Sir Ben Ainslie: Inside INEOS UK's First AC75 Launch

1 October 2019• Written by Ben Ainslie

Finally seeing the America’s Cup AC75 hulls on water this autumn will give us insights into our competitors’ thinking, says Sir Ben Ainslie

The launch of a new yacht is a big day for any team challenging for the America’s Cup, particularly when it’s the first boat built to a brand new design rule. It’s an end point, a milestone for the design and build teams, and signifies an immense amount of hard work.

It’s also a beginning: the start of a new process of learning about the boat, particularly for the sailing team. It’s the moment when the rubber hits the road, when all of our thinking and planning comes to life. It’s one of the most exciting periods in the life cycle of an America’s Cup team, and we’re right in the thick of it now.

The launch of the a new yacht is the start of a process of learning about the boat, Sir Ben says

The first AC75 launches will happen this autumn, a year and a half after the first draft of the rule was published at the end of March 2018. So this seems like a good time to review the rules around the hull of the AC75. After all, that is what this moment is really all about – hull design. The AC75’s Rule 5.1 allows us to build six foil wings and 20 foil flaps, but we can only construct two hulls (and we can’t sail them at the same time). The teams have got just two opportunities to get this right, and we’re about to see the first.

What about the test boats? Well, yes, three teams – Ineos Team UK, Luna Rossa and American Magic – have launched test boats, but at least two of them used existing hull designs. I think it’s relatively well known that we used the hull of a Quant 28 to build our version, and American Magic has revealed that its AM38, aka the Mule, was originally a McConaghy 38. There’s also some evidence that the design of the more recently launched Luna Rossa test boat originated from a third-party project.

So, let’s assume that the launch of the AC75s will be our first real chance to see the thinking of each of the teams. What do we know? Let’s start with some basics: the rule defines a monohull of no more than 20.7 metres long, extending to 22.76 metres with the bowsprit and with a maximum five-metre beam. It weighs 7,600kg with the crew of 11 on board. There are more detailed parameters – for instance, the hull must enclose a volume of at least 70 cubic metres, and it can’t be narrower than 3.2 metres at a distance 17 metres forward of the transom – but essentially this is an open design rule.

Three America's Cup teams have launched test boats so far

On the one hand this is an invigorating opportunity. On the other I’m sure it’s leading to many sleepless nights as teams wonder what opportunities they might have missed. This is particularly true on the structural side, where Rule 11.19 states: “The minimum areal density of any part of the hull shell shall be 2kg/m². (Note that this Rule does not imply any stiffness, strength or robustness targets; it exists only to ensure that a hull shell is a solid structure and not, for example, a film-covered space frame structure.)”

The rule provides a basic panel weight, but after that the designers have no help from the rule on how to design and build a structure strong enough to resist the immense loads that foiling will place on it, while also keeping within the maximum weight.

The thing to remember when you look at the first versions of the AC75 is that the design parameters for its hull are very different to a non-foiling boat. It’s really a platform for the take-off and transition to foiling, and so it only has to perform its job in a limited range of conditions. I can’t tell you what we think those are right now, but I think it’s safe to assume that no one is worried about the hull’s wave drag at 25 knots in a short chop.

They will be worried about its aerodynamic resistance. Once the boat is up and flying on its foils, the hull’s aero drag becomes – along with its structural properties – the main performance factor. So when the first AC75s start to appear in photos on websites, remember that you’re looking at a boat that needs to reach take-off speed as quickly as possible across a range of wind speeds and angles, and then needs to pass through the air with the minimum of resistance. Judge it on those parameters.

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