Clip-on Hull Apendages...?

[Willallison]

Watched the news this morning - Team NZ has just displayed ofr the 1st time the boat they will be using to Defend the America's Cup.
It features a "Hula" - a clip on hull apendage......?

[yipster]

is it a "Hoop"? just kidding but it sounds great, keep me posted.

[tspeer]

The "hula hull" is a ratings dodge. The AC rule doesn't allow any hollow in the hull section outside of 250 mm from the centerline. This makes it impossible to design a hull with a bustle like was used on the 12M boats (the bustle reduces the wave drag in somewhat the same way as a bulb does at the bow). There's also a restriction on the slope of the hull near the aft end of the waterline. Team NZ wanted to have a hull shape that exceeded these restrictions.

The AC rule limits the number of movable appendages to two (typically used for the flap on the fin and rudder), but doesn't put any restriction on the number of fixed appendages. So NZ has come up with an "appendage" that is topologically similar to a mushroom. It fastens to the hull within the 250 mm zone, then spreads out to form a huge blister under the stern. The gotcha is that to qualify as an appendage, the rest of it can't touch the boat under any circumstances. Technically, it's a giant bulb on a very short fin.

Hydrodynamically, it will be interesting to see if the drag from the slot running all around the hula will be less than the wavedrag reduction due to the hull contour. They are probably aiming to bury the slot in the hull boundary layer, with only a few mm clearance all around. Other teams say they had the same idea, but decided not to pursue it. From what I've read, both Team NZ's boats are designed from the outset with the hula as a fundamental part of their hull contours. They won't be well formed without it, so they appear to be committed to it.

The other teams will be hoping it does touch, either through flexing of the hull or the hula. Then the boat would be non-compliant with the rule because the hula would be considered part of the canoe contour instead of being an appendage. Alinghi has already filed for rulings that could become the basis of a protest. They seem to be aiming to get Team NZ to prove that it can't touch under any circumstances.

See http://www.sailinganarchy.com/genera...der.htm#finish
Note the fine gap around the large blister surrounding the rudder:
http://www.americascup.co.nz/databas...amNZlarge1.jpg
http://www.americascup.co.nz/databas...amNZlarge2.jpg
http://www.hauraki-news.com/Photos5/...eilingTNZ3.jpg

Unlike winged keels, this isn't technology that will migrate to other classes. It's strictly an AC boat rules thing.

(FWIW, it's surprising how small the wings are on these boats: http://www.americascup.co.nz/databas...comparison.jpg)

[Willallison]

Thanks Tom.
I knew that the hula was a ratings dodger.... shame the AC has so little to do with sailing anymore.......
Actually the hula was their secondary choice, but the 1st - rejected by the ruling body - involved having 50 sheep tethered to the bow, swimming madly to get away from 5 randy farmers...

[yipster]

valencia spain now hosting the America's Cup for the swiss in 2007 ?
thought that would be this year ?
info at: http://www.americascup.co.nz/

yipster