The dawn of the age of practical, sail equipped motorships - Application of sail system to large ships

THE DAWN OF THE AGE OF

PRACTICAL SAILEQUIPPED

MOTORSHIPS

-

APPLICATION OF SAIL SYSTEM TO

LARGE.

sHips

-NIPPON KOKAN K4K,

28 AW. 1983

Lab. v Scheepsbouwkund

-ARCHIEF

Technische Hogesciioo

THE DAWN OF THE AGE OF PRACTICAL, SAIL-EQUIPPED MOTORSHIPS - APPLICATION OF SAIL SYSTEM TO LARGE SHIPS

-By: T. Watanabe, Y. Endo, K. Shirnizu, H. Naínura, Nippon Kokan K.K., Tokyo Japan

SYNOPS IS

Based on the result of equippin small motor ships with sails, application of the sail equipment to large ocean-going ships has been studied.

An approximate formula was derived by calculating power gains on various proba-ble sea routes and factors affecting the gain performance were analyzed by element analysis.

A comparison with conventional ships based on the results of the analysis above, showed that ships with sails were economically advantageous. In addition, it was found that the use of sails on many ships is economically feasible.

Details on recent studies on the development of technology for large ships with sails, are also introduced.

1. INTRODUCTION

About two years after Nippon Kokan K.K. started its modern sail-equipped motorship development project, the first sail-equipped motorship tanker in the world, the "Shin Aitoku Maru" was launched.

This was followed by the launching of a similar ship and this year, two 699 GT type sail-equipped cargo ships are to be launched.

it so happened that just as the projectwas gettng under-way, the ship-ping industry worldwide was facing a serious oil crisis as a result of the first and second oil shocks. Energy conservation measures were called for and attention was drawn to the develop-ment of sail-equipped motorships as a means of using wind force.

The present short-term situation is the obvious stagnation in the ship-ping industry and the downward trend of fuel oil prices as a result of the worldwide economic recession. And in view of the fact that the supply of oil

as an energy resource is of course finite, there is little room for opti-mism on the long-term fuel oil price situation in which many issues still remain undecided.

Wind force on the other hand, is an inexhaustible natural energy

re-source. Consequently, more intensive

developmental studies are to be done in this field to ensure that maximum use is made of this natural resource.

Differing greatly from olden-day sailing-ships, recent models have demonstrated their suitability for modern-day marine transportation.

Fully computerized operation of sails resulting in an automatic control system, makes manual control obsolete although the functions of conventional motorships are maintained.

The effectiveness of this system was proven by sailing trials on the pre-vious mentioned, small sail-equipped motorships. A future consideration is the development of large motor-powered sailing ships using the above

system.

This paper intrpduces the results of studies on the use of the system in

large sail-equipped motorship.

These results were obtained from a sail-ing trial on the "Shin Aitoku Mar-u" and recent related developmental studies. 2. T "SHIN AITOKU MARU" -

SAIL-EQUIPP-ED- TANKER

The "Shin Aitoku Maru" was design-ed as a sail-ecuippdesign-ed motorship suit-able for modern shipping service, on the basis of results from development

studies on sailing equipment for

practi-cal use. Principal particulars on the

"Shin Aitoku Maru" and its general arrangement are shown in Table 1 and Fig. i respectively.

Since she was launched, two and a half years ago, the tanker has been safely sailing around the Japanese coast and thereby demonstating the effects of energy conservation.

According to results on actual voyages, sails were, ori average, used for 60% of the total cruising hours.

From various data, it was calculat-ed that she uscalculat-ed 8 " 10% less fuel than conventional ships. This is proof that initial aims were successful. 1) 2)

News from the crew of the "Shin Aitoku Maru" has also been encouraging. It was reported that the use of sails brought about a significant improvement in "seaworthiness" and that "rolling" had decreased.

Based on the results with the "Shin Aitoku Maru, as it shown in Table 1, other ships are to be built or launched.

Both the ships. to be built are cargo ships, and all the ships will be sail-ing around the Japanese coast. These are to have improved sails and dif fi-culties with the arrangement of sails are expected to be overcome.

Fig. i General Arrangement Table i Principal Particulars of

Sailing Ships

3. FEASIBILITY STUDY ON LARGE MOTORSHIP

3.1 SAIL PLANS

The large ship selected was a 35,000 DWT class one, representative of 10,000 DWT 60,000 DWT class ships. The type of ship selected was a bulk carrier having general characteristics so that results would be applicable to other types of ships.

A class of ship the same as that of a conventional ship was selected so that the performance of both would be the same.

The specifications of the two are thought to be the same with respect to the following.

The cargo transportation capacity (Average ship velocity cargo dead

weight)

Cargo handling gear The number of crew

Safety (stability) and maneuvera-bility

A sail-equipped motorship satis-fying the above, and the principal particulars of a conventional ship

cor-responding to it, are shown in Table 2 In the sailing ship, the size of the main engine was reduced - engine output was cut by 1 rank, and energy saving was targeted at 15 " 20%. The

average ship velocity was set to that of a conventional ship.

Since a sail-equipped motorship consumes less fuel than a conventional ship, the difference in the cargo dead weight of the two ships was minimal.

The transportation capacities of the two ships are thought to be almost the same.

The total sail area of about 2,600 m2 with three to six sails was envisaged. In Figs. 2 and 3, examples of an arrangement of six sails irr two rows and the general arrangement of sails are shown.

For the height of sails, an allowa-ble air draft o about 5 in was

con-siered.

The areas of individual sails can be roughly calculated from the sail height and aspect ratio in consideration of the air draft and sail performance. The total sail area also can be determ.in-ed from the stability and maneuverability of the ship by obtaining the number of sails and appropriate setting positions taking the general arrangement, includ-ing cargo handlinclud-ing gear on the deck and hatch cover storage etc. into accouzit.

a.. i a.. z a.. z

0

al .aip

Thl. Ml.a. aa..

.3

AJ3a aaa.

at1-.-.a Ca .0i.p C

.i,

Tat l.2.z

S.p0.

lOSS La.i tth 2.053 2.153

.1*.. Ap2.2.. 2.012

aal. Ili

p..pi.5..L.rl al &.O 44.0 72.0 72.0 Ial1k al 10.4 io.a 13.4 12.4 a.,... a..tt al 1.1 4.4 s.i 4.4 a., 4.75 4.1 4.70 a.M-aa4. i0y tI 1400 1300 2.2.00 2100 all. qia. Pl a r.p. 2400 a 250 1400 . 500/230 1500 . 730/100 1500 a 710/110 2 1 3 3 ?.*.1 ..Li 4,05 104.4 10.0 212.71 232.71 lp..d (It) 2.2.0 12.0 1.1.0 13.0

Fig. 2 Arrangement of Sails

3.2 SAIL SYSTEM

A concept of the automatic propul-sion control system is shown in Fig. 4. This control system is composed of auto-matic sail control system and autoauto-matic main engine control system. The total

system is controlled by the automatic

o

Fig. 3 General Arrangement

WIND DIRECTION AND WIND VELOCITY

AUTOMATIC MAIN ENGINE CONTROL SYSTEM

REVOLUTI ON

MAIN

ENGI NE

AUTOMATIC SAIL CONTROL SYSTEM

CONTROL MODES:

STRETCHED SAIL CONTROL Fot.DED SAIL CONTROL

SAIL STRETCHING OR FOLDING CONTROL

SHIP SPEED

SETTI NG

SHIP SPEED

Fig. 4 Sail System Diagram 3.2.1 AUTOMATIC SAIL CONTROL SYSTEM

Signals from wind direction and wind velocity detector are used after they are averaged and with the ini lu-erices of ship motions and others

elimi-nated.

This system has following modes of control: one is the optimal sail control for trimming the sail in the optimal direction when the wind is available,

_--_ conventional t'me sail-equipped sh L 3.?. (in) 167.0 3 MLD (m) 29.5

D MLD (in) 14.8 Saine as left

d (in) 10.5 Cb (in) 0.8 D.W. 34,960 34,550 M/E MCD PS/RPM 11,520/100 10,240/96 pRoeprTR VPP FPP SAIl.

SAIL AREA (in2) ABT. 2, 600

Vs (Xt)

FULL 85% MCO

WITH 15% S..M.

M/E ONLY 14.6 14.1

M/E SAIL - 14.8

Table 2 Comparison of Principal control system so as to become power

Particulars gain maximum.

SAIL STRETCHING OR

OLD ING

ANCI

and another one in the control for

trimming the folded sail so as to minimize the drag due to the sail when the wind is not available. The other an automatic sail folding control, to ensure safety, whereby the sail is automatically folded and the control is shifted to automatic folded sail trimming control mode when the apparent wind velocity or true wind velocity be-comes higher than 20

in/S.

Fig. 5 re-presents the concept of the automatic sail operation control system. Photo i shows, as an example, the control panel of the "Shin Aitoku Maru".

-- t:

r

-

- -

r

f -

-.tl

.'

Photo i Control Panel

4

3.2.2 AUTOMATIC MAIN ENGINE CONTROL SYSTEN

As the main engine control of sail-equipped ships, there can be considered a case in which the main engine output is almost constant saine as the case of conventional ships and constant ship speed control as described below.

The relation between the sail

thrust and the main engine output in the latter's case is shown conceptually in Fig. 6.

Ship speed

Constant Acceleration

Total outout

Wind sneed

Fig. 6 Engine Output Control As is evident from the Figure, up to a certain value of sail propulsion force, a constant ship speed control is per-. formed by controlling the main engine output, but when the sail thrust is more than the said certain value, the main engine output cannot be made less than the lower limit of service power, so that the ship speed becomes higher than the set ship speed. Within the constant controllable range of ship speed, con-trol is performed so that the ship speed becomes steady as soon as possible ac-cording to the sailing effect.

3.2.3 SAIL EQUIPMENT

The sail profile adopted is based on laminar flow type but with improve-ments made on the basis of the results of wind tunnel tests 5) conducted systematically for the purpose of improving the performance, i.e. a roundish form is adopted for both ends.

An outline of the sail equipment is shown in Fig. 7 and it principal particulars in Table 3.

3.3 POWER GAIN CALCULATION METHOD Let's suppose that a sail-equipped ship and another ship identical to that

sail-equipped ship in all respects except that it is not equipped with sail

(hereinafter called "sail-less ship") cruise at the same speed under the same

20 m/a

Region Ii1 operation T*ttd

No. Wind direction_{and velocity} S,IVI condition Autcmatic Minuil

i Fair wind Stretched o o Crosi wind or

streng wind Folded o o

3 Stona Folded x o

20 40 60 80 0O 20 140 60 90

Apparent wind direction (degree)

oceanographic and climatic conditions. In this case, there occurs a difference

in the required engine power between the sail-equipped ship and sail-less

ship. This difference in engine power

required for cruising is defined as the

power gain by sails.

Fig. 7 Sail Equipment

Table 3 Particulars of Sail Equipment

Sail Itr,tCp,H condt,o,i

SaP fo1d Cnd1t,on

That is to say, the required engine power under certain wind velocity con-ditions and certain ship speed condi-tions can be obtained from the balance between the forces in the ship's pro-pulsive direction and lateral direction and the moments concerning the hydre-dynamic forces and aerohydre-dynamic forces

acting on the hull and the sails.

iBHP (Vs:VT,&T) = BHP0 (Vs:VT,eT)

- BHPs (VS:

vT,eT) ....

(1)

BHP0 : Main engine output of the sail-less ship

BHPs : Main engine output of the sail-equipped ship

The average powec gain for a long term can be estimated from given service speed and the frequency distribution of the wind direction and wind velocity on the supposed service route.

I.BHP = IJBHP

(vT,eT) P(vT,eT) avTdeT

(2)

P(vT,eT) : Probability of occurrence

of wind velocity VT and wind direction 8T

By using the aerodynamic

character-istic data of sails obtained from the wind tunnel tests and the water tank experimental data concerning the hydre-dynamic forces acting on the hull, the appropriateness of the said method of estimating power gains has been proved

from the actual ship tests with the

Shin A.ttoku Maru.l)2) This method has

made it possible to make accurate calcu-lation by means of computers.

To investigate the effects of various conditions of a sail-equipped

ship at the initial planning, following approximate formula was devised.

CT.VS.VT2

A .... (3)

BHP = K1K2K3 _l200.fl

where

Average power gain (PS) K1 : Coefficient depending

on

dis-tribution of absolute wind direction and course

K2 Coefficient due to wind veloci-ty distribution

K3 Coefficient due to the changes in propulsion effectiveness resulting from the changes in propeller load

CT Coefficient by the aerodynamic

performance of sail Vs : Average ship speed (m/s) VT : Average true wind velocity

(in/s)

n : Total propulsion efficiency of ship

A : Total area of sail (m2)

a. Sail

Type of sail : Rectangular rigid sail

Mast Self-standing mast

with-out stay (made of HT-steel) uniting the sail with the mast

Sail structure : Steel frame covered with

-canvas (Synthetic fiber) b. Power unit

Driving system Electrehydraulic system

Hydraulic pump Flow contollable

type

c. Turning units

Turning speed About 0.18 (rpm)

° Driving system Hydraulic

d. Stretching and folding units

Stretching time: About 2.0 2.5 (minute)

Folding time About 2.0 2.5 (minute)

Driving system Sail to be stretched or

folded by hydraulic, oil

cylinder through link mechanism

3.4 POWER GAIN CALCULATION AT SERVICE ROUTES

Service routes as shown on Fig. 8 are supposed with respect to the waters of Pacific Ocean and North Atlantic Oceans respectively, the power gains by sail were approximately calculated. On the other hand, accurate calculation was carried out by means of computers. And the results were compared as shown in Table 4.

In the calculation using an ap-proximate calculation f ornula, the effects of rudder angle and drifting angle were neglected, but the result of the calculation tallies with the result of accurate calculation with the ac-curacy of t5%, which is thought to be within the allowable range for practi-cal application.

The result of calculation has shown as following energy saving effect.

North Pacific Ocean service route . . 18%

North Atlantic Ocean service route 17%

Australian service route 13%

Additional data on K1 are tabulated by wind rose and course separately for the respective service routes in Fig. 15. Correlation of these items is com-plex, but when they are considered on the basis of round voyage, they are averaged, showing nearly uniform

distri-bution.

Table 4 Calculation Results

6

Fig. 8 Supposed Service Routes

3.5 EVALUATION OF ECONOMIC EFFICIENCY The economic efficiency concerning.

-a s-ail-equipped motor ship w-as c-arried out using the power gains obtained in the preceding Section.

3.5.1 APPROXIMATE COST OF SAIL EQUIP-MENT

The principal components of the sail equipment were classified into mast, sail structure, control unit, hydraulic unit and detectors (sail

angle meter, wind direction/wind veloci-ty meter), and the cost of each com-ponent as the functions of sail area of one sail(s) and number of sails (N) was investigated. Table 5 shows the content and distribution ratio of each component in the case of this study plan.

Supcos.d s.rvic.

Load

ccnd.i-Ship Accurata calculation Calculation by approxinate formura

Vs aNO SEP SAlI. Energy-saving CT K1 K K, n

rout. tion _{SAIL effect}

(Kt) (PS) (PS) (PS) ('.) (n/a) (PS) Fufl. Load 14.20 10242 8687 1556 15.2 9.91 0.95 0.86 1.02 1.11 0.73 1593 (Wast Sound) North Pacific 0C*fl rOUtS _Ballast 16.20 10384 8222 2162 20.8 8.91 0.92 1.16 1.02 1.14 0.79 2251 (East Bound) Full Load 14.30 10354 9172 2182 21.1 8.79 0.94 1.12 1.03 1.18 0.73 2140 (East Bound) North Atlantic

Ocaan rout. Ballast

(West Bound) 15.30 10081 8737 1344 13.3 8.79 0.93 0.81 1.03 1.08 0.79 1397 Australia-n rout.

Full

Load (North Bound) 14.40 9899 8737 1162 11.7 6.91 0.92 0.88 1.23 1.09 0.73 1140 Ballaat (South Bound) 16.20 9960 8606 1354 13.6 6.91 0.89 1.08 1.23 1.08 0.79 1393

Table 5 Component of Sail Equipment

Fig. 9 K1 for Supposed Routes

By integrating each part of the sail equipment as the functions of N and S, we obtain the following equation concerning the initial cost (Unit:Yen) of the sail equipment.

'SAIL = C1(1..)2 +

Cz(th)+

C3}N +

C (4)

In the case of extremely standard specification, where hull reinforcing work is not included, the cost per unit

area to the total area, can be obtained as shown in Fig. 10. As is evident from the diagram, the minimum sail cost depends on the number of-sails and the sail area, but it almost converges into a certain value. That is to say, with an increase in the value of N, the area of

one sail tends to decrease, but it should be finally decided from the standpoint of economic efficiency in consideration of the upper deck arrangement of the ship and other factors.

3.5.2 _{ECONOMIC FEASIBILITY OF THE}

SAIL EQUIPPING

item Contents Main functIon

Distribution ratio where

A260OM2

z Mast assembly Mast structure Ladder

S, N

28 Sail structure part Sail structure

Stretching & folding mechanism Sail material S, N 42 Hydraulic system Hydraulic motor Hydraulic cylinder Hydraulic pump Piping, etc.

3, N

7 Control system Control panel Control unit Others N 2 Measuring instruments

Sail fitting equipment _N

i

Others CONST.

Others Designing cost

Transportation cost Others

S, N 20

SU AREA WINO osL AD C3US _Kl

WIND ROSE OF NORT14 PACIFIC OM (4IP RO11TE N

1,

W - USA

'q

s JAPM

i

L IAPAN 0.85 WIND ROSE OF MORN ATLPJtTIC tAREA li. 5Ol I USA J. EUROPE 1i2 W EUROPE i USA 0.31 WIND ROSE OF PACIFIC

OM

(ON-30N, UflE-17OI M

f

L AIISTRAUA 1.08 W

É1

P1STRAUA j. JAPAM 0.83

Fig. lo Approximate cost of sails Let us consider NPV per unit sail area paying attention to the sail equipment only. n NPV (l+v)T AP-(l+u)fl(l+W) n E (l+w)n _{vc - Alo} (l+u) (l+w) (5) Initial investment of the sail equipment and difference I of M/E sizes.

APVF: Present value of saved fuel

cost.

PVC: Presént value of runnirig& main-tenance costs and freight reduc-tion by deadweight loss.

C-

;'

c_ q'- ' '+

,y.

.J 6

W

8 9 ¡0

Fig. 11 NPV Evaluation of Sail Equipping

8

Fig. il shows the NPV curve for the present examination plan with respect to

the Pacific Ocean Service Route, the

Atlantic Ocean Service Route and the Australian Service Route respectively.

As is evident from the said diagram, the amortization years are 5 years 8 years, that the sail equipment is

feasi-ble.

Further, application of a sail-equipped ship to a wider field intended for general ships as shown below was studied.

Average wind velocity: 5 - 10 rn/s

Annual cruising hours: 5,000 - 7,000 H

Ship speed: 12 - 16 knots

l+V

Economic condition _l+ : 1.0 - 1.1

The calculation was made on the following conditions, i.e. the ship dition represented the full load con-dition, the wind direction distribution was uniform distribution or K1 1.0,

and the wind velocity distribution was the standard distribution, and the power gain derived

from

use

of

sails was

calculated from an approximate formula

(3) assuming

=

1.8 and CD (at CLina)

As to the fuel cost and

oil price,

the saine values as were used in the

aforementioned study, or FOC

= 142 grI

PS/hr and "C" heavy oil price

=

were

used.

The sail area was 2600 M2, and

the amount of the initial investment on

the sail equipment was obtained by

deducting from the price of sail

equip-ment the amount attributed to the

difference of main engine size between

the sail-equipped ship and the

sail-less ship.

And with the difference

of

amount assumed as about 40,000

1/PS,

calculation was made by multiplying it

by the power gain.

Besides, the maintenance and

run-ning costs also were taken into

con-sideration. As the result of our study,

the relation between the average wind

velocity and repayment term is shown in

Fig. 12 a

i.

As is evident from the Figure, on

the basis of the average, annual

cruis-ing hours, 6,000 hours and the repayment

term of 10 years, we can obtain the following results:

In case the oil price increasing rate is comparatively large

l+V

_{= 1.1),}

the average wind velocity at the limit of economic

efficiency is VT = 5.4 6.1 rn/s. According to the long-range

increas-ing rate of fuel oil price which can be estimated at present

( = 1.05), the avrage wind

velocity at the economic limit is

VT = 6.1 " 7.1 rn/s

From the results as described above, it can be seen that with the exception of a case in which ships sail on the windless waters (near the equator)

1

only, sail-equipped ships can be

economically payable in almost all, the sea areas. And in the case of the ships whose annual cruising hours are almost 7,000 hours, higher economic efficiency will be derived.

The sail performance used in the present study is the performance avail-able with the present technology. Con-sequently it has become known that sail equipped ships are feasible both tech-nologically and economically at the present stage. s S S T I

I

IO li. V (A) le I

.

T I TO a 7

i

a o i VT (o)

eLL

'L

5 'I, i V-14ai

sir sa oì

51?

sa oil

(I)

IrS

*0

5575 *0

(c) (F) !O 1W 5

Fig. 12 VT Repayment Term

4. RECENT DEVELOPNTAL STUDIES

Along with economic examinations, a technical touch-up work is being carried out towards realization of a large sail-equipped motor ship. An outline of our studies with respect to the salient problems is introduced be-low.

4.1 TRIAL MANUFACTURE OF LARGE SAIL

EQUIP!NT

As to the sail area for a large sail-equipped ship, the size of one sail in the range of about 300 through 500 M2

is thought to be economically

advanta-geous.

Since the sail area is by far larger than that of a small ship, the design standards for both structure and

strength are required to be reviewed. Besides, different phase in many points of manufacture will be presented.

Further, from the standpoint of repair

and maintenance, one which is as simple and durable as possible is required.

Large sails were made as a trial to grasp various problems resulting from the increase in the size of the ship and to achieve cost reduction.

The trial sail is a life-size partial model or a part of the

stretch-ing and foldstretch-ing sail with a size 5m x 7m, having a sail area 540 M2 (Sail width 18m x Sail height 30m). The sail

surface has a construction in which a canvas sail is fitted into a steel

frane. A completed trial sail is shown

in Photo 2. After the sail was fabricat-ed, a break-down test was carried out to confirm its structural strength.

Photo 2 Sail as a Trial

4.2 IMPROVEMENT OF SAIL PERFORMANCE5 Ever since the first year of the project for development of sail-equipped motor ships, the study on sail perfor-mance has been carried out continuously. The principal factors affecting the performance of sail includes the type of

sail, the sectional form of sail (camber and aspect ratio, etc.), the distance between sail and mast and presence or absence of end plate. The sail perfor-mance was investigated by wind

tunnel

tests with respect to these factors. From the reason of practical application, an approximately laminar flow type rigid sail in which the sectional form is symmetrical was selected and adopted for the "Shin Aitoku Maru". After that, to further improve the performance of this type of sail, studies were made on the effect of camber ratio, improvement of the form of folded sail and high lift device (slat). To improve the cost to performance ratio, other types of sail including wing type sail and rotor type sail were also subjected to wind tunnel tests and investigation was carried out.

As of today, we have developed a handy improved type of approximately laminar flow type rigid sail, that is, a type with lighter weight structure in which mast and sail structure are

inte-grated. o

Vu

87 IaiI

S $7.510

5178 ho

VT VT V1(s/s)

()

(s) (t)

4.3 MUTUkL flERFERENCE OF SAILS

When a ship is provided with two or more sails, they are subject to aerodynamic interference from each other according to the distance be-tween the sails.

In the case of a large sail-equipped ship, the number of sails in-creases in connection with the air draft limit, so that mutual interference of sails poses a big problem.

An example of the results of investigation made on these effects by wind tunnel tests in the case of

longi-tudinal arrangement is shown in Fig. 13.

(D

o (3 ,I3T1. SAIL S?ACIN/,IST 1.071)

X (3 4ASTX. MII. SPAC1M/tAST 2.1113) A _{(3 MlX1. SAIL 1P&CIN6.haST - 3.2111)}

80 Fig. 13 Interference Coefficient

Diagram

In results as Fig. 13, the attack angle of each sail is identical for all

sails, that is, it is the angle provid-ing Cx max for each apparent wind

direction.

The attack angle of each sail providing the true Cx mas is thought to be different from each other.

In case of the transverse of arrangement of sails, Photo 3 shows an example of the results of the smoke wind tunnel tests.

To make use of the function of a plurality of sails most effectively, the attack angle of each sail needs to

be optimuinly controlled. At present,

wind tunnel tests under various con-ditions are conducted repeatedly to study these problems.

4.4 DAING EFFECT BY SAIL

A report from the 'SHIN AITOKU NARU" was received that a large damping effect by the sail had been realized, and presence of air damping effect has been confirmed by the the wind tunnel test.

The test result has proved that the effect of air damping is conspicuous compared with the test conducted last

time.

lo

,jr

.

-

èi.'r

Photo 3 An Example of Results of Smoke Tunnel Test

5. CONCLUSION

Due to the success of the sail-e-quipped tanker the "Shin Aitoku Maru",more

sail-equipped ship a±e being built, and large ocean-going ships are expected to be more economical.

As a result of the feasibility study on the use of the previously mentioned sail system on large ocean-going ships - based on the results on small ships - the following conclusions were drawn.

An approximate formula, considering the various factors which are given power gains by sails, was derived and these power gains were analyzed

through element analysis. Since the appropriateness of the approximate formula was confirmed through a com-parison with an accurate computer

calculation, the applicability of this formula was proved within the range of the present study.

Power gains were calculated with respect to probable service routes in the Pacific and Atlantic oceans. From estimated calculation results

it was found that on average, energy consumption can by reduced by 13 "

18%.

Assuming that the average annual number of sailing hours is 6,000 hours, the average wind velocity at the economical limit is 6 7 rn/s. The results on the sail-equipped ship and conventional ship comparison showed that the sail-equipped ship is more economical and that the use of sails is feasible even at present.

From this result it is obvious that sail-equipped ship will be effective in major sea zones.

A long-range forecast of fuel situation shows a number of unstable

factors. It is expected, therefore,

that the promissing sail-equipped motor ships will spread widely.

As described in the text of this paper, the developmental study of large sail-equipped inotorship is in the final technological stage. We sincerely hope that the technology for the development which we have acquired will bear fruits in the actual large ships as soon as possible.

Reference

Sudo, M.et al.: "Operation Perfor-mance of Sail Equipped "Small Tanker" Nippon Kokan Technical Report, No.90

(1981) p.71 to 84

Endo, Y. et al. "Power Gain by Sails on Sail Equipped Small Tanker"

Nippon Kokan Technical Report, No.92 (1982) p.89 to p.100.

The Shipbuilding Research Association of Japan, The 163rd Research Panel, Winds and Waves of The North Pacific Ocean 1964 - 1973

U.S. Weather Bureau, U.S. Navy Marine Climatic Atlas of the World, Vol. 1, Vol. 3 (1965)

Murata, M. et al.: "Aerodynamic Characteristics of A 1600 DWT Sail Assisted Tanker", North-East Cost Institution of Engineers and Ship-builders (1981)