She may not be pretty, but this exciting Mini Transat design employs some interesting new devices to make her go fast, reports James Boyd
French yacht designer and Mini sailor David Raison has a lot to answer for. His 21ft Magnum scow, designed to the Mini class rule, was one of the most significant steps forward in offshore yacht design in recent years, particularly after it proved itself by winning the 2011 Mini Transat.
If stability is one of the greatest performance drivers, then scows, with their ultra-high-volume bows, provide added hull form stability compared with their narrow-bowed cousins, increasing righting moment just as adding lead to the bulb might. While excess hull drag in light winds is the scow’s obvious Achilles heel, in fact the Magnum design partially addressed this through its hull shape, chines and heel angle.
For this autumn’s Mini Transat race, scow Minis took a step further. Firstly there was the Mk2 Magnum in the form of Davy Beaudart’s Flexirub. This won the Proto class in the first leg of the race from Douarnenez to Lanzarote, but retired with hull and sail damage on leg 2. A more interesting development, however, was Eight Cube sailed by Swiss Mini sailor Simon Koster, which finished 7th overall.
Having come 3rd in the Mini Transat’s ‘Series’ class (for production boats) in 2013, Koster, like several other competitors, graduated up to the ‘Proto’ (one-off) class for 2015. But perhaps more than his contemporaries, Koster was keen to see Mini design progress.
Foils for vertical lift
Eight Cube was one of the first full designs from Michel Desjoyeaux’s company, Mer Forte. The boat is another scow, but compared with the Magnum has a less powerful forefoot. It also features foils to provide vertical lift. So if the Magnum is dubbed the ‘Bathtub’, Eight Cube is known as ‘The Flying Frog’ in Mini circles – her white/green paint job contributing to the nickname. And unfortunately neither would score highly at a beauty pageant.
Although teams such as Banque Populaire have used Minis as a testbed for foil shapes and configurations for their IMOCA 60s, these profiles are not permitted at present under Mini class rules. These limit draught to 2m and maximum beam to 3m, beyond which keels, deck spreaders, bowsprits and foils must not protrude.
As the IMOCA 60 L-shape foil, which extends out to leeward, would be illegal on a Mini, Eight Cube has foils that are effectively vertical daggerboards – fitted well outboard in the hull just ahead of the keel – but are fitted with an inward-pointing tip. This tip measures around 700mm and follows the curvature of the bottom of the hull to ensure it stays out of the water when it is retracted out of use on the weather side.
Fortunately, apart from the dimensional restrictions, the Mini rule is more open than that of the IMOCA 60 class, permitting for example adjustment in the rake of the foils, altering the lift they provide. On Eight Cube this is achieved with a worm drive, controlled by a line. Koster says he considered a similar system to adjust Eight Cube’s inverted T-shaped rudder-foils, but chose a simpler system whereby each rudder’s bottom bracket is padded out with spacers.
In practice, Koster says the foils start working at ten knots of boat speed, reaching their optimum performance at around 14. At this point they develop around 500kg of lift or around 60 per cent of the boat’s 800kg displacement – not quite flying, perhaps, but well on the way.
Being close to the boat’s centre of gravity, Eight Cube’s foils don’t provide much added righting moment, but the boat performs well upwind – a major weakness of the latest IMOCA 60s.
Smart canting keel
Thanks to the flexibility of the Mini rule, Eight Cube has adopted one of the class’s smarter canting keel evolutions. This is telescopic so that when vertical, draws just 2m, but when canted (up to 37°) the keel extends, thereby increasing the righting moment provided by the bulb. And that’s not all – the keel also rotates, allowing Koster to dial in lift once it is canted.
Enough of all the gadgetry, what is Eight Cube like to sail? “You can feel when the foil is working and the bow is further up than normal quite early on, even when you are not going that quick,” says Koster. “But on board, it takes some getting used to because you can’t actually see it. You have to be careful not to use the foil too early because it provides too much drag. And it is not easy to figure out what is actually providing the boat’s stability: is it the foil, the keel, the angle on the rudders or the mast rake?”
The movement of the boat can often be violent, Koster adds; she accelerates fast but she stops equally quickly.
He says the scow shape is not bad upwind, but “if there’s light air or chop, then it gets complicated. If it is normal wind and the wind with the waves, then it is all right; that works because there is a lot of power in the boat, so you punch through it. She doesn’t go as high as the older boats, but she goes very quickly.”
While it is interesting to see the scow development, this configuration might be surpassed come the next generation of Protos for the 2017 Mini Transat. For this, maximum beam will remain at 3m and appendages will have to remain within this limit for starters, but afterwards overall beam can be increased to 6m.
As the Mini rule doesn’t limit the number of appendages, boats are likely to fit DSS-style lateral boards to provide vertical lift and righting moment, and vertical boards to prevent leeway, like a miniature version of the set-up that larger racing boats such as Wild Oats XI and Rambler 88 currently have.
And with boats deriving more righting moment from their foils, this might also mean that next generation Protos will require less hull form stability and have less reason to ‘go scow’.
David Raison shot to fame with his radical scow Magnum design called TeamWork Evolution in which he won the race in 2011. In 2013 the same boat came 2nd as Prysmian in 2013 and the Magnum Mk2, Davy Beaudart’s Flexirub won the first leg of this year’s Mini Transat.
LOA 6.50m/21ft 4in
Beam 3.00m/9ft 920in
Draught 2.00m/6ft 6in
Air draught 12.00m/39ft 4in
Designed by Mer Forte
Launched May 2015
Skipper Simon Koster is tall and Eight Cube has remarkable headroom for a Mini. The canting keel head is encapsulated in a plastic bag to keep out water
On a Mini, headroom below comes at the cost of good looks externally. The cabin tops also serve to add buoyancy during the mandatory inclination test
The boards are positioned well outboard and are slightly ‘toed in’, increasing the vertical lift produced when the boat is heeled
The rake of the daggerboards can be altered via a wormdrive set-up similar to that of the GC32 foiling catamaran that adjusts the foil’s angle of attack
As is typical, the wingmast sits on a ball. The wingmast is rotated via the forward-pointing mast spanner. The rake of the wing can also be adjusted
The twin companionways and channel for halyards running aft to the pit is similar to the DNCS and Hugo Boss 2008 generation Finot-Conq IMOCA 60s
The tiller passes beneath the full-width mainsheet track. Note the Karver constrictor clutches for the runners – a simple, effective and light solution