Typhoon Wind Turbines and Maritime Propulsion

Beginning over a decade ago in response to powerful winds destroying wind turbines, Japanese researchers began developing wind turbines capable of operating during typhoon force winds. More recently, General Electric has begun developing typhoon capable wind turbines. There is potential to adapt some typhoon capable wind turbines to maritime propulsion and especially for sailing directly into headwinds.

Introduction

Almost universally, wind turbines are locked down to prevent self-destruction when wind speeds exceed 60 knots. In maritime transportation, locking down the turbine of a windmill powered vessel at mid-ocean due to excessively powerful winds would leave the vessel adrift. Excess wind speed would cause turbine that directly drives a propeller to produce destructive propeller cavitation before centrifugal force tears apart the wind turbine. Wind blows at higher speed over open sea than over land and enhancing the attractiveness of maritime wind propulsion. Wind speed increases dramatically as elevation increases above ocean surface.

Existing windmill powered boats are mainly used for private transportation and recreational purposes. In such operation, boat owners can head to port at moor the boat after a storm warning has been issued. Commercial freight carriers need to sail irrespective of stormy weather, with very few such vessels being suspended from service due to severe weather conditions. A wind power technology capable of operating during severe wind periods could sustain vessel propulsion and in some regions, likely be cost competitive to operate when sailing directly into prevailing headwinds, such as westbound across the North Atlantic.

Early Typhoon Turbines

The early development of horizontal-axis wind turbine (HAWT) typhoon capable wind turbines involves replacing the traditional three blades with axle shafts, roller bearings and Flettner rotors with a spiral fin wrapped around each rotor. A later configuration involves five Flettner rotors. Wind interacted with the spiral fin on each rotor and caused the rotor to spin. The spinning cylindrical rotors redirected wind flow in a comparable manner as turbine blades, except that in high wind the assembly rotated at about 25 percent of the rotational speed of a three-bladed wind turbine of equivalent diameter.

A competing typhoon turbine configuration is based on the vertical-axis wind turbine (VAWT) where three vertical-axis Flettner rotors are spaced 120 degrees apart at an equal radius from the vertical power shaft. Each Flettner rotor has a vertical fin. The vertical-axis wind turbine typically operates at 30 percent efficiency, compared to horizontal-axis turbines achieving as high as 40 percent efficiency with equal wind speed. However, the typhoon turbine can remain operational in above 60-knot winds while conventional wind turbines need to be locked down. During high wind speeds, typhoon capable wind turbines would be suitable for commercial maritime propulsion.

Competition

General Electric Corporation is one of the world’s leading manufacturers of large-scale multi-megawatt wind turbines. Their research and development team at Barcelona are focusing on developing a horizontal-axis wind turbine capable of withstanding wind gusts of 110 knots. The typhoon capable GE 4.2-117 turbine assembly including tower weighs 460 metric tons with 117m blade diameter and capable of 4.2MW or 5,600-horsepower. A smaller blade diameter that involves less weight would likely be more suitable for maritime propulsion when sailing directly into headwinds. However, the power output would restrict such a commercial vessel to short-sea sailing.   

While vertical-axis wind turbines are rarely used, the vertical-axis typhoon capable wind turbine design from Japan offers possible maritime propulsive application. The turbine(s) would be installed high above deck at the top of a mast-tower that encloses a driveshaft coupled to multiple electric generators or hydraulic pumping technology housed inside the vessel’s hull. As wind speed increases, engaging magnets of additional generators would generate additional power, with potential to exceed power output of the high-mounted electrical generator driven by the GE 4.2-117 turbine. Either electric or hydraulic motors would drive submerged ship propulsion.

Vertical vs Horizontal Axis:

Exposing identical cross-sectional area exposed to wind, a vertical-axis wind turbine (VAWT) rated at 30 percent efficiency could compete with a horizontal-axis wind turbine (HAWT) rated at 40 percent efficiency. Above a boat deck, a VAWT built to 10m height by 10m width exposes 27 percent greater area to the wind than a HAWT built to 10m blade diameter. That additional area raises equivalent VAWT efficiency to 38 percent The HAWT carries a heavy electrical generator high above ship deck behind the turbine hub, incurring higher structural stresses than a VAWT driving a much larger electric generator installed below deck in the hull.

Carrying the heavy electrical generator below deck lowers the center of gravity and allows the VAWT to be built to greater height than the HAWT. At 12m high by 10m wide, the VAWT would deliver up to 14 percent greater power output than the HAWT. While a HAWT would have the advantage over a VAWT in stationary land-based located power generation, it loses much of that advantage in mobile operation when installed above the deck of a boat. In maritime propulsion, a typhoon capable VAWT using three Flettner rotors would actually become competitive sailing directly into powerful headwinds.

Conclusions

The crew of a windmill-powered commercial ship encountering excessively powerful winds at mid-ocean would likely lock down conventional wind turbines in order to prevent turbine self-destruction. Such a prospect would discourage installation of conventional wind turbine technology above a ship’s deck. The emergence and development of wind turbine technology capable of operating in the excessively powerful winds offers a future propulsion option to commercial shipping. Ships could take advantage of the additional propulsive energy provided by powerful winds that would destroy earlier generations of conventional wind turbine technology.

Harry Valentine is a regular contributor to The Maritime Executive.