By John Browning
February 14, 2003
Source: www.sailtexas.com/amcupcountdown2003.html

IACC Bulbs

[Editor's Note: To view and learn more about the hulls and appendages of the syndicates discussed below, see the article What's "Down Under" On Each AC Boat. It has photos and more comments on Unveiling Day.]

By elongating NZL-82 keel bulb to 20 feet with a flattened base, the Kiwi's have a lower center of gravity for upwind sailing at the expense of increased drag from the larger immersed surface downwind than the shorter fuller round shape of the Alinghi bulb. The bulb is a hefty object on an ACC boat - about 80 per cent (20 tons) of the maximum weight of 25 tons allowed for these ACC boats.

The longer bulbs, designed by Holroyd working alongside designers Tom Schnackenberg, Clay Oliver, Mike Drummond and Andy Claughton, were the result of wind tunnel and other testing in the United Kingdom. "It is a computer-driven design and part of the appendage package I'm responsible for," said 35-year-old Holroyd, who was born and bred in Auckland, attended St Kentigern College and spent time in the UK before joining Team New Zealand in 1997.

"My decisions on the shape of the bulb are ultimately reflected all over the boat. We tested a bunch of bulb shapes in late 2001 before coming up with these."

Of suggestions bigger bulbs mean more drag, Holroyd said: "There are different sources of drag. As you lengthen the bulb you have more wetted surface. But that also means a different frontal area which, in turn, means less pressure drag."

"While the shape and weight of the bulbs on NZL81 and 82 are "pretty similar", the race boat's bulb is "slightly flatter", he explained.

How a Hula "makes the boat seem longer to the water"

waterline length = speed potential

Possibly the Kiwi's are relying on the hula to make up for the wetted surface drag downwind of the longer bulb.

Comments from Alinghi's Grant Simmer just before racing started: "On the respective designs of NZL-82 and SUI-64: We are surprised with some of the appendages that we have seen today on NZL-82, it wasn't what we were expecting to see. Firstly the hull's themselves are very different, NZL-82 is a much wider boat than SUI-64 and it has the much publicized appendage on the aft part of the hull which they call the hula."

"The affect of the hula will be to try and lengthen the boat, but the downside is that you get the drag of the gap between the hull and the hula. We've done a fair bit of testing with that concept and obviously we decided not to go with it even though we had the resources to do something about it."

"Our boat is tailored for match racing, for maneuverability, for tacking and for the pre-start and they have had less emphasis on that aspect and more emphasis on straight line speed. They came today with a very long bulb, much longer than we expected. The advantage of that is to give them more righting moment upwind and less cross-sectional drag, less frontal area but a lot more wetted surface. That's bad for light winds, but good in strong winds. It is also bad for maneuvrability. They also have a smaller fin than we expected to see, much smaller keel fin than on our boat which was also a little bit of surprise."

The Swiss team had tested the device extensively on their second boat SUI-75, and decided not to modify SUI 64 which Russell Coutts's crew took to a 29-4 record in the Louis Vuitton trials and which will be used to race Team New Zealand for the Cup.

One of Team New Zealand's principal designers, Clay Oliver, said the second skin concept had always been part of the design of both 2003-generation boats. "You want to draw a boat that is long, elegant and fast," he said. "It wasn't a matter of adding something to a boat - it was always envisioned "This is not a clip-on. It's an integrated and almost seamless part of the hull. It's taken us a long time to go through the processes of it, and we have done our homework with it."

There are a few penalties that come with the innovation - the gap between the skin and the boat hull creates extra friction and drag, and some weight has to be conceded. In heavy airs, it lacks a little stability. Team New Zealand's other principal designer, Mike Drummond, said the trade-offs were worth it. "We have tested this idea it found it to be faster. It's like many things we do that are not always faster. But it was fast enough for us to unveil two of them."

It is now said that a hula, being an appendage, can be changed in size and shape to suit the expected wind strength and sea conditions for a race without changing the boats ACC rating certificate. If so, a smaller and different shaped hula with less drag would be fitted for light winds. A larger in shape and size hula would be fitted for heavy winds/sea conditions and while the potential drag would be more, the gain in waterline length would be worth it.

"Whether the hula was one of the great design coups of America's Cup history will depend on the outcome of the best-of-nine Cup match" reasoned Schnackenberg. But if the hula proves successful in this America's Cup, he would like to work with other design teams to remove the no hollows rule for future events. "Then maybe this boat will be seen as a small milestone along the way in the development of the America's Cup."

A hollow at the end of the waterline would allow the hull to drop down for a lower transom and longer waterline length when sailing - without penalty. As the rule is written, a lower transom results in a longer waterline length and penalty.

The hula wasn't the only revelation on the black boats at the LVC Unveiling day. There was the double rod rigging with four spreaders, the longer bulb on the keel and fin position. One of the bulbs on Team New Zealand is cigar-shaped (but with a flat bottom), much longer than those revealed on the two challenger boats. "It's a lot shorter in height, so it gives us more stability," , said Drummond, Team New Zealand. "But it also gives us extra drag in lighter airs."

The weight of the bulb (at base of the keel fin), is to keep the boat upright against the wind pressure in the sails that propel the boat.

In the America's Cup Class, draft in excess of 4 meters (13 feet), carries a penalty, designers as a result want to carry the bulb weight as low as possible and with deepest keel possible for leverage.

At the Louis Vuitton unveiling day, Team New Zealand showed two boats, NZL-82 with an elongated bulb, with longest keel fin carrying the weight as low as possible but with the penalty of more drag from the immersed surface of a long bulb. On NZL-81, the designers had a shorter keel fin and fatter bulb with potential for less drag. Since then, however, they have equipped NZL-81 with an even longer keel bulb than NZL-82.