Updated: Feb 16th, 2020

About 8 years ago I was caught up, like many other sailors, in the new excitement of foiling multihulls for the 34th America’s Cup …. persuading me to put together a few articles about the event, even if they were certainly not ’small trimarans’.   The 35th Cup also showcased foiling cats, so I followed that as well and there was an article written also .. still available here.  Well, today I am offering the same for the 36th America’s Cup, even though the boats are now back to monohulls.  “But why?”, some may ask.    Because the America’s Cup is not only an amazing contest in itself, but it brings out new technology that inspires new design features that often later find their way into recreational sailing craft, so ultimately of interest to all sailors.

This first article is intended to only be ‘a quick read’ that will give the reader just the essentials, to understand what’s going on and how we got there, as there are and will surely be many more articles and YouTubes forthcoming by those close to the events during the year.  But if this is something of just casual interest to you, or you’re confused on how this all works, then perhaps you’ll find what you wanted to know, right here.  Enjoy!

First, background on this ‘Oldest Trophy in the World’ (1851) can be found in previous articles, so here’s a link to one.  [https://www.britannica.com/sports/Americas-Cup

The Protocol for the America’s Cup races dictates that the choice of geographic location and boat design criteria, goes to whoever last won the Cup, so these variables have changed significantly over the years.    The event is currently held every 4 years and in both 2013 and 2017 we had those incredible foiling catamarans.    But since New Zealand won that event, for 2021 they have chosen to go with a longer (carbon-fiber) monohull and a fairly conventional soft-sail rig, but with a hull that will primarily operate out of the water, running on T-foils which are to be identical**, being designed and manufactured by the NZ defenders, so that all boats will at least ride on the same foil design.**   In contrast to the 2017 boats, sails will be much simpler (no two-part wing sails), but the foil system will be more controllable, unlike the 2017 foils that were fixed.

**  Well, already that early 'identical foil' report must be an error, as in a recent interview with past America's Cup winner Jimmy Spithill, he refers to the 'foils being all different" !  ... so this certainly needs more clarification, something that time has now already answered ..  see here

Added: Feb 16th 2020.  Having now reviewed the AC75 Class Rules, it's become clear that it's the mounting Foil Arm Strut & Foil Control System that's supplied, but NOT the actual foils.  More below on this. 

The Protocol also calls for a Challenger of Record (COR) who is typically ‘the first team to challenge after someone wins the cup’ and this year it was the Italian Team of Luna Rossa.  Effectively this COR Team then represents all the Challengers and is the group who organizes the pre-cup contest* to choose the final challenger.  They also negotiate the final race arrangements and any required rule clarifications with the Defender – Emirates Team NZ.   For the 2021 challenge, PRADA (an Italian luxury fashion house) is the support behind Luna Rossa, so this pre-cup contest is to be called The PRADA CUP.   Whatever boat/team wins this Cup, will race against New  Zealand for the big prize … The America’s Cup.

[It's worth noting that the Defender always has a decided edge in this contest, being as they can choose both the boat design characteristics AND the location for the event.  In fact, in the 35 contests so far, the Challenger has only won 6 times, so it generally takes something special to make that happen. In fact, the very first win by a Challenger (won by Australia, 4 races to 3), was only in 1983 at the 25th contest ... 132 years after 'America' first won the Cup around the Isle of Wight in the UK].

Both the PRADA Cup and the America’s Cup will be sailed in the same Auckland Waitemata Harbour, with the Prada Cup scheduled for January/February 2021, followed by the America’s Cup March 6th to 21st, 2021.

Before getting into who will be racing for the Prada Cup, let’s take a look at the general design criteria.

Here is what I have found on-line about the 2021 AC75 Design Rules.     No reason to think it’s wrong but take no responsibility re accuracy ;)

Loaded weight 7600 kg    Yacht itself including foils & weighted foil arms (1215kg each) to not be less than 6305 kg.  With up to 400kg (880lbs) of buoyancy in the top of the mainsail and ballast in the main foil arms, these boats are intended to be self-righting.

Draft  (foils) 16ft  (5m)    T-wing foils and T-wing rudder foil.    Foil arms to hold any ballast.

LOA 75ft x (68ft hull) x 16ft  (5m) beam

Mast height  87ft  (26.5m) and rotating.  (approx section 750 x 450 with flat back to take a two-skin mainsail on rear corner tracks. This closely follows the Example Type 'E' in this article (also on this website) entitled Mast-Rig Options.

Double-ply mainsail permitted (semi-battened only) up to 145m2 (1500 sqft).  

This is a very interesting development.   After reviewing various mast-rig options for the above noted article in 2012,  I predicted that this particular design was the most likely to still 'have some life'.  Of further interest is that this 'double-cloth' concept was first proposed 95 years ago by Lewis Francis Herreshoff (son of genius Nathaniel) and has seen many variations since.  But more recently, Advanced Wing Systems (AWS) has refined this sail type and is now working closely with the US team 'American Magic' for a Cup challenge.

Single ply headsail of up to 90 m2  (970 sqft).  

Single ply Spinnaker  200 m2  (2200 sqft)     (Probably only used in very light winds so may never be seen)

Boats sailed by 11 sailors per boat (+1 optional guest),  (There may also be a requirement for a minimum % of citizens from each country competing, but I’ve not yet seen a figure)

Foil Arms to be designed and supplied by the Defender Group (NZ-Team Emirates)

Partly to reduce design and testing costs, rules specify that the FCS (foil control system) be supplied by the defending club's team and that all foil arms be made by the Challenger of Record's builder (Persico Group).     (Just for side interest, Italian Persico introduced the first computer controlled (CNC) 5-axis milling machine in Europe some years back).     Foil designs are to each competitors design but must fit within a boundary of 4000mm x 700mm.

Each team can build 2 boats but I'm understanding that only the Defenders can race their two boats against each other, as the Challenging boats will get their tune up during the PRADA Cup races.  

Most challengers chose to first build a prototype of a smaller scale to learn what works best at reduced cost but the NZ defenders have already built, launched and sailed their full-size prototype AC75 and here is a pic at the launching and an idea of how it looks while sailing on foils at speed.   (The AC75’s are over 200 times the volume (and 85 times the weight) of a sailing 11ft moth that led the way on just 2 foils).  

[Added observation:  In addition to their full size prototype, the NZ defenders also have a smaller test boat of the same basic design, (called The Hawk) ... so will be able to continue testing new ideas while their prototype AC75 participates and showcases in the 2020 AC-World Series.  Interestingly, foiling boats are not necessarily faster by being longer as non-foiling boats are. They go faster with a higher sail-power to foil-drag ratio ... and its already reported that the smaller 'Hawk' test craft has a speed not far different from the full-size AC75].

The first Team Emirates-NZ boat has been called ‘a skiff on foils’ and took about 2 years to design and build. It’s called Te Aihe (meaning Dolphin in the Maori language).  The engineers were allowed to play with the hull design, spars, sails, steering and control systems. 


By early October 2019, 3 more AC75 hulls were launched by challengers: -  

American Magic’s  ‘Defiant’;   Britains' Team Ineos launched ‘Britannia’;  and the Italians ‘Luna Rossa’ in the Mediterranean.

8 other countries also tried to enter but only 3 met the requirements to be provisionally accepted.

Of these 3 (Malta, Holland and USA-W.Coast) only the Stars & Stripes from Long Beach, CA is still a possibility as the other two have withdrawn, but even this entry is doubtful at the moment due I understand to financial issues, though we hear that NZ has reserved space for the team in Auckland.    As it now stands, it would appear that, all teams already legally entered would have to agree to some Protocol revision, in order to allow the late Californian entry to compete.   They do have a boat however .. and the hull is a basic copy of the NZ Emirates team prototype.

Here are a couple of pics of the ‘Defiant’, who at the moment is the sole official competitor from the USA (a NY group).    The first shows the hull in a shed being worked over and the 2nd shows their prototype on trial.   


To help get these new boats ‘up to speed’ and also raise their profile in other sailing areas of the world, three ‘AC75 World Series’ events will be run in 2020.  

Here are the planned dates & locations.  Tickets are already being sold for the first two.   

#1  Apr 23-26, 2020   AC75 World Series event in Cagliari, Sardinia                         ..  [Cancelled due to COVID-19]

#2  June  4-7,  2020    AC75 World Series event in Portsmouth, England                 ..  [Cancelled due to COVID-19]

#3  Dec.17-20, 2020   AC75 World Series event in Auckland, New Zealand        .. [went ahead with NZ and 3 Challengers]


             Check out this short YouTube for a digital view of what to expect.

If you are looking for further information, here are three links you may find of interest

www.americascup.com      www.sailingscuttlebutt.com       www.sail-world.com                        Mike, February 8, 2020


LATEST NEWS  (Feb.10, 2020).  American Magic team in their Florida trials at Pensacola, Gulf of Mexico,  have apparently been thwarted by foil arm issues, (something all teams might face, as these arms share the same designer and manufacturer.

All four AC75's (USA, UK, NZ & IT) have already had some exciting moments .. including a dismasting and some capsizes as they learn what works and what does not.  But the 'word of the hour' is that these amazing boats are 'highly addictive' ;)


Craig Leweck (Scuttlebutt Sailing News) recently paid a visit to American Magic and here is how he described his brief visit to the hull of the Defiant while it was in the shop for fine-tuning.

QUOTE:   “Once at deck level, the immense depth of the cockpit reminds me of the emphasis toward eliminating windage. Four sets of grinding pedestals, two on a side, will keep eight crew humming the handles with their heads out of the wind.

The cockpit appears small, positioned well aft, with a [huge] expanse of deck forward.  It is 'scow-massive', but not needed for crew work. Sails aren’t going up and down, with buttons and joysticks aft to control the performance variables. However, it was noted how the forward set of grinders also double as jib trimmers that actually must handle jib sheets… so some tradition still remains.

With 11 crew, and 8 on the handles, that leaves first stringers Dean Barker on helm and Paul Goodison on mainsheet trim in the aft of the cockpit, with the futuristic role of flight controller Andrew Campbell at the front of the bus. Utilizing tools more familiar to naval flight school than sailors, Campbell’s job is to ensure Defiant has smooth air travel”


ADDED:  February 16th, 2020

Here are two sketches from the 64 pages of Official Design Specifications for the AC75's that 1) show the main foil arrangement and 2) a diagrammatic of the Foil Control System (FCS), that is designed to clarify what is fixed (and supplied) for all boats and what is not.   This FCS diagram is shown for those particularly interested in digital Data collection and use, something that will certainly play a very important role in controlling how well these giant foilers perform,

For the main foils themselves, as long as the foil outline (in transverse section) fits within the 4000 x 700mm rectangle shown, its acceptable within the rules.  The support arm stock is standard though, so in practice, the foils from one boat could be mounted on another, even if highly unlikely. Power to operate these foils is hydraulic and comes from pumps operated by the human 'coffee-grinders'.


Note: Mike Waters has no direct connection to the America's Cup organizers. While technical views may be those of the writer, the data come from official releases or openly published data. While info has been reasonably researched and believed to be correct, there can be no guarantee of absolute accuracy. His opinions are purely personal ones covering his assessment of the situation based on data currently publicly available.