Figure 4. Albedo spray vessels. They would sail back and forth square to the local prevailing wind. Flettner rotors with Thom fences can give lift coefficients up to 20 and lift drag ratios of 35, much higher than cloth sails. Artwork by John MacNeill.
I think this Salter and Latham paper is currently the best on the topic: The Reversal Of Global Warming By The Increase Of The Albedo Of Marine Stratocumulus Cloud. In Section 4. Practical hardware you will find a description of their proposed solution, together with specifications for the 45 m water line length by 20 m beam spray vessels.
The requirement for operations with a good solar input points to mobile equipment which can draw all the spray energy from the wind and so stay on station for long periods. The direction and magnitude of the thrust from a Flettner rotor are controlled by its rotation speed which is much easier to control by a computer in an unmanned vessel than would be the case for a vessel with conventional textile sails. It is possible to apply brakes and, with two or more rotors, to rotate about the vessel centre. Heeling moments are proportional to the first power of wind speed rather than its square and so Flettner-powered vessels should be much safer from capsize in heavy seas. The addition of Thom fences can give lift coefficients up to 20 and lift drag ratios up to 35 so that they can tack much closer to the wind than a vessel with a conventional rig.
Figure 3 is an artist’s impression of a spray vessel. Turbines much larger than propellers for a vessel of this size would be dragged through the water to generate energy for spray generation. About 10% of the turbine output would be needed to spin the Flettner rotors. Vessels would be fitted with satellite navigation and an Iridium communications system which would allow them to be directed to suitable spray sites and also to send back to eager meteorologists data on sea temperatures, atmospheric pressure, wind and current velocity and direction, solar input, cloud cover, wave height and period, plankton and aerosol count and even to relay emergency messages. Once at the chosen site each vessel would sail back and forth across the prevailing wind producing a wake of treated air downwind.
For informed criticism of this concept, see Roger Pielke Jr. (PDF). The paper that Roger is critiquing is An Analysis of Climate Change as a Response to Global Warming, by Dr. J Eric Bickel and Lee Lane. Both papers are from the Climate Change Project of the Copenhagen Consensus Center.
Marine cloud whitening with a fleet of unmanned ships would be extremely cheap: for about $9 billion, all of the global warming for the century could be avoided, with benefits adding up to about $20 trillion.
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