Modern Windships; Phase 2

12. Future Work and Improvements

Improvements of the Efficiency of the Rig
Reducing the Price of the Rig
Conclusion on Rig Optimisation
The Superstructure, Air Drag Improvements
Possible Improvements under the Waterline
Other Aspects
Computer Control System
Minor Items in the WindShip Design Still to be Considered
Planning of Future Work

During the course of the project lessons were learned as the tests and calculations were finished. To some extent these experiences were incorporated in the current WindShip design. However, since resources were limited, a number of possible improvements had to be left out untried. In the following chapter these possible improvements and their potential will be described.

There are also aspects of the WindShip which where not considered in this project, which needs to be addressed if the masts are to be used in the future. Notably the computerised sail control system has not been considered.

Improvements of the Efficiency of the Rig

Apart from testing different positions of the slat and the flap no optimisation of the wing mast profile has been done. The limited budget for the wind tunnel tests did not leave room for testing alternative profiles, designs of the slots and relations between the cord lengths of the three wing parts. Therefore we do not doubt that it must be possible to optimise the profile with at least 10% if further wind tunnel tests are conducted.

Furthermore a winglet could be fitted at the top of the mast to reduce the vortex loss and if an aerodynamic screen was fitted on the weather deck the vortex loss at the bottom could be almost avoided. The efficiency of the mast could also be increased if the mast was taller with a higher aspect ratio.

The height of the mast is only a problem when passing bridges, but if the upper part of the central mast (above the uppermost shaft) was hinged the bridges could be passed by turning this part as well as the upper panels to a horizontal position. In this way the height of the mast could be increased by 5 – 8 m (depending on whether the number of horizontal sections is 4 or reduced to 3).

Reducing the Price of the Rig

One very efficient way to reduce the price for the total wind ship is to reduce the number of masts but maintain the total sailing performance. The area of an 8 m taller mast would be about 1050 m², giving a total area of 5 masts of about 5250 m². The corresponding area of 6 of the present masts is 6 * 890 m² = 5340 m², which is only 90 m² more than the 5-mast solution. The increased mutual distance between the individual masts in the 5-mast constellation may very well more than compensate for this difference.

Another way of reducing the price is to simplify the design e.g. by reducing the number of horizontal shafts and rotating sections from 4 to 3. This should be possible, especially if the cord length of the flaps is reduced (to lower the turning moment), and the design value of the wind speed where the flaps gives way is reduced from 20 m/s to 18 m/s.

One other way to simplify the structure is to change the design of the asymmetrical leading edge of the mast and the slat. This could be done in two ways:

1. The leading edge could be symmetrical and be part of the steel mast, so that only the slat is rotating.
2. The slat could be deleted and the asymmetrical leading edge made correspondingly longer.

Several possibilities are shown in Figure 73 below.

Figure 73. Some of the possible profile improvements.

Decreasing the design loads as previously described and thereby also the scantlings will reduce the price. The weight of the mast could also be reduced if the thickness of the central mast could be slightly increased (e.g. from 2000 mm to 2500 mm) without reducing the performance.

The final option for reducing the price is to build the rig or at least the central mast in a region with low labour costs as Asia. A steel mast built in Western Europe would cost about 25 DKK/kg. In for example China the price would be about 8 DKK/kg, excluding transportation costs.

The weight of the central mast and mast foot in the present design is about 65 tonnes so the price reduction would be approximately 1.1 million for the mast.

Conclusion on Rig Optimisation

In our opinion it is not unrealistic to imagine 5 masts of a total European price per mast of 5.5 million DKK, performing like the present solution with 6 masts of 7 million per mast. (A price reduction of 34%.) Figure 74 shows a wind ship with a 5-mast design.

Figure 74. Five mast proposal.

The Superstructure, Air Drag Improvements

Visualisation from the wind tunnel indicated that a significant vortex was developed at the bow of the ship when tacking against the wind. This vortex was triggered by the sharp edge of the bulwark at the front. The vortex clearly disturbed the airflow over the foremast sails.

Recent designs of fast ships show enclosed mooring decks, using rounded corners. This feature was included in the updated WindShip design in order to reduce the vortex size. Further wind tunnel testing and CFD calculations should be performed in order to determine the optimum shape of the bow. There is a possibility that intelligent positioning of "vortex-triggers" at the bow can actually increase the performance of the sails. An example of such a screen can be seen in Figure 74 above.

There is no doubt that such a screen will increase the efficiency of the rig/hull combination considerably, but the screen is not free of charge. Alternatively a compromise between a different design of the weather deck and a smaller screen could be developed.

The aft of the WindShip was designed with lowering the drag in mind. Again from the wind tunnel visualisation it was apparent that further improvements can be made. In the updated design the forward facing corners have been rounded in order to decrease drag. It may be possible to further reduce drag from the superstructure by even more "radical" design. This should be investigated by CFD and wind tunnel measurements in a future phase.

In general a WindShip will benefit to a larger extent by including aerodynamic aspects in the design stage than a conventional product carrier. Since the wind is being used to propel the ship disturbing the airflow unnecessarily not only increases drag, it also reduces the actual force driving the ship forward.

As general rules of thumb all surfaces should be as smooth as possible. Forward and sideward facing corners should be rounded as much as possible. Masts, pipes, cranes etc. protruding from the hull should be minimised. As much as possible of the deck equipment should be placed in "lee" behind the aft superstructure. The further forward on the ship the more important it is to "keep decks clear".

Making a very aerodynamic superstructure and deckhouse will also reduce the yawing moment so that less rudder forces are needed to keep the course, but on the other hand smooth panels are more expensive than flat ones. Further wind tunnel tests will be needed to get a total picture of the possibilities in optimising the above-water hull.

Possible Improvements under the Waterline

Further optimisation is mainly possible in conjunction with the engine, propeller and rudder choice. Depending on route and target speed large improvements can be expected in certain cases. Coupled to this is the balancing of the sail plan with the underwater body. Here some improvements can be expected, resulting in less use of rudder forces to balance the ship.

The somewhat unusual shape of the underwater body has proven effective in towing tank tests. Although a few percent of drag maybe can be shaven off through further hull line optimisation, we feel that the effort is better spent on investigating the items mentioned above.

Other Aspects

Many aspects of the modern WindShip, such as the environment, were not covered in the original task. Other reflections have come up during the project. Some of them are summarised below.

Computer Control System

A significant and important aspect in all sailing is the control of the sails. In this phase of the project emphasis has been put in making for a mechanically sound sail system, which requires little maintenance and little or no extra crew handling. The condition for having minor extra crew handling is however that a computerised sail control system is developed. This has not been a part of this phase.

To sail the WindShip at optimum speeds, using as little fuel as possible for a given target speed, will require a close interaction between the engine power output, rudder angles and individual sail positions. The VPP developed in this phase of the project is a first step in predicting these quantities. For a real ship a complete "digital cockpit" may be envisaged. Developing such a computer system is a large, but necessary, step in order for any WindShip to be commercially competitive with existing ships.

Not having automatic devices for the optimum trim of sail-power-rudder will result in the WindShip sailing in non-optimum condition, as well as using skilled extra crew to constantly monitor and trim the WindShip propulsion parameters. These two drawbacks can significantly add to the cost of a WindShip. An obvious solution is to use computers to constantly monitor and adjust the settings.

The development of an automatic sail system was not included in the current phase of the project due to its large cost. It is however not considered as an insurmountable engineering task to design such a system. The development was therefore naturally postponed to a later stage, where the economic feasibility has been demonstrated, and a go-ahead with building an actual structure has been granted. The amount of work, and the complexities involved, should however not be underestimated. It is recommended that an initial study using control theory expertise should be performed in case there is a continuation of the project. The goal of such a study should be to judge the work involved, and to estimate a development cost.

Minor Items in the WindShip Design Still to be Considered

There are a number of small items specifically concerning a WindShip. Some of them are mentioned below. More of course exist, but it is our view that employing some good engineering work can solve them all.

	The WindShip will often have a certain inclination, about 7° -8° in strong wind. For a product carrier this does not pose a large problem, but for a bulk carrier the cargo could over a longer period of time, with strong wind from the same side, be shifted towards leeward. Additional longitudinal bulkheads might have to be incorporated to counteract this.
	The masts will block most of the view from the bridge so alternative solutions must be found. Traditionally the conning position on the bridge will be in the centre line but in a wind ship two conning stations – one at each side – probably have to be fitted. Apart from these two stations it might be necessary to fit a third station in the foremost part of the ship to be used in crowded or narrow waters.
	The navigation lights will also pose a minor problem. The sidelights can be fitted as normal on the bridge wings but the two white top lights will be a problem. One of them can be fitted on a mast in the centre line forward of the wing masts, but the other one must be fitted on the top of one of the masts. However, as the mast will be turning, a safe system that turns the navigation light the opposite way has to be incorporated.

Planning of Future Work

The project has had a significant "tool-building" phase, the VPP, the weather routing and Mærsk Brokers economical model had to be specifically developed for the WindShip. These tools are now readily available for further use and refinement in future projects. It is our sincere hope that these development costs were not wasted, but that future WindShip project phases can benefit from the work presented here. The work that should be performed in conjunction with the modern WindShip can be divided into several separate studies:

Further post-processing of results. There are significant amounts of results from the weather routing to be investigated further. Fuel consumption on specific routes at specific times of the year etc. can be deduced.

Customer identification. Finding the correct market, trade routes and goods to transport in order to take advantage of the benefits of the modern WindShip.

Environmental analysis. Provide the necessary knowledge and arguments to make environmental beneficial decisions.

Optimisation. When the market has been identified, notably the ship’s size, target speed and typical routes, weather data can be compiled and all tools developed brought into use in order to optimise the technical solutions. This corresponds roughly to a "phase 2.5", where another round in design spiral will be carried out.

These studies were not rated in any specific order, although the customer identification is thought to be vital for a successful deployment of modern WindShips in the future.

Phase 3. The originally planned Phase 3-study includes development of a computer system and building of a prototype wing mast.