Above left to right: big disturbance where Britannia 2’s clunky-looking cranked foils enter the water; a fine atomised spray comes off Patriot; clean wake on Team NZ suggests those fine lower arm sections are working as they should; and a fine spray off Luna Rossa similar to Patriot. Left: Team NZ’s second AC75 appears to incorporate the best bits of all of the first generation designs with a bold drive to top-end performance with that hollowed out bow, bulbous buoyant keel with razor sharp blade (as on Patriot) rolling aft into a bustle that rises into a board-flat stern – which in light air looks very sticky. Yet even with those small, straight foils it all works pretty well… which feels ominous


lower aspect ratio increases manoeuvra - bility but the choice is a risk for all-round speed. In fact, the first Ineos wing, with an aspect ratio of 4.4, is close to a delta wing used in supersonic aircraft where the focus is on laminar flow. A strange option!


Dihedral The dihedral corresponds to the angle formed by the two wings of the foil when viewed from the front. For example, the dihedral of the early Ineos foils makes a steep inverted V pointing downwards. Increasing dihedral gives each foil


hydrodynamic stability (not to be confused with Archimedean stability). This seems to be important for a boat with a hull/keel bottom that is 25-40cm from the water surface but did not prevent the Defender from designing a foil with virtually zero dihedral that was still very efficient. The class rules of the AC75 limit the


wingspan of the foils. The active surface of the foil, ie the one that produces the lift, is not its real surface, but the one that is projected onto the horizontal plane (the water). As wingspan is limited the root chord of the foil must be increased (thus decreasing the aspect ratio) if one wishes to increase the working surface to take off sooner. Dihedral has no effect on the active surface but dihedral increases the wetted surface. Drawing two foils with a large dihedral and with a low aspect ratio, as originally seen on Ineos, appears to restrict the efficient range of performance. It is important to remember that Great


Britain has a famous history in the evolu- tion of flight and especially in the develop- ment of wing sections. How Ineos had ever arrived at the first solution we saw before Christmas remains a great curiosity to me. It is enough for me to say that when the Prada Cup itself began in January I was relieved to see that the famous sailing nation had rejoined the game!


SEAHORSE 65


q


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120