hether the images of the yacht with one

foil raised/one lowered remind you of

a peeing dog or an aggressive praying

mantis, the fact is there is no reference

point on which we can lean to understand

the viability of the proposed design.

Because it is so far removed from anything seen thus far.

Even the most advanced of the current crop of IMOCA 60s

only become partially foil-borne when reaching.

Without doubt the ETNZ and Luna Rossa design teams

are among the best and the brightest, with the most

sophisticated simulation tools at their disposal. If they

believe the numbers to be true, who are we to doubt them?

To my mind Schrödinger’s Cat would be applicable here.

In his 1935 thought experiment, Erwin Schrödinger

presents the scenario of a cat in a sealed box. Until the box

containing the cat is opened, and its fate known, the cat may

be regarded as simultaneously both alive and dead. I think

until we actually see an AC75 sailing, both possibilities exist

simultaneously – they will either be an amazing spectacle or

an incredible lop.

I’m banking on the former. But why might they be a lop,

with all that brain power directed to ensuring they’re not?

Well, fundamentally, in setting out to do for monohulls

what the AC50s did for multihulls – raising the technology

level with foils, wingsails and control systems – the concept

of a fully-foiling monohull has to overcome a number of

unavoidable encounters with the laws of physics.

Foils don’t aid stability until they are moving forward

through the water – they need low over them. he force

generated varies with the speed of low squared. If you

double the speed you get four times the lift.

he converse is also true. If you halve the speed, you get a

quarter of the lift. So the transition from displacement mode to

foiling will see huge changes in speed and lift, as will falling of

the foils or losing lift through either ventilation or cavitation.

In the event of losing lift through ventilation, the righting

moment will ‘switch of ’ but the heeling moment will not (or

at least not instantaneously, no matter how fast the main is

eased), so we could see capsizes.

To keep the yacht upright before the foils generate enough

lift, and to prevent the yacht from inverting if capsized,

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W

WORDS BY

CHRISTIAN STIMSON

PHOTOGRAPHY SUPPLIED

feature

The AC75

The divided opinions

regarding the new

AC75 design for the 36th

America’s Cup show no

signs of converging after

the recent publication of

the Class Rule.

fly?