Longer is Better
Catamarans sail best when the hulls are very narrow for a given length. The slender hulls create less wave making resistance at higher speeds allowing better acceleration through the 10 to 12 knot "resistance hump" that many fuller bodied cats experience. Also a significant gain in seakeeping, comfort in waves, is experienced due to the narrow area of water plane. In simpler terms, slender hulls more easily slice through waves and do it with less pitching and rolling.
The disadvantage to narrow hulls is that the volume below decks is reduced and this generally makes it impractical to design a cruising cat less than 60' in length with hulls as fine as desired. However, if the length of the boat is allowed to stretch out to 60' or more while at the same time keeping the overall weight of the vessel down to the lower end of cruising displacement spectrum an extremely efficient hull form results that, due to its sheer size, has plenty of internal volume to provide excellent accommodations.
The Case for Limiting Size
The size of a boat is a product of many dimensions, length, width, height, surface area, and weight. While increasing the length of the hulls is very desirable it is not always as beneficial to increase all other dimensions. While longer is better, bigger boats cost significantly more to construct and require a great deal more effort to sail. The typical 60+' catamaran is often a VERY large boat. With overall beam of 30' or more, a loaded displacement of 50,000 lbs. and a mainsail of 1,000+ sq/ft which weighs upwards of 300 lbs. Cats of this magnitude are usually too large to be handled without experienced full time help. And the sheer size and weight of sails necessitates electric or hydraulic powered winches for halyards and sheets; adding further to the weight, complexity and cost of the vessel. Also, the mast height of a sloop rigged cat is well over 65' which prohibits access to much of the Intracoastal waterway and other harbors that could provide shelter in a blow.
Therefore, in the design of the Concept 63, the primary goal was to incorporate the benefits of long slender hulls without making the vessel so large and unwieldy that it no longer can be handled safely by a cruising couple or family.
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Sailplan
A modern ketch rig with fully battened main and mizzen and roller furling jib is appropriate for this design. A ketch splits the sails to more easily managed size and keeps the center of effort low which is more in keeping with the design concept of moderate overall beam. It also offers substantial advantages for offshore sailing; a reefed mizzen makes a great riding sail while waiting out a gale either hove to or hanging on a parachute anchor. Ketch rigged boats are also extremely fast. While they typically give up a slight bit (approximately 3%) of windward ability in light air compared to sloops this is usually of little concern in a cruising context because usually once boat speed drops to 6 knots or less the engines are started.
Masthead height is under 65' from LWL. As previously mentioned, this offers increased flexibility in cruising the East and Gulf coast since the Intracoastal Waterway is always an option in foul weather as well as other harbors that are obstructed by highway bridges or power lines. To take full advantage of the super shoal draft possible in a cruising cat it is also necessary to keep the overhead clearance below 65'.
Spinnaker and mizzen staysail can be flown in light winds for incredible off wind speed. Using both of these sails should enable reaching speeds nearly 1.5 times wind speed in light wind conditions. There is nothing as fast a ketch on a reach. Just look at the favored big boat rig among the round the world racers of the Whitbread Race, they are nearly all ketches.
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