Left: Oracleʼs own AC50 raceboat was the guinea pig for the transformation of AC50 into F50 and the boatʼs tooling was employed by Core Composites to manufacture any AC50 parts directly transferable to the new fleet. In spite of moving to battery power to pump oil the conversion (above) from manual hydraulics actually delivered a net weight saving. The joys (right) of modern pre-preg – where rubber gloves are all you need to stay clean (and theoretically they are only required to prevent material contamination)
done on the wings to be able to produce similar, if not identical, twist distribution between them. For example, some wings had a slightly greater twist range. Those have been limited so all the boats now have standard ranges of camber and twist.’ As mentioned last month, Coutts is keen to replace all the wings with a new ‘modular’ version as soon as is practical. The current plan is for these to have common tops and bottoms, but with three interchangeable mid-sections of different lengths, enabling the F50 to sail across a wide wind range. Drummond points out that this is not so crazy given that the wings are already semi-modular due to their having to fit into 40ft containers. The aim is Coutts’s target of being able to race the F50s well in 3kt or 30. ‘That is an extreme wind range,’ says Drummond. ‘But in light winds you just need span, so the taller the wing the better.
‘For example, on Lake Geneva where very tall rigs are king, they race well. If you go to the other extreme, 1m radio- controlled yachts race quite well in 3kt and can race well in 30kt by having an ext - remely tall rig or extremely short rig.’ The new F50 wings will be developed over 2019 with the aim of coming on line for 2020. While the one-design AC50 components are being recycled wherever possible, large swathes of the F50s are new. This includes the foils and rudders. All the cockpits have also been adapted to the new crew of five (instead of six) and the variation of their roles, including there now only being two grinders. The pods (running fore and aft down the centreline) have also been changed and much larger aerodynamic fairings have been introduced.
The absence of any constraints of a design rule, plus encouragement from Coutts to let rip with their creativity (albeit
within a tight timeframe), left the develop- ment team in a ‘kids in a candy shop’ situation when creating the F50. The foils and foil-control mechanisms have particularly benefited from this. As Drummond explains: ‘There was a restric- tion in the maximum beam that the foil could go out to under the AC50 rule. The new foils exit the hull and curve outward a bit more, plus the corner radius between the vertical and the horizontal foil parts is larger and the latter has much greater span, so the light-air performance is expected to be better.’
These improvements, plus the use in the new boards’ construction of previously prohibited ultra-high modulus carbon, much of it oriented at 45° for torsional stiffness, mean that they start cavitating in the high 40s of boat speed, significantly higher than the AC50s, and so will now be able to operate into the mid-50s. There are also significant improvements in what was a critical area structurally of the AC50 foils. ‘The elbow in the foil was a source of trouble for quite a few of the teams in the last Cup,’ says Drummond.
Being able to alter the trim of the rudder ‘elevators’ was introduced to the AC50s as a step on from the AC72s (when trimming them was prohibited), initially to alter fore and aft trim as on a Moth. However, teams found a much more effective way to use this horizontal T-foil by introducing differential between them, ie the leeward rudder pushing up, the weather one push- ing down. The effect of this was to offer a dramatic increase in righting moment. This maximum differential has been massively increased to 8° on the F50s. Holroyd explains: ‘Whereas with 3° [on the AC50s] you weren’t generating a huge amount of righting moment, with 7-8° on the F50s you can generate very significant
amounts – and that gives you a lot of performance gain in medium-breeze, upwind conditions.’
Obviously wanging on 8° at high speed could instantly rip the rudders right off the boat, so this is one area where the F50’s intelligent electronics come into play. The hydraulic controls not only auto- matically change the elevator rake to pre- set positions when tacking, but the degree to which the elevators are deployed is automatically altered according to boat speed. How much positive elevator is dialled in to leeward and how much nega- tive to weather is also used to manage the overall pitch of the boat.
However, inducing racking into the platform – as some teams were doing in Bermuda to enhance the effect of rudder differential – is outlawed on the F50s. Holroyd explains: ‘Some teams [starting with Oracle] had cottoned on to the fact that if you reinforced the mast tube above the basic spec, then you could slacken the lower shroud and cause the platform to rake more. The one-design fix for that is just to put a constraint on the lower shroud tune to force all of the boats to come back into line.’
The result of the centre of lift of the main foils moving outboard slightly and the dramatically increased rudder differ - ential is that the F50 potentially has much higher righting moment than its predecessor.
The systems used to drive the F50’s new foils and new rudders have also been totally renewed. As mentioned last month, every function onboard is now driven electro-hydraulically, apart from the wing sheet which is cranked on by two grinders. To spec this, Holroyd and the team carried out a comprehensive energy audit, ‘from booting the boat up in the morning, doing
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CHRIS CAMERON
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