I have proposed that Transition sail modules can be fitted to larger ships with available deck space, for example tankers and bulk carriers, so that they can reduce fuel-use.

This video gives a brief overview of the Big Rig proposal:

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Here is a short video showing a model sail module:

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When sails are placed in close proximity with each other,
they interact with each other. The following video
explores the interaction between closely-placed
Transition Rigs:

The following is a paper I presented at a conference about sustainable shipping held by the Royal Institution of Naval Architects in London in 2010.

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SAIL MODULES FOR WIND ASSISTANCE

SUMMARY

There is growing concern about the impact that marine transport is having on planetary systems. Fines for environmental damage, rising fuel costs, and increasing public concern are providing powerful incentives to ship owners and operators to look for alternative ways of propelling cargo ships. In the longer term, new propulsion solutions and more sustainable ships will be developed. In the shorter term, we have the opportunity to apply well-understood and achievable approaches such as wind assistance to at least a proportion of existing ships. Sails, kites, and rotors are all viable options for wind assistance. The proposal put forward here is for folding sailing rigs contained in streamlined pods that can be reversibly fitted to existing ships such as tankers and bulk carriers to reduce their fuel use on favourable routes by approximately 20%. The rationale for this approach is discussed.

“Let us tread lightly on the planet so that our children

and grandchildren can follow in our footsteps.” [1]

1.             INTRODUCTION

Sustainability is about living now in a way that does not compromise future generations - not only of humans, but also of the other life forms with which we are interdependent. It requires us to be aware of the potential that humans have to upset planetary balances and to deplete irreversibly the resources on which we depend. We are having to reconsider many of our activities in order to find less environmentally-damaging ways in which to live.

In recent years, the shipping industry has enjoyed growth as it successfully responded to the commercial pressures for more rapid, reliable, and economic distribution of raw materials and products. However, the industry is now being asked to become more sustainable in its operation. At the recent Copenhagen summit on climate change, the International Maritime Organisation recognised the need for commercial shipping to reduce emissions, possibly by as much as 50% by 2050 [2]. This significant reduction will have to be achieved during a period when the demand for shipping is projected by the Ocean Policy Research Foundation (OPRF) of Japan to increase by a factor of 2.5 [3].

Although there is widespread awareness of sustainability issues within the maritime industry, there are concerns that the response so far has been too slow [3]. The required changes will not be easy, particularly since the evidence and interpretations relating to human impact on the environment and biodiversity are still incomplete and inconclusive. The UN Intergovernmental Panel on Climate Change (IPCC) has reported a scientific consensus that greenhouse-gas emissions resulting mainly from the burning of fossil-fuels have been a major contributor to recent global warming and precipitation changes [4]. At the same time, the IPCC acknowledges that fundamental gaps exist in our knowledge [reviewed in 5]. Climate-change sceptics highlight these uncertainties and it is perhaps not surprising therefore that there is reluctance within the shipping industry at this time to take what may appear to them to be costly steps into the unknown. It is possible that commercial pressures still outweigh sustainability considerations.

A move towards greater sustainability will require changes in the design, construction, operation, repair, and disposal of future generations of vessels [6]. During the operational phase of a ship’s lifecycle, one of the key issues relating to sustainability is the means of propulsion. Since most ships today use fossil fuel for power, thus depleting a finite and precious resource and contributing to environmental damage, we need to find alternative means of propulsion, both for existing ships and for next-generation ships. Several alternative energy sources have been proposed so far, including wind, solar, wave, hydrogen, fuel cell, and nuclear energy [1, 7, 8, 9, 10, 11]. A glimpse of possible future designs for ships using a variety of alternative sources of propulsion has been provided by, for example, Orcelle [7, 12], Aquatanker [13], and Greenwave [1]. However, it will be several years before such ships become available, and in the interim it will be necessary to find modifications that can be made to the existing fleet if environmental targets are to be met.

Wind power has been used by ships for many centuries, and it would seem both sensible and achievable to use it once more without delay while other longer-term alternatives are being developed. It is worth recalling that the age of the cargo-carrying square-rigger continued into the 1930s. In their heyday, loaded square-rigger ships in the hands of talented captains and crews and under optimal conditions could travel 300 miles in one day under wind power alone [14]. The best transit time for Captain Erikson’s steel four-masted barques carrying grain from Australia to the UK was 87 days [15]. Contemporary interpretations of the square rig have been developed for the superyacht Maltese Falcon [16], the designs of Captain Schwab [17], and sail-assisted coasters being planned by B9 Shipping [10, 11]. More recent methods of harnessing wind power include the Flettner rotor which uses the Magnus effect [1, 18], and kites [19]. It is probable that each method of harnessing wind energy has both advantages and disadvantages in comparison to the others when applied in the marine context. They are not necessarily mutually exclusive options or in competition with each other, and hopefully they can each make a useful contribution to the development of more sustainable ships in the future. It is possible to envisage, for example, the same ships using sails for wind assistance in crowded sea lanes and kites in the open ocean. However, ship operators still need to be persuaded that such approaches can make commercial sense.

Most commercial ships have to meet tight operating schedules when moving materials around the world, and wind power alone would be unable to meet these requirements given the variable nature of the wind and its uneven distribution across global shipping routes. For this reason, wind power alone is commercially viable only for certain types of cargo for which a longer transit time is not a disadvantage [20]. For other time-dependent cargoes, it is more practical to use wind power as a form of assistance to engine-power.

The focus in this paper is the provision of wind assistance to certain types of ships – those with sufficient areas of open deck space - by add-on sail modules. Sail modules will allow vessels to throttle back their engines in order to conserve fuel and reduce harmful emissions.

To some ship owners and operators, the proposal to fit sails to commercial ships might be seen as a retrograde step, and imply the need for more crew, greater risk to crew members, increased dependence on specialised weather knowledge, costly vessels vulnerable to storm conditions and awkward to manoeuvre in port, and erratic performance in relation to schedules. The purpose of the following proposal is to allay at least some of these misgivings, and show that in addition to environmental benefits there are also potential commercial benefits from wind assistance.

2.             CRITERIA FOR PRACTICAL WIND ASSISTANCE

For wind to become once again a significant source of propulsion for commercial shipping operating in the contemporary commercial context, several key requirements will need to be met. These were identified in a major study of the issues relating to wind power for larger ships initiated in 1995 by the Danish Government and carried out by Knud E Hansen [21, 22]. To be effective under today’s conditions, sailing rigs for commercial ships:

• need to be operational without the need for more crew

• must not endanger the crew

• must not interfere with cargo handling

• must not jeopardise the safety of the vessel

• must be reliable with the minimum of maintenance

• must work well when sailing upwind

• must not exceed 60m mast height (a limit imposed by the Panama Canal and some harbours)

• should not obscure visibility during manoeuvring

• ideally should be suitable for existing ships.

Figure 1: Multiple sail modules fitted to a ship with suitable deck space.

3.             SAIL MODULE PROPOSAL

The proposal is made here to fit folding sail modules to existing ships with suitable deck space (Figure 1). This would include some tankers and bulk carriers, but the concept might also be applicable to other classes of ships such as coasters, research vessels, and fishing vessels. The aim would be to provide wind assistance so that the ship’s normal power plant can be throttled back, rather than replacing the need for engines completely. It is anticipated that a worthwhile reduction in fuel use would result, probably in the order of 20% on suitable routes. It will be suggested that this approach is able to satisfy most, perhaps all, of the requirements for practical wind assistance listed above.

The design of the sail module is innovative, and has been granted a GB Patent (No. 2381515: "Engine powered vessel with removable sail modules", 2005). The concept has been described previously [23], and arose during the development of folding, variable-geometry rigs known as ‘transition rigs’ for smaller craft such as dinghies, kayaks, and sailboards over a period of 23 years [24, 25].

Each module consists of a substantial base plate and a jointed rotating mast that can extend upwards and fold downwards. The foot and leech of the sail are tensioned out to the end of a horizontal boom. The base plate of the module is strongly but reversibly attached to the deck of the ship. The sail is made from a material that can accommodate the changes in mast geometry during deployment and folding whilst having an effective aerodynamic shape in use. Radially-arranged battens support the upper part of the sail, and the lower part of the sail is double-skinned, enclosing and protecting the mast between the laminae. The mast is rotated by an actuator that drives the rim of the circular mast base, allowing the rig to be trimmed according to the direction of the apparent wind. Two hinged doors attached to the sides of the base plate form a streamlined cover for the sailing rig when folded, and open to allow the rig to be deployed. When the rig is fully extended, the doors close around the base of the rig to protect the control and operating systems at the mast foot and to provide additional stabilising support to the lower segment of the mast. Before the rig is lowered, the doors open again and the rig folds, with the doors collecting the folds of sail material before closing over them.

The choice is made here to use a ‘soft’ sail to enable the rig to readily conform to the wind on either tack and to deploy and fold. In Modern Windships Phase 2 [22], the preference is for rigid foils resembling aircraft wings, since it is proposed that these can be more aerodynamically efficient in steady airflow conditions than soft sails, and with appropriate materials they are likely to be more durable. However, rigid sail panels would not be feasible for the sail module design. The sail module rigs described here have an aerodynamically clean and efficient form, with the mast and its operating equipment enclosed within the pod and between sail laminae, and there is no standing rigging to generate drag. They also have the capacity to absorb some of the shock loadings produced for example by gusts which in the case of rigid foils would be transmitted more directly to the ship. The ability to fold the sail away into the pod means that it is protected from harmful influences such as ultraviolet radiation when it is not in use, and this will prolong its useful life.

Figure 2: Sequence showing deployment of sail module: (a) folded rig protected within closed pod; .(b) pod doors open; (c) rig beginning to extend; (d) rig unfolding; (e) rig fully extended, pod doors open; (f) pod doors close around lower segment of mast.

A suitable sail cloth will be required. The material forming the leading 2/3 of the sail will need to be sufficiently resilient to allow repeated extension and folding of the rig without tearing. It has been found from extensive experience with small scale versions of the rig that the trailing 1/3 of the sail can be made of a non-stretch material to stabilise the leech of the sail when the rig is deployed and tensioned. This gives an optimal aerodynamic form when the sail is powered up. Given the large sail areas that will be required for larger ships, ideally the sail cloth will be derived from sustainable or recycled materials.

The actuators that open and close the module doors and produce extension, folding, and rotation of the mast can be hydraulically or electrically powered according to the requirements of the ship. An umbilical connects the module to the ship’s power and control systems to enable deployment and control of the rig from the ship’s bridge. Solar panels may be fitted to the module doors for power generation if required.

Modules would be lifted by crane onto the suitably-modified deck of the host vessel, and fixed securely in place. The power and control umbilical would be connected to the ship’s systems. After a test deployment in port, the rigs would be folded away into their pods. After leaving port, and when conditions are suitable, some or all of the rigs could be deployed and the ship’s engine(s) throttled back. The sail area provided in this way will depend on the dimensions of the sail modules and the number of modules in use. To give an example, a mast height of 40m will carry a sail of approximately 400sqm, so eight rigs of this type would provide 3,200sqm of sail.

Having several rig modules on the same ship provides flexibility and redundancy. At any given time, some, all, or none of the rigs can be deployed, depending on weather conditions and how best to trim the vessel to counteract leeway and helming forces. If a rig fails, it will have a natural tendency to fold down to deck level, assisted by gravity. This is a safe-fail situation. The remaining rigs could still be used. In a potentially dangerous situation such as a storm, the rigs can be folded to deck level to reduce windage.

The sequence of deployment for a 1/20^th scale pneumatic model of a sail module is shown in Figure 2.

4.             DISCUSSION

4.1          PRACTICALITY OF THE PROPOSED SAIL MODULES

In section 2 above (criteria for practical wind assistance), several requirements were identified by which proposals for wind propulsion should be judged. It is helpful to apply these to the sail module proposal:

sailing rigs need to be operational without the need for more crew; and

sailing rigs must not endanger the crew

The proposed modules will be controlled from the ship’s bridge, without the need for any other direct crew involvement. Thus, there will not be the need for additional crew, and no crew will be required to climb the rigs or make any other interventions over and above their normal duties. Servicing and repair of the modules will be carried out on land after removal from the ship.

sailing rigs must not interfere with cargo handling

In port, the rigs remain folded within the pods, giving good access to the decks and hatches.

sailing rigs must not jeopardise the safety of the vessel

Folding rigs have certain advantages over fixed rigs, since they can be brought down to deck level and enclosed in their pods when not required or during storms. In their folded and enclosed configuration, the modules will have minimal influence on the safety of the vessel.

sailing rigs must be reliable with the minimum of maintenance

Sail modules have various moving and highly-stressed parts and there will be the possibility of malfunction. However, by suitable design, choice of materials, and redundancy within the control systems, it should be possible to make the modules reliable in operation. By having multiple rigs on one vessel, the malfunction of one or some rigs will not interfere with the normal function of the others. The natural default position for the module rig is the folded configuration due to the effect of gravity, so it should be possible to cope with a malfunction without the safety of the ship being compromised.

sailing rigs must work well when sailing upwind

The fore-and-aft sail arrangement of the kind proposed here has been found to work effectively at a smaller scale when being used close-hauled. It is anticipated that the same will be the case when the design is scaled up for the sail modules. The rig is also effective on other points of sail.

sailing rigs must not exceed 60m mast height (a limit imposed by the Panama Canal and some harbours)

With folding rigs, the height restriction does not pose a difficulty since the rigs can be brought to deck level when approaching restricted areas such as canals and harbours. The main constraint on the dimensions of the sail module will be the sailing forces generated in use and their effective dissipation into the ship’s structure through the deck.

sailing rigs should not obscure visibility during manoeuvring

When the rigs are folded, they will not obscure visibility during manoeuvring.

sailing rigs ideally should be suitable for existing ships.

The sail module concept was developed with certain types of existing ship in mind, for example tankers and some bulk carriers. For a particular ship, the defining features that determine whether or not sail modules could be fitted are the availability of free deck space and the capacity of the deck to absorb sailing forces.

Figure 3: a) tilting forces generated by the rig; b) a schematic cross-section through the base of the rig showing the relationship between the mast foot, base plate, and deck.

4.2          CHALLENGES PRESENTED BY THE SAIL MODULE CONCEPT

The main engineering problem associated with the sail module approach will be to dissipate the sailing forces generated by the rig without having the benefit of a mast that penetrates deep into the ship’s structure. Stays and shrouds which are used in traditional rigs to give added support to the mast would not be applicable here given the folding, rotating nature of the rig. The base plates of the sail modules will have to disperse the forces into the deck and its substructure. Whichever is the windward side of the base plate will have a tendency to lift from the deck, so the anchorage points will have to be able to resist this force (Figure 3).

(There are parallels here with the situation faced by trees. Contrary to popular belief, the root systems of 80-90% of trees have shallow root systems within the top 60cms of the soil to resist the toppling forces produced by the wind [26].) The module doors, when closed, could provide some additional buttressing to the lower segment of the mast whilst still allowing it to turn within a bearing. Given the stresses involved, it is probable that the deck will need additional reinforcement in the area of module attachment.

Unlike fixed standing rigging, folding rigs have the advantage that they can be protected from extreme conditions by being stowed in their protective pods, and only deployed when forces lie within the range that the module has been designed to withstand. If an acute situation arises that overwhelms a sail module while it is in use, or if the safety of the vessel is being threatened, there is also the potential to release the module from its fastenings and sacrifice it from the ship.

The mechanisms producing extension, folding, rotation of the mast, and opening and closing of the module doors, together with their control systems, will be comparable to those already in widespread use in equipment such as cranes and derricks.

Existing ships will need modification before the sail modules could be attached. This will probably involve repositioning of some equipment to clear suitable areas of deck space, reinforcement of the deck beneath the modules, locking devices to hold the base plate securely to the deck, and links with the ship’s hydraulic, electrical, and control systems. For ships with more limited deck space, for example bulk carriers with midline hatches, it may be feasible to cantilever the pods partially out from the sides of the ships so that they do not obstruct loading and unloading. All of these structural changes will have a cost penalty, and this will need to be recouped from the fuel savings provided by the sail modules over a reasonable operating period.

With wind assistance, a ship will be able to throttle back its main engine(s). This may result in the engine and/or propeller working sub-optimally. Laboratory research and experience at sea will be required in order to find ways of balancing the sails, engine(s), and propeller(s) in particular cases to obtain the greatest benefit from wind assistance.

In recent years there has been considerable progress in the understanding of the aerodynamics of sails. There has for example been rapid evolution in the design of windsurfing sails which because of their small scale have lent themselves to experimentation. This experience has subsequently influenced sail design at larger scales, for example in the America’s Cup. This progress in understanding will provide a valuable resource when developing sails for larger vessels.

Multiple sails in proximity to each other interact, so obtaining optimal performance from multiple sail modules on a single vessel will require testing and experience. The interactions depend on the direction of the apparent wind, so that on some points of sail the rigs might facilitate each other while on other points of sail there may be wind shadowing of rigs to leeward. To develop a better understanding of the aerodynamics and control of multiple rigs, a dinghy was modified to accept 3 rigs of a similar design to the one proposed for the sail modules and tested on the water [27].

4.3          ENCOURAGING THE UPTAKE OF SAIL MODULES

In addition to finding solutions to the engineering challenges described above, it will be necessary to convince the shipping industry that the adoption of wind assistance makes commercial sense. Ship operators face two main categories of risk if they decide to invest in wind assistance [28]:

• operational risk, including risk of damage to the ship’s structure, risk of capsize, risk of not keeping to schedule, risk to crew members, and risk of not complying with existing legislation

• financial risk, including cost of purchase, cost of maintenance, reliability of revenue, and length of return on investment.

The initial funding for the development of sail modules through the prototype and testing stages would probably need to come at least in part from governments firmly committed to the reduction of carbon emissions. The international research institute that has been proposed by the OPRF might be a suitable body to coordinate this process [3]. The major class societies ABS, Lloyd’s Register, and Det Norske Veritas will also be key elements in encouraging the required innovation.

When a suitable design has been achieved, then there is the potential for the rig modules to be provided and serviced by companies on a leasing basis to the ship operators. This approach would remove from the ship operators the initial capital investment required for module development, and allow them to focus on the potential for fuel conservation and the cost of adapting their ships to accept the sail modules. The leasing costs could be linked to the savings achieved in such a way that the ship operators have a financial incentive to adopt wind assistance while the income to the leasing company is also sufficient for long-term viability.

With the sail module approach, risks are therefore reduced by removing development costs from the ship operators, by leasing the modules on an as-needed basis, by carrying out servicing and repairs with the modules on land, by operating the sails remotely from the bridge without the need for crew members to take risks, by having redundancy in multiple rigs, and by their ability to be folded away to deck level when not required. It is hoped that these qualities of sail modules, together with the growing pressures for shipping to become more sustainable, will encourage uptake.

Sails and other forms of wind propulsion obtain energy from a free and sustainable source, albeit a variable one, and with the exception of their manufacture and decommissioning these technologies have minimal impact on the environment during their use. The experience gained with the sail module system proposed here will be of benefit to designers of next-generation ships, perhaps encouraging the incorporation of folding rigs during the design process.

5.             CONCLUSIONS

The sail module proposal offers a practical approach to wind assistance for commercial vessels, complementing other approaches such as kite and rotor propulsion. It has the advantage that it can be developed and implemented over a relatively short time scale since it draws upon generally well-understood principles and practice and can be applied to a proportion of existing ships. It can therefore help to improve the sustainability of the shipping industry over the shorter term while more radical designs are developed for the next generation of ships. It will be possible for ship operators to achieve commercial benefits by the adoption of this form of wind assistance.

6.             ACKNOWLEDGEMENTS

I wish to acknowledge funding from the National Endowment for Science, Technology and the Arts (NESTA) for development of the Transition Rig concept in 2000-2001.

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Richard Dryden