H
EF
HNICAL
N
f Propelle
el Testing
by u KAMURISA OrtO ISHII UASATechnische Hogesdioci
Deilt
October 1984Full-Scale Observation of PropeHer Cavitation and
Model Testing
By:
Hikaru Kamiirisa, Nono Ishii* and Hajime \'uasa'
Full-scale observation of propeller cavitation is important in follo wing up the design procedures for reducing erosion, thrust breakdown and hull vibrations. This paper introduces the change of the instrumentation from the
conventional inboard method based on seeing through a window to the present outboard method with watertight color
TV-camera and color VIDEO MEMORY device which can hold on an instantaneous picture taken by a stroboscope until the next scene is taken. The latter can also shorten the preparation time and increase the effiiencv of the ob-servation work in comparison with the former.
Moreover, the results of the observation of propeller cavitation fbr two VLCCs are shown as typical cases, and they are used to investigate the details of full-scale propeller cavitation. By comparing them with the model test results obtained under similar conditions in a cavitation tunnel, the influence of air content of water, the draft re-presenting cavitation number and the roughness of the blade leading edges are investigated in the model testing to
simulate the full-scale more accurately.
I. Introduction
The appearence of high-speed container ships in the l960s saw a new era in propeller design: a new kind of
propeller with a large diameter operating in shallow
draft conditions.
At that time, our company carried out the basic
studies on the propeller design1 of such a single screw container ship including the full-scale observation of propeller cavitation in cooperation with The Ship Re-search Institute of Japan (SRIJ).
It was one of the earliest breakthroughs in our
country.
Till then, cavitation was regarded as the important problem at the stage of propeller design to eliminate erosion on the propeller blades and to avoid the thrust breakdown. In order to make clear the correlation between model and full-scale from the view point of such influences, The International Towing Tank Corn-mittee23 recommended a call for contributions on the
full-scale observations of propeller cavitation.
In the cource of the series studies promoted by SRIJ,
the results of the high-speed container ship was also
applied, which gave the opportunity for Dr. TA KA-HASH14 et al. to propose the variation of cavitation volume being the main factor of stern hull vibration in case of marine propeller operating in non-uniform wake
field. After that, the further studies were accelerated to make clear the relation between stern hull vibration and
* Akishima Laboratory, Aero-Hydrodynarnic Research Div.
propeller cavitation.
As marine services have wider applications and owners requirements toward the quality of ship
per-formance become higher, naval architects have made their efforts to apply the newest results of research and development to ship design. Less vibration and low
noise are very important factors in maintaining the
quality of ships, which can mainly be realized by minute and carefull design of propellers.
In this case, a more accurate design can be achieved by adopting the newest results of the study on propellers and carrying out model tests in a cavitation tunnel in
addition to the conventional work based on data for
the design. Moreover, if these designs could be proved by full-scale observations, valuable data for the design would be stored and applied.
The methods of full-scale observations are gradually improving and developing corresponding to the varia-tion of these needs. Especially quantitative analysis of
propeller cavitation has become more important in
recent studies. Moreover, it is planned to make tlìe
observation works more efficient and accurate by
adopt-ing such observation instruments that have been
de-veloped.
This paper firstly summarizes the change of full-scale observation methods for propeller cavitation and some typical examples of its preparation works. Secondary, showing some results of the observation, the usefullness of the information obtained from the full-scale observa-tion is described. Moreover, by comparing these full-scale observations with the model tests corresponding to them, it is explained that the full-scale observations
L
are also important in order to improve the methods of the model tests.
2. Observation systems and techniques
Some results of full-scale observations of propeller
cavitation were reported by Holden, Narita6 and
Okamoto7, however papers presenting the details of
observation methods, i.e. observation systems and tech-niques, are rather few. in this chapter, we will explain the observation systems with high reliability and effici-ent techniques including the manual for the preparation and observation works which have been developed by our company.
Principal examples of the propeller cavitation
ob-servation are shown in Table i in connection with the
development of the above observatioii systems and
techniques.
2.1 Observation systems
When our company started the full-scale
observa-tion1>, it was carried out on a container ship. For this observation the windows for observation and lighting were set on the stern hull obliquely locating just above to the propeller. However, increasing the ship speed the observation were sometimes interrupted due to air bubbles passing over the windows.
For ship A, in order to obtain a more clear view, the observation windows were set on the upstream stern hull of the propeller. Three (3) windows were set on the
starboard side of the hull as shown in Photo 1. The stroboscope, TV-camera and still camera (including eye observation) were installed in each window from the inside of the hull. Consequently, enough visual scope field could be obtained and made possible to observe clearly the back surface of the propeller blades.
How-ever, it required much time and effort to set these blisters on the hull. Besides, the pictures taken by TV-camera were not clear enough to be observed because it only photographed at the instant when the stroboscope
flashed. Since the frequency of the stroboscope flash is in the oder of one Hz in the case of the full-scale, the propeller does not appear to stand still on the monitor TV screen virtually, not the same as in the case of the cavitation tunnel tests.
For ship B (Photo 2), the VIDEO MEMORY device was introduced which could hold on an instantaneous picture for a period of arbitrary length that was synchro-nized with the stroboscope flash, so that the observation was carried out more clearly and efficiently. However, it was difficult to discern between halation and cavita-tion on the surface of the propeller blades.
For ship D, the stroboscope and TV-camera were set in watertight shells, then fitted directly on the hull in order to simplify the work of installing these observation instruments (Photo 3). In this work, the cables were passed through the steel pipes fitted on the hull. Con-sequently, the preparation time could be shortened by adopting this method.
For ship F (Photo 4), the color TV-camera was fitted on the hull in order to measure the cavity thickness by
2
Table i Principal Examples of Propeller Cavitation Ob-servation Ship Type A B E F VLCC VLCC RO/RO Vessel ULCC VLCC Passenger Boat Observatìon System
3-Observation Blisters (Stroboscope, BW TV-camera, & Still Camera)
3-Observation Blisters, B/W Video Memory Watertight Strobo & B/W TV-camera fitted on thehulldirectly, B/W Video Memory 2-Observation Blisters fitted on both P & S
sides. Moreover, Watertight Strobo & B/W TV-camera fitted on the hull directly, BW Video Memory
Watertight Strobo & B/W TV-camera fitted on the hull directly, B/W Video Memory Watertight Strobo, B/W TV-camera &
Color TV-camera fitted on the hull directly. Color Video Memory, 2-Laser Emitters for Cavity Thickness Measurement
Photo i Cavitation Observation Blisters Fitted on
Ship A
Pgoto 2 Cavitation Observation Blisters Fitted on Ship B
C
laser emitters. Rotating the mirror set in the shell with a color TV-camera by a remote control system, the
ob-servation scope could be widened more and more. Moreover, introducing a color VIDEO MEMORY
device, the cavitation observation could be carried out more accurately.
As mentioned above, the observation systems have been improved and developed at every event in the full-scale experiment. Summarizing these results,
By moving the position of the observation
windows from the bottom hull above the propeller to the upstream starboard side, the interuption due to the mixing of air bubbles could mostly be eliminated. How-ever, if the draft is shallow, it may be difficult to ob-serve the cavitation because of much mixing of air
bub-bles.
introducing the TV-camera and VIDEO MEM-ORY device, the observers could be free from the hard
work in the narrow and dangerous space for many
hours. Using this system, the sketches could be done after finishing the observation tests because the picture
Photo 3 Cavitation Observation Blisters, Watertight Strobo & B/W TV-Camera Fitted on Ship D
Watertight Strobo. B/W TV-Camera. Reciever (Color TV-Camera) & 2-Laser Emitters Fitted on Ship F
could be recorded and reproduced.
The photoes taken by the still camera were very
clear with respect to the quality of the picture. but it
was impossible to know the average pattern in the case of the cavitation pattern changing at every moment due to the ship motion since the photoes were taken in an instant. lt is desirable that the sketches may be drawn as comparing the TV monitor with the photoes men-tioned above.
Fitting both watertight stroboscope and
TV-camera directly on the hull, the time of preparation
works could be shortened.
2.2 Observation techniques
2.2.1 Test area at sea
The observations are carried out by using the strobo-scope as a source of light during a night at sea with a high degree of transparency. For example the area 50 miles off Hinomisaki Cape in the Kinki district may be
good for the observation as well as the south of
Izu-Oshima island in the Kanto district. Along the coast the observation can hardly be carried out because the sea water may be remarkably impure and muddy. The present Tokyo Bay may be out of the question for ob-servation.
2.2.2 Components and functions of the observation
systems
The observation systems are composed of the equip-ment shown in Fig. 1.
The observation windows are used for TV-camera, and stroboscope, and they are fitted on the starboard
side of the upstream hull of the propeller (Photo 1).
The scope of each window is usually installed to cover the field from O (top position) to 60 degrees starboard side of the propeller blade angle and to adjust the center of visual field to the midchord of 0.7 R blade section at
30 blade angle corresponding to the position of one
o'clock looking forward. This is due, in the case of single screw ship, to the high wake region generally
existing at the top position of the propeller disk, and the largest extent of cavitation occurs at about 30° blade angle due to the tangential wake. Owing to the owner's requirements or the severe conditions of fitting observa-tion windows on the hull, both watertight TV-camera
and stroboscope are installed on the hull directly as
mentioned above (Photo 3).
The signal to the syncronizing device with the strobo-scope (preset counter) is obtained from the pulse
gener-ator which has 180 pins wound around the propeller
shaft through the pulse pick-up (Photo 5). Setting the
angular position of the standard pin with long size
equal to that of the generator line on the standard pro-peller blade (blade A), it is possible to lighten the
strobo-scope when a certain blade just rotates to a certain blade angle corresponding to the number of pulses
after the standard pin passed through the pick-up. The pictures are taken by still camera with its shutter at bulb. During the test, the monitoring and recording by the TV-camera are continued. An instantaneous
Propeller
4
h Ofita)
\\ ater Tight Vessel TV.
Still Camera
ater Tight Vessel)
H Strobo Sro1e Pulse Pick-U1) Propeller Shaft Hull Plate ( onert ion lias AC -* loo y Breast i r apilone
Aft Peak Tank
'1V. Camera
Cahie)
n t
Photo 5 180-Pins Set on the Propeller Shaft and Pulse Pick-Up for Stroboscope
VIDEO MEMORY device until the next scene is taken.
2.2.3 To perform the preparation work efficiently The schedule of the preparation work in dock for the cavitation observation is shown in Tabk 2. The other works overlap in dock, so that it is necessary to plan the schedule enough in order not to disturb each other.
On the surface of the propeller blades black lines are marked by turning the propeller to indicate each radius (nR) and generator line in order to be able to accurately observe the extent of the cavitation. While turning the propeller to mark lines, it is necessary to make close communication between inboard and outboard. More-over, at the design stage of the preparation works, the
Cable)
Monitor
TV.
Fig. i Block Diagram of Cavitation Observation System
clt
Video Microphone Memory 100V .\VR I reset ( c,un t e r 10 A i alge Phones set -temporarily Monitor V'i'R TV.00
Engine CR. Measurement Room Observation Compartment AC 100 V Qn Camera ReleasefPhones set temporarily
Fig. 2 Communication Network for the Observation
fitting
position and angle of both TV-camera and
stroboscope to the hull must carefully be decided in
order to make their scope wide enough. lt is also
neces-sary to design their profile to minimizing the loss of
ship speed by their resistance.
2.2.4 Manual for the observation
Keeping the ship speed constant and direction straight, the observation is carried out according to the manual shown in Table 3. For example, in the
condi-tion of advancing at the propeller turning speed 40
rpm, it can be ascertained whether the propeller
cavitation occurs or not. If the cavitation does not
oc-cur the turning speed is gradually increased every 5
rpm. Once the cavitation occurs, the observation should be carried out and the turning speed is recorded
AC loll V -. AC 100 V
('A ater Tight Vessel j
10 10 V 'o * 200mm.
as the inception speed together with the other operating conditions. Until the cavitation inception, only a
specific blade may be observed. After confirming the inception, the observation should be carried out within the range of blade angles which can be seen in the whole
visual field.
Table 2 Schedule of the Preparing Works for the Cavitation Observation
Table 4 Measuring Items during the Observation
Place Staffs Items
In order to carry out the observation works efficient-ly, it is necessary to set the measuring items during the observation beforehand as shown in Table 4 and Fig. 2.
3. Full-scale observation
The results of full-scale observations for two VLCCs (called ship A & B) are described as the following typ-ical cases obtained by applying such observation
sys-tems and techniques as mentioned in chapter 2. These two results contributed to the verification of the
propel-ler design and the study of the correlation between
model and full-scale propeller cavitation which is to be explained in the next chapter.
3.1 Results of the observation for ship A
3.1.1 Ballast condition (Photo 6)
No cavitation observed at 40 rpm. The cavitation
inception was at around 50 rpm, and it was sheet
cavitation that occurred from 0.8 R leading edge to tip
1 2 3 4 5 5 7 8
Ship Schedule Dry Dock Dock Out Observation
In or hooting around the Propeller Carrying Instruments Setting instruments Si.) Setting Strobo TV-Camera Blisters jLet Cables pass through Pipes 4-9-Withdrawal Preparing
Power Supply Welding SteelPipes Welding S.T.B.
)
'si
Marking CL. etc. on Propeller Blades
'- 'i Restoration -In Ship Instruments Preparing
P.S..Tahles sr. instruments & Vt ring l.ast Adiusting Withdrawal
a '- Arranging g & Lightings 4 Propeller Shaft Shaft Cleaning Setting Pulse
Turning Turning ithili usai
_
p_ z;
Setting Pins Strobo Power Unit P.P.S. S.J. Wiring Withdrawal_;
Remarks. Dock Crane Chain Block Transceivers Divers) Bridge A BShip Speed. Motions, Sea States & etc. (General Control)
jr Engine
Control Room Revolution, Power & etc.
RPM
Measurement
4
every 5RPM increasing Room C, D Cavitation Observation: Videoords, Sketches & PhotosRec-V
MCO Observation
Compartment D Cavitation Observation with the eye
30 40
Table 3 Engine Control Manual for the Observation
Interval Main Engine Start
10 30 MCO 30 1/2 30 34 MCD 'o 'V 30 cSo
Blade Angle Blade Angle 10 Blade Angle 3O Blade Angle 4O 6
Kr=O.118 i13.O4 KTO.l3O N835
KO.l36 N575
Photo 6 Results of the Cavitation of Ship ABallast
KT=O.l58 CN=3.22 K=O.l62 iN=2.O5 KT=O.l73 N161 101 rpm 1l4 rpm
with the narrow width along the leading edge.
Increasing rpm, the extent of the cavitation became gradually larger and at lOI rpm sheet cavitation covered from 0.8 R to tip. At 114 rpm (MCO) the extent became larger and the light and shade of the cavitation became more remarkable because of the
difference of the cavity thickness.
Judging from the fact that the variations of cavitation extent at all blade angles were comparatively small, it might be considered that the wake distribution was flat. Moreover, it might be suggested that the propeller design was appropriate because sheet cavitation, which is considered less harmful, was dominant at each rpm. 3.1.2 Full load condition (Photo 7)
The inception of cavitation was at 1/2 MCO
condi-tion, and the cavitation extent was the largest at
20-30° as the blade rotating from 0° to 60° at MCO con-dition. The extent decreased rapidly when the blade turned more than about 40° and only tip vortex cavita-tion (TVC) was observed. lt might be suggested that the high axial wake and the tangential wake had much influence on the cavitation in the range of 20-30°.
Moreover it is the same as the trends of the ballast
condition that the variation of the cavitation extent
gradually varied from 0° to 40°.
lt might be suggested that these kinds of cavitation would cause less stern hull vibration, because the meas-ured results of the pressure fluctuation on the stern hull surface above the propeller were in the region of permis-sible levels'1 not only in full load but also in ballast
con-dit ion.10'
3.2 Results of the observation for ship B
The observation for ship B was carried out in both
8
conditions with and without MIDP. It was recognized by comparing them that MIDP was available for reduc-ing the cavitation.' In this paragraph, only the results in the condition without MIDP will be discussed since its results are to be utilized for the basic study of the correlation between model and full-scale propeller cavitation in the next chapter.
Typical sheet cavitation occurred from 0.9 R to tip at 2-30° of blade angle, and sheet cavitation decreased gradually and turned to TVC at 40-60°. lt is said that
such types and variation of cavitation have no risk of erosion.
The variation of the cavitation against each blade angle is somewhat larger than that of Ship A. It is
noticed that the concentration of wake in the top region is more severe than that of Ship A.
From the result that the measured value of pressure fluctuation was small,
it was found that the above
cavitation did not have much influence on the surface
force.
Concerning the results of the above two VLCCs,
it was found that the above cavitation has less risk of erosion.
These results of the observation can make the con-ventional design data more complete and contribute to the routine works of propeller design. Moreover, they are utilized to increase the accuracy of the model tests in a cavitation tunnel and the theoretical calculations. On the other hand, for the other full-scale observa-tions, very accurate results of the observation could be obtained by adopting this observation system as
fol-lows.
(I) The fluctuation of the extent of cavitation
oc-Blade Angle O' Blade Angle 10' Blade Angle 20' Blade Angle 30'
Blade Angle 40 Blade Angle 50' Blade Angle 60'
Photo 7 Results of the Cavitation Observation of Ship A
curing in the same condition and at the same blade
angle could be observed more clearly and the average extent could be recognized accurately.
The kinds of cavitation could be distinguished clearly and make it possible to predict the erosion more accurately.
By making the interval of the blade angles smal-1er, the variation of the cavitation extent against each blade angle could be observed in more detail, and the
qualitative estimation of the surface force could be
carried out.
It made it possible to judge the cavitation incep-tion more accurately.
in the following chapter, the present condition and some problems of the model test will be shown. More-over the authors will propose the method of model tests for estimating the full-scale propeller cavitation mcre accurately by investigating the correlation between the results of the full-scale observation of both ships A and B obtained here and the results of their model tests.
4. Model test
In the model test, for simulating the cavitation phen-omenon which corresponds to the full-scale cavitation, the law of similarity must be satisfied at all points over
the blade surface. Namely, it is required that the
following principal parameters be adjusted to the
full-scale.
thrust coefficient
local cavitation number (including Froude
Num-ber)
Reynolds number
non-uniform wake distribution
IHowever, it is impossible to satify (2) & (3) at the
same time. So, for (2) the value at the shaft center or at a given radius when the blade being at the top posi-tion is taken into account representatively. For (3), the propeller rpm and diameter are adjusted approxi-mately to exceed the critical Reynolds number.
It is known that the results of the test carried out in the cavitation tunnel have such characteristics as men-tioned below especially in the condition of non-uniform
fields.
Sheet cavitation often occurs intermittently This phenomenon is called the flashing. In the case of
the full-scale, sheet cavitation occurs stably and this
flashing has never been observed.
The extent of the cavitation is usually smaller than that of the full-scale.
Taking these characteristics into consideration, the full-scale propeller cavitation has been predicted and until now the results of the test using some series pro-pellers have been compared to each other for predicting the full-scale.
From recent studiet by Weitendorf1, Kato et al), it was indicated that the nuclei or the air content of water in the cavitation tunnel did not correspond to
that of sea water as the reason for (5) and (6). More-over Noordzij'4 represented (2) by the value at 0.7 R, and Kuiper5 described some ideas for corresponding (3) to that of the full-scale. Especially the latter showed the model testing techniques in the cavitation tunnel with bonding carborundum to the leading edge of the propeller blade for stimulating the flow into turbulence.
In this chapter, the above items proposed as the meth-od for simulating the cavitation on the full-scale
pro-peller accurately are investigated in the following details:
Blade Angle 2 Blade Angle 10 Blade Angle 20 Blade Angle 30
Blade Angle 40 Blade Angle 50 Blade Angle 60
Photo 8 Results of the Cavitation Observation of Ship B
the influence of the air content of water
the influence of the position represents the cav-itation number
e. the influence of the leading edge stimulator to
make the flow into turbulence
The model tests were carried out in the cavitation tun-nel of The Shipbuilding Research Center of Japan by setting the conditions corresponded to the ship A and B mentioned in the previous chapter.
4.1 Test condition
The wake used in the test corresponded to the full-scale wake and it was estimated by Sasajima-Tanaka's method from the model wake measured in the towing tank.
The following conditions were applied where 4 con-ditions for ship A and 3 for ship B.
For ship
Acor-responding to the full-scale in ballast condition (I) cavitation number (o-N):
the value of the propeller shaft center height ("Shaft center")
air content (/c)=abt 2O%
o-N: Shaft center
/a=abt 8O%
o-N: Shaft center
/=abt 4O
with bonding carborundum to the leading edge of the blade ("With roughness")
Blade Angle o, Blade Angle lo. Blade Angle 40'
lo
o: the value at the tip of the blade angular
top position ("TIP") x/x=abt 40%, "With roughness"
For Ship Bcorresponding to the full-scale in full load condition
Two (2) model propellers with diameter of 250 mm were tested under the above conditions.
4.2 Correlation with the full-scale ship
The correlation of the results based on the previous
chapter with the results of the full-scale observation
shown in chapter 2 were investigated, Its results are
shown in Fig. 3 and Fig. 4. These results give the fol-lowing conclusions.
in the case without carborundum on the leading edge of the blade, the cavitation occurrence is inter-mittent with low air content but tends to stabilize at
increased air content of the water.
Adopting the cavitation number of "Shaft Center", the extent of the model cavitation is less than that of the full-scale observation.
Bonding carborundurn on the leading edge of the blade and the local cavitation number of "TIP" gives
the stable cavitation and better agreement with the
extent of the cavitation on the full-scale, even with low
Fig. 3 Comparison of Propeller Cavitation between Model- and Full-Scale on Ship A
' A'
--.-Full Scale Observation Model Smooth N 1.606 (Shaft Center) Air Content's20% Model Smooth = 1.606 (Shaft Center) Air Contents80%Model With Roughness
= 1.606
(Shaft Center) Air Contento40%
Model With Roughness 0v 1.253 (TIP)
(5) o-N:
"TIP", /=abt 30%
(6) o-N:
"TlP",/5=abt9O%
Blade Angle I O Blade Angle 2O Blade Angle 3O
Fig. 4 Comparison of Propeller Cavitation between Model- and Full-Scale on Ship B
content of the water.16
Within the present test results, it is concluded that
stimulating the flow on the blade into turbulence and representing the local cavitation number of "TIP" are more important than increasing the amount of air con-tent in order to estimate the excon-tent of sheet cavitation on the full-scale ship more accurately.
Further investigations are required for testing whether the same results will be obtained in other cases. By
this reason, the full-scale observation of propeller
cavitation must be important and should be carried Out more efficiently and easily.
Nomenclature
«N=(Po P +pgh)/( I /2)pn2D2
cavitation n um ber P0: atmospheric pressure
P: vapour pressure
acceleration due to gravity
water depth representing the cavitation num-ber
n: number of propeller revolutions D: propeller diameter
p: density of water
= T/pn2D4
K: propeller thrust coefficient
T: propeller thrust
cì/ca: amount of the air content of water
5. Conclusion
The Authors presented the observation systems and techniques in detail and showed the manual for carring
out the full-scale observation of propeller cavitation
more efficiently. By showing typical examples of the propeller cavitation observation the comparisons be-tween the full-scale and the corresponding model tests were conducted. Moreover, the authors discussed the method of model testing to simulate the full-scale more accurately, and proposed the stimulation of the leading edge of the blade into turbulence which was
significant-ly useful for the simulation. It was suggested that
further investigations be required for model testing to
find whether the same results would be obtained in other cases, and the full-scale observation should be
carried out at every opportunity hereafter.
The principal conclusions of this paper are as follows:
(1) For the observation systems, the adoption of the color TV-camera and VIDEO MEMORY device are efficient and have high reliability. Moreover, by
adopt-ing watertight stroboscope and TV-camera, the
pre-paration works can be performed more efficiently than the fitting works of windows. However, the observation TB 84-02 AI
r
11ii
r r r
4l---r
f'
r
r
Full Scaler
Model Smoothr
Model Smooth Model With Roughnessr
Observation Cg3.162 (TIP) Cg3.162 (TIP) N3.162 (TIP)
windows are probably adopted according to the con-dition of stern hull form et cetera.
For the observation techniques, the methods efficiently to perform were shown as fitting the
observa-tion instruments on the hull, supplying power to the
measuring instruments, scheduling the work of wiring
and arranging the manual for the work, in addition.
the measuring items, communication network and
engine control manual during the observation were also shown.
The results of the observation for two VLCCs
were shown as typical cases obtained by adopting the above observation systems and techniques. From the results it was proved that the propeller design for them was appropriate. Also, the characteristics of the full-scale cavitation could be investigated in detail.
Conducting the model tests for the same two
V1.CCs, the influence of air content of water, the posi-tion to represent the cavitaposi-tion number and the leading edge stimulator to make the flow into turbulence were investigated. From these results, it was found that the latter two were important in order to simulate the full-scale cavitation more accurately. Moreover, it is claimed that the further investigations like this should be con-tinued.
When the full-scale observations of propeller cavita-tion are carried out, whether the ship is new or not, the
preparation works and the real tests should be carried
out under the close control and adjustment with the
schedule of the dock. By this reason, much cooperation of the staff in each department is indispensable for the success of the full-scale experiments. In addition, it is often proposed in accordance with the needs not in the stage of research but in the stage of design. Therefore,
the staff in the design department should propose it
with consideration of how the results could be applied more validly and effectively to the works of research and development.
12
References
I) T. Ito. et al. : Full-Scale Observation on Propeller
Cavita-tion, Report of Ship Research institute, 9, 7 ( I 972). Proc. of I ith 1TTC (1966) and 12th ITTC (1969).
T. Ito, et al: Cavitation of Marine Propellers (Part 2), Proc. of the 2nd Syinpo.rium on Marine Propellers, SNAJ, (1971). p. 61 (in Japanese).
H. Takahashi. et al.: An Experimental Investigation into the Effect of Cavitation on Fluctuating Pressures Around a Marine Propeller. Proc. of 12th ITTC (1969) or Papers
of the Ship Research Institute, 33 (1970).
K. O. Holden, et al.: Propeller Blade Cavitation as a
Source of Vibrations, Full Scale Experiences, Norwegian Maritime Reserch, 2, 4 (1974), p. 22.
H. Narita. et al.: Investigation on the Ducted Propeller
Cavitation and the Duct Erosion Prevention by the Air
Injection System, Norwegian Maritime Reserch, 5, 2 (1977).
p. 29.
I-E. Okamoto, et al.: Cavitation Study of Ducted Propellers on Large Ships, Trans. SNAME, 83, (1975).
H. Tanibayashi: Cavitation of Marine Propellers (part 1), Proc. of The 2nd Symposium on Marine Propellers, SNAJ, (1971), p. 47 (in Japanese).
H. Yuasa. et al.: Practical Calculations for Prediction of Propeller Cavitation and Propeller Induced Hull Surface Pressure. J. of the Society of Naval Architects of Japan, 147 (1980). p. 65 (in Japanese).
SR 183 Research Panel: Study on Propellers and Stern Hull
Forms Aiming at Reducing the Stern Vibration and Noise, Report of Japan Shipbuilding Research Association, 342, (1981), p. 79 (in Japanese).
H. Narita, et al.: Development and Full-Scale Experiences of a Novel Integrated Duct Propeller. Trans. SNAME, 89
(1981).
E. A. Weitendorf: Conclusions from Full Scale and Model Investigations of the Free Air Content and of the Propeller Excited Hull Pressure Amplitude due to Cavitation, AS/tIE,
Dec., (1979).
H. Kato. et al.: New Marine Propeller Cavitation Tunnel
at The University of Tokyo, Its Design Concept and Special FeaturesOn the criterion of air content in Water, J. of the Society of Naval Architects of Japan. 150 (1981), (in Japanese).
L. Noordzij: Some Experiments on Cavitation Inception with Propellers in the NSMB Depressurized Towing Tank, In!. S/zipb. Progress, 23(1976).
G. Kuiper: Cavitation Inception on Ship Propeller Models, Netherlands Ship Model Basin. Pub!. 655 (1981).
N. Ishii. et al.: Model Testing of Propeller Cavitation by Roughening the Leading Edge of Blades, J. of the Society of Naval Architects of Japan, 153 (1983).
