Update


BELIEVE ME, MY YOUNG FRIEND – JACK GRIFFIN And we’re off! A major new development cycle shifts into high gear with the publication of the AC75 Class Rule at the end of March. Design teams need to develop first principles on how these three- legged spiders will sail. A good place to start might be how to keep them right side up and how to get one back on its feet when it capsizes. The last time we had boats over 70ft long in the America’s Cup Oracle demonstrated that their only plan for righting a capsized AC72 was ‘don’t capsize’.


First principles The Protocol forbids wind tunnels, tank testing and a wide range of surrogate yachts. Money saved with these cost-reduction mea- sures will no doubt be spent on simulators. Lots of processor cycles will be expended, many focused on the four principle factors that determine lift: angle of attack, density of the fluid, speed of the flow and foil shape. The AC72s and AC50s varied the angle of attack by raking the daggerboards. But they were not permitted to have movable control surfaces. (Let’s not say the foils weren’t allowed to change shape, since they certainly deflected under load – some teams had control of this dynamic shape- changing better than others.) When Emirates Team New Zealand introduced the AC75 they


said there would be no foil arm rake, and that flaps or other control surfaces would be used to vary lift. They later added that generating downforce with an immersed windward foil would not be allowed,


12 SEAHORSE


given the enormous structural loads that would generate. It’s logical and easy to say that downforce will not be allowed. It may be considerably harder to write a rule for that. How much of the AC75 will be one-design or even supplied


equipment? There have been hints that the foil-lifting mechanisms and even the foil arms would be one-design. The foil wings and the 1.5-tonne ballast bulb shapes are logical areas for each team to express their creativeness. Some important trade-offs will be the same as for the AC50 foils: lift-off speed, onset of cavitation, top- end speed, structural integrity, stability and complexity of the control system. The electrical power pack for the lifting mechanism might also be one-design. The rules about battery capacity and charging will be interesting. ETNZ have said there will not be any cyclors and internal combustion engines will definitely not be allowed. Simulating transitions will be key. What lift-off speed do you need


to go from floating to foiling? Do you always start in ‘stable mode’ with both foils immersed? How do you transfer lift from the windward foil to the leeward foil and raise the former? Would it ever be desir- able or possible to do a windsurfer-style water start, with the wind- ward foil already raised? How do the humans onboard operate the foil controls? Raising and lowering the foils should be a simple button push. Regulating lift during a tack or gybe will be more complex. Hull design has been left open. We may see a wide range of


shapes and big changes when each team launches its second boat in February 2020. Do we build a narrow, slender hull for minimum drag in displacement mode? Perhaps with wings like the New


XX


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