Page 24: of Maritime Reporter Magazine (March 15, 1981)

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Sail-Equipped

Motorship (continued from page 24) is constant, ship speed is not con- stant as it depends on wind uti- lization. However, if the average ship speed throughout the entire voyage is the same as in (1), it becomes possible to use a smaller main engine than is used on con- ventional ships.

After comparing the two pos- sibilities and considering the im- plications of propulsion control concerning ship schedules, it can be seen that possibly (1), in which the ship speed remains con- stant, is far more practical.

In the case of the speed being kept constant, the relationship between the propulsive power of the sails and main engine output is as shown in Figure 2. The main engine is controlled in such a way that total output will be constant as much as possible.

In this system, when a fixed- pitch propeller is used, the num- ber of revolutions is controlled. If a variable-pitch propeller is used, the blade angle and number of revolutions are controlled result- ing in an engine load that achieves maximum fuel economy while keeping constant speed.

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Figure 2 — Relationship between propul- sion power of sails and main engine with ship's speed being kept constant.

Conclusions

Through these studies and tests, main results were obtained as follows: 1. The sail-equipped motorship in which sails are used as aux- iliary (not as main) source of propulsion seems to be most fea- sible at the present stage. 2. Laminar flow type rigid sails which were mechanized fully were found to be one of the optimums for practical sail equipment. 3. Considering the increase of the fuel oil price in the future, sail-equipped motorships seem to be economically feasible at this time, by the effect of the cost- down of sailing equipment.

Ocean transportation is in a state of emergency due to recent rapid increases in the price of fuel for ships and to the growing uncertainty of fuel supply, both of which have made it impera- tive to take measures for the con- servation of fuel. Under such con- ditions, the re-emergence of wind force as a natural source of en- ergy for the propulsion of ships through modern techniques has become of great significance.

Even during the period of two years while this research and de- velopment was being conducted, the petroleum situation has un- dergone drastic changes. These conditions indicate that the time is fast approaching when sail- equipped motorships will become feasible on a commercial basis.

As a result of feasibility stud- ies made using a 10,000 to 35,000- dwt bulk carrier, the first stage of the development process, it was established that this type of ship can be operated profitably.

However, when the actual equip- ping of the ship was considered, there were and still are many problems to be solved regarding maneuverability which must be studied in more detail; maneu- verability in docking, mooring and when in harbor movement; the crew needed for this type of ship and their mastery of the operational techniques; the selec- tion of the most suitable routes for specific voyages, etc. Solving these problems has thus become the task that will be undertaken (continued on page 28)

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