A Hard Look at Wind Propulsion for Commercial Ships The Royal Institute of Naval Architects Conference, November 1980 By Sta nley Gerr Responding to the ever-increasing cost of fuel, several conferences on the prospects for wind propulsion of commercial ships have been held during the past few years. The latest was held in London , November 4-6. The findings? A return to pure sail is still unreali st ic. There was, however, strong sentiment that so me combin ation of conventional power assisted by windpropulsion is rea listic . The opening paper by C.T. Nance surveyed the whole problem and introduced six categories of windships for consideration. H e neatly summ ed up the matter: "The ce ntral problem of commercial sail at the outset of the 1980s is to match to each individual requirement the most suitable type of sailing rig, the most appropriate ship size, th e best wind / fuel engine power ratio, and the optimum service speed." Among th e proposals there wa~ only one which co nsidered developing a pure sailing vessel. This was for a 60,000-ton vessel with seven masts, each rigged wit h a simple , quadrilateral kite-shaped sail, much larger than any sail ever made or co ntemplated. The vessel is intended to sail before the wind in the Roaring Forties carrying wheat from Australia to Cape Town for tran sshipment there to a powered vessel which would take it to Europe on the much less wind-reliable run to Europe, while the fir st ship ret urn ed to Australia, running down these same reliable Westerlies in a cont inu a l circuit of the globe . After presenting his idea as technically feasible, however, the author concl uded that it was not economicall y feasible. Two papers dealt with the stud y of weather stati stics and their application to routing of sailing vessels for improved sailing times. With improved communication s, weath er foreca sting and mathematical analysis, optimum routes may be plotted with far greater accuracy than in th e past. A novel kite-sail idea was proposed to utili ze the higher wind speeds aloft, as well as utilizing the change in wind direction at ex treme height s. (In the Trades, the wind at 1000 feet is often blowing in the opposite direction to that at sea level.) Two further papers found promise in the wind turbine and related windm ill-type windship. Another anal yzed the theoretical advantages of the rigid, sy mmetrical airfoi l rig, as tested in a wind tunnel. Among the advantages listed: external structural simplicit y (no rigging), low drag, good upwind performance and suitab ility for motor-sailing. An important paper on "Standard ized Speed Prediction for Wind Propelled MerSEA HISTORY, SPRING 1981
Wind turbine
Airborne sails
Square rig-Dynaship
Fore and aft rig
Aerofoil rig
Magnus effect (Ffe11ner rotor)
The Six Major Categories of Windships chant Ships" usi ng detailed aero- and hydrodynamic considerations and statistical analy sis of available data, developed a general method for predicting the speed performance of the vario us system s under consideration . The results are applied to a wide range of hypot hetical cases, and equations and graphs are provided to serve as a basis for further work in this area. A paper on "The Design Challenge of the Wind Powered Ship" summed up th e problem as follows: 1) to design a windship with high lift-drag ratio (approaching 10!) in wind s up to 40 knots; 2) the des ign to have little heel even in stro ng winds; 3) to possess hig h "survivability" in the harsh marine environment; 4) remain within the cost limitations laid down. Such a vessel mi ght well be a catamaran motor-sai ler with airfo il rig. Finally, a design proposal for a 15 ,000-
ton 5-mast, bark-rigged motor-sailer for the Australia-Europe run was presented with the justification that only sq uare rig has been proved successful for centuries, and that the high cost of research and deve lopment for other kinds of rigs would be eliminated. A service speed of 12 knots is projected for thi s eno rmou s motor-sailer to which modern technology would be applied ch iefly in the use of lighter, more durab le materials, as well as the latest communications technology for weather routing. The conference was indeed a "hard" look at the prospects for commercial sail. Yet , as the introductory survey observed, "So diverse is world maritime activity, so var ied are the characteristics of potential windships, and so limited is our present knowledge about them, that development of a ll potentially viable systems should co ntinue ." J,
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