Published 13.11.2022 14:08 by
Harry Valentine
In the 1980s, the paper by economics professor Dr. CK Prahalad from the University of Michigan with the title “Competing for the Future” on “the convergence of technologies”. There is an opportunity to combine recent technological developments to advance maritime wind propulsion, and technologies from Sweden, Japan, the US, Germany and the UK offer such an opportunity.
introduction
In the early 1980s, physics professor Brad Blackford entered a wind-powered sailboat competition in Halifax, Canada, with a windmill-powered boat. He sailed his boat directly into a headwind and won the race using an angled axial wind turbine driving a small boat propeller directly. In later years Blackford improved the concept and reached a speed of eight knots while sailing directly into a headwind. He sailed his wind turbine boat in moderate-speed winds along the East Coast of the United States, with the wind turbine and propeller subject to overspeed and cavitation limitations.
High efficiency at low speed
Several inventors have experimented with flukes to increase the propulsion efficiency of small boats at low speeds. A Swedish manufacturer called “Dol-Prop” markets such a product, which is modeled after a dolphin’s tail fin. Enthusiasts have developed both vertical and horizontal mechanical tail fins to achieve more efficient propulsion. The demonstration of the technology on small boats suggests the potential to develop large-scale versions of mechanical fin propulsion technology, possibly powered by Typhoon-capable vertical axis wind turbine technology utilizing the Magnus effect, which originated in Japan .
The Taifun Turbine’s vertical-axis, cylindrical Magnus Effect rotors are capable of spinning at extreme speeds while exerting the force of a lever to drive a central driveshaft that carries extremely high torque at relatively low speeds . An ideal future concept would combine the performance characteristics of such a turbine with a large mechanical fin capable of propelling a large ship sailing westbound across the North Atlantic into violent headwinds that occur in the second half of each year . An alternative layout would use one of two competing designs of proven vertical axis drive technologies.
Vertical axis turbine
While vertical-axis turbines convert energy less efficiently than horizontal-axis turbines, they can be built with a lower center of gravity, providing stability advantages in mobile applications. The recent innovation of installing Magnus effect rotors in vertical axis wind turbines enables operation in extremely fast wind conditions. Such rotors are currently being manufactured as an alternative to sails for the maritime sector. There is an option to adapt the same rotors to deck mounted large vertical axis turbines with the ability to run the upper and lower sets of rotors on the same assembly.
The combination of detachable train-like wheels running on a curved track would support the weight of the rotating turbine assembly, with each rotor fitted with a brake and an electric or air starter motor, along with the trailing fin concept that Challenergy in Japan has developed . Magnus effect vertical axis wind turbine technology promises to solve operating problems of previous vertical axis wind turbine designs at extreme wind speeds. The lower center of gravity allows for a larger design than horizontal axis tower mounted wind turbines intended for marine propulsion.
Future development of wind turbines
The wind turbine industry has focused on the development of tower-mounted horizontal axis turbines to generate electricity for the utility grid, with the largest offshore turbines being 14 MW (18,700 hp) with three blades and blades with 354 feet in diameter. Such a level of performance is the result of many consecutive years of continuous research and development, with a hurricane-capable version of the technology now being developed. Tower-mounted horizontal-axis wind turbines were used to power small boats using a mechanical gearbox.
A wind turbine rated at 500 kW (670 hp) at a wind speed of 30 mph and rotating at 240 rpm would produce nearly 15,000 lb-ft of torque. A planetary gear set could increase speed to 2,400 rpm with 1,500 lb-ft of torque transmitted via 90-degree spiral bevel gears and concentric, counter-rotating vertical shafts.
Horizontal axis turbine
The development of typhoon-ready vertical-axis wind turbine technology in Japan offers an opportunity to conduct further research to develop a practical and competitive multi-megawatt, mega-scale version capable of providing marine propulsion. Vertical axis technology allows the turbine to drive vertical axis propulsion technology directly, with the option of planetary gears to adjust relative speeds, or use crank and connecting rod technology to drive large-scale mechanical tail fin propulsion technology. The center shaft of a mega-scale, two-story Typhoon turbine spinning at 90 rpm and carrying 250,000 lb-ft of torque would deliver just over 4,300 hp or 3,200 kW to a vertical-axis propeller.
Voith-Schneider drive
Voith-Schneider’s vertical-axis drive technology has proven itself in tugboat applications and could be powered by a vertical-axis wind turbine. Adjusting the vertical blade angle to the neutral zero thrust setting would allow a wind turbine to operate with negligible starting torque. While increasing the height of the propulsion blades would increase the maximum propulsion thrust, such a modification would increase the bending loads on the blades. Research may be required into the benefit of using disc plates on both the upper and lower levels to secure each vertical drive vane at both ends on a mega-scale version.
It is possible to drive Voith-Schneider with vertical-axis wind turbine technology by installing either a direct gearless drive or a vertical-axis planetary gear system between the wind turbine and the drive unit. Engine blades include pivot joints and associated technology that require periodic inspection and maintenance. A competing axial flow propeller operating vertically would require less frequent inspection and maintenance due to the lack of trunnions and associated technology. A wind turbine-powered vessel used for overseas sailing would require a high level of long-term reliability, as well as easy inspection and maintenance of the power and propulsion system.
Axial propeller with vertical axis
A UK company offers a vertical axis axial-flow propeller installed in a duct that is steerable. While a vertical axis self-launching wind turbine could directly drive a vertical axis propeller, an overdrive gearbox would likely need to be installed between a slow spinning wind turbine and a fast spinning propeller. Planetary gear systems based on the combination of ring gears and multiple parallel planetary gears would be able to sustain high torque loads at low speeds. A vertical axis propeller built with an oversized diameter with variable pitch blades would operate with high efficiency at comparatively low speeds.
Downstream of the propeller, a horizontal section of rectangular duct with variable area outlet would allow adjustment of sailing speed. A bank of multiple deck-mounted vertical axis turbines, each driving a 3-pitch vertical crankshaft, may be interconnected by stay cables and drive a single vertical axis propeller. Each vertical axis turbine may alternatively drive its own vertical axis propeller with a duct connecting to other ducts at the stern of the ship. Variable pitch blades would adapt to a range of power outputs and regulate wind turbine speed while sailing longer distances in strong wind conditions.
Mechanical tail fin
A vertical axis turbine would drive a vertical crankshaft with two throws 180 degrees apart. The crankshaft would drive a pair of connecting rods attached to the activation levers of a pair of parallel, spring-loaded vertical mechanical tail fins. The forward end of each lever would be attached to vertical axis rudder-type pivot shafts attached to the ship’s hull. Each connecting rod would be attached to each lever at a vertical axis pivot located between the tail fin and the rudder-type shaft. During operation, the tail fins would cycle in opposite directions to provide propulsion.
A future major version of the parallel tailfin concept would likely replace the spring-loaded system with the combination of vertical-axis front and rear crankshafts spaced 90 degrees apart. A forward set of upper and lower tie rods would be attached to the forward section of the tail fin, while rear tie rods would be attached to the rear section of the tail fin. Installing the mechanical tail fins in a rectangular variable area outlet duct would likely improve propulsion efficiency while adjusting sailing speed. A mechanical linkage would connect the vertical axis turbine(s) to the propulsion system.
Conclusions
Over the past decade, typhoon/hurricane capable wind turbines have been developed in both horizontal axis and vertical axis configurations. Combined with related developments in mechanical tail fin propulsion and vertical axis axial-flow propellers, these technologies offer new prospects for large wind-powered vessels that would be restricted to sailing routes and ports with unlimited vertical headroom. A future mega-scale, vertical-axis Magnus effect wind turbine could directly drive a vertical-axis, variable-pitch, axial-flow propeller.
