KEY POINTS:
When it was launched in December 2005, Team New Zealand's first America's Cup weapon, NZL84, didn't exactly strike you as a black beauty.
A super-skinny yacht with slab sides, NZL84's standout feature was its big, blunt bow.
Pretty it may not have been, but potent it certainly is on the water, giving the hull a much sleeker look.
A year later, big bows are in, and many syndicates are heading to the same design corner as Emirates Team New Zealand.
Yachting commentator Peter Lester thinks narrower boats mean fuller bows.
"When you make the boat incredibly narrow you still have to get enough volume into the boat and the most effective place to put the volume is in the bow so when the boat leans over it doesn't go bow down and nose dive," he says.
"It means the boats sail quite long."
It's the first time in recent history that America's Cup yachts have possessed so much volume in the bow but Lester says it is probably a natural progression.
"If you look back at 1992 and in 1995, the boats were near maximum beam. As the boats have evolved they have got narrower. They were at around five metres and the boats were very V shaped - as the boats have got narrower, they have become very slab-sided.
"In the last Cup Alinghi were slab sided but were heading in this direction. These newer boats are more extreme. The Alinghi boats were obviously for the Auckland conditions, these boats are being modelled for Valencia conditions which means they can be a bit narrower and they are not getting tossed around by the waves.
"I think it is quite venue-specific ... Luna Rossa seem to change their bows often but from what I am reading they have gone in the same direction as Team New Zealand.
"Team New Zealand led the charge which is a huge compliment."
He calculates the current designs could be as narrow as 3.5m. The maximum is 4.5m.
"One of the restraints of going narrower is sheeting the genoas, these boats are sheeting at a narrow angle. Another issue is the sidestay attachments which support the rig."
In other words, the narrower the horizontal base, the harder it is to support a vertical structure.
Although modifications are part and parcel of the America's Cup, it has been suggested that three syndicates have already replaced their bows.
Auckland yacht designer Brett Bakewell-White says much of the bow shape is about measurement rather than pure performance.
"The America's Cup is a weird old game where the rules make them do weird things, which is why the boats are rather ugly and funny. So it is likely the change to bow shape will be in order to get the best answer in terms of rule and in particular the measurement for length.
"So they mess around with various angles to get the maximum-length boat that measures as short as possible which is why we ended up with those double knuckle bows that they all have these days. One of the problems with those bows is that they throw a lot of water around so they spend a lot of time trying to tidy that up."
Bakewell-White says that unless it is an innovation, slapping a new bow on a boat would probably not make a huge difference speed wise. Changing bows or/and sterns is easy enough and does not create weak points in the hull structure.
"You can rebuild the composite structure so it is strong as it ever was," he says.
"I would imagine any gains are going to be small but that is what they are all looking for these days, the rule has been flogged to death and there are not too many places to find many gains."
Teams are allowed to build only two boats during an America's Cup campaign and can alter only a certain percentage of a new boat, meaning syndicates could find themselves with improvements they could not use, says Bakewell-White.
"If these guys could build 10 boats they probably would, if they had the budget, but they are limited by the rules ... so their only option is to chop around the old ones.
"Or if their new boat is proving way faster than their old one, then it is not much use to them as a trial horse so they end up modifying the old one so it is closer in speed to their new boat."
