Long and slim… As the latest performance cruiser-racer cats grow in scale, so the inevitable escalation in displacement with the requisite onboard ‘comfort systems’ means that overall beam does not need to expand to what would be expected on a pure race design. But the relatively narrow shroud base – for a boat of this type – does in turn place demands on the rig designers while also increasing mast-step compression
A change of direction
Designer Nigel Irens and rig architect Torbjørn Linderson take note of some of the lessons from their latest joint creation… the high-tech composite 78ft cat Allegra, launched recently by Green Marine
Design – Nigel Irens
After 35 years spent trying to make ocean racing trimarans go faster than the compe- tition you get a bit obsessive about keeping the weight of a multihull to a minimum. It’s not complicated – righting moment is the product of multiplying half-beam (centreline to centreline) by displacement. Unsurprisingly, performance is maximised by achieving a high RM through pushing half beam up and displacement down, and doing that better has been the key objec- tive in achieving radical performance improvements over the years.
Where cruising multihulls are concerned the story is very different, and an abun- dance of weight is obviously inevitable
from the outset. In fact, the weight spirals upwards. As the desire for more living space and a higher degree of comfort increases, so a heavier and more powerful rig is needed, together with the machinery and deck gear necessary to power the whole thing up. Against this background, promising a catamaran that can offer both high levels of comfort and great perfor- mance seems a bit rash, but there is a third element that can change the game and that is budget.
For decades cruising catamarans have been perceived as the low-cost way of taking as many people to sea as possible. They are usually shallow drafted, they sail more or less upright, and, yes, you can see out of the windows. Performance has to take a back seat because it is an attribute that is usually too expensive – both to buy and maintain. The charter market, for example, in which many of these boats serve, will simply not pay the premium needed for high-performance sailing. Now, however, a relatively new market is beginning to open up. Green Marine, who built the recently launched 24m Allegra, have coined the phrase ‘Premium Catamaran’ to describe such boats. Pioneers like Gunboat have been paving the way over the past 15 years, but now
the cat is, so to speak, finally out of the bag, and it looks as though this fledgling market is going to see some interesting developments in the coming years. As designers of Allegra we recently took the opportunity to join the delivery trip from Southampton to Palma. We were lucky enough to experience a wide range of weather conditions which is obviously ideal when trying to get an overall feel for how the boat works. Although we are sup- posed to be able to predict performance with some certainty, the prediction tech- nology available in this field is not yet able to provide a simulation of the response of the vessel to different sea conditions; and even if this did exist there would still be no way of knowing how the movement of the boat will feel to those aboard.
We suggested during the build period that our experience of raceboats led us to be concerned that an ‘all-carbon’ boat can be very noisy inside – a feature that can become disquieting on a long trip. We also suggested that it may be necessary for such a boat to be equipped with a set of vertical posts – to be installed for offshore voyages. I imagined that moving around the large open-plan deck saloon could be difficult (and even dangerous) in bad weather. On both the above accounts we were
SEAHORSE 31
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