Modern Windships; Phase 2

Summary
Conclusion

Summary

Modern WindShips - Phase 2 has proposed an innovative technical solution with regard to rig- and hull-design for the modern WindShip.

New materials for the construction of sails were suggested and an asymmetrical rig has been designed. The rig incorporates a novel method of shifting the asymmetry from side to side by use of horizontal shafts.

Towing tank tests and wind tunnel tests were used to determine the efficiency of the suggested rig-system. Tools regarding speed-predictions and weather routing were developed and used to predict the behaviour of the WindShip.

Detail design of the wing mast was carried out in all the major areas where complications could be expected. Detailed drawings of the mechanical systems were presented. The underwater hull properties were investigated. The final hull used a bow-fin, a forward thruster and double rear azimuth propellers.

A feasibility study was carried out. The impact of variations in fuel prices was stressed. The effect of varying the average speed was investigated. A product carrier was chosen as study example. The study pointed out some of the commercial limitations of WindShip-application at present time. It proved uneconomical to use WindShips on typical product carrier routes. A cost increase of approximately 10% was calculated when comparing the WindShip with an equal-sized conventional product carrier.

The results showed that by lowering the average speed of a conventional ship by 1 knot a reduction of approximately 25% in fuel consumption could be achieved. However, by adding the rig of the WindShip on average an additional three tons of fuel per 24 hrs could be saved in the more windy areas. This corresponded to 10-15% of the total fuel consumption.

Conclusion

The WindShip project, phase 2 was logically divided in two major parts. One was the technical work, the design of a new type of rig, development of velocity prediction programme through testing both in wind tunnel and towing tank. The development work involved here was purely engineering, to get the optimum rig and ship design. The other part was mostly economical, starting with the decision of which type of ship will be simulated, routes to be sailed and the commercial comparison with conventional tonnage.

These two separate investigations were kept together by the weather routing, which used the technical data from the first part, translating them into numbers which could be used for calculation of the fuel consumption. With the fuel consumption as input, the economical feasibility analysis could be performed.

The project spanned over a large field of knowledge, aerodynamics, hydrodynamics, test- and experimental methods, programming, meteorology and economy. The basis of the project was however a profound knowledge of ship and mechanical construction, good and bad practices when designing complicated mechanical structures. On this basis models were created, experiments, tests and calculations could be carried out.

Treating these two parts separately and starting with the technical side, we can conclude that a highly advanced rig type has been developed. The drawings of the rig at the end of this report and the corresponding calculations are the results of one turn in the so-called "design circle". This phrase reflects that all aspects of the project has been calculated or tested at least once, uncovering most problems.

The results from this part were good from an engineer’s point of view. We believe the technical results to be reliable, realistic and re-producible. Any design work will normally involve several circles with increasingly smaller "radius" narrowing into the final optimal target point. This approach is called the "design spiral". As the time and the budget in phase 2 have been limited we do not claim that the result of this phase represents the final, optimal solution.

However we have shown the great potential in a high-lift design. Optimisation work still remains, especially with regard to reducing the price and weight. All the calculation tools are now developed and available so that the calculations can be re-run with new coefficients.

The weather routing was a success, producing such amounts of data that there were not resources in the project to evaluate them all. The exhaustive database should prove valuable as reference for future WindShip projects.

On the economical side the results may be less inspiring at first sight. There is no doubt that the results were both reliable and realistic. However, the main conclusion that emerged was that a product carrier is not the preferred choice for a modern WindShip. There was no economical advantage in using a WindShip, instead it cost 10% more to sail with. Worse yet, the fuel savings were marginal, under certain assumptions and conditions a WindShip even consumed more fuel than a conventional ship.

However, on the route between Rotterdam, Holland and New York, USA an average HFO saving of 20.5 to 27% was shown, depending on average speed. It was only here that the average wind speed of 8 m/s initially estimated during phase 1 could be found. Decisions on sail area etc. were based on this estimate early on in phase 2 of the project.

At the same time the feasibility study showed that the comparison had been made at a sub-optimal speed for a WindShip. Calculations using 11 knots instead of 13 lowered the required freight rate with up to 5%. Due to the special requirements of the product carrier trade the larger internal volume of a WindShip was not used to its advantage in the study.

Taking the above issues into account we see the potential of modern WindShips concept. If speed is reduced, but same productivity is maintained due to the larger volumes carried, money will be saved. It is in this market segment that the WindShip should operate. Careful routing, including effects of seasonal weather variations could then prove the WindShip both environmentally beneficial and economically favourable.