Mastering the hula harder than it looks

By HELEN TUNNAH

Ask designer Clay Oliver how Team New Zealand's new hula works, and he starts with a basic outline.

"It essentially changes the wave profile by changing the volume distribution in conjunction with the very after part of the boat."

Frankly, his number eight wire and duct tape explanation is simpler.

Oliver, Team New Zealand's principal designer, was the man who first drew the new hula (hull appendage) when the America's Cup holders first sat down almost three years ago to think about their new boats.

A 50-year-old naval architect originally from Rhode Island, Oliver said he decided to draw the longer boat that he wanted, and then with the full design team worked out how it could be achieved within the rulebook.

"It says that 20 per cent of the volume of the boat can be appendages and that's where the idea came from.

"With an appendage, you can integrate the shape you want and lower the transom."

The hula, just one new feature on a boat which includes a long, thin bulb, lighter boom and a return to a four-spreader rig, aims to increase its waterline length and thus its speed.

Team New Zealand will for the first time in the America's Cup use a hula in Saturday's first race against Team Alinghi, and it will soon become clear if the package of innovations has lifted the sport's design to new levels.

A non-movable appendage, the hula stretches along the stern of the boat for about 7m, sitting snugly but only touching the hull along a narrow channel. The rules state it can be attached only within 250mm either side of the centreline of the hull.

Experts are split over whether the hula will work, if it provides an upwind or downwind advantage, and even whether it is legal. It has been described as the biggest innovation in the event since the Australians launched a winged keel 20 years ago, but others reject it as rule-bending.

Oliver said yesterday that the concept was reasonably straightforward.

"The hula's job is actually to try to reduce the wave resistance ... If the boat's ghosting along at three knots of boatspeed, there's no waves so the hula's not doing anything. If you're doing 14 knots, it's doing quite a lot."

For two years the New Zealanders tested the device, working to come up with a design which could fit the rigid hull appendage very closely to the hull, to limit the drag caused by water flowing through the tiny gap.

Consideration also had to be given to the hula's weight, and whether the friction caused by the water flow outweighed any advantages from the improved waterline length.

Designers studied gap measurements in the tank-testing programme, in which large-scale models are tested in a special British facility, before full-size models were considered.

Prototypes were attached to the team's boats from the winning 2000 campaign, but both NZL81 and NZL82 were designed and built with hulas.

To the naked eye, the visible gap between the hula and the hull appears to be just millimetres. But it is apparently not the same all the way along its length, and it is not known how big the internal gap is.

"We know what that gap is," Oliver says. "Because the boat changes shape in different conditions you have to set different gaps depending on where you're at along the boat.

"Water does flow through there, and it flows through there at different speeds depending where it is in there."

Oliver reveals even less when asked how the hula actually is attached, and whether it is attached for its full length or just at a single or selected points.

"It's basically Kiwi ingenuity and it's something like baling wire, duct tape and that kind of thing.

"That's how the country was made and that's how the hula's attached."

Convincing regatta officials the hula meets the rules has taken several months, but both boats have been declared valid.

nzherald.co.nz/americascup

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