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Headwind Propulsion for Articulated Two-Section Vessels

DOE
Floating offshore wind technology has established a precedent for large turbines mounted on hull structures (US DOE illustration)

Published Jul 23, 2023 2:23 PM by Harry Valentine

Multiple technical precedents have occurred over the past 40-years that provide a basis by which to develop wind turbine powered vessels capable of sailing directly into headwinds. The concept combines ocean-going tug-barge technology, floating wind turbine technology and a proven system for sailing into the wind while powered by a wind turbine. For mega-scale wind turbines to achieve mobility behind ships, future research will need to combine twin-hull catamaran technology with floating platform technology to carry the turbine.

Introduction

During early 1980s, a Canadian professor of physics at the Technical University of Nova Scotia, Dr. Brad Blackford, entered a windmill powered boat into a sail boat race across Halifax harbor. He sailed his vessel directly into a prevailing headwind and crossed the finish line ahead of sail-powered competitors. In later years, he eventually achieved a speed of eight knots sailing a windmill-powered houseboat directly into a headwind. His achievement provides a basis by which to further explore the potential of wind turbine powered commercial freight vessels directly into headwinds, including into trade winds.

Research has shown that wind usually blows at greater speed across large bodies of water than across land. Wind speed also increases with elevation, allowing larger-scale vessels to place larger-scale wind turbines in the faster wind streams that blow at higher elevation. The result would be higher power output from the turbine, in turn providing the necessary power to propel a larger and heavier vessel directly into a headwind, including at potentially higher sailing speed than achieved by Dr. Blackford. His achievements combined with developments in floating wind turbine technology offers the maritime sector a future propulsive option.

Tug-Barge Option

The design of modern ships and many ports complicates the placement of a large-scale wind turbine above the deck of the vessel. An alternative approach would involve installing a large-scale wind turbine above the deck of a companion vessel, with a tug-barge layout being a possible option. A future super-wide, twin-hull catamaran tug that carries a wind turbine would borrow from recent design precedents involving floating wind turbines. In service, a mobile floating wind turbine vessel would provide propulsive power between the entrances of distant ports, but never enter any port due to its extraordinary dimensions.

Successful tug-barge operation on the North American Upper Great Lakes as well as in coastal service have involved tugs pushing and navigating large barges carrying commercial bulk freight. An expanded concept of a coupled two-unit vessel technology may include either a tug pushing and navigating a barge or a towed power generation companion vessel providing electrical power to a full-size ship driven by electrically-powered propellers, placed ahead of the turbine vessel. An interconnecting electrical power cable would transfer electric power from towed unit into the ship which would include crew accommodations and a control bridge.

Propulsion Trailing Unit (Tug)

The weight and dimensions wind power conversion installed on to a tug or towed unit would require that the twin-hull catamaran tug be built to considerable length, width, sailing draft and height. Severe ocean wave conditions may likely require the installation of coupling mechanism between barge stern and tug bow that allows for relative vertical movement. Wind conditions would likely require up to 200 feet between the twin hulls of a catamaran unit that would carry twin counter rotating vertical-axis turbines based on the Japanese Typhoon turbine designed to operate in winds of 90 miles/hour, installed in multi-stacked configuration.

Each vertical drive shaft from the turbines would directly drive an axial-flow propeller with variable pitch blades installed on a vertical axis, with an option for planetary gearing to optimize propeller rotational speed. Ducts would redirect intake water from horizontal to vertical upon entry to each propeller and the output water stream from vertical to horizontal, with an optional rectangular variable cross-sectional area outlet. The pair of vertically-stacked wind turbines would operate between 250 and 450-feet above water.

For ocean sailing, control bridge and crew quarters could be installed on the barge, with future potential for autonomous control on trans-ocean voyages. Further research may be required to develop the tug-barge concept for trans-ocean sailing through severe wave conditions.

Towed Trailing Unit

Precedents in floating platform technology would form the basis of research required to develop a mobile twin hull catamaran assembly that would carry floating wind turbine that would be towed behind a ship. Interconnecting power cables would transfer electric power from the wind turbine to the ship’s electrically driven propellers. The ship would also house a control bridge and crew accommodations. An inter-vessel articulation that provides relative vertical movement between ship stern and catamaran along with some propulsive capability built into the towed unit would reduce mechanical stresses across the articulation coupling.

The catamaran twin hull configuration would allow propellers backwash to pass between the twin hulls on ocean voyages. Local port vessels including with onboard energy storage or onboard power generation would assist the main vessel during extreme low-speed sailing within the confines of a port. The dimensions of the wind turbine catamaran section of coupled vessel would require that it be coupled to the ship outside the port area upon departure and upon arrival at a distant port at the end of the voyage, be detached from the ship outside of the port area.

Power and Speed

The stationary and anchored Wind-Float semi-submersible platform designed by Principle Power and installed offshore from Scotland carries the 9.5MW Vestas model V-164 wind turbine. A Japanese consortium proposes to develop a floating wind turbine of 15MW (20,000-horsepower). To save fuel cost, some ship companies have slowed their vessels to 12-knots sailing speed. A ship that requires 100,000-horsepower to sail at 25-knots would require 12,600-horsepower (9.4MW) to sail at 12-knots and around 7,500-horsepower (5.6MW) to sail at 10-knots. The 4.2MW (5,600-horsepower) General Electric 4.2-117 axial-flow wind turbine is designed to withstand wind speeds of up to 125-miles per hour.

A ship that requires 40,000-horsepower to sail at 25-knots would require just over 5,000-horsepower to sail at 12-knots. Selsam Wind Power installed 2-twin bladed rotors set 90-degrees apart on the same drive shaft that operated at a small angle to the wind. One rotor was installed upwind of the tower and the other far downwind, with the central axis of drive shaft installed to the side of the central axis of the tower. If GE were willing to adopt the Selsam concept, the output of the GE typhoon capable turbine would increase to over 5MW (7,000-horsepower).

Conclusions

The precedents and hardware required to develop a mega-scale wind turbine powered ship capable of sailing directly into a headwind, already exist in seemingly unrelated areas of the maritime sector. Combining the precedents and hardware offers the basis of a potentially viable wind turbine powered ship capable of sailing directly into prevailing trade winds over perhaps several thousand nautical miles. The ship would be able to sail with the trade winds and especially during extreme wind speeds. Based on the precedent from Halifax, a wind turbine powered ship would likely sail at greater speed into a headwind than a schooner.

While a two-section wind turbine powered ship would be a competitor to a modern mega-scale schooner, it could be built to much larger scale than a schooner and be capable of carrying greater payload. Wind turbine powered ships and modern mega-scale schooners would likely operate along different international routes and serve different markets. The presence of wing-sails on the deck would restrict the kinds of cargo a mega-scale modern schooner could carry while a wind turbine carried by a twin-hull catamaran platform placed behind a ship increases the variety of freight that could be carried aboard the ship.

The opinions expressed herein are the author's and not necessarily those of The Maritime Executive.