a
TeOtritSPearMs-gARCHIEF
NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER
A PROPOSED NEW STERN ARRANGEMENT
by
Pao C. Pien
and
J. Strom-Tejsen
Distribution of this document is unlimited.
HYDROMECHANICS LABORATORY RESEARCH AND DEVELOPMENT REPORT
-
The Naval Ship Research and Development Center is
a U.S: NaVy.,center:for labOrator
effort directed 'iii...aChieving,imprOved sea and air Vehicles.
It WaS:formethh .March 197 b
merging the David -Taylor Model Bitsin'.it:Carderocic,*Maryland and,the`Marine;Engineering
- .
Laboratory at Annapolis, Maryland.
.'Naval Ship Research arid Development Center
Washington,
.260.07 .-.ABSTRACT
The trend of ship designs toward high speed and
power has led to increasing propulsive difficulties due
to the problems of cavitation and propeller-induced
vibration. Consequently, in the design of stern arrange-ment, considerations must be focused on these problems
in addition to propulsive efficiency.
This report deals with the factors that influence
the hull-propeller interaction problem. It discusses the advantages and disadvantages of single-screw and
twin-screw arrangements presently used.
A new twin-screw arrangement is described. In this stern arrangement the two propellers are mounted
close to the ship centerline with overlapping propeller
fields. The propulsive efficiency, cavitation, and
vibration qualities of the new arrangement are discussed. Preliminary model tests with the new stern
arrange-ment are presented and considerations to be taken in the
design are mentioned.
ADMINISTRATIVE INFORMATION
The model experimental portion of the work was authorized and
funded by the Naval Ship Research and Development Center Foundational Research program under Project Z-R011 01 01.
OOOOO OOOOOOOO ADMINISTRATIVE INFORMATION ... HULL PROPELLER , ' POTENTIAL OO OOO . ... TABLE OF CONTENTS . ..' . . .. . .. . . ..
UCTION.
.... . . ... .......
.. '-11.yiscOVs wOtt,
15THAust DEDudtj*
CURRENT PRACTICE i0-,g0IP:PitopuisloN ... :.
-sINGII=s,CRE1440ANUM017 ... .... . . .. . .
Modifications in Propulsive Device . .. . .. . . .. . . : '
.HurlIMod.ificàtion ...
TWIN-SCREW ARRANGEMENT
.... , .
... ..,9A'PROPOSED NEW -STERN ARRANGEMENT .:,.:.,:..,...:... i 10
, :.,.
.-
:.
:OBJECTIVES
. . . ,. ...
. .. ...
: ... , .... : ... , .. ..,-.
10'DESCRIPTION . ...
...
o' ..... ..
... do: 12'. ,. .._
SOME MODEL EXPERIMENTAL RESULTS.OP'THE'NEW'STERN:.,
ARRANGEMENT1- ' e
.. '. ...
. .... .15
, '
DISCUSSION 'c-it. TEST RESULTS. .,,.-...-
-'
. .16'
-.
."'
''
'CONSIDEiATIONS'IN:THE_DESIGN OF THE NEW.STERNARRANGEMENT -,,:.,:.; . ..
- 1,:liol:.T14.4,xt'pis101:-. ' DESIGN:;p0-.STERN CONFIGURATION .. .. .... :.2-1 : .- . !
26
20
-'CONaLUSTONS. .... . ... . oe, ... .. .. ... 21 . , ..-1-.2
.LIST OF FIGURES
Page
Figure 1 Variation of Thrust Deduction and Wake Coefficient with Speed for a Vessel Propelled at Deeply Submerged
Condition and Surface Condition 7
Figure 2 Lines of Representative Models, Open-Type Sterns ... 11
Figure 3 Photographs of New Stern Arrangement on Model 4971
Showing Stern Form and Shaft Positions 13
Figure 4 Photographs of New Stern Arrangement on Model 4971 Showing Overlapping Propellers and Rudder
in Position 14
Figure 5 Power, Propeller RPM, and Coefficient Curves for
New Stern Arrangement on Model 4971 ... . 17.
Figure 6 Power, Propeller RPM, and Coefficient Curves for New Stern Arrangement on Model 4971, Starboard
Propeller Only .. 18
Figure 7 Comparison of Shaft Horsepower and Propeller RPM for Model 4971 Powered with Different.
A PROPOSED NEW STERN ARRANGEMENT
by
Pao C. Pien and J. Strom-Tejsen
INTRODUCTION
The main objective in the design of a propeller has been to meet an rpm requirement at an acceptable propeller efficiency. During recent
years, however, as the trend of ship designs has been toward high speed
and power, the problems of propeller cavitation and propeller-induced hull vibration have magnified. In many cases they now become major concerns
in the design considerations.
The cruiser stern with a single-screw arrangement used to be the favored choice in ship propulsion due to the high propulsion coefficient and simplicity in machinery and shafting system. Unfortunately, for
high-powered ships, such a stern arrangement would present severe problems of propeller cavitation and propeller-excited hull vibration. Consequently,
various modifications have been introduced with the hope of minimizing
these problems, but so far no entirely satisfactory solution has been
found.
The propeller cavitation and propeller-induced hull vibration can
be reduced by introducing a twin-screw stern arrangement. However, there
are many disadvantages with the conventional twin-screw arrangement. The resistance of the ship increases due to an appreciable appendage drag of the shafting arrangement. The propulsion coefficient is Lower despite a
higher propeller efficiency because the hull efficiency is very low. Also, the conventional twin-screw arrangement might necessitate added machinery units with corresponding additional running and maintenance costs..
In this report the problem of ship propulsion is briefly discussed',
and the various factors influencing the propulsion coefficient and the problem of cavitation and propeller-induced hull vibration are mentioned. A proposed new twin-screw arrangement is described. This new arrangement
-combines the advantages of both single-screw and conventional twin-screw
propulsion systems. 'With this newarrangement, a high-propulsive
lbe_reduced.
' The performance Of a.propeller behind a hull greatly influenced
by'the-velocities with which the water flaws to the propeller disk. Hence,
mOit,ofrthe problems associated with ship propulsion can be traced to the wake of the ship If the wake pattern could be adequately controlled,
solufionstoliost of our ship Propulsion problems would be well in hand.
From considerations of the efficiency of a
ship
propulsion system,we cite the following familiar expression for the
prOpulsion
coefficient .
-P.C. = ep err. -0/(177';) [1]
Where
err'
'where
Some :model experimental results with the new arrangement are giVen._
propeller thrust, and
HULL PROPELLER INTERACTION ..,
w
v-Ve5A1'
is7Veloc1ty Of the ship, and
is velocity- of'Water relative to the
Ship.'
-_The thrust deduction coefficient is defined by
t. = (T-Rj/T;
is propeller efficiency,
is relative rotative efficiency,
,
is
thrust deduction coefficient, andis
wake coefficient.The wake coefficient, as defined here, is the same as the Taylor.
wake fraction
R is Corresponding resistance of towed ship.
[3]
From Equation [l], it is seen that a high wake coefficient
apPar-emtly is beneficial and results in a high hull efficiency and propulsion
3
propeller loading and, consequently, more severe cavitation problems.
Furthermore, a high wake would be associated with large wake variations
over the propeller disk. These variations are the source of
propeller-excited hull vibrations. Thus, by the effects on efficiency, cavitation, and vibration, it should be obvious that the wake is indeed close to the
heart of most of our problems related to ship propulsion. A main
objec-tive in the design of a stern arrangement would be to obtain the
advanta-geous effects of the wake and avoid the detrimental effects.
The velocities with which water flows to a propeller disk differ
from the ship velocity due to three different physical phenomena. It will be convenient at the present to consider the wake as composed of three components corresponding to each of these phenomena, namely, the potential
wake wp, the viscous wake wv, and wave wake ww. Hence we may write
w = w + wv +
wW [4]To visualize the potential wake component wp, consider a body that
moves at a great depth in an inviscid fluid. The velocity field, which is produced in the vicinity of the body under such ideal circumstances, can
be obtained from potential flow theory. The potential wake is due to the
velocity field which can be obtained from theoretical computations.
In real water this body will experience a viscous drag force.
Addi-tional velocity is imparted to the water particles, and the viscous wake component is the wake due to this additional velocity.
When the body is brought up to the surface and is considered moving
through an undisturbed free surface, surface waves are created. The wave
motion also adds velocity to the water particles. The wake produced by the wave motion is the wake component denoted as the wave wake ww.
The three wake components are certainly not independent of each
other. However, for the purpose of understanding the problem of hull-propeller interaction, it is expedient to consider them as independent
items.
For a well-designed ship, the wave wake is a small quantity in
com-parison with other wake components. Thus, in the following discussion of the components of the hull-propeller interaction, the wave wake will not
be .considered.
-POTENTIAL WAKE
The- potential wake wp over a .propeller disk is determined by the
location of the disk and the geometry of the hull form, especially in the
vicinity of the propeller Let us consider a single-screw ship with a.
cruiser stern. The value of w is influenced by the clearance between the propeller disk and the stern frame, the fullness of the waterline endings,
the rudder clearance, the displacement volume of the rudder, etc. Equation
[1] may give the impression that .a large positive potential wake value wp
by increasing the value of w will give .a higher value of P.C. But this is
not the case; in reality, an increase of w is accompanied by a correspond-ing increment of the thrust deduction coefficient t. Furthermore,
the,pro-peller loading is increased for two reasons: (1) the increment of t results in a higher thrust value to be delivered by the propeller, and (2) the mass flaw through the propeller disk is reduced due to a positive wp value.
(A reduction of Mass flow through the propeller disk can also be considered
as giving a reduction of the effective diameter of the propeller.) Hence,
any gain in P.C. due to a positive-potential wake value is more than offset by the increment in thrdst deduction and the decrement in propeller
effi-ciency ep due to the higher propeller loading.
1
A higher potential wake usually means greater wake variation over
the propeller disk, thus increasing the problems of cavitation and
-propeller-induced hull vibration. Consequently, in the development of
a propulsioniarrangement, great effort should be made in reducing the potential wake over the propeller disk; and, if possible, a negative
wake-should be_created.
, A Kort nozzle, in reality, can be regarded as
a
device that producesa negative-patential wake over the propeller disk. Hence, the propeller
1
loading is reduced because of the increased mass flow and a negative thrust
deduction that, in effect, produces a thrust on the nozzle. Accordingly,
a Kort nozzle reduces the propeller loading in two ways. One is the
in-creased mass flaw, and the other is dein-creased propeller-thrust loading,
VISCOUS WAKE
Unlike the potential wake which exists only in the vicinity of the body, the viscous wake extends to infinity behind. It represents work
done by the viscous drag force. If a propeller is operating in a viscous
wake belt, a part of the kinetic energy within the viscous wake belt can
be recovered. Therefore, the higher the viscous wake over the propeller
disk, the greater the propulsive coefficient will be. Unfortunately, the viscous wake, like the potential wake, will aggravate the problems of
propeller cavitation and propeller-induced hull vibration.
THRUST DEDUCTION
The thrust deduction is often discussed in terms of the suction force on the tail end of the hull. However, when using the conventional
definition of t as given in Equation [3], the thrust deduction represents
not only the suction force, but also any change in the resistance R due to the action of the propeller. Such a change could be caused by a change
in both the viscous and the wavemaking resistance components of R. For
instance, should separation exist in the viscous boundary layer, the
pro-peller action could shift the location of the point of separation, and, as
a result, the viscous resistance of the hull would be changed. Also for
a surface ship, the propeller, being close to the surface, will produce
surface waves that will interfere with those created by the hull. Further-more, the propeller suction will change the effective stern geometry of
the ship and modify the stern-wave system. Hence, a propeller may change
the wavemaking resistance of a hull form significantly. Both of these
changes in resistance will be reflected in the value of thrust deduction. In the design of a stern arrangement, any change in resistance
due to the propeller action could be taken into consideration to obtain
a small and thus favorable thrust deduction.
In general, the propeller submergence is large, and the top of the
propeller disk is well covered by the stern overhang; the wave interfer-ence produced by a propeller is insignificant. Frequently, however, when
the submergence is small, and the propeller disk is not well covered, the
propeller influence on the wavemaking resistance can be substantial It is not uncammon to have a thrust deduction greater than the wake value.
To illustrate this idea, thrust deduction curves of a vessel propelled at
the deeply submerged condition and at the surface condition are given in Figure 1. At the submerged condition, t is nearly independent of the speed
and dependent mainly on. the potential wake of the body. Its value is rel-atively small. However, at the surface condition, the value of t is not
only much larger, but is also dependent on the speed. It is quite evident
that at the surface condition the propeller has greatly influenced the
.wavemaking resistance of the vessel.
The degree of propeller influence in Wavemaking resistance in this case is surprisingly large. This is probably due to the top of the
pro-peller being uncovered..
CURRENT PRACTICE IN SHIP PROPULSION
With the previous discussion in mind, it is interesting to examine
briefly the current practice in ship propulsion. Among the many propul-sive schemes that exist, the single-screw and twin-screw arrangements will be mentioned.
SINGLE-SCREW ARRANGEMENT
The most familiar single-screw arrangement is the cruiser stern... The propeller disk in this arrangement is located close to the hull where
the Viscous wake is the largest. Consequently, a high propulsive
'coeffi-cient can be Obtained. As the shaft overhang is small, and the shafting
support is very simple, also, the appendage resistance is insignificant.
'The main drawback is the great wake variations over the propeller disk. .
The arrangement is for that reason very susceptible to propeller
cavita-tion and propeller-induced hull vibracavita-tion. These problems become critical,
if this arrangement is applied to the propulsion of ships, where high
speed and power are involved.
Because of its many. desirable features, a great effort has been
uo-p-fpuoD aoagans pue. uoTl-Fpuo0 paiataqns krdaaa
pauadoia
TassaA iogpad.
141-cm.luaiougaop
exam
pue
uoizanpala
lsnally
go
uoTlaTivii
-
aireBia SIONN NI 03 3 dSLINii...
maps:Ants: ostiiiansilli hi: ::::::::::::::::thistile etralimmeifiesiiimen:: les 1. a. e I:::-.h-
1.----
---:
-mus..-
iiiiiiliglAissmirms sumhussiss::,--iiihiiiiiir i...
11.1 i :sissus...
urn:::
MilffigNMEILLTIM
i ., L'
1 , ,Ihiiiipip_
....ihnir...,..::::::
Higiiiii'lmilirdid.:.i
_
Ilmo_....1.1121111Bilumagaitnia2112...
1:Ehrns=silurs'mum
irradleminlinPan
-411ffliggillwMpislisa+---:::raiiiii
n-asaignomansys:::::::;:::
1 rl 1Mhos
AfinumenutuIf
ht
nu
EdIEUMENSIBEIREillifil'
MIME
i- /1111EIMIP:::::::::2::
NELNIMBIEMEINIENHE
L''''"
LMIME
El
ME,:
STVii11.111ENEEEMIMI
ht." 0 INH 4 E16325;1:1=152-2111211 1;1' 1 tEEENErisirRIENHERIONMEEE
:11IlliilliENTSPAMili
MEM
4-
11 philummiNm , ,imprimp=7.-m...:
...
iiiiiiiiiiillo...
le4111111-IfillirsiLLValliomploordpimplEIMILTENE::::;::::
Milli
iiiiiiiragh:2::::21122r....aNannn
EMIIIIMPLIIIMMEINI
MEP
tiumiiimwdiff:*
.EINET:1111111E111
Film
f_t:44,llrenmrawirene:
MEP
NO1110NO3 33 yawlsnr.:1"raligigrih...
-----
''''''''
se=
1:::,.:1u
1l
h.--
-
:...
..MIEdiiiiiiiiiiNEIMMIIIIIIMPAIMMlliiiiiiinillummth:
ENEEINEE
11/1ENEFIIEE
'EINEM
MEEILIEE
11111111111iliiiillEMIIIIIIIEMIlhdiummilizahim!
11i.
H2IrnroIr
i 111111E11111111111111ilira
eanionenMin=
=1=11ms=
9..-Ishoss
limp
pirm
RION11d1114111111111111":"'""`
stqLpjliMP":: I EelgilliBIBIREBEVIMEIHMIliarlida liMBERIMEHEbilinaMMEHR IIIIIM12::: ..""'"'
Munninissumusumunnuaunnuanuninniunummutmulisammunomisamassaiiimzwrium: ... ... 11111111111110111M11110411:72:1E2
IBBILIHROMME
MEE
IME1111111111111E
, _IMMEH
IMERE1111411110111111111111111111111111111111111111111101111111himilithmisuisilnissllouiiimashuilisirmainumsdisolloillimingrou
N01/10103 030113WEIns Aid 330 'r
09 OL 08 06 001 09 OL 08 06 91 Pt Z 01 9of the single-screw stern arrangement. This effort has been given to both
the modification of the propulsive device and to modifications of the stern
geometry.
Modifications in Propulsive Device
Hadler et al.' considered a single-screw ship with various
modifi-cations of the propulsive device. They studied the contrarotating, tandem,
and 9-bladed propellers adapted to a single-screw stern of the cruiser type
and compared the performance with a conventional twin-screw arrangement.
This was done on an existing model of the tanker SS MANHATTAN. Among other
findings, they have drawn the following conclusions:
The contrarotating propeller, in the case of MANHATTAN, requires 7.5 percent less SHP than the twin-screw ship as built.
The tandem propeller required only 2.2 percent more horsepower than
the twin-screw ship. However, it can absorb more power than a single
propeller of the same diameter.
The 9-bladed propeller required only 4.1 percent more power than
the twin-screw ship.
All three devices have a large number of blades and may mitigate hull vibration problems. The contrarotating and tandem propellers will
have less cavitation problems since the loading on each propeller is only
half. However, due to the mechanical complications of the contrarotating propeller, and the relatively law efficiency of the tandem and the 9-bladed
propellers, none of these devices offer a satisfactory solution.
Van Manen and Kampsa considered as another modification the
applica-tion of the Kort nozzle propeller to a single-screw stern arrangement. To the extent the propeller loading can be reduced with part of the thrust
being carried by the nozzle, this arrangement can show a definite
improve-ment in P.C. An improvement with respect to cavitation and vibration can
References are listed on page 22.
also be expected due to a homogenizing effect of the nozzle upon the non-uniform inflow to the propeller, but such an effect has not been confirmed
as yet. Unfortunately, a reasonable reduction of the propeller loading
can only be attained for heavily loaded propellers. Consequently, the
Kort nozzle propeller would only be advantageous for propulsion of ships such as tankers, where practical limits on propeller diameter and rpm exist.
Hull Modification
Another approach in solving the problem of propeller cavitation and
propeller-induced hull vibration associated with a conventional
single-screw ship is to modify the stern geometry. Two such modifications are
the open-type stern and the Hogner stern.
Figure 2 gives versions of a single-screw ship with an open-type
stern. In this case, the propeller disk is essentially out of the vis-cous wake belt and may have a more uniform inflow to the propeller.
The hull efficiency will always be very low when compared with a conventional single-screw ship with a cruiser stern. Furthermore, due to the long
over-hang of the shaft, more elaborate shaft supports are necessary. As a
re-sult, the appendage resistance is appreciable. Despite these drawbacks,
this arrangement may offer trouble-free operation.
The Hogner stern may reduce the maximum wake variations over the propeller disk if the modification is extended far enough ahead.of the
disk. Then the problem of propeller cavitation may be less severe. How-ever, as far as propeller-induced hull vibration is concerned, the relevant wake variation is the blade-rate and its neighboring components. It is not
always safe to assume that a Hogner stern will have less wake components which cause the hull vibration. Hence, the Hogner stern may not always
solve the vibration problem.
TWIN-SCREW ARRANGEMENT
-There have been many ships built with a twin-screw arrangement.
Because of the severe problems encountered with single-screw ships, it is
on each propeller is only about one-half of that of a single propeller, and
it also operates in a more uniform inflow. Hence, the propeller cavitation
and propeller-induced hull vibration problems are far less severe. However,
on a conventional twin-screw ship, the propellers are far apart and operate
outside the viscous wake belt. Thus the hull efficiency is inevitably law. Also, because of the long overhang of the shafts, the shafting system will
cause a large amount of appendage resistance. Even though a twin-screw arrangement may offer a satisfactory solution to propeller-cavitation and hull vibration problems, the cost of this solution is very high.
A PROPOSED NEW STERN ARRANGEMENT
OBJECTIVES
The advantages and the disadvantages of both single-screw and
twin-screw ship propulsion arrangements have been discussed briefly. It is
clear that it would be of great interest if a new propulsion scheme could
be developed that would have the advantages of both single-screw and
twin-screw arrangements and none of their disadvantages. The desirable features
of such an ideal stern arrangement can be listed as follows:
High recoverage of the energy in the viscous wake.
High propeller efficiency.
Minimum propeller cavitation.
Minimum propeller-induced hull vibration.
Minimum appendage resistance because of shafting.
Single propulsion machinery unit.
To obtain a propulsion arrangement that possesses all of the above
listed features has been the objective of many development and research
projects. Numerous technical papers have been presented by many experts in this field of engineering. So far, no single propulsion scheme has
ac-complished all of these desirable features. It is felt that the proposed new stern arrangement, to be described in the following section, might come
close to a realization of the desired objectives.
MODEL
5004
MODEL
4912
MODEL
4882
Figure 2 - Lines of Representative Models, Open-Type Sterns
11 71111 ntnir
Ift-'1111111111
taink,"411INWIMPWI
Wir
...SIEMP", 4IA
INAW
1 __-L. ''.1201111631WMP/
EIMWMIIMIWAI
. ,&MI
... .4400ir
iliiimair
-11111111.
, .-
_____--mag.
-"VIM...
.. .1
. ,41111111111P7411ftf.--, --- -111101
. x '''"IMIIIIIN2S- i ."..iglk.
.11.
Ioremw__,
Aida
N.P.-.4.1....1...
A
. ,.. ;--rm--4..i.m..
11----:,WINIE111111110M...%9ME LWIMIii-\31.
. ,, ,,IIMICIT-19="1""
1111111ffig''''.
NorrImm
110.111:21.1W
Iffsb..-,
ILILMUMMIIIMINProm ni-_,,,,--
---474 18In order to describe this new arrangement, let us, as a point of departure, consider a conventional single-screw ship with a cruiser stern.
First we move the shaft line to the side a distance of about 35 percent of
the propeller diameter. Then a second shaft line is introduced
symmetri-cally on the other side of the vertical center plane. The twa propellers,
one on each shaft, are partially overlapped. Figures 3 and 4 show such
an arrangement. With the total disk area much greater than the original single propeller, a much larger portion of the viscous wake belt will go
through the propeller disks. Hence, a larger portion of energy in the viscous wake belt can be recovered. Also, the propeller loading is
smaller; therefore, the propeller efficiency will be higher.
Since the propeller-induced velocity field is overlapped in the
region where the wake value is highest, the action of one propeller will greatly increase the inflow velocity to the other propeller, especially
over the overlapped region where the wake value is very high. Hence, the
inflow to both propellers will be far more uniform. The cavitation prob-lem is greatly reduced, both because the loading on each propeller is
halved and because the load variation on each propeller is greatly reduced. Besides the more uniform inflow to each propeller due to the
over-lapping of the velocity field, any particular wake component over the disk
can be further adjusted by varying the amount of overlap. This would re-duce the propeller-inre-duced vibratory force of each propeller. By phasing
the two propellers properly, within the limit of preventing the blade of
one propeller from touching that of the other propeller, any of the three vibratory forces (the vertical, horizontal, and the torsional) can be
min-imized. To obtain the complete freedom of phasing one propeller with
re-spect to the other, either the propeller disks can be slightly separated
in the longitudinal direction or one propeller can be raked forward and
the other one backward. The chance of exciting two hull vibration modes at the same operational speed is most unlikely. Since any of the
vibra-tory forces can be minimized by properly phasing the two propellers, the propeller-induced hull vibration problem can be virtually avoided.
-= Photographs of New Stern Arrangement On MOdel 4971
Showing.
Stern
Form and Shaft FO§tOlons13
MM.Figure 4 - Photographs of New Stern Arrangement on Model 4971 Showing Overlapping Propellers and Rudder in Position
Both propeller shafts are close to the central plane. Hence, the
shaft overhang is relatively short, and both bossings or struts will be much shorter than those used in a conventional twin-screw ship.
There
will also be less horizontal flow crossing the shaft line due to the
sym-metry of the flow with respect to the central vertical plane. These facts insure that the appendage resistance due to the shafting supports will be
small.
For a single-screw ship, because of the unequal loadings between
the left half and the right half of the propeller disk, it is necessary
to have a small rudder angle to maintain a straight course. This rudder
angle will increase the resistance. But the symmetry of the overlapped propellers does not require rudder angle, and no additional resistance is
experienced.
Because of the slight distance between them, the two shafts can be
extended from the same gear box and can be driven by a single propulsion
machinery unit.
From the above discussion, it can be concluded that the six items
previously listed as desirable features for an ideal propulsion system have all been achieved in the proposed stern arrangement.
SOME MODEL EXPERIMENTAL RESULTS OF THE NEW STERN ARRANGEMENT
In view of all the possible advantages of the new stern arrangement,
model experiments have been conducted to obtain a performance comparison
between the new arrangement and other propulsive schemes. Fortunately,
the model of MANHATTAN (Model 4971) was still available for this purpose,
and the experimental results obtained could be compared directly with
those reported in Reference 1.
Figure 3 shows the general views of the stern form and the shaft
positions, and Figure 4 gives the same
rudder in position. A self-propulsion ditions as in previous self-propulsion perimental results are given in Figure
main feature of the mew arrangement is
induced velocity field. Due to mutual
15
views but with the propellers and
test was conducted at the same
con-tests with other devices. The
ex-5. As mentioned previously, the the overlapping of the propeller-interference of these overlapped
velocity fields, more uniformity of inflow to the propeller disk is
ob-tained. It is highly desirable to get some quantitative information about the mutual interference. For this purpose the self-propulsion test was repeated with one propeller removed while the thrust loading on the
re-maining propeller was kept the same. The results of this test are given
in Figure 6.
A pair of stock propellers (3626 and 3627) were used in the
self-propulsion test. Propeller characteristics are listed as follows:
DISCUSSION OF TEST RESULTS
It is interesting to compare the wake curves between Figures 5 and
6. For two propellers, the value of wt in the vicinity of the design
speed (19.5 knots) is about 0.37. For one propeller, a wt value of 0.43
was obtained.
In the case of one propeller, the wake over the disk area will be highly nonuniform. The wake value is much larger over the inner half disk near the central vertical plane than over the outer half away from this
plane. The high wake level over the inner half disk area is reflected in the high value of wt measured for one propeller.
The reduction in the wake value obtained with two propellers is a
direct measure of the mutual interference between the propellers. It is
very obvious that the high wake peak over the overlapping region has been eliminated or greatly reduced, and the wake comparison definitely proves
the effectiveness of the mutual interference and one of the motivations
of the new stern arrangement.
Figure 7 shows the SHP curves obtained with various propulsive
devices. The new stern arrangement requires much less power in
compari-son with the twin-screw arrangement built, the tandem propeller, or the
9-bladed propeller. It requires 5.5 percent more power than the contra-rotating propeller at 19.5 knots. All propellers, except those in the
new stern arrangement, are specially designed for optimum performance.
16
Diameter = 22.9 feet Pitch Ratio = 0.839
90 X a. 80 0 4 fel w 70 4 z. u 60 a. 50 40 30 20 10 17 85 80 75 70 65 45 w 0 35 30 25 20 15 10 5 -0 Ship Trim Displacement Type TANKER Model No. Propeller ' 4971-3 -' Ft
M
EMI
1!:1ill
I 111111ME/11111111111111MIIIMMEHEIMM
Fill
136.190 No 3626 8 3627 tons Draft Date 49.08 NONE _ DEC 1966 Appendages Wetted Surface installed: 176.500 Sq. Ft.'111111111M01
, . NOTE: PROPELLERSRUDDER, TWIN BOSSINGS
OVERLAPPING
Mil
RIM
..11111
1111111111111 111 - ..
-. .1 . 1 ! AMMINNNWHOWMIENVIIIIII
IM1 NMI allivik.
MEM=
II
.
11itiMifAl
i
.
I.
it, MEE 111511111111111E
r r
III 111111111111E1
110.21111111N ! i .I
1111...j=vm
wino
r 1 pl"..iiillFAME/
Wm
Animmuilim
-RIM
iimangsmig
.wr
iota limn malarimemMEINNIMINI111111111111111111WAH1111111110211. I
... ::.. EHP/SH l'7
ins.
....aem '111111111
Id
. _. ,.. .,..wririTirrumum
A111111111
ordmiggii
Marl !raj
Milli
.I!
morimma 111111111110111 'ril
11111111FAIN Wll
morailamasss.. .III Piii
Itlifirmill
irmillui
111111.111111 I I . 'iciur girls
.olir..ipmerliv, :Qua,. aaressaatmoiaaabaiwtr
...
lilli
II
i..
. .. . . . . . . . . . . , .. , ..: 14 15 16 17 18 19 20 21 22 SPEED M KNOTSFigure - Power, Propeller RPM, and Coefficient Curves for New Stern Arrangement on Model 4971
140 130 120
110
90 ._117t DIP . .1 .
illffil1ffillffillffirM111111111111
1111111111111ffili 1111111011011101 11111101111111111111MMEMIMMIIMEV 11111111111111111111
111111101111011111111111111111111111111ilintill11111111111E
IiI00llJ111111111111
IIMIZEINIMMINIIIMMENiiiiiill
1111111151111111111
11111111111111111011 I: 11112111111111EC
III
1111101111211,111.11111ME
MIME PSITINAM
1111Prinfall111111111111111
1111111.10011
Imiummommin
rdwasvi
mrargarairmaymnim
Pr
1111
wes11115111 MI-1
inummosamm..mmemege12 10 '
Ship-Type TANKER:
Model NO 4971L3
PropellercNo..36"
Displacement 136,190 ' tons ;Draft 49.08 Ft
Trim 'NONE Date DEC 1966 '"
. Wetted Sui-f,ke Sq. Ft.
Appendages installed RUDDER, . TWIN BOSSINGS
RPM
NOTE: STARBOARD PROPELLER ONLY
17 - 18 19
SPEED IN KNOTS
Figure -6 -
Power, Propeller
RPM, and Coefficient Curves for New SternArrangement on Model 4971, Starboard Propeller Only
18 140 130 120 ' 110 z 100 70 60 50 40 .34 3 30 2 26 24 22 o.: 18 0 16 .
0 0.a M 01 Pi w-va "sJ 0 0 -h 1.3Q , 0 *.tri fto CD . fD .
a
P3 13Q I-h fD 0 IJ a 11 ,T) FIORSEPOWER X111110111111
1111
I.
MMME 16.
1111111111110
1IL
niP.p.§
III
,imernit
.410>1
< ZZWwrncp Mr
>mar s.
>0: -P4'.A:2-13 m .cp -.51°
1111,E
NMI
kvaN
1111111111111111111111111111k11111
_11NUN' \:-11111-1
Em
111E11111
The stock propellers used in the new arrangement are too high in pitch,
and also the area ratio can be reduced. .If a-pair of new propellers are
specially designed and built for the new stein arrangement, an estimated
increase in propeller efficiency of 2.5 points can be expedted. This
.
-would make the power requirement of the new arrangement about the same as
that of the contrarotating propeller. On the basis of this comparison,
it is felt that the new stern arrangement offers the following advantages
over the contrarotating propeller arrangement; namely, less complex
shaft-. .
ing arrangement and the greater flexibility of dealini with the Problem
of propeller-induced hull vibration
CONSIDERATIONS IN 'THE DESIGN 0F THE NEW STERN ARRANGEMENT,.
"PROPELLER DESIGN
In the case of a pair of overlapped propellers working behind a
ship, each propeller is operating in the ship wake as well as in the
in-duced velocity field of the other propeller. Since the propeller-induced
velocity field is a function of propeller, loading, the design of a pair of
overlapped propellers has to be carried out through an iterative procedure. In the initial step Of a design procedure, the first propeller is
designed on the basis of the ship wake alone, and the inducedvelocity
field of this propeller over the disk area of the other propeller is
com-puted . Next, the second propeller is designed based on the combined
velocity field due to the first propeller design and the ship wake. Then,
the first propeller is redesigned by including the velocity field of the
second propeller design, and this iterative procedure is continued until'.
proper convergence is obtained.
The amount of Overlepping of the propellers Will effect their mutual
',interference and, consequently, the harmonic contents of the inflow
veloc-ity field of each propeller as well as the overall propulsive efficiency.
An experimental exploration as well as theoretical analysis should be
carried out in order to determine the optimum amount of overlapping.
DESIGN OF STERN CONFIGURATION
With the propeller cavitation and propeller-induced hull vibration
problems controlled by proper overlapping of the propeller velocity fields
and by phasing the two propellers, the design problems in the development
of an afterbody are greatly simplified, and we can concentrate our efforts
on increasing the hull efficiency. As it appears from the discussion of hull-propeller interaction, it will be beneficial having as much of the
viscous wake going through the propeller disk as possible. Consequently,
design efforts can, for instance, be concentrated on channeling the water
flowing close to the wetted surface of the ship to the propeller disk.
In order to see where the water, entering the propeller disk, comes
from, it is helpful to think about towing the model backward, tracing the
stream tube starting from the propeller tip circle. This can be done, of course, by using a computer program without building the model. If there
is no viscosity effect, this tube will not change shape when the model is
towed forward, but the flaw within the tube will change direction. This stream tube clearly indicates to what extent the viscous wake belt is
going through the propeller disk. The viscous effect will distort this
stream tube. However, for the purpose of obtaining a general idea of the propulsive quality of an afterbody, this technique will be very
informa-tive.
CONCLUSIONS
A new stern arrangement has been described, having a twin-screw
propulsion system with overlapping propeller fields. The new arrangement possesses the advantages of both the single-screw and conventional
twin-screw propulsion systems without any of their disadvantages.
It is concluded that the new stern arrangement constitutes a
propul-sion system with inherent qualities such as high recoverage of the energy
in the viscous wake and high propeller efficiencies, greatly reduced
sus-ceptibility to cavitation, and possibilities to minimize propeller-induced
hull vibration. These qualities are obtained with a minimal appendage
drag from the shafting. A single propulsion machinery unit can be utilized
by mounting the:propellers-close enough so that they can be driven through
la compact and simple gearing unit positioned in
front of
the stern-tubePreliminary
model
tests .stern arrangement..ACKNOWLEDGMENTS
22
have confirmed the potentials of the new
The authors wish to thank Mr. H. M. Cheng and Dr. C. Kuo for their
interest and stimulating ideas which have contributed greatly to the
:development of this study.
J.13.., et-al., "Advanced Propeller Propulsion for High-Powered Single-Screw Ships," Transactions Society Of Naval Architects and Marine
Engineers; VOl. 72., pp. 2.11-293 (1964).
Van Meilen, J.D. and Kamps, J., "The Effect of Shape of Afterbody on
Propulsion," Transactions Society Of Naval Architects And Marine Engineers,"
Copies
5 NAVSHIPSYSCOM
2 Scientific Doc Br (Ships 2021)
2 Ship Res (Ships 0341) Attn: Mx. G.M. Boatwright 1 Aux Br (Ships 527)
9 NAVSEC
1 Comp-Aid Ship Des (SEC 6102C)
1 Ship Concept Des Div
(SEC 6360)
1 Surface Ship Des (SEC 6362)
1 Prop, Power & Aux Sys (SEC 6140)
1 Project Coordination
(SEC 6122)
1 Hull Struc Br (SEC 6132)
1 Mech & Weapons Sys
(SEC 6135)
1 Naval Ship Eng Cen
(SEC 6000)
1 Prop, Shaft & Bearing Br
(SEC 6148) NAVMAT 1 (Code 0331) 1 NAVAIRSYSCOM 1 NAVORDSYSCOM 1 CRONR 1 ONR, Boston 1 ONR, Chicago 1 ONR, New York
1 ONR, Pasadena 1 ONR, San Francisco
1 DIR, USNRL
Attn: (Code 2021) Library
1 DIR, ORL
1 CO, USNROTC & NAVADMINU MIT
1 CDR, NAVSHIPYD BSN INITIAL DISTRIBUTION 23 Copies 1 CDR, NAVSHIPYD CRASN 1 CDR, NAVSHIPYD LBEACH 1 CDR, NAVSHIPYD NORVA 1 CDR, NAVSHIPYD PEARL I CDR, NAVSHIPYD PHILA. 1 CDR, NAVSHIPYD PTSMH .1 CDR, NAVSHIPYD BREM
1 CDR, NAVSHIPYD SFRAN BAY VJO
20 DDC
2
AMIN MARAD
1 Mr. Vito L. Russo,
Office of Ship Const
1 Mr.. E. Scott Dillon
1 DIR, Natl BuStand
Fluid Mech Div
1 USCG
Attni. Sec, Ship Struc Comm
SNAME
SIT, DavidsonA,ab, HobOken Attn: Dr. J.P. Breslin
3 MIT, Dept NAME, Cambridge Prof. M.A. Abkawitz 1 Prof. P. Mandel
2 Univ of Calif, Berkeley
1 Prof. J.A. Schade,
Dept of Eng Res
1 Prof. R. Paulling
2. Univ Of Notre Dame, Dept of Eng Mech, Indiana
Attn: Dr. A.G. Strandhagen
Univ of Michigan, Dept NAME, Ann Arbor
1 Prof. H. Benford
1 1:1r. F.C. Michelsen
1 DIR, Hydrodynamics Lab, CIT,
INITIAL 'DISTRIBUTION (Continued)
Copies
1 DIR, St. Anthony Falls Hydraulic Lab
1 Iowa Inst of Hydraulic .Res Attn: Prof. L. Landweber
ADMIN, Webb Inst of Naval Arch
2 Hydronautics, Inc, Laurel, Md. 1 Mr. P. Eisenberg
1 Dr. B. Silverstein
Cornell Aeronautical Lab, Inc, Buffalo, N.Y.
1 Oceanics, Inc, Plainview, L.I., N.Y.
Attn: Dr. P. Kaplan
Robert Taggart, Inc, Fairfax, Va. 1 Mr. Robert Taggart
1 Mr. S. Hawkins
1 Bethlehem Steel Co, Central Tech Dept, Shipbldg Div, Sparrows Point, Md.
Bethlehem Steel Co, 25 Broadway, New York Attn: Mr. H. DeLuoe
Sun Shipbldg & DD Co
Attn: Chief Nay Architect
Newport News Shipbldg & DD Co Attn: Mr. John Kane
1 Editor, Engineering Index, Inc, New York 1 Editor, Appl Mech Review, San Antonio
1 Librarian, Inst of Aero Sciences, New York
UNCLASSIFIED
Security Classification
UNCLASSIFIED Security Classification
' DOCUMENT'CONTROL DATA - R&D
-(Security classification of title; body of abstract and indexing annotation must be entered when the overall report is classified)
1. ORIGINATING ACTIVITY(Corporate author)
Naval Ship Research and Development Center. Department of the.Navy
Washington, D.C. 20007
2a. REPORT SECURITY CLASSIFICATION Unclassified
2b. GROUP
3. REPORT TITLE
klroposed New Stern Arrangement
4. DESCRIPTIVE .NOTES (Type of report and inclusive dates)
S. A UTNO R(S)(Last name, first name, initial)
Pien,.Pao C. And Strom,Tejsen, Jorgen
6. REPORT DATE
May 1967.
7e. TOTAL NO. OF PAGES
27
7h. NO. OF REFS
2
13a. CONTRACT OR GRANT NO.
b. PROJECT NO.
- Z-R011 01 01
C.
.
9a. ORIGINATOR'S REPORT NUMBER(S)
9 b. tOWirsHrUoRtyPORT NO(S),(Any other numbers that may be assigned
10. A VA IL ABILITY/LIMITATION, NOTICES
:
Distribution of this document is unlimited.
11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY
Naval Ship Research and Development Center Foundational Research Program
13. ABSTRACT
The trend of ship designs toward high speed and power has led to increasing propulsive difficulties, due to the problems of cavitation and propeller-induced vibration. Consequently', in the design of stern arrangement, considerations must be. focused on these problems in addition to propulsive efficiency.
This _report deals with the factors that influence the hull-propeller inter-action-problem. It discusses the advantages and disadvantages of single-screw_ and twin-screw stein arrangements presently used.
A new twin-screw arrangement is described. In this stern arrangement the two propellers are. mounted close to the ship centerline with overlapping propeller
fields. The propulsive efficiency, cavitation, and vibration qualities of the
new arrangement are discuseed.
'Preliminary model tests with the new stein arrangement are presented and .
considerations to-be taken in the design are mentioned.
UNCLASSIFIED Security Classification LINK A KEY WORDS Ship Propulsion Stern Arrangement Overlapping Propellers
Propellers with Overlapping Fields
ROLE WT
LINK 13
ROLE WT
LINK C
ROLE WT
1, ORIGINATING ACTIVITY: Enter the name and address of the contractor, subcontractor, grantee, Department of De-fense activity or other organization (corporate author) issuing the report.
REPORT SECURITY CLASSIFICATION: Enter the
over-all security classification of the report. Indicate whether "Restricted Data" is included. Marking is to be in accord-ance with appropriate security regulations.
GROUP: Automatic downgrading is specified in DoD Di-rective 5200.10 and Armed Forces Industrial Manual. Enter the group number. Also, when applicable, show that optional markings have been used for Group 3 and Group 4 as
author-ized.
REPORT TITLE: Enter the complete report title in all capital letters. Titles in all cases should be unclassified. If a meaningful title cannot be selected without classifica-tion, show title classification in all capitals in parenthesis immediately following the title.
DESCRIPTIVE NOTES: If appropriate, enter the type of report, e.g., interim, progress, summary, annual, or final. Give the inclusive dates when a specific reporting period is
covered.
AUTHOR(S): Enter the name(s) of author(s) as shown on or in the report. Enter last name, first name, middle initial. If military, show rank and branch of service. The name of the principal author is an absolute minimum requirement.
REPORT DATE: Enter the date of the report as day,
month, year; or month, year. If more than one date appears on the report, use date of publication.
7a. TOTAL NUMBER OF PAGES: The total page count should follow normal pagination procedures, i.e., enter the
number of pages containing information.
76. NUMBER OF REFERENCES: Enter the total number of references cited in the report.
8a. CONTRACT OR GRANT NUMBER: If appropriate, enter
the applicable number of the contract or grant under which the report was written.
86, Sc, 8c 8d. PROJECT NUMBER: Enter the appropriate military department identification, such as project number, subproject number, system numbers, task number, etc.
9a. ORIGINATOR'S REPORT NUMBER(S): Enter the
offi-cial:report number by which the document will be identified and controlled by the originating activity. This number must be unique to this report.
96. OTHER REPORT NUMBER(S): If the report has been assigned any other report numbers (either by the originator or by the sponsor), also enter this number(s).
10. AVAILABILITY/LIMITATION NOTICES: Enter any
lim-itations on further dissemination of the report, other than those INSTRUCTIONS
imposed by security classification, using standard statements such as:
"Qualified requesters may obtain copies of this report from DDC"
"Foreign announcement and dissemination of this report by DDC is not authorized." .
"U. S. Government agencies may obtain copies of this report directly from DDC. Other qualified DDC users shall request through
"U. S. military agencies may obtain copies of this report directly from DDC Other qualified users shall request through
.1, "All distribution of this report is controlled. Qual-ified DDC users shall request through
If the report has been furnished to the Office of Technical Services, Department of Commerce, for sale to the public, indi-cate this fact and enter the price, if known.
IL SUPPLEMENTARY NOTES: Use for additional explana-tory notes.
SPONSORING MILITARY ACTIVITY: Enter the name of
the departmental project office or laboratory sponsoring (pay-ing for) the research and development. Include address.
ABSTRACT: Enter an abstract giving a brief and factual summary of the document indicative of the report, even though it may also appear elsewhere in the body of the technical re-port. If additional space is required, a continuation sheet shall be attached.
It is highly desirable that the abstract of classified reports be unclassified. Each paragraph of the abstract shall end with an indication of the military security classification of the in-formation in the paragraph, represented as (Ts). (S), (C), or (U).
There is no limitation on the length of the abstract. How-ever, the suggested length is from 150 to 225 words.
KEY WORDS: Key words are technically meaningful terms
or short phrases that characterize a report and may be used as index entries for cataloging the report. Key words must be selected so that no security classification is required.
Identi-fiers, such as equipment model designation, trade name, military project code name, geographic location, may be used as key words but will be followed by an indication of technical con-text. The assignment of links, roles, and weights is optional.
UNCLASSIFIED
