Nigel Irens’s latest slippery and easily driven motor launch was designed with sailors in mind. Nic Compton steps on board Wilhelmina

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It’s a beautiful autumn afternoon in Salcombe, and half a dozen of the local yawls are tacking up and down the estuary. A motorboat is anchored off Sunny Cove beach: long, low and painted a soft grey, it’s slightly reminiscent of a naval pinnace or one of the local working boats.

But, as the anchor is raised and the boat sets off, something strange happens: the boat slides forward quietly and, without the least commotion, accelerates from zero to ten-plus knots in a matter of seconds. Soon, it’s disappeared out of sight, and all that’s left is the slightest wash on the surface of the water.

This is Wilhelmina, the latest creation from one of the most original and brilliant minds in contemporary yacht design, Nigel Irens. Although best known for a string of record-breaking multihulls, such as ENZA New Zealand, B&Q Castorama, Fujicolor and IDEC, for the past few years Irens has turned his attention to motorboats – and specifically, motorboats designed for sailors.

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Wilhelmina looking right at home in Salcombe

“I’m on a personal crusade to help people understand that there doesn’t need to be this huge cultural divide between a sailing boat and a well-designed motorboat,” he says. “I believe a motorboat can give you a real sense of well being in the same way a good sailing boat does.”

The problem with motorboats, says Irens, isn’t that they are intrinsically less appealing than yachts but that manufacturers have put all the emphasis on interior volume. While engines have got lighter and more powerful, manufacturers have simply piled on ever more gadgets and ‘creature comforts’ and used the extra power to push more weight through the water less efficiently. The result is heavier boats with larger and larger engines and astronomical fuel bills.

Applying physics

The nub of the problem is the hull speed rule, which insists the maximum speed of a displacement hull is 1.34 times the square root of its waterline length in feet. Try to go any faster, and the stern will get sucked down, creating an enormous wash with no corresponding increase in speed. The usual way to overcome this rule is to design a hull that, at high speed, will rise over the water and plane, thereby minimising drag and allowing almost unlimited speed.

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Minimal wake is a feature of the Irens-designed hull

But the hull speed rule, it turns out, is a rule of thumb rather than an inescapable natural law. As far back as 1894, the 104ft Turbinia proved that a long, narrow, hull can go faster than its designated hull speed, without having to plane – 34.5 knots, in her case, compared to a theoretical hull speed of 13.7 knots.

Taken to its logical conclusion, this approach would produce an incredibly skinny hull supported by a pair of floats – which is just what Irens created with motor trimarans such as ILAN and Cable & Wireless. Translating that concept into pleasure boats has proven more elusive. Instead, he delved back to his very first experiences of the sea and the origins of his devotion to fast, slippery boats.

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Wilhelmina’s long cockpit can seat up to a dozen people

“When I was a child I spent a lot of time messing about on boats in Salcombe in Devon. That’s when I discovered those wooden launches, and I was fascinated by the speed at which they travelled.

“They used to race those boats, of course, but at some point in the early 1900s, someone turned up with a planing hull, and that was the end of slender hulls. We’re only now picking up where they left off.”

Overcoming limitations

The main limitations of the wooden launches Irens admired so much as a child was the weight of their traditional carvel or clinker construction, and their relatively heavy and inefficient engines. Sixty years later, these obstacles have been largely overcome, and it’s possible to design a lightweight hull fitted with a lightweight engine that will minimise drag and go considerably faster than its hull speed – without planing.

It’s this concept which Irens has christened ‘Low Displacement/Length ratio’, or LDL. The basic approach is to combine the narrow, wave-cutting entry of his trimarans with the beamy stern of a modern monohull.

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The fine bow (starting, in the case of the 31ft Wilhelmina, with a 10mm wide cutwater) reduces drag, while the wide transom prevents the stern being sucked down by steeply rising buttocks and also provides the necessary stability.

The result is an ultra-light hull, which does much better than a conventional displacement hull without compromising seaworthiness. The benefits are especially apparent in rough weather, when a traditional planing boat will either pound the crew to smithereens or, if taken off the plane, stop dead at every wave. By contrast, an LDL boat will simply slice its way through and carry on regardless.

Faster and less thirsty

Because the hull is so easily driven, it can be powered by a far smaller, less noisy and less thirsty engine. Thus Wilhelmina is fitted with a 25hp engine, which gives her a cruising speed of 10.5 knots – considerable faster than her theoretical hull speed of 7.5 knots.

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The roomy cabin is light and airy but without standing headroom

I joined Nigel for the 14-mile trip from Dartmouth to Salcombe. With her plumb stem, bronze deck fittings, and curved windscreen, Wilhelmina is an intriguing combination of old and new.

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A cabin heater keeps things warm and cozy below decks

There’s really nothing else quite like her around, which is partly why it’s such a surprise when she suddenly accelerates and starts slicing across the water at ten knots – very quietly and comfortably, without any of the noise and splash you associate with high-speed motorboating.

The boat has a very large cockpit with a pair of white engine boxes in the middle, and a scrubbed wooden sole. Below decks, the open plan layout gives a surprisingly spacious feel, and his designer’s eye has created an ambience which is both cosy yet airy – albeit without standing headroom.

A curtain separates the heads compartment, which has a large hatch to save having to scramble over the windscreen to access the foredeck.

It’s easy to see the potential use of this boat as a superyacht tender, but Irens’ vision is more towards coastal cruising, such as overnighting in the Scillies or even a weekend trip to Ireland.

“We’re interested in the experience of doing 30 hours at sea with friends, with nice meals and lovely coastline slipping by. It’s about the journey not the arrival, something which is normally in the domain of the sailing boat, but which can be experienced on motorboats too.”

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About the designer

Nigel Irens credits a childhood obsession with ‘slippery hulls’, notably the Salcombe motor launches, with everything that followed in adult life. His designs include a string of record-breaking multihulls, which dominated the race circuit throughout the 1980s and 1990s, and some very slippery powerboats too. Along the way, Irens also found time to design a range of modern classics, including the 29ft carbon-sparred lugger Roxane and her little sister, Romilly.