John Shuttleworh Yacht Design.

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New 31ft Wood Epoxy or Foam Sandwich Cruising Cat.

This 31ft catamaran is part of a range of fast cruisers which developed from the highly successful Spectrum 42. Designed and engineered with the latest thinking on structures and computer designed hull forms, the boat is nevertheless suited for skilled amateur construction. The first boat is currently under construction in Brazil by Multimar, built from PVC Foam Sandwich with E glass and polyester resin, although the design lends itself equally well to wood epoxy construction.

The Shuttle 31 is the 10th design in a line of development that started with the Spectrum 42, which itself represented a major advance in cruising catamaran design. Next came the 40ft Capcat which took line honours in the 1987 Atlantic Rally for Cruisers*, followed by the 35ft cruiser racer 'Two Hoots', winner of the prestigious Scottish 3 peaks race in 1989, then the Tektron 50, Tektron 35, the Advantage 43 and 44, which won the Atlantic Rally for Cruisers in 1988, the Shuttleworth Supercruiser 63, and my own Shuttle 40. The Clyde Cats Cheetah, and Private Dancer, an Arrow cruiser racer micromultihull which won the Round Isle of Man race in 1991, and has a string of racing successes behind her.

The Spectrum 42,s, Capcat 40's, Advantage 43's, Tektron 35, Tektron 50, and 63's, and 70, now have many ocean passages behind them, including 4 around the world voyages, and the features of exceptional pitch damping and bow slightly raised on a reach have been well tried and tested, and have proven to be outstanding features in improving general cruising comfort at sea, along with greater safety and fine seakeeping qualities. ( Ref 1 ) (Ref 2) In fact the first Shuttle 31 will be the twenty sixth catamaran of mine the be launched with flared topsides, and a further 13 are under construction at the time of writing. This flare is now a benchmark of all my cruising designs, and is incorporated in designs ranging from 26 to 70 ft. At the time of writing one Shuttle 31 had completed an around the world voyage, and two others have sailed the north Atlantic from France to the Caribbean and back.(Refs 3, 4, 5, 6.)

One of the main aims of this new design was to produce a boat of outstanding comfort and living accommodation space, with as little sacrifice as possible to the excellent sailing performance, windward ability, and seakeeping qualities of this well proven type of hull form.

Apart from the great benefits that can be derived from flaring the hull above the waterline, in terms of keeping the bow up on a reach, the flare gives a massive increase in interior volume without increasing the windage of the hulls at all. For instance, above the waterline the hull flares outwards to give a maximum beam at eye level of 1.95m (6'4"), the impression of space is tremendous and cannot possibly be matched by any similar length catamaran whose topsides rise almost parallel from the waterline.

Construction and long term fatigue.

By using integrated structural techniques the hull weight can be carefully controlled and the net effect is a strong, light displacement hull with a high long term fatigue life. Integrated Structure is a computer aided design method which I originally developed for the highly stressed ocean racers of the North Atlantic circuit . The structure of the boat is designed in a similar way to a sail where highly loaded areas like reef points and clew are patched out into the lighter body of the sail, the layers of cloth increasing from the lighter body of the sail out towards the clew or reef cringle. (ref 7). On a wood epoxy design this is achieved by laying unidirectional fibres along the line of greatest stress in highly loaded areas, and spreading the fibres into the body of the hull or deck until the stress is distributed over a large enough area to ensure that structural failure of the boat itself is virtually impossible. Fibre quantities are carefully calculated to avoid any stress build up in the structure at vulnerable points, thereby increasing the fatigue life of the boat dramatically.

Windward Performance.

In the past it was not unusual to find a bridgedeck saloon type Cruising Catamaran which would tack through 100 degrees or more. This poor pointing ability is caused by the combined effect of heavy displacement, inefficient under water foils, small sail area, and poor attention being paid to windage and the streamlining of hull shapes in the air. ( Ref 8.)

By keeping the boat light (through Integrated Structure), by using efficiently shaped daggerboards and rudders, and by minimising the aerodynamic drag - i.e. designing the bridgedeck and hulls to be as streamlined as possible, the Shuttle 31 will have excellent windward performance. Bearing in mind that a sailing boat must be streamlined with the air flowing across the deck at 30o to the bow, because that is the direction the that the wind actually flows across the boat when she is sailing to windward. All the other existing designs in the range have already proven themselves to be outstanding windward boats, tacking through 80 degrees at maximum Vmg, and outsailing all but the stripped out racing multihull machines, on all points of sail.

A wing mast has been chosen as the standard rig (although other options are available.) A wing provides a very efficient and simple rig, which can be home built. Gougeon brothers provide plans for Wood Epoxy masts and I can provide plans for carbon wing masts. The high aspect jib is self tacking, which means no winching or flogging lines when coming about. Fantastic for cruising! The mast size is designed so that the mast itself becomes the storm sail.

A single outboard is mounted in the centre of the cockpit. A Yamaha or Honda 9.9 HP outboard will push this boat at 8 knots. The outboard box lowers and the outboard kicks down when in use, and when retracted there are no propellers in the water to cause unwanted drag, and no holes through the hull. In the cockpit the box doubles as a table. It is possible to install 2 outboards, one each side of the cockpit if more control at very slow speeds is required.

Accommodation

The Accommodation is straightforward and spacious, with the saloon aft in the port hull. 2m (6'7") long and 2.3m (7'6") wide at eye level. The flare in the hull makes this a very spacious and comfortable social area. Ford of the saloon is the 1.9m (6') long galley with ample space for storage and food preparation. The single daggerboard, with our special kick up system, is unobtrusively canted towards the hull side at the ford end of the galley. In the bow is a forward stateroom with a large double bunk. 2m ( '7") x 1.35m (4'6"). Ford of the berth in each hull is and anchor locker or sail stowage.

The starboard hull aft has a very big double berth 2m (6'7") x 1.6m (5'4"), with good locker space and standing area for dressing. Next is a fair sized chart table, and oilskin locker with a separate W.C. / shower area. The forward area is the same as the port hull.

On deck, all controls lead to the 3.2m (10'6") x 3.6m (11'9") cockpit, and with the mast standing on the main structural beam at the forward end , there should be few reasons to leave this safe area. Reefing is carried out while standing by the mast, and sail controls lead to near the helmsman, making this boat very easy to single hand. Spray dodgers over the entrance hatches protect the helmsman from spray, a system that has proven to work well on a number of boats. A tiller extension connected to the centre of the tiller bar, gives the helmsman considerable choice of where to sit. Visibility of the sails and forward is very good, which will increase the enjoyment of sailing this exciting performance cruiser. Displacement in racing trim is 2.2 tons with an additional cruising payload of 1.25 tons.

Plans consist of 20 very detailed drawings, and full size computer lofted frames on Mylar film.

References.