Left: Figure A – stability/reserve stability (y-axis) plotted against heel angle (x-axis) for a current 46ft cat and the new Neel 47 tri. Right: Figure B – stability (y-axis) versus heel angle (x-axis) for the same 46ft cat and an older-style light-displacement trimaran
So margins of safety have drastically
improved on modern multihulls, making inversion very unlikely except in the most extreme circumstances.
Weight and performance As is well known, besides waterline length, multihull performance is mainly a function of the ratio of power to carry sails versus overall weight. So are modern trimarans heavier than modern cruising cats? Actually, as safety margins have increased,
so the weight difference between the two types has declined dramatically. The reason for this, despite the slightly higher shell area of a trimaran, is that rig loads are easier to support with a trimaran’s central hull, compared with a big cat where all the longitudinal loads are resolved via the floats and beams. The structural weight of today’s best trimarans is only marginally higher than a cat of similar length. And there are other benefits to the tri-
maran platform for our purposes, aside from the greater margins of safety: l A simpler steering system with only a single rudder and so lighter and less complex controls. l A single engine that is lighter than the twin engine installation necessary on cats. l The generator and all of the tanks are situated in the main hull, saving weight and with better mass concentration. In terms of accommodation, the total
living area is generally rather bigger on tri- marans, but expect the guest cabins in the floats to be smaller than the equivalent cabins in the larger hulls of a catamaran. In terms of weight, with the new Neel 47 the choice of a simple contemporary treat- ment of the accommodation led to a total interior weight rather smaller than on an equivalent catamaran. At the end of all this, compared to a cat of
similar size the trimaran ends up with a slightly lower displacement yet slightly greater
sail-carrying power primarily
because of the greater width of the platform. Ultimately the ‘real world’ loaded dis-
placements will end up similar, but there are other benefits of three hulls… In light airs, as soon as there is any pressure the tri’s windward float lifts out of the water and the combined wetted surface of main hull plus float becomes smaller than the cat with both hulls still immersed. In turn,
52 SEAHORSE
the total friction drag with the single daggerboard and rudder is substantially lower than on a cat at small heel angles. The result is that the tri will demon-
strate better performance in winds under 12kt. This is an important consideration when looking at a cruising boat that will typically spend much of its life sailing in light conditions. At the same time the air flow across the
sail plan is more stable with the small amount of heel of a tri, which tends to settle the sails. The result is more stable laminar flow over the sails, increasing efficiency and performance. With a single rudder and a deeper fin
(even with a fixed fin) the trimaran config- uration also has all the characteristics needed to deliver a nice feel to the helm, especially upwind where steering these boats can feel closer to a monohull in light to medium conditions at least. On other points of sail, and in higher
winds, the performance is just as good as on cats, the only real difference being a slightly higher downwind VMG because the tri is able to sail deeper angles on account of its lower wetted area. So overall a rather good sailing pattern for the trimarans.
Comfort The modern idea is to provide accommo- dation not only in the main hull but also in the floats and across the large nacelle. Of course, to allow this, the boat needs to be quite high on the water with generous free- boards, but in combination with high- volume floats it becomes possible to main- tain an acceptable aerodynamic form along with some nice aesthetics. The trimaran configuration offers a more
private layout with the totally independent guest cabins in the floats. And with the master suite situated in the middle of the boat, at cockpit level, it really offers a differ- ent configuration than on cats. After the Neel 45 and the 65, Neel’s innovative 51- footer introduced the ‘Cockloon’ concept, where the interior and exterior living space blend into a single volume. This also elimi- nated an issue we had with the 45 where for- ward vision from the outside cockpit space was obscured by the saloon bulkhead. Following the first steps taken with the
the galley and navigation areas forward, giving a panoramic view in the kitchen and at the ‘watch station’. In fact, on the Neel 47 you can (almost!) stand your watch from your bed in the master cabin because the front of the cabin is mostly made up of large plexiglass windows. With additional beds in the floats the Neel 47 offers no fewer than five totally independent cabins. So our new trimaran has as much living
space as an equivalent cat but with several distinctive characteristics: a master suite up at the deck level, more independent areas for guests, two further small cabins, one large shared bathroom plus two smaller bathrooms in the floats.
Structure and construction A complete finite element model of the Neel 47 was built to allow us to engineer for minimum platform distortion along with high longitudinal rigidity of the main hull to withstand rig loads and ensure a tight forestay for good performance. Detailed modelling also helped us optimise the boat’s scantlings and address the struc- turally difficult forward areas of the floats. This led to the addition of extra unidirec- tionals in the deck and floats to improve rigidity and strength in the critical areas. The construction process is efficient
with a one-shot infusion using quadraxial glass lay-up, UDs and various grades of PVC foam. The main infusion incorpo- rates the inner sides of the floats, the main hull and the accommodation nacelle. Only three primary moulds are employed
with secondary bonding confined to the installation of the composite structural bulk- heads plus the later internal inner mouldings for cabin floors and so on.
Conclusion The first trials of the Neel 47 have confirmed a new era in cruising trimaran design, a yacht delivering a large interior, outstanding sailing performance that is a pleasure to steer and easy to manoeuvre. On the water our latest design has been
behaving just as expected and the commer- cial success is already a reality with more than 25 boats sold and five boats already sailing… meaning an expansion in our build facility. The future is bright. The trimaran is back.
51, with the new Neel 47 we have moved Marc Lombard, ML Yacht Design q
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