. The port hull has double cabins forward and aft with head and shower in the middle. The alternative layout offers a two-cabin starboard layout identical to the port. The main saloon, at the bridgedeck level, has a large U-shaped dinette, navigation station and galley with 360 degrees visibility and can be opened to the cockpit for additional seating.
Auxiliary power is provided by two 40-hp Volvo marine diesels and saildrives with three-blade folding props as standard equipment. The engine rooms, aft in each hull, are accessed through large deck hatches. There is plenty of room in each for easy access to all machinery.
Catamarans are considerably more expensive than similar size and quality monohull models. Their higher price becomes more understandable when comparing accommodations rather than overall length.
Naval architect Jack Hornor was the principal surveyor and designer for Marine Survey & Design, Co., based in Annapolis, MD. He was on the boards of the American Boat and Yacht Council, the National Association of Marine Surveyors, and the Society of Boat and Yacht Designers. He and his wife sailed their Catalina 42, Legacy, based on Maryland's Eastern Shore.