A vertical axis wind turbine designed with two cylindrical Magnus effect rotors mounted on a rotating drive unit (Image courtesy Challenergy)

Posted on November 13, 2022 at 2:08 p.m. by

harry valentine

During the 1980s, University of Michigan business professor Dr. CK Prahalad’s treatise “Competing for the Future” focused on “the convergence of technologies”. It is possible to combine recent technical developments to advance marine wind propulsion, and technology from Sweden, Japan, the United States, Germany and the United Kingdom offers such a possibility.


Introduction


In the early 1980s, physics professor Brad Blackford entered a windmill-powered boat in a wind-powered sailboat competition in Halifax, Canada. He sailed his boat directly into a headwind and won the race, using an inclined axial flow wind turbine which directly drove a small boat propeller. Over the next few years Blackford improved the concept and achieved speeds of eight knots while sailing directly into a headwind. He sailed his wind-powered boat along the eastern seaboard of the United States in moderate wind speeds, with the wind turbine and propeller having overspeed and cavitation limitations.


High efficiency at low speed


Several inventors have experimented with moats to increase the propulsive efficiency at low speeds of small boats. A Swedish manufacturer called “Dol-prop” markets such a product which is based on the tail fin of a dolphin. Enthusiasts have developed vertical and horizontal mechanical tail fins to achieve more efficient propulsion. Demonstration of the technology on small boats suggests potential for development of large-scale versions of tail fin mechanical propulsion technology, potentially driven by wind turbine technology capable of withstanding vertical-axis typhoons using the Magnus Effect , originally from Japan.


The Typhoon Turbine’s Magnus-effect vertical-axis cylindrical rotors capable of spinning at extreme rotational speeds while exerting the force of a lever to drive a central drive shaft that carries extremely high torque at relatively low rpm . An ideal future concept would combine the power characteristics of such a turbine with a large-scale mechanical fin capable of propelling a large ship sailing westward across the North Atlantic in severe headwinds that occur during the last part of each year. An alternative layout would use one of two competing designs of proven vertical axis propulsion 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, which provides stability advantages in mobile applications. The recent innovation of installing Magnus effect rotors on the design of vertical axis wind turbines enables operation in extremely fast wind conditions. Such rotors are currently manufactured for the maritime sector as an alternative to sails. It is possible to fit the same rotors on large-scale, deck-mounted vertical axis turbines, with the option of operating an upper and lower rotor group on the same assembly.


The combination of removable rail-type wheels rolling on a curved track would support the weight of the rotating turbine assembly, with each rotor fitted with a brake and either an electric or air-powered starter, as well as the fin design trailing launched by Challenergy in Japan. . Magnus-effect vertical-axis wind turbine technology promises to solve the operational problems of previous vertical-axis wind turbine designs at extreme wind speeds. The lower center of gravity allows for larger scale construction than horizontal axis tower mounted wind turbines for marine propulsion.


Future development of wind turbines


The wind industry has focused on the development of horizontal axis turbines mounted on towers to generate electrical power for the power grid, the largest offshore three-bladed turbines rated at 14 MW (18 700 horsepower) using blades 354 feet in diameter. Such a level of power is the result of many successive years of continuous research and development, with a hurricane-proof version of the technology now having been developed. Horizontal axis wind turbines on towers have been used for the propulsion of small boats using a mechanical gear transmission.


A wind turbine rated at 500 kW (670 horsepower) in a wind speed of 30 mph and spinning at 240 rpm would deliver nearly 15,000 lb-ft of torque. A planetary gearbox could increase rotational speed to 2,400 rpm at 1,500 lb-ft of torque to be transmitted through 90-degree spiral bevel gears and counter-rotating concentric vertical shafts.


Horizontal axis turbine


The development of vertical-axis wind turbine technology capable of withstanding typhoons in Japan provides an opportunity to undertake further research into the development of a practical and competitive multi-megawatt, large-scale version capable of supplying maritime propulsion. Vertical axis technology allows the turbine to directly drive vertical axis propulsion technology, with the option of planetary gears to adjust relative rotational speeds or to use crank and connecting rod technology to drive a large-scale mechanical propulsion technology. The centershaft of a two-stage mega-scale Typhoon turbine spinning at 90 rpm with 250,000 lb-ft of torque would deliver just over 4,300 horsepower or 3,200 kW to a vertical axis propeller.


Voith-Schneider Propulsion


The Voith-Schneider vertical axis propulsion technology has proven itself in tugboat applications and could be driven by a vertical axis wind turbine. Setting the vertical angle of the blades to the neutral zero thrust setting would allow operation of a wind turbine with negligible starting torque. While increasing the height of the propulsion blades would increase the maximum propulsive thrust, such a modification would increase the bending loads on the blades. It may be necessary to undertake research into the merit of using upper and lower level disc plates to secure each vertical propulsion blade at both ends on a full-scale version.


It is possible for vertical axis wind turbine technology to drive the Voith-Schneider using either a direct gearless drive or by installing a vertical axis planetary gear system between the wind turbine and the propulsion unit . Thruster blades include pivots and related technology that require regular inspection and maintenance. A competitive axial-flow propeller that operates vertically would require less frequent inspection and maintenance due to the lack of pivots and related technology. A wind-powered ship assigned to transoceanic navigation would require a high level of long-term reliability as well as ease of inspection and maintenance of the power and propulsion system.


Vertical axis axial flow propeller


A UK company offers a vertical axis axial flow impeller installed inside a duct which includes a steerable capacitance. While a self-starting vertical-axis wind turbine might directly drive a vertical-axis propeller, it would likely be necessary to install an overdrive gear 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 withstand sustained high torque loads at low rotational speeds. A vertical axis propeller built on an excessive diameter with variable pitch blades would operate at high efficiency at relatively low RPM.


Downstream of the propeller, a horizontal section of rectangular duct with variable outlet section would make it possible to regulate the navigation speed. A set of several deck-mounted vertical-axis turbines that each drive a vertical 3-turn crankshaft can be connected to each other by tension cables and drive a single vertical-axis propeller. Each vertical axis turbine can alternatively drive its own vertical axis propeller with a duct that combines with other ducts at the stern of the vessel. The variable-pitch blades would adjust to a range of power output and regulate the speed of the wind turbine while sailing long distances in powerful wind conditions.


Mechanical tail fin


A vertical axis turbine would drive a vertical crankshaft with two jets spaced 180 degrees apart. The crankshaft would drive a pair of connecting rods attached to the activating levers of a pair of parallel spring-loaded vertical mechanical tail fins. The forward end of each lever would attach to vertical-axis rudder-type pivot shafts attached to the ship’s hull. Each connecting rod would attach to each lever at a vertical axis pivot located between the tail fin and the rudder-like shaft. During operation, the tail fins would cyclically move in opposite directions to provide propulsion.



A future large scale version of the parallel tail fin concept would likely replace the spring system with the combination of front and rear vertical axis crankshafts spaced 90 degrees apart. A forward set of upper and lower links would attach to the tail fin attack area while the trailing links would attach to the tail fin trailing area. Installing the mechanical tail fins inside a rectangular duct with a variable area outlet would likely improve propulsion efficiency while allowing for adjustment of cruising speed. A mechanical linkage would connect the vertical axis turbine(s) to the propulsion system.


conclusion


Over the past decade, wind turbines capable of withstanding typhoons/hurricanes 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 insights into large wind-powered vessels that would be restricted to shipping lanes and harbors with unlimited vertical clearance. A future large-scale Magnus-effect vertical-axis wind turbine could directly drive a vertical-axis axial-flow propeller with variable-pitch blades.

The views expressed here are those of the author and not necessarily those of The Maritime Executive.