Wind Propulsion - Turbines rather than sail appear the most promising

The continuing increase in the cost of oil and the associated search for alternative energy sources is nowhere more apparent in its effect than ri the field of ship

prop-ulsion. Dependance on spot price fuel

charges for operators who are unable to make advantageous long term contractual arrangements, coupled with a supply situ-atiori which itself is not always dependable

in many areas, has made ship owning

increasingly less attractive even in trades where large scale lay-up of tonnage has not yet become the rule. Inevitably, therefore. there is a temptation to look back at the closing stages of the transition from sail to steam to see what lessons if any, can be learned regarding the possibility of a return to wind propulsion.

Recent studies in the UK and elsewhere have suggested near parity of building and running costs for Diesel and wind driven ships, on the basis of current oil prices, with an increasing advantage to the latter as oil costs rise in real terms relative to wages. Coal firing will also soon be acceptable on a capital arid running cost basis but development is required before a viable refuelling and burning system suitable for modern labour requirements is achieved and there is also the problem that once the demand for coal is significantly increased the normal process of supply and demand will correspondingly increase prices

bey-ond their present relative

level. Furth-ermore, there is at the moment no refuel-ling infrastructure for coal, which.since the demise of the British Empire, with its world

wide control of convenient islands and

seaports, would present a much more dif-ficult problem to establish, than in the late

8OO's when coal was the usual ship fuel. Nuclear propulsion also has its supporters, but these do not include ship owners and recent studies at the University of South-ampton on the viability of wind propulsion zuggest that operating cost of a nuclear propelled vessel are something like 1/4 those of the. equivalent oil fuelled or wind

ship.

There is also considerable public

resis-tance to the adoption of this means of

powering, despite its widespread use in warships. Thus, in view of what has been said so far, there would appear to be at least some incentive to give consideration to wind propulsion. As the starting point, a ship superficially similar to those used in

the closing days of sail has been

con-sidered by some. This could employ well understood handling

techniques, new

materials and perhaps a higher level of mechanisticn than in earlier days. There are also those who suggest that it is better to take advantage of recent aerodynamic dev&opments in racing sailing yachts, but

' JAN.

WiND PROPULSION

A.RCHIEF

this argument does not always take proper account of differences in the ratio of length to weight for pleasure craft and load car-tying merchant ships. This accounts for the apparent over-crowding with sail

to be

seen in illustrations of the latter vessels. In

the University of Hamburg particularly,

there have been developments in the

design of the traditional square rig which

REL. WtND /3

Balance of fOrces on a vessel sailing to windward. L-lift. 0-drag. Y-side force. have done much to overcome its aerody-namic disadvantages. These have involved closing the gaps between individual sails and attaching them, top and bottom, to cambered tracks in the yards which impart

a more controlled aerofoil section. The

result is that the assembly of square sails on each mast form as a Continuous shape of surface which can have much improved aerodynamic properties.

Yet another school of thought discounts

the possibility of sail aftogether on the

grounds that it is potentially labour

inten-sive and takes no account of more

advanced engineering ideas which can use wind to dr;ve rotating machinery. Recent advances in the field of wind turbine have looked particularly attractive for shipboard use and investigations are currently being undertaken to consider how a normal type

of propeller might be driven effectively

from such a device. Considerable sophis-tication is involved since the propeller and the turbine must have contro!!able pitch to ensure their proper matching under all cir-cumstances. A vertical rotation axis for the turbine is preferred for various engineering

Balance of forces on a vessel running before the wind.

VA

A

Lab,.

v. Scbeepbouwkumk

Iedinische Hogesdiool

Delfi

reasons, and this also raises the question of how desirable cyclic pitch control, rather like a helicopter, might be.

Finally there are those who believe that the Flettner rotor, which was originally tried at sea in the early years after the first war, may hold the answer. In this device wind blowing on a cylinder rotated by a small power source is converted into a force cap-able of propelling a ship. The force is some seven times larger than that produced by a sail of equivalent area and as a result

cylin-ders of quite manageable size can be

employed.

A more recent development based on the same ideas arises from work aimed at the improvement of helicopter rotors. In this case the cylinders do not rotate but have air blown from correctly positioned slots around their circumference.

Of the three broad systems outlined only the. Flettner rotor or its static variént could befitted relatively easily and quickly to con-ventional ships in the event that oil supplies

were almost completely cut off for one

reason or another, such as political action. All the alternatives which employ wind as a prime mover are in a position to benefit considerably from the use of modest diesel auxiliary power in light'wind and together with the use of weather routing, based on meteorological advice from centralised agencies, this could be expected to make a considerable contribution to reliability and speed of passage.

Despite the relative optimism of those

working in the field of wind propulsion

there is a certain reluctance on the part of shipowners

to show other than an

academic interest in the commercial pos-sibilities of such vessels. The reason for this is not hard to discover. In general terms

economy of operation lies in large size

ships, certainly much larger than anything

produced in even the last days of sail.

Unfortunately, a basic law of physics of size dictates that larger ships need stronger winds to drive them at the speed approp-riate to their size and the one aspect which does not change is the amount of wind available. As a result, at the upper end of ship size, wind must be considered more as an auxiliary than as a main propulsion source, at least within present economic constraints.

At the small ship end of the range lie such

short-haul craft as coasters arid fishing

boats. The latter,

in particular, are extremely sensitive in their operational economics to the cost of fuel to the extent that serious consideration is already being

given, in New Zealand for example, to

return to sail propulsion. None of these smaller craft seem likely candidates for a return to coal fuelling and it is probably in MARINE PROPULSION

Turbines r.ther than saIs

thissizerange that, if at all, we shall see the first return to the commercial exploitation of wind.

Having thus set the scene, it is of interest to consider in some detail the various fac-tors which have been introduced and which

are likely to effect the choice or otherwise of wind propulsion.

Technical alternatives for wind

propulsion

All wind propulsion systems, including the wind turbine system operating as a power

source to drive a conventional marine

propeller, develop aerodynamic forces by inducing a circulation of air round the rig, in exactly the same way as an upended aero-plane wing. It isthe foreward component of this force which produces ahead motion df the vessel. The lateral component pro-duces a sideways force and, because of the vertical separation of the hydrodynamic and aerodynamic centres of lateral force, cause the vessel to heel.

As with any other aerofoils (e.g. wing. rudder, propeller blade etc.) the amount of lift is limited by the well known penome-non of stalling. Because sails are relatively highly cambered in comparisons with other aerofoils, high lift coefficients up to about DL = 1 .8 can be achieved. Rotating cylinder devices exploiting the Magnus effect pro-mote circulation directly and the air flow does not detach from the cylinder in such a way as to produce a stalling characteristic. Lift coefficients to the order of CL = 20 are certainly achievable, so that a given Uft can

be produced by a rotating cylinder of a

much smaller size than a conventional sail-ing rig.

Sailing performance, however, is not governed by lift alone. The total

aerody-namic force, like that on wings, can be

resolved into a lift component per-pendicular to the "relative" or "apparent" wind direction, together with a drag com-ponent parallel to the apparent wind. The drag component has a strong influence on performance, particularly when attempting to sail as close to the wind as possible. it is also important to realise that the drag is dependent on lift and varies-approximately

as:

CD = C0o + KCL2

CDO = Profile drag coefficient

CL = Lift coefficient CD2 = Total drag coefficient

KCL2 = Induced drag coefficient It should be noted that these coefficients represent forces non-dimensionalised with respect to wind speed and sail area.

The factor K depends upon the aspect ratio of the individual "sails" (rig height/sail width) and upon the numbers of 'sails" operating in close proximity.

-The balance of forces on a sailing vessel seiling to windward is indicated in Fig. 1. In the steady sailing mode the total aerody-namic load is equal and opposite to the total hydrodynamic load. An inspection of the

Sail plan for the Dynaship concept by Prolss of Hamburg.

geometry of this diagram shows that the angle /3 between the vessel's track and the relative (or apparent) wind direction is related to the so called drag angles EA and

Hby the simple equation: /3 = E + Ef.

By definition we have also:

tan E4 = D/L = Co/CL and tan H =X/Y It can thus be seen that ability to sail close to the wind depends on the ability to achieve a high lift/drag ratio for the rig and a high side force/resistance ratio for the hull. The minimum values of EA and EH are usu-ally comparable in magnitude, being of the

order of 100 for a good modern yacht and of

the order of 250 for a conventional square rigged clipper ship.

Because of

the dominating influence of induced drag the use of high CL values, beyond maximum

L/D, is precluded for windward sailing, norrnal values being of the order of CL = 0.8

forconventional sails and CL = 2.0 for

rotat-ing cylinders (Flettner Rotors). In other

words the ability of rotating cylinders to produce high lift is of less advantage in windward sailing than might at first sight be expected.

The balance of forces on a sailing vessel running before the wind is shown in Fig. 2.

It can be seen from this that high drag

(including high induced drag as being the easiest way to achieve high total drag) is a positive advantage in

this casequite

unlike the windward case. Thus the rig which is best suited to windward work will be ill adapted for off wind sailing, and the best off-wind rig is not capable of sailing close to the wind.

Modern yachts carry special sails (spin-nakers) for downwind sailing, but these would not be practical for large commercial vessels.

Traditional square rig and other sail

configurations

The windward sailing ability of the trad-itional square rigged vessel was basically poor but, in an up-dated version, could be significantly improved by a number of rela-tively simple modifications, which were briefly mentioned earlier and are as fol-lows:

Close the gaps between the individual

sails on each mast so that the sails combine

WIND PROPULSION

to form a large, single, narrow aerofoil on each mast. The aerodynamic effect of this is to improve the ratio of lift to drag and thereby rotate the driving force in to a more effective direction.

O Curve the horizontal yards on which the sails are spread to obtain the correct sail camber for optimum performance. o Shape the overall aerofoil planform o the optimum configuration.

o Reduce the numbers of masts to a prac-tical minimum. The reason for this is that each mast, apart-from the first, operates in

the "down wash" wake of

the one

immediately up-stream and this has the effect of rotating its aerodynamic force in a direction which is progressively less advan-tageous for sailing to windward.

Some of the features outlined above are

to be found in the "Dynaship" (Fig.

3) design study. This vessel has been pre-dicted to have a significantly better per-formance than a traditional square rigged ship. The rig changes suggested need not impair the off wind performance, for which additional sail area can be set on the lower yards as with the traditional studding sails so beloved of sailing ship artists. These additional sails are relatively small in com-parison to a modern spinnaker because fabric strength ultimately limits sail sizes. Other sail configurations of the so called "fore and aft" variety will suffer from the down wash problem in multi-masted ves-sels and the basic requirements of sail are-a/displacement for a cargo carrying ship will make multi masts inevitable un!ess an extremely cleverly engineered single aerofoil

propulsor could be conceived.

What then are the more "modern" alter-natives?

Flettner Rotors

The Flettner rotor was mentioned briefly earlier and since it may be classed as a strong favourite for practical ship prop-ulsion with today's technology it is worthy of fairly close attention. The mechanism by which wind blowing on a rotating cylinder is converted into a force capable of propelling a ship is illustrated in Fig. 4.

The possible performance of a Flettner rotorship is not vastly different from a con-ventional sailing vessel, since although the lift generated is a great deal larger than that of a sail the ratio of lift to drag is no better. The "rig" is much more compact however, presenting about 25 per cent of the

WIND PROPULSION

jected area of a square rig. t is also very much less complicated mechanically.

At any particular heading and wind

strength there .is a sharp optimum rotor revs/wind speed ratio corresponding to the ship speed. At this optimum condition the power absorbed in spinning the rotors is about 5 per cent-lO per cent of the power required to propel the ship at the same speed using a conventional marine prop-eller. The total fuel saving is nowhere near as high asthis rotor power figure suggests, however, since weather routing studies indicate that for perhaps 50 per cent of the time either.the wind is too light or from the wrong direction to use the rotors to best

advantage and the ship would then be

propelled either...wholly or in part by her main engines. Fuel consumption for this motor sailing mOde could amount to that normally used to propel a merchant ship at

service speed, and the most economic

speed under power would need careful

consideration. However, of the several

unorthodox systems of wind propulsion, the rotor is the only one that has actually

been tried at sea on a ship sized vessel. The

lack of enthusiasm for its final adoption between the wars was probably influenced more by relatively cheap fuel oil than other technical considerations.

Wind turbine propulsion

A wind turbine or windmill device can be used to propel a ship in a number of ways which can be listed as follows:

The turbine can extract wind energy and use it to propel the ship via a conventional propeller. The propeller thrust will need to overcome the fore and aft component of turbine drag as well as the ship resistance.

In this mode the ship can be propelled

directly to windward and models have

demonstrated the feasibility of this.

nego?ive prezure w;nd 40 Wind pceitive preswre Atu force produced by ot

/

/

Drag )

/

o The turbine can be allowed to freely

rotate under wind action to generate an aerodynamic lift which propels the vessel. This is the antogyro mode. The horizontal axis mill type is probably better adapted to this purpose than the vertical axis turbine. This may be the most efficient operational

mode in beam winds.

O The turbine can be allowed to fre&y

rotate under wind action to generate an aerodynamic drag which propels the

yes-sel. This is a possible downwind

oper-ational mode.

O The conventional water propeller may be used to extract energy from the water to drive the wind turbine as an air propeller driving the ship. This is a possible mode of operation downwind if the ship is travelling faster than wind speed. Such a mode of operation could only be achieved by using auxiliary power to bring the ship up to self-propulsion speed.

Performance estimates for this quite

unorthodox propulsion system are as yet

incomplete and there would be

con-siderable engineering problems in applying such a system to a ship, not the least those stemming from the fact that the wind tur-binewould be larger than any so far built for land use. The system's primary claim for serious attention is that it is omni-directional and therefore better adapted to navigation in restricted channels by sailing directly head to wind.

In the open sea this apparent advantage is clouded by a source of hull resistance to which the conventional sailing vessel is less prone. This arises from operation in waves, which provide a drag component over and above the calm water value. It is a function of wave height squared and varies roughly as the cosine of the ship's heading angle relative to the waves.

4'"ActucI force

/

produced by rotor

/

/

Principle of operation of the Flettner rotor showing wind direction, thrust and force produced by the rotating cylinders, to impart motion to the vessel.

While discussing hydrodynamic, rather than aerodynamic requirements for the wind driven ships it has already been noted. that all the propulsion systems generate a considerable force at right angles to the direction of motion and this may, when proceeding to windward, be something in the order of three times the thrust. Like the, sails, the resistance of the hull, to a first

approximation is given by CD = CDO + KcL2

and the value of K will depend on the clev-erness of the designer in shaping his hull to

provide the most efficient generator Of

sideforce or "lift" for the minimum drag

penalty. The Co0 term is to some extent favoured by the relatively slim form of the

ship, so that a CD/CL of isachievable with less prominent keel apendages than the typical smaller sailing yacht. There is also the consideration that, with the exception

of

the wind turbine and the entirely

hypothetical (and probably impractical) single aerofoil sail

propulsor, the

mul-timasted configurations cannot in general sail very close to the wind and this reduces the necessity to attain such good values of

D/L.

How can the performance of ships with the

alternative wind propulsors be expected to

compare? As mentioned

ear-her the so called Dynaship rig is appropriate to a highly developed square rigged mul-timasted vessel and, as might be expected it is particularly good on points of sailing in which the wind is either on the beam, or further round towards the stern.

In contrast, the wing sail, which has the area capable of propelling the ship

effec-tively when sailing to windward can be

seen to have poor performance in the

down-wind mode, where its small plan-form area makes it less efficient. However, it must be remembered that the envisaged configuration upon which the estimate is based is assumed to be the best that could be achieved with existing aerodynamic data, so that in practice the windward sail-ing envelope would be degraded while the

down-wind portion would probably be

somewhat improved. In all, it seems con-ceivable that a compromise between the performance of the isolated aerofoil sail

and that the "Dynaship" might be

achieved, placing such an arrangement close to the regime occupied by the rotor ship or the wind turbine.

One point of interest in these predictions is that in order to achieve the wind power absorbtion which such a relatively large ship is capable of, it has been necessary to assume a wind of gale force (force 8 on the Beaufort scale) and this size of ship would tend to be underpowered for a great deal of the time due to relatively light winds. As ship size is reduced its wind speed regime for optimum performance moves down the scale, so that one can make a plausible argument for himitingsize to a value which gives the best average transport

momen-tum, loosely defined as cargo capacity

times speed. However, there are other

aspects of the economics of ship operation MARINE PROPULSION

which reflect on this and these will be con-sidered later.

In assessing the performance of the

wind propelled ship one is concerned with both the direction and strength of the wind. Thus techniques which allow prediction of these quantities form the basis of so called "weather routing". In this the course of the vessel is constantly directed relatively to the ever changing weather systems so as

to optimise its speed towards its

des-tination. Basically the problem is one of seeking strong and advantageous winds and curiously enough this is the reverse of what the already well established methods of weather routing for power driven

yes-sels seek to do. Undoubtedly a

com-mercially viable wind propelled ship would

need to make constant use of such

weather information and since auxiliary motor propulsion would also be available the choice of the optimum track would pro-vide a nice problem in routing.

Table 1. Example of Routing around a Depression

Assumptions: The weather pattern consists of a stationary low pressure system. The ship's required passage is from X to Y. Ship A is routed according to knowledge of pressure distribution and development. Ship B has knowledge of current weather con-ditions only, and lays a course as near to the required objective as the wind will allow. Rotors only are used with no auxiliary engine power.

*percentage of total available power used.

Time oh passage for ship A: 94 hours. Distance: 1362/14.49 knots average speed. Time on passage for ship B: 120 hOurs. Distance: 1233/10.28 knots average speed. Time saved: 26 hours!

Economics of wind propulsion

Numerous studies have been carried out on the potential economics of wind prop-ulsion and these have produced answers which, depending on the enthusiasms or prejudices of the authors, provide optimis-tic or pessimistic projections. Typical examples are given in References 2 to 15.

The present authors attempted to first

hypothesise the likely conditions under which wind propulsion would be seriously considered in the immediate future. The conclusion they came to was that it would most likely involve some political action which cut off supplies of oil suddenly and made conversion of existing vessels more probable than new construction of special craft.

On a

conversion cost basis

it appeared that the fitting of Flettner rotors would cost about half the price of a com-parable sail-based rig of traditional type. Operation by bridge control could easily be achieved with almost no special training or

WIND PROPULSION

additional manning. This propulsor was therefore chosen .for the economic study.

Costs of freight shipping

It seemed reasonable to assess the relative costs of freight shipment by oil, wind, coal or nuclear propulsion systems by simulat-ing two contrastsimulat-ing voyages for each type, which

also allowed the simultaneous

examination of weather routing

techni-ques, since time at sea was one of the

economic factors to be considered in the costing process. The weather conditions assumed on these example passages were chosen on a random basis. It is felt how-ever that the associated voyage time and costing estimates are not wildly different from those that would have been obtained

from averaging a large number of

pas-sages.

For the conventionally powered ship a popular vessel with shipowners we's cho-sen. This is designated the Series 111 SD14 by its builders, Austin and Pickersgill, and is one of the most successful quantity produced ships currently

under

con-struction in the UK. It is highy suited to

those trades most likely to offer immediate gains to wind powered .ships, and is in

series production in the UK. The same ship, modified, in a conversiOn sense to incor-porate two 60 metre Flettner rotors, was chosen as the wind powered vessel. For the coal powered ship a newly built SD14 employing a fluidised bed combustion sys-tem was costed, while for the huclear ves-sel an SD14 incorporating an integral pres-surised water reactor of 10 000 shp was used.

Two routes were chosen for the com-parisons:

Southampton-New

York-Southampton; because of wind

con-ditions which could involve a substantial proportion

of windward

sailing, and

because of the density of the route in terms of movement of minor bulks, which it is generally accepted are suitable for carriage in wind powered ships.

Southampton-Fremantle-Southampton; because its considerabe,

length should offer large potential fuel

economies to the wind powered ship.

The cost comparisons for each route are summarised in Table 3.

Port costs are not included in Table 2 figures but are estimated to be approx-imately the same for each of the four ves-sels, with a likely extra cost of more sec-urity police for the nuclear merchant ship. At fuel prices for the 1st April 1979 it will be noted that the conventional vessel is the cheapest to operate for each route. The Rotorship offers greater fuel savings the longer the route, but due to the need in our model to use the main engine foran apprec-iable amount of time because of adverse wind/current effects, these do not, at cur-rent oil costs, compensate for the higher operating costs due to longer voyage time. This situation would bea little different fora wind propulsor which did not itself con-Ship Time

Course Wind Wind'<NelocitySpeed of v/s Dist.

Remarks

day!

°true

°true °apparentiknots

knots miles

l2hr period

A 1/000/1200 272 162 110/20 12.2 146 B 1,0000/1200 272 160 110/20 12.2 146 A 1/1200,2400 281 161 120,20 12.2 146 6 1/1200,2400 270 160 110,20 12.2 146 A 2/0000/1 200 293. 153 140/30 16.0 192 B 2/0000/1200 270 180 90/30 15.3 190 A 2/1200/0000 273 153 140/40 18.6 223 B 2/1200/0000 270 200 70/40 11.76 141 8O°,i taken* A 3/0000/1200 270 360 90/40 17.2 206 B 3/0000/1200 300 250 50/40 8 96 80°!o taken A 3/1200/0000 240 330 90130 15.9 191 B 3/1 200/0000 265 320 55,30 8.4 101 80% taken A 4/0000/1200 240 320 80/20 11.5 138 B 4/0000/1 200 265 325 60,30 9.4

113 80% taken

A

4/1200/0000 240 330 90,20 12.0 120 Arrive 2200 B 4/1 200/0000 265 325 60,20 8.3 100 A

-

-

-

-

-B 5/0000/1 200 265 325 60/20 8.3 100 A

-

-

-

-B 5/1 200/0000 265 325 60,20 8.3 100 Arrive 2400

Table 2. Cost comparison for ship tyres

Cost/tonne (E) Cost per tonne/mile (p)

Route I

Conventional 8.23 0.12 Rotorship 8.60 0.13 Coal 10.19 0.15 Nuclear 14.77 0.22 Route 2 Conventional 25.79 0.12 Rotorship 28.83 0.12 Coal 30.28 0.14 Nuclear 47.29 0.22

WIND PROPULSION

sume fuel.

The coal ship is more economic than the Rotorship on Route 2 because of its higher average speed and hence reduced voyage time and operating costs, butit is still more costly for

both routes than the

con-ventionally powered ship. The nuclear

powered vessel incurs very high capital costs through its nuclear reactor, which are reflected in its operating costs; these more than wipe out any comparative fuel cost

advantage, making nuclear power an

economic non-starter for this size of ves-sel, at least for the present time.

It should be noted in passing that the costing of non-operational technology is a hazardous process and consequently the above figures. particularly for the coal and nuclear powered ships, should be regarded with a certain amount of caution. Further, costs are sensitive to the depreciation and capital financing methods used.

Because the cargo carrying capacity of each vessel, as rflected by its deadweight tonnage, is likely to differ, and because the

distance travelled by the Rotorship will

differ from that of the other three vessels,

costs have also been estimated on a per tonne basis and on a per tonne/mile basis,

the latter most accurately reflecting the carrying capacity of the vessel. The results are shown in Table 2.

No attempt has been made to cost a

completely wind powered vessel, nor has any attempt been made to cost at present

prices other fuels,

e.g. hydrogen, methanol, or oil extracted from coal. Vir-tually all such studies concentrate on the dry bulk cargo trades and most choose 15 000 dwt as the standard size of vessel,

both for the sailing ship and the

con-ventionally powered ship.

In nearly all

studies, specific routes have been chosen for comparison. Accepting the difficulties of exact costings. the main donclusions appear to be:

O The higher the cost of fuel rises, the

more economically

competitive would

seem to be sailing ships;

o The larger the trade route, the greater the relative gains (or the lower the relative costs) of operating a sailing ship compared to a conventionally powered ship;

For a comparison of similar sized yes-.sels, at present the sailing ship would gen-erally appear economically competitive

with the conventionally powered ship.

However, these conclusions do not apply to every saiJing ship.

The various authors' costing estimates make no allowance however for the inven-tory costs of shippers' working capital tied up for longer time periods on voyage, for the increased irregularity of vessel

am-vals/departures, nor for the capital costs of any necessary port cargo handling con-versions. Also, the more labour intensive. operations of sailing shis may well impose extra training costs and present problems

in respect of actually obtaining crews.

Finally, no consideration is given either to

the occasional port limitations due to

bridges under which such vessels would probably not be able to pass. These factors suggest that in the medium to larger run, coal burning ships are likely to offer the

greatest overall advantage.ust as they

did in the 1870s and 1880s.

Changes in economic conditions The major factor likely to affect the fore-going comparison in the foreseeable future is further rises in oil prices, and holding operating costs constant in real terms, a sensitivity analysis suggests the following conclusions:

For Route 1 fuel oil prices must rise 45 per cent in real terms for the Rotorship's

total costs to equal those of the

con-ventional vessel, and 56 per cent in real terms for the coal ship's total costs to equal thàse of the conventional vessel;

For Route 2 fuel oil prices must rise 140 per cent in real terms for the Rotorship's total costs to equate with those of the con-ventional vessel, and 30 per cent in real terms for the coal ship's costs to equate

with those of the conventional vessel. No similar exercise was attempted for

the nuclear vessel, since other studies

suggest that only vessels with propulsive units more powerful than 100-120 000 shp will benefit from nuclear power.

When oil price rises of the significant magnitude indicated are likely to occur is anybody's guess. It is interesting to com-pare them however with three forecasts from differing authors, all relating to the year 2000. These predict, in ascending

-order, a 60 per cent increase, a two-fold increase, and a three-fold increase, all in real terms.

On the basis of the foregoing discussion, the use of wind power does not seem to have a particularly bright future;especially where the economy of size is a dominant feature. However, the situation must also be looked at from the point of view of those

nations whose economic position

or

natural resources are less well endowed than our own. India on the one hand and Japan on the other are good examples of each. A Press release dated November 1979 from a consortium consisting of the Japan Marine Machinery Development Association, Asian Venture Ltd., and Mitsui Engineering and Shipbuilding Co. Ltd.

details their plans to design and construct an experimental 14 000 ton sailing vessel during 1980,81.

Finally, the author would like to

ack-nowledge the kindness of the UK Ship-building and Marine Technology Require-

-ments Board for permitting the use of

much material in this article which originally formed part of a study into the feasibility of wind propulsion carried Out for them.

..

REFERENCES

1. Performance Prediction for Sailing Ships (Fahrtgeschwindigkeitsberechnung fur Segelschiffe). B. Wagner. The Story of the Rotor 1927. Anton Fleitner.

A Bràad Appraisal of the Economic and Technical Reguisites for a Wind Driven Merthant Vessel RINASymposium. The Future of Commercial Sail 1975. .1. Welhcom A Technical Description and Performance Analysis of the Dynaship. RINAibid. J. F. R. King.

The Economics of Commercial Sail. AlMAibid.. A. S. Miles.

A Commercial Sailing ship for the SW Pacific Ocean: R!NAbid. P. R. Warner. W. L. Hood.

Sails for the Auxiliary Propulsion of a VLCC Trading on the Northern Europe-Persian Gulf Route. RINAibid. J. B. Wynne. Power from the Winds. Surveyor Magazines. E. Guigley.

Feasibility of Sailing Ships for the Merchant Marine 1975. The Woodward Report.

Symposium on the Techncal and Economic Feasibility of commercial Sailing Ships 1976. Various Papers, Liverpool Polytechnic Dept. Marine Studies. The Economics of Sail. Journal of Navigation May 1977The Practicability of Commercial Sail. A. D. Couper.

Commercial Sailing Shipsan Economic Assessment. Naval Architect. September 1978. H. M. Close. Feasibility Study on Commercial Sail for Department of Industry 1978 lunpublished), Windrose Ships Ltd.

Reducing the Running Costs at Sea. Journal of Navigation May 1977The Practicability of Commercial Sail, Cohn Mudie. Weather Rouung ol Sailing Ships. Journal of Navigation May 1977ibid. W. Burger.

MARINE PROPULSION Route 2

Ship Type Operating Costs (E Fuel Costs (f Total Costs (

Conventional 252 500 83020 335520

Rotorship 310 940 58 300 369 240

Coal Ship 274 900 82 130 357 030

Nuclear Ship 595 790 33 100 628 890

Table 3. Cost comparisons for two routes

Route 1

Ship Type

Operating Costs ()

Fuel Costs ( Total Costs

_(fl

Conventional 77 230 29840 107070

Rotorship 87 660

22530

110190

Coal Ship 84 090

36060

120150