Proceedings of the 15th ATTC, American Towing Tank Conference, ATTC'68, Ottawa, USA, June 25-28, 1968, Transactions, Volume 3

ARCH1EF

th

VOLUME 3

15

American

owing

A

rank Conference

Ottawa June

25t-h-TRANSACTIONS

VOLUME III

28th

1968

TRANSACTIONS

OF THE

FIFTEENTH MEETING OF THE

AMERICAN TOWING TANK CONFERENCE

VOLUME III

Held at:

Ship Laboratory,

National Research Council,

Ottawa,

Canada

CONTENTS

STATE OF THE ART REPORT

-RESISTANCE, PROPULSION AND CAVITATION

LIST OF PAPERS

RESISTANCE, PROPULSION AND CAVITATION -STATE OF THE ART REPORT

for presentation to the Fifteenth Meeting

of the American Towing Tank Conference

National Research Council Ottawa, Canada

FOREWORD

The State-of-the-Art Report on Resistance, Propulsion and Cavitation is

presented as summaries on the following topics:

Wave resistance Viscous resistance Powering prediction Propulsion-hull interaction Cavitation inception Cavitation erosion Cavity flows

This Committee was most fortunate to be able to induce a number of "experts" to

prepare these summaries. Specifically the Committee wishes to gratefully acknowledge

the work of the following persons: L. W. Ward P. S. Granville C. J. Wilson R. E. Henderson F. B. Peterson A. Thiruvengadam R. L. Waid

The summaries are written to stimulate discussion. In the resulting discussions

the Committee hopes to obtain the diversity of opinion on the various topics.

Resistance, Propulsion and Cavitation Committee

J. B. Nadler R. E. Henderson J. W. Holl J. W. Hoyt L. Landweber (Recorder) W. B. Morgan (Chairman) R. L. Waid

WAVE RESISTANCE

(part of report on resistance)

for presentation to Fifteenth Meeting of American Towing Tank Conference

National Research Council Ottawa, Canada

WAVE RESISTANCE

INTRODUCTION

An extensive report was given at the last A.T.T.C.

Meeting in

1965 by Newman (1), summarizing

_{progress in this}

area to that time;

_{thus the present statement deals only with}

progress made in the intervening three

_{years which supplies}

new insight or confirms or destroys previous conceptions,

which poses new problems to be solved in

_{the next three years}

in this important area of tank testing and

_{in related theoretical}

developments.

_{For continuity, Newman's subject headings will}

be repeated here with an additional

_{one, "Model Scaling,"}

presumptuously added at the end.

_{Some of the statements to}

follow are deliberately made provocative,

_{rather than "safe,"}

in order better to promote discussion

_{so that the satement of}

the Committee at the end of the meeting shall contain the views

of all.

ANALYTICAL PREDICTION OF WAVE RESISTANCE

In regard to this phase of the

_{subject, Newman's quite}

complete statement in

_{1965 can be seen to be, unfortunately,}

with only minor changes for 1968!

_{Calculations based on the}

Michell theory are easily done

_{for any ship, and the second-order}

theory is still

_{in process of development}

_{due to the difficult}

Laboratory for a year, being the one most hard at work

this problem.

The former is still used for most "calculations

of wave resistance" and

is the criterion in virtually all

optimizations of hull form.

is unfortunate, but seemingly

unavoidable, that so much effort is expended on optimizing

hull forms based on this approach (see Pien (3)).

Tuck's (4)

analysis of the circular cylinder still stands as the best

theoretical evidence of the need for a nonlinear approach,

though W.D. Kim (5a) has added a

Chey (5h)

a spheroid,

and Salvesen (6) has contributed further to the Michell

insecurity by his second- and third-order wave terms.

The H-5

Panel, Analytical Ship-Wave Relations, of the Society of Naval

Architects and Marine Engineers continues to be the forum at

which such questions are explored from time to time.

Guilloton, of course, can claim that his approach is

second-order in

its nature, and he has made revisions

direction;

however, this approach remains limited by

graphical nature and lack of a consistent theoretical base.

No further progress has been made in applying the

slender-body approach to the resistance problem in calm water.

No theoretical progress on viscous interaction effects

has been published

in the interim period.

Breslin and Eng (7)

repeated Havelock's attempt to explain the major effect as an

Still within the linear approach but nevertheless

of great potential usefulness as a guide to experimenters with

rectangular tanks of limited section

is the extensive work

of Kirsch (8)

in applying the results of Sretensky to such

cases.

In summary, this field from a theoretical point of

view is still much like the field of structures in being

stuck between an inadequate linear approach and an intractable

exact approach.

We need a Timoshenko to come along and

identify the one or two important terms to add to the linear

equations to patch them up and get us started along the

analytical road again.

EXPERIMENTS AND EXPERIMENTAL METHODS

Happily, this section can be written more in the

present than that preceding it.

While tests have not been

run

in the quantity one might desire, progress in the

development and establishment of experimental methods and

instrumentation has been reasonable, and application ofthese

tools to actual problems has been started and

in

institutions a matter of routine.

In the discussion to follow,

Newman's breakdown of the effort by people and institutions

is not followed (for one thing the people move around too

much!) but rather a general discussion first of the validity

VALIDITY OF EXPERIMENTAL METHODS

One of the most important aspects of the

_progress

made in this field

in the last three years has been the

establishment of the basic validity of certain of the methods

proposed for direct experimental determination of the

resistance from measurements of the wave pattern generated by

the model

in the model tank or by the ship at sea.

The latter

has, of course, yet to be attempted.

An extensive

investigation of this question, from a combined theoretical,

computational, and experimental point of view, was given by

Eggers, Sharma, and Ward (9)

thus it will not be

necessary to go into as much detail

in the present statement.

Briefly, the methods investigated, vis.:

Transverse Cut, based on wave height data from

probe or stereocamera,

X-Y Method, based on forces on a cylinder,

Longitudinal Cut, based on wave height data

with a truncation correction,

Longitudinal Cut, based on wave-slope data,

were found to be self-consistert from all three points of

view although the tests in 4. were inconclusive due to difficulty

with the instrumentation.

A study by Kobus (19) also confirms

viscosity.

_{While 3. seems to be gaining the edge}

_{as a good}

overall method for any facility, the

_{historically older}

X-Y and Eggers' transverse cut methods are still employed

at Webb and at the National Physical

_{Laboratory (with sufficient}

variation in the latter case to justify calling in the

"Matrix" method), a small and

_{large tank, respectively.}

Tank size and type of carriage

_{are important considerations in}

selecting the most feasible method

(10)has had better

_{success with the instrumentation in 4., and}

Wehausen has applied I., using

_{a stereo-camera setup already}

available at Berkeley( II), with

some success.

The Newman and F.C. Michelsen

_{method and an}

"Autocorrelation" method

_{were tried by H.C. Kim at the}

University of Michigan (12).

_{These seem basically equivalent}

to the longitudinal cut method but with some added

computational problems.

APPLICATIONS OF THE METHODS

Let us now look at

_{some of the results which have}

been obtained by this

_{new experimental tool}

_{in the last three}

years."*

* Results obtained

_{from applying these methods are bound to}

lead to controversy.

_{Some people seem to "know"}

beforehand

what percentage of the

_{residual resistance the wave resistance}

should be.

To find otherwise,

_{even after careful}

experimentation,

is to invite criticism

_{about the method used}

or the means of applying it.

_{However, much can be learned}

by

looking at the results

_{in the light of assumed}

Sharma (13) has used a

_{longitudinal cut method to}

generate information about optimum

_{size and location of a}

bulb on a particular hull form from only

_{two series of tests}

with and without the bulb by assuming

_{linear superposition of}

the wave patterns.

_{This appears to be}

_{a useful way to save}

a great deal of model construction and testing time

_assuming

the latter assumption can be shown -to

_{be valid for this case.}

Some results show the wave resistance to be

constant portion of the residual and others

Steele

(14) found only 10 percent in the case of tests on a tanker

in the new circulating water channel at N.P.L., and some

recent tests by students at Webb (15) showed about

_{40 percent}

in the case of a destroyer type hull.

_{The latter tests also}

destroyed faith in the idea of linear superposition of

waves

from local protuberances on the hull for this type

of ship.

On the other hand, Sharma (16) shows almost 100% for

_{a strut}

form.

There is no reason to believe any of these results to

be invalid, and much can be learned from

a closer inspection

of them, especially in the case of the N.P.L. tests in which

a preston tube survey of the hull friction was carried out as

we

There is evident in the Americas and overseas an

encouraging increase of commercial

interest in carrying out

tests of this nature on full tanker forms with and without

resistance afford by the latter;

the first of these tests

were accomplished in Japan by Mizuno (17).

While as yet, no full-scale testing has been

considered, an interesting study anticipating such tests

carried out by Snyder (18) who investigated the technique of

signal-averaging to decontaminate longitudinal cut records

from effects of an ambient statistical

The foregoing, though an attempt was made to solicit

progress information from people and institutions doing this

type of testing,

is bound to be incomplete.

For this reason,

the author would like to hear from

any persons concerning

additions to the list of accomplishments during the

years in this specific area of wave resistance testing.

MODEL SCALING

Progress in the improvement of model scaling

techniques in the fast three years is

easy to summarize:

This heading is

_{introduced to provoke discussion of how the}

theory or experimental techniques could

_{contribute to this}

important activity.

_{How can we help the model tank personnel}

with their most pressing problems?

SUMMARY

The foregoing state-of-the-art report

and this summary even briefer.

_{Analytically, we need at least}

resistance, we know it, and we are looking for a hero.

Experimentally, we have several valid techniques in hand which

are being applied at a

limited number of institutions on

interesting and worthwhile investigations and these

yielding challenging results.

We should have more of these, as

well

_{as the means and courage to go "full-scale" to the ship.}

And we should do some hard thinking about what

_{we can do for}

the model experimenter in terms of his scaling problem.

REFERENCES

I.

_{Newman, J.N., "Wave Resistance}

_{- The State of the Art,"}

Fourteenth Meeting of the American Towing Tank Conference, Webb

Institute, September 8-10,

Eggers, K.W.H., "On Second Order Contributions to Ship Waves

and Wave Resistance," Sixth Symposium on Naval Hydrodynamics,

Office of Naval Research, Washington, D.C., September 28

-October 4,

Pien, P.C., "Review of DTMB Research on Wave Resistance, Report

to the H-2 Panel of the Society of Naval Architects and Marine

Engineers, March 29,

Tuck, E.O., "The Effect of Non-Linearity at the Free Surface

on Flow Past a Submerged Cylinder," Journal of Fluid Mechanics,

Kim, W.D., "Non-Linear Free Surface Effects

Submerged Sphere," Davidson Laboratory Report

_{1271, February 1968.}

Chey, Y.H., "Second Order Wave Resistance

_{of a Submerged}

Spheroid," Doctoral Thesis, Stevens

_{Institute, 1968 (proposed).}

Salvesen, N., "On Second-Order Wave Theory

_{for Submerged}

Two-Dimensional Bodies," University of

_{Michigan, Department of}

Naval Architecture Report, April

Breslin, J.P. and Eng, K.,

_{"Theoretical-Experimental Study of}

Viscosity on Wave Resistance," Davidson Laboratory Report 1236,

October 1967.

Kirsch, Maria, "Shallow Water and

_{Channel Effects on Wave}

Resistance,"

Journal of Ship Research, Vol,

September 1966.

Eggers, K.W.H., Sharma, S.D.,

_{and Ward, L.W., "An Assessment}

of Some Experimental Methods

_{for Determining the Wavemaking}

Characteristics of a Ship Form,"

_{Transactions of the Society of}

Naval Architects and Marine

_{Engineers, November 1967.}

Ward, L.W., "Experimental

_{Determination of Wave Resistance}

from Lateral Wave-Slope Measurements," Webb Institute Report,

September 1967.

II.

_{Wehausen, J.V., Report to the}

H-5 Panel of the Society of

Naval Architects and Marine

_{Engineers, 12 June 1967.}

12.

_{Kim, H.C. and Michelsen,}

F.C., "Experimental Wave Component

Department of Naval

Architecture Report, June 1966.

Sharma, S.D., "An Attempted Application of Wave Analysis

Techniques to Achieve Bow-Wave Reduction," Sixth Symposium

on Naval Hydrodynamics, Office of Naval

Research, Washington,

D.C., September 28 - October 4,

Steele, B.N., "Measurements of Components of Resistance

on a Tanker Model," National Physical Laboratory, Ship Report

106, December 1967.

Moran, F., Johnson, A., and Bartholemew, C., "An

Investigation into the Feasibility of constructing Wave Resistance

Influence Diagrams by Application of Linear Superposition

Principles,"

Webb Institute Thesis, May 1968.

Sharma, S.D., "Some Results Concerning the Wavemaking of

a Thin Ship,"

Hamburgische Schiffbau-Versuchsanstalt Report

F 8/68, 1968.

Bessho, M. and Mizuno, T., "A Study of Full Ship Forms,"

Journal of Kanzai Zozen Kiokai, Vol.

117, June 1965.

Snyder, J.D.,

Ill, "Investigation of the Use of Signal

Averaging to Eliminate the Effect of the Ambient Sea

Determination of a Ship's Wave Resistance in the Open Ocean,"

Webb Institute Thesis, May 1968.

Kobus, H.E., "Examination of Eggers' Relationship Between

Transverse Wave Profiles and Wave Resistance", Journal of

PROGRESS IN THE ANALYSIS OF VISCOUS RESISTANCE

(part of report on resistance)

for presentation to Fifteenth Meeting

of American Towing Tank Conference

National Research Council Ottawa, Canada

PROGRESS IN THE ANALYSIS OF VISCOUS RESISTANCE

Turbulent Boundary Layers

Since the viscous resistance of a body moving through a real fluid

is so intimately connected with the development of the boundary layer on the

body, attention must be first focused on progress in the analysis of boundary

layers, especially for turbulent flow.

The analytical study of turbulent boundary layers is still plagued

by the lack of an adequate theory for the Reynolds stresses, especially for the

shearing stress. (In fact most effort is still being devoted to two-dimensional

flows.) The usual procedures have been to develop similarity laws for the

velo-city profile or to convert the partial differential equations of motion into

ordinary differential equations by suitable integrations which produce the von

Karman momentum equation, the energy equation, the moment-of-momentum equation,

etc. _{Factors are produced which empirically have to be related to boundary}

layer parameters like momentum thickness, shape parameter, etc. Improvements

in these methods are still being developed.

Similarity laws for boundary layers, with pressure gradients have been

presented by McQuaid (1) and Mickley et al (2). Instead of the wall shearing

stress as the nondimensionalizing factor, McQuaid uses the rate of change of

momentum thickness with streamwise distance and Mickley et al use the maximum

shearing stress.

In the case of integral methods, Walz (3) provides _{a more general}

rela-tion for the dissiparela-tion integral of the energy equarela-tion and McDonald (4)

pre-sents a more general relation for the shearing stress integral of the

moment-of-momentum equation.

differen-has been prompted by the availability of high-speed automatic computers and by

the interest of investigators of more complicated boundary-layer phenomena which

involve heat and mass transfer, compressibility, chemical reactions, etc. which

do not readily fit into similarity laws or the integral methods. Procedures

which once were discarded as being too crude have been revived for the shearing

stress such as Boussinesa's eddy viscosity (5,6) and Prandtl's mixing length

theory (7). A more sophisticated procedure is to relate the turbulence

trans-port equation to the shearing stress variation which provides a more flexible

model as well as incorporates more empirical relations (8,9).

In general, three-dimensional turbulent boundary layers lag in

develop-ment behind two-dimensional ones. Progress has been very desultory with

indif-ferent comparisons between theory and experiment. Correlation is worse for large

cross flows according to the experimental findings of Francis and Pierce (10)

on flows in curved channels.

Ship Hulls

An analytical study of the boundary layer on a ship hull was attempted

by Webster and Huang (11) who used Cooke's method of small cross flows to simplify

the calculation. The objective was to ascertain trends in the prediction of

separation as a function of Froude number.

Measurements of the distribution of skin friction over the hulls of

ship models by Steele and Pearce (12) using Preston tubes showed that hull form

influenced the skin friction; a bulbous bow gave less frictional resistance,

especially over the bottom. It was also found that propeller action had only a small influence on skin friction.

resistance showed fluctuations with Froude number. See also (19).

In an attempt to scale wave-making resistance by reducing the

frictional resistance by adding polymers to the towing tanks, Emerson (14)

could detect no appreciable effects.

Viscous Drag Reduction

Continued studies of polymer additives have shown their effectiveness

in reducing turbulent skin friction. The exact mechanism responsible for the

phenomenon is still subject to controversy (15). However, the development of

the similarity laws (16) for the drag-reducing phenomenon have shown that

hydro-dynamic predictions can be made without the need of a theory for the effect. It

has been shown (17) that the drag reduction occurs in the wall region card and

only affects the inner similarity law.

The effect of polymers secreted by microorganisms has been shown by

Hoyt (18) to account for anomalous drag effects in towing tests and cavitation

incidence effects in water tunnels.

REFERENCES

McQuaid, J., "A Velocity Defect Relationship for the Outer Part of

Equilibrium and Near-Equilibrium Turbulent Boundary Layers," Aeronautical Research

Council, ARC 27, 287 FM 3639, October 1965; also C.P. 885, 1966.

Mickley, H. S., Smith, K. A., and Levitch, R. N., "Nonequilibrium Turbulent

Boundary Layer," AIM Journal, Vol. 5, No. 9, September 1967.

Walz, A., "New General Law for the Turbulent Dissipation Integral,"

Physics of Fluids Supplement, 1967, p. S161.

Mellor, G. L., "Incompressible, Turbulent Boundary Layers with Arbitrary

Pressure Gradients and Divergent or Convergent Cross Flows," AIM Journal,

Vol. 5, No. 9, September 1967.

Smith, A.M.O., Jaffe, N. A., and Lind, R. C., "Study of a General Method

of Solution of the Incompressible Turbulent Boundary Layer Equations," Douglas

Aircraft Co. Report LB 52949, November 1965.

Spalding, D. B., "Theories of the Turbulent Boundary Layer," Applied

Mechanics Reviews, Vol. 20, No.8, August 1967, p. 735.

Bradshaw, P., Ferriss, D. H., and Atwell, N. P., "Calculation of Boundary

Layer Energy Equation," Journal of Fluid Mechanics, Vol. 28, Part 2, 26 May 1967,

p. 593.

Glushko, G. S., "Turbulent Boundary Layer on a Flat Plate in an

Incom-pressible Fluid," NASA TT F-10,080, April 1966 (translated from Iz. Akad. Nauk.,

Ser. Mekh, No. 4, 1965, pp. 13-23).

Franics, G. P. and Pierce, F. J., "An Experimental Study of Skewed Turbulent

Boundary Layers in Low Speed Flows," Trans. ASME, Journal of Basic Engineering,

September 1967, p. 597.

Webster, W. C. and Huang, T. T., "Study of the Boundary Layer on Ship Forms,"

Hydronautics, Inc., Tech. Report 608-1, January 1968.

Steele, B. N. and Pearce, G. B., "Experimental Determination of the

Townsin, R. L., "The Frictional and Pressure Resistance of Two 'Lucy

Ashton' Geosims," Quarterly Transactions of RINA, Vol. 109, No. 3, July 1967,

p. 249.

Emerson, A., "The Calculation of Ship Resistance: An Application of

Guilloton's Method," Quarterly Transactions of RINA, Vol. 109, No. 3, July 1967,

p. 241.

Lumley, J. L., "The Toms Phenomenon: Anomalous Effects in Turbulent Flow

of Dilute Solutions of High Molecular Weight Linear Polymers," Applied Mechanics

Reviews, Vol. 20, No. 12, December 1967, p. 1139.

Granville, P. S., "The Frictional Resistance and Velocity Similarity Laws

of Drag-Reducing Polymer Solutions," Naval Ship R&D Center Report 2502, September

1967 (to appear in Journal of Ship Research).

Wells, C. S., Jr. and Spangler, J. G., "Injection of a Drag-Reducing Fluid

into Turbulent Pipe Flow of a Newtonian Fluid," Physics of Fluids, Vol. 10,

No. 9, September 1967, p. 1890; also NASA Contractor Report NASA CR-852, July 1967.

Hoyt, J. W., "Microorganisms - Their Influence on Hydrodynamic Testing,"

Naval Research Reviews, Vol. 21, No. 5, May 1968.

Tzou, K.T.S., and Landweber, L., "Determination of the Viscous Drag

of a Ship Model", Journal of Ship Research, Vol. 12, No. 2, June 1968.

THE PREDICTION OF POWER REQUIRED TO PROPEL A HULL

(part of report on propulsion)

for presentation to Fifteenth Meeting of American Towing Tank Conference

National Research Council Ottawa, Canada

THE PREDICTION OF POWER REQUIRED TO PROPEL A HULL

GENERAL COMMENTS

Some of the basic problems concerning the prediction of the power

required to propel a ship were discussed by Todd in the last report of

this conference. These problems are: the separation of a hull's

resistance into components whose effects can be predicted with complete

confidence for all types of forms, the lack of complete understanding

of scale effects on hulls and propulsors, and of interaction effects

between hulls and propulsors.

These areas have been studied for many years, and it would be

optimistic to state that solutions are immediately at hand. Some very

informative work has been done in the last three years, however, and

it would seem that we could understand our problems to _{a degree that we}

can at least make rational engineering judgements.

The high state of development of instrumentation for making _measurements

during conventional resistance and self-propulsion tests of _{model hulls,}

and open water tests of propellers has been examined on a 7 meter tanker model by Watanabe.1 A statistical analysis was made of the variations

in relative rotative efficiency, wake and thrust deduction factors. At a

Froude Number of 0.2 the standard deviation for e and w from the mean

rr

curves was 0.006 and for t was 0.01. _{The scatter from test to test was}

=4.11 percentage point for

reasonable to believe that these standards of measurement are typical for

tanks with adequate instrumentation and staff. The major problems in

prediction for conventional hulls and propellers then, would seem to be

those associated with scaling, extrapolation techniques, and local effects

such as blockage and tank "storms", rather than instrumentation.

A ship rarely moves in completely still air consequently there is a

component of resistance due to the natural wind as well as to the ship's

motion. The resistance of a typical cargo ship in still air is estimated

to be of the order of 2 to 3 percent of the total resistance for the ship. With the advent of the 25 knot cargo ship the SHP required to overcome

wind effects has become significant in still air. When the natural wind

effects encountered in rough weather are added, the investment in power

required for wind is quite large. For example, trials are run on occasion

in true winds of 30 knots or more with a typical increase in resistance due to wind in excess of 10 percent of the total resistance. Since a normal

service allowance is 20 percent on SHP for wind, waves, fouling and other

causes, it may be seen that wind effects along can require an unduly

large part of this allowance.

In addition to higher ship speeds the modern ship superstructure and

above water fittings are growing proportionately larger. Taylor2 used an

\

approximation of half the ship's beam squared (f B2) for estimating the

area of the athwartship plan of pre-World War II ships. This was a useful

approximation of the time, but a check of recent ship designs indicates

With regard to determining the resistance due to wind, White3 has

published a note which cites the work of Hughes, _{Shearer and Lynn, Aertssen}

and Colin, among others. _{This note seems to be an adequate summary of}

current knowledge on this subject, in that there is _{an allowance for the}

natural wind gradient over water (older methods _{did not), and there is}

presented a method and accessory data for _{computing the EHP and corresponding}

SHP to overcome the wind.

It should be noted that there is _{no direct applicable data available}

for cargo ships of recent design with the heavy cargo handling _{gear which}

is coming into current use. _{The booms and king posts}

on some of the new

designs are quite large, and since they are circular in cross section the

individual drag coefficients _{are, of course, very large.}

Also it has been

the practice in the past to ignore the drag of deck cargo in making _estimates. This oversight, particularly in the _{case of container ships, should be}

remedied.

Based on data currently available, we can make a reasonably precise prediction of the resistance due to wind for conventional hulls. _{We should}

conduct wind tunnel tests _{on models of cargo ships with and}

without large

handling gear and deck cargo components to determine whether _interference effects are large enough to affect predictions made from _{existing data.} Models of more specialized form, such _{as catamarans and hydrofoils, should}

also be tested to obtain wind _{resistance coefficients.}

There are several areas of tankery which can best be explored _{by the} use of large geosims. _{It is understood that discussions}

are currently

taking place between

Administration and SNAME concerning the construction of a large model,

or experimental test-bed, approximately eighty feet in length. This

proposed model,which is described in detail elsewhere in this report,

would be equipped with up-to-date instrumentation, and used for a

variety of experiments to determine the significance of scale effects

for both hulls and propellers, in smooth and rough water. Needless to

say, this information is required to fill a very large gap in our current

knowledge of scaling and extrapolation techniques. The project should

TYPES OF HULLS

DISPLACEMENT - SMOOTH WATER POWERING

In recent times the work of Inui4 revived the interest in the bulbous

bow as a method of reducing the resistance of ships. _{Additional work in}

this field has been carried on by several investigators with emphasis

being placed on the ships of high block coefficient. _{Much of the original}

work was considered as an attempt to reduce wave-making resistance. _The

decreases in EHP obtained, however, have been quite large at fairly

low Froude Numbers with the inference that viscous resistance _{must also}

be affected. _{The investigations have also spread into the area of high}

speed cargo liners where the pay-off range is usually above _{a Froude Number}

of 0.25 as originally indicated by Taylor.2

The recent experimental and theoretical work _{on bulbous bows started}

out considering resistance in calm water. _{Subsequent investigators considered}

resistance in rough water in connection with projects to _{determine ship}

motions.

There has been very little work done in determining _{the effects of a}

bulbous bow on the propulsion of ships in _{a form where a direct comparison}

can be made with the performance of a hull with _{a conventional bow.}

Van Lammeren and Muntjewerf5 have reported research on the calm water propulsion performance of a 24,000 DWT bulkcarrier. _{The original design}

was a conventional single screw ship with moderate _{U shaped bow sections.}

had little effect on either PC or thrust deduction in the loaded condition.

The EHP with the bulbous bow configuration in the ballast condition decreased

by about 15 percent at design speed; there was little significant effect on PC, but a decided effect on thrust deduction.

Couch and Moss6 conducted an investigation into the calm water

resistance of three series of bulbs on a high block coefficient form.

The results of the resistance tests fell into line generally with previous

work indicating a decrease of as much as 20 percent in EHP for the bulbous

bow designs in the ballast conditions. They reported propulsion test

results for the conventional bow and two bulbs, each representing one of

the two most promising series of bulb configurations with regard to

resistance results. Of particular note is a substantial improvement (about a

5 percentage point maximum) in PC. The authors commented that improvements

in propeller efficiency were small, while those in hull efficiency ranged

from marginal to substantial at design speeds. They noted that wake fraction

increased with the installation of a bulb in all the load conditions, but

thrust deduction fractions decreased in the full-load condition and increased

in the ballast conditions. Although no comment was made regarding relative

rotative efficiency it, too, would have to vary between load conditions to

obtain the rather general increase in PC noted with the bulbs in all conditions.

Takehei and Pardo in their discussions of this paper stated that they had

also found increases in propulsive efficiency with bulbs.

A wake survey test was run with and without a bulb during the experiments

Similar results have been noted at NSRDC. This is additional confirmation

of sizeable interaction effects.

The work on high block coefficient hulls with bulbs is rather typical of the state-of-the-art for displacement hulls _{generally and has the}

advantage that deficiencies in our ability to make adequate predictions

are emphasized. _{It is understood that some tanks use different correlation}

allowances for predictions for load and ballast displacements for tankers. Other tanks compensate for changes in _{displacement by using different form}

factors with Hughes formulation. _{It would seem impossible for a new tank}

to make reasonable predictions without first obtaining trial correlation

data. _{We must continue our efforts to obtain}

rational theories and

experimental verification of those theories _{concerning viscous and}

wave-making resistance, separation of the boundary layer, and the change of flow around a hull due to the influence _{of the propulsor.}

DISPLACEMENT HULLS _{- ROUGH WATER POWERING}

As ships grow larger and are driven at higher speeds the environmental conditions in which they operate become more important. _{One of the areas} in which a significant amount of productive work has been accomplished in

The theoretical work of Maruo7 was based on the assumption that

the added resistance of a ship was proportional to the second power of

the wave height. More recent experimental work by Sibul8 in regular,

composite, and irregular waves indicates that this assumption is not

always valid as the wave-induced resistance may vary in a nonlinear

manner with hull form and with wave steepness also. This rules out the

use of spectral methods, based on linear superposition, for prediction

purposes without further qualification as to type of hull and test conditions.

Powering of ships in waves was also explored experimentally in connection

with a project to evaluate the relative merits of U and V shaped bows in

calm water, rough water, and with regard to motions and slamming. This

study was stimulated by Townsend9 who was interested in the development of

a hull which could maintain high speed in a seaway without severe slamming

and consequent bottom damage. The results of the study, conducted at NSRDC

in irregular waves have been reported by Ochi.10 Measurements were taken

of thrust, torque, speed and wave height while rpm was maintained constant

for any given run. Ochi notes that the V form is generally superior to two

U forms with regard to the SHP required to maintain constant RPM in waves.

Of particular interest is the prediction that at 14 knots ship speed SHP

would have to be increased about three-fold for Sea State 7 over that

required for calm water for the V and one of the U forms (the second U

form was not tested at conditions equivalent to Sea State

7).

An area which should be explored by future research on powering in

waves is the extension of the work already underway to determine

PLANING HULLS

For a long time the research in this field was devoted to work in

the smooth water resistance of hulls of various _{geometric shapes. Recently,}

however, there has been a growing _{concern with propulsion performance and}

with performance in waves as a number of boat _{designs failed to meet the}

operational requirements for which they were built.

Savitsky11 has presented a summary of existing information _{on planing} hulls in a seaway, giving the variation in rough-water resistance increment with speed-length ratio for head and following _{seas. He notes that the}

information discussed is primarily for regular waves.

Hadler12 _{combined the research work available on the propeller on an}

inclined shaft with the forces contributed by the appendages to develop a method for predicting the powering performance of _{a planing boat system.}

He points out the need to consider the normal, side and pressure forces generated by the propeller on the hull and the appendage lift, drag and

interference effects.

Blount, et al.13 report on a comprehensive program where special instrumentation was installed in a full-scale planing hull and trials were conducted at several displacements in _{deep and shallow water.}

Model

resistance and propulsion tests were conducted for correlation _purposes. Resistance tests were conducted on the model with and without appendages. Open water characterization tests _{were run on both the model and}

cavitation tunnel. _{The authors comment that correlation of thrust, power}

and trim was not very good above the planing hump, but _{that propeller}

performance correlation with series data, even in the cavitating region, was good. _{The comparison of measured appendage drag with}

that calculated

according to existing methods was rather poor particularly in the higher

speed ranges. _{Particularly disturbing are pictures taken of model and}

full-scale spray patterns in the planing region. _{The difference is}

remarkable.

There is one additional problem that is becoming apparent _from

planing boat - model correlation; trim angle does not correlate well in

the planing region. _{As the resistance of a planing hull is sensitive to}

trim angle this is a matter of concern which should be investigated.

Most planing hulls of any size must be able to operate in a seaway

to meet design requirements. _{We do not have enough data at the present}

to make accurate predictions of the rough water powering performance for

all the types of planing hulls presently in use. Recommended areas for

research are: the investigation

of

waves to determine the degree of confidence which may be placed in using

linear superposition for prediction purposes, tests of systematic series

of hull forms in waves, experimental determination of the effect of varying

hull trim angle on performance in waves, and correlation between trial and

CATAMARANS

Multiple hull craft are receiving much attention _{in the small boat}

field and in certain areas such _{as oceanographic research ships. In}

addition, there seems to be a number of advocates for this type of hull who feel that it is suitable for _{a rather wide variety of uses. The}

experimental and analytical work of Eggers14 has served as a base for most of the new work in this field. _{Michel15 had a double hull model run} for resistance at several hull _{separations at Davidson Laboratory. He}

reports that there is no practical _{separation between hulls which does}

not have adverse effects on resistance due to wave interference between

the hulls. _{In spite of this interference,}

and the inevitable increase in

frictional resistance due to the larger wetted surface of the twin hulls,

he concludes that it is possible for a catamaran to be less resistful _than an "equivalent" single hull at the higher _{speed length ratios. He}

indicates that the break-even point on EHP is VJE-of 1.15 for his design as compared to two single hull forms whose resistance is deduced from

the Taylor contours. _{It should be noted, however, that the dimensions}

for the single hull "equivalent" designs are L/B of 4 and a B/H of in

one case, and an L/B of 5 and _{a B/H of 2.5 in the other.}

It is questioned

whether most designers would _{attempt to push either of these}

single hulls

to the speed length indicated.

Voyevodskaya16 presents the results of a fairly extensive experimental program on the resistance of double hull _{ships, wherein he tested five}

symmetrical hulls of the same length and draft, where the first hull had the same displacement and beam as the second and third _{hulls combined,}

and the fourth and fifth hulls combined _{are equal in displacement and}

beam to the second hull. _{The tests were carried out for Froude number}

up to 0.8 and with clearances between the double hulls from 0.2 to 2.0

times the beam. Results are presented in the form of residuary _resistance

coefficients. _{There is a strong relationship between hull clearance and}

resistance for a given Froude number _{as previously stated. The determination}

of a specific clearance for a given design speed is, _{therefore, quite}

critical particularly at high speeds. He also reports a comparison of

the resistance of assymmetrical hulls with the symmetrical hulls, and concludes that there is a possibility of decreasing resistance with a

suitable asymmetrical hull design.

Everest17 has reported on analytical and experimental work performed

at NFL. _{The analytical methods are based on Gadd and Hogben's extension}

of Egger's work. _{He reports that it is possible, depending on the hull}

form and separation of the hulls, to operate in a rather narrow range of Froude Numbers where wave interference effects are beneficial. He concludes,

however, as does Voyevodskaya, that a catamaran ship would require more

power than an equivalent single hulled ship unless the single hull had

unusually large wave and viscous pressure drag components.

There is a small amount of unpublished data concerning self-propulsion

tests of double hull ships. Unfortunately, as with a conventional single

that the powered performance _{will be superior to}

a form which may have

higher resistance. _{The indications}

are that the hull-propeller

interactions are of rather _{complex form due to the}

additional problem of the wave interference _{between the hulls.}

From the scanty evidence

available it does not

appear reasonable to anticipate _{the high propulsive} coefficients for each _{hull that might be obtained with a}

more normal single

hull form of higher

displacement-length ratio. _{Obviously a great deal}

of work is required

in this field to be able to predict the _propulsion

performance of double-hull

ships in any reliable fashion.

Although a fair amount of effort has been _{devoted to determining}

the

resistance of multiple

hulls the problem still exists, and presumably _in

even more complex fashion,

of extrapolation to full-scale. _{Since little}

is known about the propulsion performance _{of catamarans}

more effort should be expended in determining how the

propulsion coefficients vary with respect to speed, loading _{and trim.}

It seems logical to

anticipate that the component

of thrust deduction

and wake friction due to wave-making _{may change more}

than for a conventional

hull where wave

interference is not a problem.

Finally, since full-scale

trial correlation data are not yet _{available the}

magnitude of the problems

of prediction is _{not known even in}

HYDROFOILS AND SURFACE EFFECT SHIPS

The prediction of the propulsion requirements of hydrofoil _{and surface}

effect ship systems is not yet a reality. A growing amount of experience

is being obtained with the performance of components of _{systems but in}

many cases information is not generally available for proprietary reasons.

Ellsworth18 has published a state-of-the-art report on hydrofoils which indicates there has been some analytical work done on propulsion in order

to make estimates of performance but no experimental data _{are available}

as yet to compare with the estimates. Nakonechny19 has published a report

on surface effect ships from which the same inferences may be drawn. We

are evidently in the same stage of progress with these craft that the

automobile was in 1900. It is not a question of how well the system performs,

but to overcome the problems with hull and machinery components to keep

COMMENTS ON INTERACTION AND SCALE _EFPECTS

THRUST DEDUCTION

One of the major problems with _{thrust deduction has always been}

that

it is the difference between

two large variables, and is, consequently,

much more sensitive to change _{than either of the two.}

There has been

a fair amount of effort in recent

years devoted to gaining understanding

of this factor by using _{analytical methods.}

Much of the earlier work _along

these lines was devoted to

studies of submerged bodies of revolution,

cylinders, wedges, and other

elementary hull forms in conjunction with

simplified representation of propellers in order to treat _{the problem}

as one of potential flow.

The purpose of these simplifications was, of

course, to reduce the mathematical

complexities of the problem _{to the}

point where a solution _{could be obtained with}

a reasonable expenditure of

effort. _{Progress has been made in}

this field, however, _{and it now appears}

possible to study more realistic hull and _{propeller forms.}

Analytical work has been done, based on the Lagally steady-motion

theorem, for the prediction of thrust deduction for _{surface ships at low Froude number.}

This work

assumes that the influence of _{the propeller on the}

hull is primarily potential in nature while that of the hull _{on the propeller is due to}

for the propeller, _{a combination of the Douglas-Neuman}

program with typical

experimental data to obtain the _{potential flow from the hull, and/or}

the real total wake which is determined experimentally.

The major advantage to _{an analytical method of this type is that it}

permits the investigation to make _{economical parametric studies relating}

hull and propeller forms _{and locations with respect to each other.}

Experimental studies to determine _{the effects of scale}

on thrust

deduction have usually followed _{the approach of using geosims.}

Todd commented on past efforts along _{these lines with the conclusion}

that most

investigators had decided that t _{increased with length of model,}

but that

there was a certain amount of _{conflicting data.}

Yakoo21 and Taniguchi22

have also conducted experimental _{studies with geosims.}

Yakoo's data

indicates that t decreases with _{an increase in model length.}

Taniguchi

also comes to the same conclusion but states that t may be taken as

approximately constant for models of 7 meters and longer.

It sould appear that sufficient _{data are still not available}

to permit

a meaningful judgement as to whether thrust deduction is identical for the ship and its model, as has been assumed for many years for lack of any better assumption.

Suggested areas for further research are the extension of the analytical methods for predicting thrust deduction _{to include the component due to}

wave-making, and the construction and testing _{of a better geosim series}

as discussed in more detail in another section of _{this report.}

Meanwhile

the magnitude and direction of scale effects on thrust deduction have not

been documented sufficiently to warrant _{changing the assumption that there}

PROPELLER SCALE ECTS

It has generally been acknowledged, _{since Lerb's early work23, that}

there could be significant scale effects on the performance of _propellers.

22

Taniguchi _{has presented data for three propeller geosims in the form} of the variation of KT and K _{in open water with Reynolds Number. The} experiments with the two larger propellers follow the trend predicted by Lerbs in that KT increases with Reynolds Number, while _{K decreases,} with a consequent sizeable _{increase in propeller efficiency}

due to Reynolds Number effects.

_Watanabe1

An approximation of the Reynolds scale effect on _{propeller performance}

can be obtained by taking the _{equations derived by Lerbs}

KT (Ship) KT (Model) [1-2(CD/CL)A.] _Ship

E1-2(CD /CL )A.

j

Model

and

K

(Ship) ---Kg (Model) [1 + (2/3)(OD/CL)(1/A

i(Ship)

[1 + (2/3)(CD/CL)(1/A )1

i(Model)

and, ignoring interaction _{effects, assume that}

CD varies as the ATTC friction

line and that the variations _{of CL and}

with Reynolds Number _{are negligible.}

Estimates from these _{equations indicate that the}

ship propulsive coefficient, could be from )4 to ₈

percent higher than the model. _{Taniguchi, for}

example, indicates _{an increase in optimum}

rip for his tanker propeller of

approximately 4 _{percent due to the change}

_{inonly; he}

assumes that the Kg

In connection with these scale effects it _{is to be regretted that} there are so few trials on commercial ships _{where thrust has been measured.}

It is generally thought that the scale _{effects on those elements of propulsion}

coefficients connected with thrust _{are probably smaller than those involving}

torque. _{The use of thrust identity is making predictions from model tests}

is wide-spread for a variety of _{reasons, but primarily because it is}

considered the most reliable measurement _{of the two, yet we are nearly}

in the dark as to how thrust really does _{scale. It would seem to be of}

utmost importance to obtain good quality thrust data from trials of several types of ships, expensive though it may be. _{Incidentally this is one}

area where new instrumentation is needed very badly. _{The cost of installing}

thrustmeters, even of the type where elements of the thrust bearing are strain gaged, is prohibitive to ship owners.

Recommendations for future work on propeller _{scale effects include the}

development of a less expensive thrustmeter for ships, obtainment of full-scale thrust data for correlation purposes, and the experimental verification of Lerbs work over a wide enough range of Reynolds Numbers to be meaningful. This is an area where the eighty-foot model previously mentioned would be

invaluable. _{It would permit the exploration of propeller performance in an}

unsteady flow field at a reasonably large scale. _{There is enough controversy}

over the magnitude of the scale effects on propellers that it does not

appear feasible to make corrections to predictions for these effects until

WATERJETS

Development of waterjets is being pushed as an alternative solution to several problems encountered with more conventional methods of propulsion on some of the more modern types of craft. _{Brandau has recently completed}

a

comprehensive review of the state-of-the-art on waterjets which contains

a sizeable bibliography. _{The work to date has been rather heavily}

oriented towards developing _{components of the waterjet system such}

as

the inlet, the ducting, the _{pump, or the exit ducting.}

Most systems

analyses to date are based on theory supported by elements of experimental

data for components. _{Such data as are available for}

waterjet systems

are almost exclusively from trials of small boats where precise instrumentation

has not been installed.

Similarly the problems of predicting the performance of a hull fitted

with a waterjet are more complex than for the hull fitted with _{a conventional}

propeller. If for no other reason, the _{lack of information as to the}

significance of interaction effects between hull and waterjet make the problem more complicated.

Interaction effects which should be considered

in a prediction are duct losses, _{change of pressure}

distribution on the

hull due to operation of the waterjet, changes in boundary _{layer flow due} to the intake of the'j t, and

changes in trim and available thrust due to

induction and ejection of the water.

Areas which could be studied profitably are overall propulsion performance of waterjet systems, _{the magnitude of interaction}

effects, the

optimization of ducting, and of _{hull inlet and diffusers}

In testing models of waterjet systems the familiar problem of scaling

is encountered. _{To model a complete system is would be}

necessary to

attain Froude, Reynolds and cavitation numbers _{simultaneously. The}

technique of testing parts of the system using _{appropriate scaling laws}

is usually followed. _{Full-scale testing is also complicated by a familiar}

REFERENCES

Watanabe, K., "Repeated Self-Propulsion Tests on a Tanker Model," Proceedings of the Eleventh ITTC (1966).

Taylor, D.W., "The Speed and Power of Ships"

White, G.P., "Wind Resistance, A Suggested Procedure for the Correction of Ship Trial Results," NPL Ship Division Tech. Memo. _{No. 116}

Inui, T., "Wave Making Resistance of Ships," SNAME, Vol. 70 (1962)

Van Lammeren, W.P.A. and Muntjewerf, J.J., "Research _{on Bulbous Bow Ships} Part IIA, Still Water Performance of a 24,000 DWT Bulkcarrier with a Large Bulbous Bow," Int'l. Shpbldg.

Progress, Vol. 12 (Dec 1965).

Couch, R.B. and Moss, J.L., "Application of Large Protruding Bulbs _{to Ships}

of High Block Coefficient," SNAME, Vol. 74 (1966).

Marvo, H., "The Excess Resistance of a Ship in Rough Seas," Int'l Shpbldg

Progress, Vol. L. _{(July 1957).}

Sibul, 0.J., "Increase of Ship Resistance in Waves," California University Berkely Report No. NA-67-2 (March 1967).

Townsend, H.S., "A Series of Cargo Hull Forms," United States _Salvage Assoc. Ing. (1965).

Ochi, M.K., "Slamming and Powering Characteristics of the Challenger and Townsend Forms in Irregular Waves," Section II of SNARE

Panel HHS-1 Report on the Influence of Ship Form _on

Seaworthi-ness (June 1967).

Savitsky, D., "On the Seakeeping of Planing Hulls," _{Marine Technology,}

Vol. 5 (April 1968).

Hadler, J.B., "The Prediction of Power Performance _{on Planing Craft,"}

SNANE, Vol. 74 (1966).

Blount, D.L., Stuntz, G.R., Jr., Gregory, D.L., _{and Frome, M.J., "Correlation} of Full-Scale Trials and Model Tests for a Small Planing

Boat," RINA (1968).

Eggers, K., "Uber Widerstandsverhaltnisse von Zweikorperschiffen," J. Schiffbautech Gesellschaft (1955).

Michel, W., "The Sea-Going Catamaran Ship, Its Features and Feasibilities,"

Int'l Shipbuilding Progress, Vol. 8 (Sep

1961).

Voyevodskaya, Y.N., "Comparative Evaluation of the Drag of Double-Hull Ships," Symposium of Articles on Ship Hydrodynamics, Part II, Sudostroyeniye Publishing House

(1965).

Multi-Hulled Vessels in Calm Water," Northeast Coast

Institute (March

1968).

Ellsworth, W.M., "The U.S. Navy Hydrofoil Development Program - A Status Report," AIAA SNAME Advance Marine Vehicles Meeting

(May

1967).

Nakonechny, B.V., "Survey of Present State of Technology and Practical Experiences with Air Cushion Vehicles," Naval Engineers

Journal (August

1967).

Todd, F,H., "The Model-Ship Correlation Problem," Proceedings of the

Fourteenth ATTC

(1965).

Yakoo, K, "Scale Effect Experiment on Tanker Models," Proceedings of

the Eleventh ITTC

(1966).

Taniguchi, K., "Study on Scale Effect of Propulsive Performance by Use of Geosims of a Tanker," Proceedings of the

Eleventh ITTC

(1966).

Lerbs, H.W., "On the Effects of Scale and Roughness on Free Running Propellers," Jour. Am. Soc. Naval Engineers, Vol. 63

(1951).

Brandau, J., "Performance of Waterjet Propulsion Systems - A Review of the State-of-the-Art," Journal of Hydronautics Vol. II, No. 2 (April

1968).

PROPULSORHULL INTERACTION WITH BLADE CAVITATION

-A Summary of the State-of-the-Art

(part of a report on cavitation)

for presentation to Fifteenth Meeting of American Towing Tank Conference

National Research Council Ottawa, Canada

PROPULSOR-HULL INTERACTION WITH BLADE CAVITATION

Introduction

The design of a propulsor for operation with a given hull form

must consider the so-called phenomenon of

_{thrust-deduction.}

_This

quantity, which represents the effect of the propulsor

_{on the flow}

over the hull only, can be determined from potential

_theory

predic-tions or by the use of experimental data

_{on similar hull forms.}

_The

experimental determination of thrust deduction

_{is best conducted}

by comparative measurements of hull drag

_{and propulsor shaft thrust.}

A discussion of recent programs and developments in the

deter-mination of this quantity in the absence of

_{propulsor blade}

cavita-tion is presented elsewhere in this

_{summary report.}

_{This section}

will be concerned with the thrust deduction associated with

cavitating propulsor.

Discussion

Although considerable data and theoretical methods exist for

determining the thrust deduction associated with a propulsor-hull

combination in the absence of propulsor cavitation, little

infor-mation is available for the

_{combination with propulsor cavitation.}

Perhaps the initial attempt

_{to determine the effect of cavitation}

is that reported by V. F.

_{Bavin and I. J. Miniovich, Reference (1),}

at the Tenth International

_{Towing Tank Conference, 1963.}

It was

reported in (1) and in further

_{detail in References (2) and (3)}

the existence of propulsor blade cavitation acts to reduce the thrust

deduction experienced and that with extensive cavitation, this

quan-tity's value approaches zero.

A theoretical method developed by

Nelson(4)

substantiates the

results reported by Bavin, et al.

This method calculates the velocity

field induced by a propeller with the effect of cavity thickness

length included.

Employment of this method assumes an infinite number

of propeller blades but justifies the use of this assumption on the

basis that the thrust deduction is a function of the mean

rather than

the instantaneous induced velocity.

The results of Nelson's analysis

indicate that (1) the presence of cavitation on the propulsor

reduces

the thrust deduction, and (2) the condition of zero

thrust deduction

occurs when the cavitation is fully developed, i.e. the cavitation

number is zero.

This analysis substantiates the experimental results

of Bavin et al.

A later program conducted at

NSRDC(5)

acts to further verify

earlier conclusions.

This program consisted of experimental

measure-ments of thrust deduction caused by a

fully cavitating propeller

operated behind a hydrofoil at various

cavitating conditions.

analysis of the induced velocity field of a fully cavitating propeller

based on Kerwin's

analysis(6) indicates that the induced velocity field

upstream of the propeller can be negative when the blades experience

by the blade-cavity thickness.

Experimental results confirm this

analysis and a zero value of thrust deduction.

Summary and Recommendation

The determination of the thrust deduction associated with a

cavitating propulsor has received little attention.

Those programs

which have been conducted are both theoretical and experimental and

indicate that the effect of cavitation on the blades of the propulsor

is to reduce the experienced value of thrust deduction.

As the

cavitation becomes fully developed the thrust deduction tends to a

zero value.

It is recommended that additional studies be conducted to better

define this effect; it is necessary to distinguish between the effects

of cavity thickness, blade loading and cavity length.

REFERENCES

Bavin, V. F., and Miniovich, I. J., "Experimental Investigations

of Interaction Between Hull and Cavitating Propeller," Tenth

International Towing Tank Conference (1963).

Bavin, V. F., "Theory of Interaction of an Ideal Cavitating

Engine with a Vessel Hull" Collection of Articles on Ship

Hydrodynamics (1965).

Bavin, V. F., "Experimental Study of the Interaction of a

Cavitating Propeller with a Vessel's Hull" Collection of Articles

on Ship Hydrodynamics (1965).

Nelson, D. M., "A Theoretical Examination of the Effect of

Propeller Cavitation on Thrust Deduction," U. S. Naval Ordnance

Test Station, IDP No. 2026 (Feb. 1964).

Beveridge, J. L., "Induced Velocity Field of a Fully Cavitating

Propeller and Interaction Experiments with a Fully Cavitating

Propeller Behind a Hydrofoil," DTMB Report 1832 (April 1964).

Kerwin, J. E., "Linearized Theory for Propellers in Steady Flow,"

MIT, Dept. of Naval Architecture and Marine Engineering (Jul 1963).

CAVITATION INCEPTION

(part of report on cavitation)

for presentation to Fifteenth Meeting

of American Towing Tank Conference

National Research Council Ottawa, Canada

CAVITATION INCEPTION

INTRODUCTION

During the past several years many investigations have been reported

that this author feels will lead to state-of-the-art advances in cavitation

research_ This report will attempt to present only a brief review of the

recently completed and the current research that directly relates to cavitation

inception and instrumentation in water tunnels and model basins. An exhaustive

listing of all research in cavitation inception will not be attempted. It

is felt that research not presented in this report is included in the

ref-erences of the research considered here.

The International Towing Tank Conference Cavitation Committee recently

initiated a comparative cavitation inception program using geometrically

similar head forms_ These tests were performed at a large number of test

facilities_ The widely varying results [1] indicate that many aspects of

the cavitation inception process have not yet been clearly defined and

evaluated,

As pointed out by Holl [2], the entire mechanism of cavitation

incep-tion is based on the hypothesis of a nucleus_ In the broad sense, nucleation

of a cavity is possible from a wide variety of causes. _{These include entrained}

gas, trapped gas, broken liquid-solid interfacial bonds, and high energy

particles, _{To this writer's knowledge, no definitive work has been reported}

to clarify the mechanism of nucleation_ _{For the purposes of this report,}

any nuclei produced by high energy particles will be considered as