Two graphs to raise a smile from every Imoca skipper weary of being smashed around as their boat takes off and then crashes back into the water. These two displays show (left) the dramatically reduced range of trim switching from a conventional rudder (blue line) to a small T-rudder with an elevator area of just 0.10m2
. It’s suggested that with even
a small foil it may be possible to all but eliminate current nosediving into steep waves. A similarly dramatic effect is seen on speeds (below) using elevators; a current rudder is seen at the bottom (blue) up through elevators of 0.10m2 (red), 0.15m2
(green) and 0.20m2 The small 0.10m2 rudder elevator (red)
does not affect maximum speed but the average speed (and ride) is much better
increased average speed for an elevator- equipped Imoca to above 40kt, with far less porpoising and incredible dynamic stability. In a bear-away the boat can simply ‘sail-fly’ off downwind, no heel, no trim. Extra stability in pitch is also acquired
due to the damping effect of the elevators – which will employ symmetrical sections with zero lift at neutral incidence and no dynamic adjustment, no different to the stability that is gained with heel using the existing main foils. The ‘flight’ would also be very consistent and much steadier – in the 16kt TWS used in the simulations the bow touch-down would occur in the worse-case scenario seven times less than with a conventional current configuration. Is there a price to pay for all these
benefits? Not if there can be a cost trade- off, according to the study. To achieve neutral cost VPLP propose a combination of a rudder elevator with a surface area of 0.15m2 (up to 0.4m2 was trialled during the evaluation) combined with new Dalì foils limited to a maximum of 200kg each. This way the extra cost for the elevators is offset by a reduced cost of the main foils, while speed and stability will still increase dramatically. There is also another not-so-irrelevant
will see the biggest design differences, com- pared to current Imocas, in the stern area as designers try to further minimise residual drag in the touchdowns and lift-offs. The main schools of thought in current
Imoca stern treatments range from Juan K’s very flat transoms to the deep-V by VPLP seen on Charal and to a less extreme extent on Hugo Boss. VPLP are another powerhouse in ocean
racing yacht design and they were tasked by the Imoca class president, Antoine Mermod, to study what advantage the rudder elevators may or may not bring to the current line of yachts. At Seahorse we have been granted an exclusive sneak preview of the study and its results. The Imoca class rules can only be changed and adopted in between Vendée
46 SEAHORSE
Globe races every four years. So with the next AGM scheduled for July 2020, will the sailors go for the elevators or will they postpone the decision to 2024? The VPLP study considers an ‘average’
hull made by mixing the lines of recent top boats and applying elevators of different sizes in different wind and sea conditions, with true wind angles of 70°, 110° and 135°. One of the key elements considered is
that the elevator surface should be small enough to retain the kick-up system used now by all boats to minimise the risk of damage from floating objects – and also to reduce wetted surface by lifting the weather rudder blade. So this is an evolution rather than a revolution. The most interesting findings of the study and the VPLP simulations show an
aspect to consider: given the size of current foils Imoca boats must be spaced at least 16m apart in the harbour at the start of the Vendée Globe, limiting the number of boats. A return to smaller main foils means that more boats can be accommodated! Which would certainly be a welcome opportunity for the class and for the Vendée Globe organisers. Do the teams feel the same way? Pierre-
François Dargnies, the technical director of Team Charal, is keen to try the elevators as soon as practical. He suggests that the best solution would be to begin working on the design as soon as the boats start this Vendée Globe in order to have prototypes ready for their return to shore 70-odd days later. ‘The Route du Rhum in 2022 will then be the perfect race to try the new development, if not at the Transat Jacques Vabre in 2021.’ Antoine Mermod will certainly preside
over an interesting class AGM this year: free the Imoca and let them fly or chain them to ground?
q
(purple).
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