REPORT No. 59 M June 1964
STUDIECENTRUM T.N.O. VOOR SCHEEPSBOUW EN NAVIGATIE
AFDÉLING MACHINEBOUW DROOGBAK la, AMSTERDAM
(Netherlands' Research Centré T.N.O. for Shipbuilding and Navigation)
ENGINEERING DEPARTMENT DROOGBÀK la, AMSTERDAM
*
CONTROLLABLE PITCH PROPELLERS,
THEIR SUITABILITY AND ECONOMY FOR LARGE SEAGOING SHIPS
PROPELLED BY CONVENTIONAL, DIRECTLY-COUPLED ENGINES
(VERSTELBARE SCHROEVEN,
HUN GSCHIKTHEID EN ECONOMIE VOOR GROTE ZEEGAANDE SCHEPEN MET CÖNVENTIONELE DIRECT-GEKOPPELDE VOORTSTUWINGSMACHINES)
by
Ir. C. KAPSENBERG
issued by the Council This report is not to be published unless verbatim and unabridged
Ir. J. P. Huisman
1r C. Kapsen.berg
Ir. H. Klaasseñ
Prof. Dr. Ir.J. D. van Manen Ir. W H. C. E. Rösingh Ir J. IJ. Sonneveld N.J. Visser
CONTENTS
page
Summary ...
.. . . .....
5IntroductiOn - ., . 5
2 Scope of the stUdy . . .
.' ...
63 Data to be obtained, from model teSts . .. . .
....
. 84 Testing the single 'scteW taíiker-, mOdel No. 1733, in the
Nether-lands Ship Model Basin at: Wageningen 9
4.1 Resistance tests 9
4.2
Propulsion tests...
.94.-3 Overload tests ...12
4.4 Other tests . . 13
5 Testing the single screw dry cargo vessel, modl,No. 2211, in the
Netherlands Ship Model Basin at, Wagenirigen . . . . 13
5.1 Resistance tests . . . . .. . . . 13
5.2 Propulsion tests. . 13
5.3 Overload tests . . . - .14
6 ' Fuel consumption and the ABC setting. . . .. .. . . 16
7 The propulsion plant and the ABC setting . -. . - 16
7.1 The turbine tanker . . 17
7.2 The motor tanker.
... .
18-7.3 The dry cargo vessel - . . 19
8 Economiç aspects . . . 20
PROPELLED BY CONVENTIONAL, DIRECTLY-COUPLED ENGINES
by
Ir. C. KAPSENBERG
Summary
Models of a tanker of 32,000 t.dw., 16,000 BHP and a freighter of 12,300 t.dw., 7,800 BHP, each propelled alternatively by a fixed bladepropeller and á coñtrollable pitch propeller, were extensively tested in the towing tank.
In additiOn to the hydrodynamic results some thought is given to the possible consequences of an engine room arrangement. in which the main engine is constantly turning in the same ditection with only restricted variation in the number of rpm.
The economic aspects ôf controlläble pitch propellers are also considered.
i Introduction
-There is a rapidly growing interest in controllable pitch propellers (abridged ç..p.'s). Their numbers
have increased so much already that the total
propulsion power has passed the 3 million SHPmark.
The dimensions of the c.p.p. are also on the
increase.
The "Silver Isle", a 25,000 t.dw. ore-carrier
of the Mohawk Navigation Company of Montreal, has a c.p.p. of 19 ft. (5,800 mm) diameter, driven
by a diesel engine developing 9,000 BHP at
Ï15 rpm.
Most of the c.p.p.'s now in use, however, have
been fitted on small or medium-sized ships and
even then principally when the type of service leads
to this special type of propeller.
In this respect we may mention ships like
fishing craft and tugs, which run freely to theirrespective destinations at full speed and, arriving
there, tow either a fishing net or another craft;
also dredgers which upon reaching their destina-tion at full speed take up their dredging activities
at an extremely low speed; ice-breakers which
also vary their speed considerably when on the job and muSt develop a very high thrust.
Larger ships have been equipped with a c.p.p.
for special reasons.
The already mentioned "Silver Isle" sails the
St. Lawrence Seaway and consequently does a lot of extra manoeuvring.
The 22,000 t.dw. ore-carriers of the Wilson
Marine Transit Co. also sail the St. Lawrence
Seaway. Their engines develop 6,000 BHP whilst their propellers are c.p.p.'s;
Mr.K. N. Fjeldstad wrote in a SAE publication about the favourable experienceS gained with
these propellers in the course of a four years'.
service.
The very frequent manoeuvring required of
ferries has also stimulated the installation ofc.p.p.'s in these craft.
The Danish twin-screw passenger-car-ferry
"Jens Kofoed" is a recent example. She has been
provided with two c.p.p.'s, each driven by twin
geared high-speed diesel engines delivering 2,600
BHP to the c.p.p.
For ships with non-conventional propulsion e.g.
with gas turbines or gçared high-speed diesel
engines, the c.p.p. may be an obvious advantage.
This does not apply to tankers or freighters
pro-pelled by directly-coupled geared turbines or large marine diesel engines.
As a rule these ships sail the high seas for the
greater part of each year. They do not manoeuvre
too frequently and, when in port, are berthed
alongside well-equipped quays. There is no para-mount argument for fitting a ç.p.p. to these types of ships. It is true that these ships also sail under all sorts of conditions, they may be eithef empty
or loaded, clean or dirty, encounter good or bad. weather conditions. Nevertheless, in view of the.
fact that very few of these ships have been specially
equipped, there has been no reason for installing a c.p.p. Moreover the difference in design between the c p p and the normal type of propeller may be
expected to have an unfâvourable effect on the
propulsive efficiency.
The Netherlands Research Centre T.N.O. for
6
important to investigate the problem of what
effect the c.p.p. will have on the latter catégory of ships in particular.
This study is based on the supposition that the
construction and controllability of the c.p.p. is
highly reliable; this reliability has been proved by
experience.
2 Scope of the study
The primary intention was to establish what
differences there are in the power delivered tothe propeller (DHP) at all speed ranges depending on whether the propulsion is by means of a c.p.p.
with various bl3de settings Or by a fixed blade
propeller (abridged f.b.p.).
For this, extensive model tests both at full draft and at ballast cóndition are necessary.
Increased resistance as a result of fouling or
wind should be taken into consideration.
It is important to consider possible
modifica-tions and/or simplificamodifica-tions in the engine room as a result of fitting a c.pp.
Finally an evaluation of the results should be
made.
Naturally the study has to be restriçted to a couple
of ships. Two ships were chosen which were
recently built in Dutch yards. For the tank teststhe existing ship models were used after consent of Owners and Builders.
The ships concerned are:
A 32,000 ton d.w. tanker, propelled by a marine
steam turbine or a marine diesel
engine developing. 16,000 BHP.A 12,300 ton ¿w. dry cargo vessel, propelled by a marine diesel engine developing 7,800 BHP.
LENU11O BETWEEN PERPENOIDJURS - 192.02 m BOEAOTIO OTOULDER - 27.13 00
DRAFT MOULOED - 20.200 m
IMMERSED VOLUME MOULDED - LIlLO .
!TERN Willi SCOEW APERTUROO. 11.0001
STERN
Willi BElOW COORIUBEX. TUBETTO UNO FITTO OLA000 P0OPELLRR
Principal dimensions of these ships and the propellers used.
A. Singel screw tanker,, ship model No. 1733.
Ta I.
Model No. 1733 was constructed of paraffin wax, the rudders of wood; it was tested with 2 different
rudders and 2
different screw apertures, viz. Rudder I and Screw aperture I for tests with thef.b.p.; Rudder a and Screw aperture II, to suit
the c.p.p. for tests with this propeller.
The propellers were designed by the
Nether-lands Ship Model Basin according to' the circula-tion theory.
The radial wake distribution was determined
by experiment. The modèls of the propellers were
made of aluminium, the blade thickness was
determined for production in bronze.
TABLE II.
Details of the ship and the propellers are shown
in Fig. 1, 2 and 3.
BODY PLAN
Fig. 1. Hull details of Tanker, Módel No. 1733.
STEM
L"
1iH
Main dimensions of ship Loaded Ballast
Length b.p. 192.02 m 192.02 m Breadth, moulded 27.13 m 27.13 m Draft at FPP 10.285m 5. 13 m Draft at APP 10.285m 7.38 m Mean draft ' 10.285m 6.255m Displacement, moulded 41,145 m' 23,836 m' Model scale 1: 27'/2
Max. output °f main engine 16,200 BHP
Delivered horsepOwer 15,700 DHP Main dimensions of propellers fb.p. (No. 2568) c.p.p. (No. 2578) Diameter 6,500mm 6,500mm
Dign pitch at hub 4,785 inni 4,900 mm
Design pitch at tip 5,850 mm 5,850mm Design pitch at 0.7 R 5,470mm' 5,470 mm
Blade area ratio 0.541 0.461
Hub diameter ratio 0.178 0.277
No. 2211. TABLE III. B r PITCH DISTRIBUTION IN PER CENT
-Model No. 2211 was constructed of paraffin wax,
the rudders of wood; it was tested with twO dif-Terent screw apertures, viz. Rudder I and Screw aperture I for the tests with the f.bp.; Ruddçr Ja
and Screw aperture II made suitable for the c.p.p. for the tests with this propeller.
The propellers were designed by the
Nether-lands Ship Model Basin according to the
circula-tion theory.
-The radial wake distribution was determined
by experiment. The models of the propellers were made of bronz; the blade thickness of the
propel-1ers was determined for production in bronze as
well.
Details of the ship and propellers are shown in Fig. 4, 5 and 6.
Fig. 2. Fixed blade propeller for Tanker, No. 2568.
PITCH DISTRIBUTION
IN PER CENT
Fig. 3. Controllable pitch propeller for TânkCr, No. 2578.
B. Single screw dray cargo motor ship, ship model TABLE IV
3 Data to be obtained from model tests
The modified form of the c.p.p., chiefly due to thebigger hub and the associated modified blade
form, as well as the enlarged screw aperture will effect the required power.
Propulsion tests with a f.b.p. as well as with a
c.p.p. in the design setting, whereby the
relation-ship is determined between the required DHP
and the ship speed and also between the rpm of the propeller and the ship speed, will prove this effect.
Pitch control does nOt take place during these
tests. Both propellers will follow the propeller law.
By pitch control, the c.p.p. makes it possible to
sail at any ship speed below the maximum, at a
number of rpm of the propeller çliffering positively
or negatively from the propeller law.
The propeller rpm may also be kept constant
for all ship speeds e.g. equal to the normal
max-Máin dimensons of propellers f.b.p. (No. 3247) cp.p. -(No. 3246) Diameter 5,300mm 5,300 min
Design pit.ch at hub 3,765 mm 4,226 mm
Design pitch at tip 4,455 mm 4,610mm Design pitch at 0.7 R 4,675mm 4,610mm
Blade area ratio - 0.520 0.417
Hub diameter ratio 0.164 0.306
Number of blades 4 4
Main dimensions of'ship Loaded
Length bp. 142.50 m
Breadth moulded 20.00 m
Draft, on even keel 8.35.m
Displacement, moulded 16873 m' MOdel scale 1: 23 Maximum output 7,800 BHP 119 rpm Delivered horsepower 7.566 DHP 6500 0.BU2 £ 0.541 0179 D PO2R/0
tWit:
z LIL WJ: W.____-
AP/Ao8 RR .0.0 R 07R ORR OES R O IR
LENGTH BETWEEN PERPENDICULARS lu_50 M
BREADTH MOUISES 20.00 M DRAFT MOULUES . B.35
IMMERSED UDLUME MOULSED 16070
S TE R N STERN BODY PLAN STEM
111
IuImir,
Fig. 4. Hull dei ails of Dry Cargo Vessel, Model No. 2211.
PITCH DISIRIRUTION
IN PER CENT
Fig. 5. Fixed blade propeller for Dry Cargo Vessel, No. 3247.
PITCH D(STRIBUTION
IN PER CENT
00.0
99,
95,6
imum. The propulsion power will in all cases
differ from the already established values of the c.p.p. in the design setting. Propulsion tests will
have to determine this difference.
It should be borne in mind that blade setting has
two restrictions. Firstly the propeller rpm can
never rise above the maximum deter mined by the
engine and secondly the engine output for a
reduced number of rpm can neyer surpass the maximum corresponding to this number rpm.This maximum is defined in a marine turbine by
the maximum steam 'flow at the prescribed working
pressure and temperature; in a diesel engine, by
the maimum admissible mean effective pressure.
L.
i
LUPi
- ..
-Fig. 6. Controllable pitch propeller for Dry Cargo Vessel, No. 3246.
Under these circûmstances the maximum torque is
developed. . -.
Furthermore' the question arises as to what effect
the c.p.p. has in case of an overload due to
in-creased hull resistance (dirty ship etc.). The
high-est output which can be developed under these circimstances with a f.b.p. is determined by the
number of propeller rpm which is to be òbtained
at this overload and the maximum torque which
the main engine can develop.
This output, is smaller than the maximum. With a c.p.p. the maximum propeller rpm can
always be obtained by adjusting the pitch and thus the maximum output.
5300 0.970 ¿ 0.1.17 0.387 1111M PD,R/D .
T
-j z Ao/Ao AP/AIt is expected that in this way a higher speed will
be obtained, when there is increased hull resistance.
Overload tests will have to determine whether this is true and what values are involved.
In ballast condition and when using a f.b.p. the
maximum ship speed depends on the maximum
propeller rpm.
It is not certain that the engine then.also devel-ops its maximum output.
With a c$p.p. however, the. pitch can be in-creased so that the engine does develop its max-imum output; consequently this may result in a
higher speed.
The model tests have to prove whether this is true or not.
4 Testing the single screw tanler, model,
No. 1.733, in the Netherlands Ship Model
Basin at Wageningen
4.1. Resistance tests
It is possible that enlarging the screw aperture. which is necessary to accommodate the c.p.'p.,
will have an unfavourable effect on the hull
resistance.
To determine the latter, model No. 1733 was
first towed with screw aperture I for the fb.p. and
after that with screw aperture II for the c.p.p.
with a loaded draft of 10.285 metres and ballastdraft of 5.13/7.38 metres. The ship model was not provided with propellers.
Table V shows the results:
TABLE V.
The resistance of the model increased somewhat owing to the enlarged screw aperture.
For the rest, the increase in resistance is slight and relatively unimportant, since the performance of the ship depends on the DHP, which does not necessarily change with the resistance.
4.2 Propulsión tests
Propulsion cUrves were determined for the model with the f.b.p. as well as with the'c.p.p. To a base of speed, they indicate the DHP and the propeller speed. .The c.p.p. remained in the design-setting
(0° blade angle variation).. Comparison of the
DHP curves gives a direct indication of the
differences in performance.
Propulsion tests with a c.p.p. at various blade
angles are extremely laborious. A large number of propulsion tests have to be made, each test with a
different fixed blade angle.
Beginning with 0° blade setting (design setting)
tests were made with blade settings of 8°, 6°,
4°, 2.°, +3°, +7°, + 12°, ±18° and +24°.
The sign - indicates a pitch reduction, + a
pitch increase.
The tests with negative blade angle variation
were not conducted at ship speeds beyond the maximum propeller .speed and the tests witi a positive blade angle variation not beyond.
max-imum torque.
From this large number of propulsion tests an
equally large number 'of ordinates could 'be
deter-mined with which, to a base of ship speed, the
curves were drawn for:
DHP at constant maximum. propeller speed;
blade settings for a;
DHP at. constant maximum torque;
blade settings for C;
propeller rpm for c;
DHP fOr a range of constant speeds, d.epending
on the propeller rpm.
Fig. 7. Propulsion curves of Tanker propelled by the con-trollable pitch propeller iC the design position.
-10C 120 120 -' ..,oo too z REVS/MPH. E to 00 - 000 RO 60 120 - 657 -10 60 E § TORDUE 60 tOO - . -1O
ii
-. OHM 00 60 - THRUST - 6000 '60- ' -4000 tO SPEED IO OF SHIP -Ill tO KNOTS 16 ' IT 18Resistance with screw aperture I for the f.b.p: better (+) or worse () than with aperture II for the c.p.p.
speçd draft = . speed draft =
in knots 10.285 m in knots 5.13/7.38 m 10
0.8%
14' +1.3% 111.4%
15 +l.4% 12 +0.3% , 16 +1.4% 13' +1.6% 17 +1.7% 14 ±1.1% 18 +1.4°/ 15 +0.9% 19. +0.8% 16 +1.3% 17 +1.2% 18 +0.5%lo
The results are shown in the following Figures: Fig 7 shows the propulsion test with the c.p.p. in
design setting- (0° blade angle variation).
The maximum output of 15,700 DHP is absorb-ed at a ship speabsorb-ed of 17.40 knots and a propeller
speed of 106.6 rpm. The torque appears to be
0.7162x15,700-106.6= 105.5 m.t.The above values of 106.6 rpm for the propeller
and of 105.5 m.t. for the torqùe were accepted as maxima for further studies.
Note: In this Figure and in the following ones no
allowances on the DHP values as determined
duritig the tank-tests were taken into account, as
these are not required for the comparison of
propulsion methods. The determined values forFig. 8. Propulsion curves of Tanker when propelled by the fixed blade propeller and when propelled by the controllable
pitch propeller; the latter respectively iii the ØO blade setting (design setting), in settings for constant revs per min. and in settings for constant torque.
+30 +2b°-e +10 --
--.--BLADE ANGLE VARIATION
-._.
-O -
/
-18000 120 - -16000 100 2 i- - -14000 80 4---
-/
REVS/MIN//
-12000 60 --- - - ---100:40
- FIXED BLADED POELLER
- 1PTCH
CONS-TANT----,.'
DHP C.P.P.4 REVS./MIN CONSTANT -- LTORUE COÑSTANT--- 6000 - - -13 -11. 15 - 16 1 18-DHP, rpm and ship speed are therefore valid for 0% allowance on the tank results.
Fig. 8 shows the comparison of the various propulsion methods with the f.b.p. and the cp.p. in the design setting (00 blade angle variation) as well as with
blade settings for constant propeller rpm and
constant torque respectively. The corresponding rpm at the various blade settings are indicatedas well.
The following conclusions may be drawn:
The DHP curves for the f.b.p. and for the c.p.p.
with blades in the design setting are practically the same.
Any unfavourable effects due to the big hub of the c.p.p.
and other deviations from the f.b.p. are hardly noticeable.. At low ship speeds the DHP increases
slightly for the c.p.p.
The propulsion with the c.p.p. at constant
TABLE VI.Fig. 9 shows the results of the propulsion test in
ballast condition for the f.b.p. and the c.p.p. with constant maximum rpm.
From it the following conclusions may be drawn:
The DHP for the c.p.p. with constant maximum
rpm is higher than for the f.b.p. over the,whole
speed range. This. is even the case at maximum ship speed, where the c.p.p. has the design pitch.
At the maximum output of 15,700 DHP the
speed of the ship with the f.b.p. is 18.38 knots
at 105 rpm of the propeller; with the c.p.p.
(0° blade angle variation) 18.28 knots at 106.6
rpm. This loss did not appear at the loaded
draft. Most probably this slight speed loss with the c.p.p. is due to the somewhat unfavourable
form of the aperture, the effect of which is greater at small draft than at loàded draft. When in ballast condition the f.b.p. also
ab-sorbs the full engine output without exceeding
the maximum number of propeller rpm (105
maximum rpm is unfavourable, especially over
the- lower speed range
If the torque is kept constantly at its maximum the same applies to the propulsion as under b. The maximum ship speed of 17.40 knots is the same for either propeller.
The f.b.p. turns somewhat more slowly than.
the c.p.p. with design pitch. This is shown by the propeller speed of 104.5 rpm of the f.b.p.
ánd 106.6 rpm of the c.p.p. at the maximum
ship speed. This small difference will however hardly affect the propulsion.
Keeping the torque constant requires a far
greater positive variation of the blade angle than the negative variation required. to keepthe propellet rpm constant.
A constant torque results in a considerable
decrease of the propeller rpm.
In Table VI some comparative values arç shown:
Fig. 9. Propulsion curves of Tanker in ballast condition,
when propelled by the fixed blade propeller and by the con-trollable pitch propeller at constant maximum revs per min. Single.screw tanker, ship model No. 1733, with c.p.p. better (+) or worse (-.) in DHP than with f.b.p.
Loaded draft (10.285 m)
knots design setting
cpp
rpm constant blade variation torque constantc.p.p. max. blade variation13 14 15 16 17 - 1.3% -1.3% 0% +0.6% -0.4% -20.4% -17.1% - 9.3% - 3.8% - 0.9% -8.5° -6.5 -5.0° -3.2° -1.0° -23.6% -15.5% - 7.9% - 3.8% - 0.9% +22.2 +16.5° ± 11.0° + 6.7° + 2.0° -1800
/
'° "/
--i000 io, 5 -REVS/MIN/
/
/
/
/
/
/
./
..i,000 la D'IFFIXED OLAOED PROPELLER C.P.P. REVS.fI4IN. CONSTANt
Ii 15 IX 17 la
12
instead of 104.5), and gives the ship the highest
attaiñable speed (18.38 knots).
It is sometimes claimed that a ship sailing in
ballast and fitted with a c.p.p. can attain a
higher maximum speed by increasing the
pro-peller pitch. This is not true.
In Table VII some comparative values are shown for the propulsion in ballast condition.
TABLE VII.
Fig. 10. DHP curves of Tanker for constant ship speed at varying revs per min. of the controllable pitch propeller. Propeller law (00 blade setting), optimum curve and ABC
setting.
Fig. 10 shows DHP plotted to a base of rpm of the
c.p.p.. for a range of constant ship speeds.
Naturally each point of the speed curves represents
a certain blade setting.
The speed curves are bounded by the vertical
indicating the maximum number of propeller
rpm and the slanting line indicating the maximum
torque.
At the maximum torque the DHP is directly proportional to the rpm.
In addition, the relation between DHP and
rpm is indicated for the c.p.p. at 00 blade setting (acting as a f.b.p., i.e. without changing the blade angle). This relation is the propeller law.
From this figure it appears that for each ship speed the co-ordinates, of minimum DHP and
propeller rpm practically fòllow the propeller law. It also appears that a good approximation can be found by the line ABC which follows the propeller law up to
about 80% of the maximum rpm and then the vertical
through this number of revolutiòs.
Down to about half the output of the engines the maximum propulsive efficiency is obtained in this way, while at a lower output there is only a very
slight difference.
For the engines this means that they will work at any number Of rpm between 100% and.80% of
the. maximum, never slower than 80% and, of
course, always in the same direction.
For the c.p.p.. tbis means that it works as a
f.b.p. down to about 80% of the maximum rpm, which corresponds to about 50% of the output, and then with a constant rpm by means of pitchcontrol.
This method, which does not give any noticeable loss in propulsive efficiency, Ópens up the
possibil-ity of some interesting arrangements in the engine
room.
This will be commented upon later.
Naturally the above mentioned 80% of the
max-imum rpm is arbitrary and can be fixed at a higher
or lower value as well. It may even be advisable to
sail the lower ship speeds with about 80% rpm but the extremely low speeds with 50% rpm for
example or ti1l less in order to improve the
propul-sive efficiency. However such measures will only be necessary when the extremely low ship speeds have to be maintained for long periods.
4.3 Overload tests
If a ship has an increased resistance e.g. owing to fouling and if she is fitted with a f.b.p., the engine
output can be eontrolled to obtain the highest
pôssible ship speed. until the maxïmum enginetorque is reached.
Neither the maximum propeller rpm nor the
Single screw tanker, ship model Nò. 1733; with c.p.p.
better (+) or worse () in DHP than with f.b.p. Ballast draft. 5.13/7.38 m
- c.p.p. blades c.p.p. constant blade angle
OtS in design setting max. rpm
variation 14 18.9%
8.2°
15 14.0%6.6°
16 9.2%4.9°
17 5.3%3.0°
2.0%
- 3.40/02.0°
18 2.2%. - 2.8%8°
18'!,2.9%
. -
2.6% +0.2° 16000-15 ODO. 15700 DHP MAXC.PF BLADE SETTING FOR MAG.TORDLIE Al EACH SPEED 17 KNOTS
14000-13000- t4Gl'S
CP.P. DESION PITCH D BLADE SETTING)
12000-V
lB KNOTS
11 C.P.P BLADE SETTING FOR CONSTANT
__4
REVS/SIN. AT EACH SPEED
ISSKNOTS 1000G -15 KNOTS 9000 - S-O ANOTO
:::::
13 KNOTS 6G00 O- 12.NBNQTSI
o 5000 ¿000 -3000 C - 10 30 ¿o 50 60 70 90 90 100 110 . REVSJMIÑ.maximum engine output will then have been
reached.
-If the ship is fitted with a c.p.p the pitch can be reduced a little in order to increase the number of propeller rpm. to the maximum, thus allowing the maximum horsepower to be. developed.
It may be expected that in doing so the speed
loss, due to increased resistance, will decreases
In both cases the propellers deliver an iicreased
thrust, in óther words they are ovêrloaded.
DHP lines for increased resistance with 25%50%75% and 100% allowances on the 'DHP -0% have been drawn. in Fig. li. The ship: speed
cannot be increased above the vailue whereby the
engiiles develop either their maximum torque or.
their maximum number of rpm.
Fig. 11. Attainable ship speeds of Tanker at increased resistances with the fiied blade propeller and the controllable
pitch prOpeller MAX -
/
/
D 12500 120, 100 -1000O 80_;;
;.
bkP
0° - ._
- 7500z
-r-
-°
BLADE ANGLE VARIATIONo-..
-
5°-w -5000 -Jz
--FIXED BLADED PROPELLER -. -:
CONTROLLABLE
PITCH
PROPELLER--4
--- 2500
I -- - J
14 - 15 - 16 - - 17 18
-14
For the ('b.p. the line "DHP at maximum torque"
and the line "revs./min. at maximum torque"
are therefore drawn.
Both lines have been determined by extensive
propulsion tests for increased hull resistance.
The intersections of the line "DHP at maximum torque" and the DHP lines with àllowances
indi-cate the highest possible ship speeds attainable with the f.b.p. under the varioús resistance increases.
With pitch control a c.p.p. can always absorb
the full power, irrespective of resistance increases.
The maximum ship speed therefore is
deter-mined by the
intersectionof the
horizontaldotted line "Max. 15,700 DHP" and the dotted line "DHP +25%", etc.
The setting of the blades, whereby the c.p.p. absorbs the maxirnum.-power. is determined by
TABLE VIII
Example:
At a DHP allowance of 50% a 0.25
knot speed increase may be attained at a cost of
870 DHP, or in other words a speed gain of 1.6% for a power increase of 5.9%.
4.4 Other tests
The following tests were carried out to complete
the investigation.
-Wa/ce tests with a pitot tube and with blade wheels. These tests serve to obtain the radial
and circumferential wake distribution curves
in order to design a wake adapted propeller and to adjust the wake field in the cavitation
tunnel respectively.
Open water propeller tests to analyse 'the propeller open water efficiency and the various
propul-sion factors.
Measurement of torque- and thrust-variations during one revolution of the propeller.
Cavitation tests.
The following results may b'e mentioned:
b. The maximum efficiency of the c.p.p. with
bl4des in the design setting is equal to that of the f.b.p.
sepûate and extensive propulsion tests for in-creasing resistance and various blade settings.
These blade settings are indicated by the line
"Blade angle variation" in Fig. 11. It is strikingthat this blade variation is only slight i.e. between 0° and 1.1°.
The dotted line DHP-0%, although strictly
speaking to be defined by thç blade settings of the
liñe
"Blade angle variation"
actually hardly deviates 'at all from the line "DHP-0%" for thec.p.p. in the design-setting.
Fig. il shows that with the c.p.p. working at full power, a higher ship speed is attainable for each allowance than with the f.b.p. working at
maximum torque.
In Täble VIII some values are shown:
The variations in torque and thrtist are slightly smaller for the c.p.p. than for the f.b.p.
This is due to the wider screw aperture required
for' the c.p.p.
Both propellers show slight sheet cavitation on the back of the blades and a small tip vortex. They are both a little more pronounced on the c.p.p This is caused by the somewhat heavier load on the slightly smaller blade area, which
is a consequence of the thicker hub.
Note: The propellers used in the foregoing tests
show a number of rpm at full load, specially fitted
for a turbine-drive. For a diesel-drive the propellers
would have been designed for a number of rpm 10
or 12 revs higher at full load. It is not expected however, that' the testresults will then show any
fundamental deviation.
5 Testing the single screw dry cargo vessel,
model No. 2211, in the Nethedands Ship
Model Basin at Wageningen
In gèneral the same tests were conducted as for
the tanker model. Nof tested were:
The propulsion in ballast condition, the
varia-tion in torque and thrust, and the cavitavaria-tion. 'allowance fixed blade propeller
- controllable pitch propeller
--.
,DHP rpm speed of ship DI-IP ' rpm speed of ship b!ad7settin
on DHP -- 0% 15,700 106.6 17.39 15,700 106.6 17.40
0
25% 15,200 103.1 16.46 15,700 106.6 '16.560;35
50% 14,830 100.7 15.57 15,700 106.6 15.820.65
75% 14,640 99.4 14.87 15,700 106.6 15;160.90
100% 14,520' 98.4 14.28 15,700 106.6 14.60 '1.12
The results found for the tanker are considered
to be representative for the dry cargo vessel as well.
5.1 Resistance tests
The following, table gives the results:
TABLE, IX
The same considerations obtain as under 4.1.
5.2 Propulsion tests
It appears that just as for the tanker tests, the dry cargo ship attains the same speed with a f.b.p. or with a c.p.p. at the maximum power absoi-ption.
For the dry cargo ship the maximum power is
7,566 DHP at 118.5 rpm for the f.b.p. and 119.8
rpm for the c.p.p. The calculatèd maxi mum torque
therefore is: 0.7162x7,566119.8
=
4523 m.t.The results of the propulsiOn tests with the f.b.p.
and the c.p.p. with blade settings adjusted for a
costañt maximum propeller speed and for a
constant maximum torque respectively, are shown in Fig. 12.
This Figure is comparable with Fig. 8 under 4.2 and the conclusions drawn naturally with other data are identical.
In Table X, which corresponds to Table VI
some values relating to the above are shown.
The diagram of the DHP curves for various ship
speeds to a base of rpm of the c.p;p. is shown in
Fig. 13. It is comparable with Fig.. 10.
The latter showed that the propeller law gave the most favourable relationship DHP and rpm; hère is shown that a slight increase of pitch and thus a decrease in the number of rpm results in
some gain - about 1% at higher speeds.
A favourable ABC setting follows the optimum
line down to about 80% of the maximum rpm of the propeller and then vertically down. This means a small increase in pitch down to 80% of
Fig. 12. Propulsion curves of Dry Cargo Vessel when propelled by the fixed blade propeller and when propelled by the
controllable pitch propeller, the latter respectively in the 0 blade setting (design setting), in settings for constant revs per min. and in settings for constant torque.
Resistance with aperture I for the f.b. better (+ or
worse () than with aperture II fbr the c.p.p..
speed in knots percentage
10 ±1.8 Il ±1.1 12 +1.6 13 +2.8 14 +2.6 15 +1.6 16 +1.0 17 +0.9 18 +1.6 ,200_ +10
/
-ioabBLADE ANGLE VARIATION
150 0°
-- -
/
/
_1 0-. - .-.-- ..--.----.
-/
-- -: :--- - -'
100 ./
8000 -/
z o . . --REVS/MIN.z.
50 -,,,..
6000.--
.
o -- ._D0OFIXED BLADED PROPELLER
DHP rPITCH CONSTANT
-C.P.P.. REVSJMIN. CONSTANT
-,----LTORQUE CONSTANT
- 2000
10 11 12 13 -- I 15 16
...
ii
-16
TABLE X.
Fig. 13. DHP curves of Dry Cargo Vessel for constant ship speed at varying revs per min. of the controllable pitch propeller. Propeller law (0° blade setting), optimum curve
and ABC.setting..
TABLE XI.
the rpm followed by a decreasiñg pitch once the
80% line has been reached. This is a suitable
method and it mäkes the ABC setting still moreattractive.
For the rest the same considerations obtain as
for the tanker on page 12.
5.3 Overload tests
Jig. 14 is analogous tO Fig. 11 under 4.3. The same
considerations obtain., The results show that with
a c.p.p. adjusted for absorbing maximum DHP
a higher ship speed is obtainable than with a f.b.p. working at maximum torque.
Table XI gives some values.
The speed .gain is only slight.
6 Fuel consumption and the ABC setting
Although the ABC setting permits the ship to
operate with high hydronarnic efficiency, it is possible thät the relatively high rpm in the lower ship speed range may cause a higher specific fuelconsumption of the main engine, as a result of
which makes ABC setting a not attractive
propo-sition.
As regards steam consumption geared steam
turbines are especially insensitive to speed changes
at constant power. Values are slightly more
fa-vourable when the speed increases at low output, but the gearing then becomes somewhat less effi-Smgel screw dry cargo ship, ship model No 2211 with e p p better (-r-) or worse (-) in DHP than with fb p
Loaded draft. (8.25 m)
knoth design settmg rpm constantC41 blade variation c.p.p. fliaX.
-constant blade variation
11 -49.5% -10.1° 12, 13 -0.6% -30.5% -15.3% - 8.6°- 7.1° 14 -0.6% - 7.2% - 5.5° -3.6% + 15.1° 15 -0.7% - 4.2% - 3.7° 0 + 10.3° 16 -0.2% - 2.3% - 1.6° +0.2% + 4.2° 17 -1.3% 18 -1.2% ' 8000 . , -- 7556 DHP MAX. A -- J 16.5KNOTS 7000
- CEP. BLADE SE7IINO FOR MAX. TORQUE AT EACH SPEED
-' ' TB KNOTS
CEE OESION PITCH IOBLADE SETTINDI
6000
- CEP. BLADE SETTINO FOB CONSTANT HOTS
BETS/SIN. AT EACH SPEED
5000 - -IB SHOTS 3000T -r r 2000- -c io Lo 50 60 70 90 80 100 110 120 U0 RE VS/HIN. -allowance
' fixed blade propeller controllable pitch propeller
blade setf
DHP rpm speed of ship DHP rpm speed of ship in
7,566 118.5 1&69 - - 7,566 - - - 119.8 -,- i6.66 O
25% 7,470 117 . - 15.86- ' 7,566 - 119.8 15.90 ' -0.18
50% 7,360 ' 115.2 15.07 7,566 119.8 15.14 -0.42
75% 7,240 113.4 14.30 7,566 . 119.8 - 14.46 -0.75
cient. Lines of constant specific steäm consumption
of a geared turbine plotted to a base of rpm run
horizontally for each constant load.
The diesel engines of the tested ships are all of
the single
acting two-stroke type with turbo
chargers. The required power of 7,800 and 16,000
BHP çan be developed with, as little a 6 or 8
cylinders.
The curves of constant specific consumptiOn fQr
one make of this engine type have been drawn in
Fig. 10 and Fig. 13 and reprinted as Fig. 15 and Fig. 16 for the tanker engine and the dry cargó
engine respectively.
From this we learn that fór a constant lóad at
varying rpm there is no appreciable difference in the specific fuel consumption.
The ABC setting will therefore, not result in
a higher specific fuel consumption.
7 The. propulsion plant and the ABC setting
Although a setting for constant propeller rpm, ï.e. pure pitch control, is very. simple. in a way-, it is
too inefficient to be considered.
The ABC setting according to Fig. 10 and Fig.
13 gives high propulsive efficiency, requires a
Fig. 14. Attainable ship speeds of Dry Cargo Vessel at increased reslstances with the fixed blade propeller and the
-controllable pitch propeller.
__119.8 REVS/MIN.. AT .7566 .DHP
REVS. MIN AT MAX. TORUE
io
...
/_-
./
- lN.-/
/
/
/
. ./
/
/
//
/
/
/
/
/
i"
:Y
/
/
-10000100 >,/
//.
/
/
/
/
/
/
f
.7
/
. .. 7 . . . w//
//
/ .
/
- /
.. . -8000 80.í____.
. .PT Mx.T.Rau/
./
/
I/ i
. -I/
iv
I/I
I I/7
.JZ
I.. 0° - -'
uLvR1rlQlL
6000 wFIXED BLADED PROPELLER .
co CONTROLLABLE PITCH PROPELLER.
-
- 2Q00I . I. I - - I. .
I..--
--13 14 15 - 16 17 18
-18
Fig. 15. Curves of constant fuel consumption of the Tanker main diesel engine shown in the diagram of constant ship speeds, Fig. lo.
restricted propeller speed variation and no change in direction of rotation.
These features are bound to be value in the
design of the engine rOom.
It is obvious that the main engine should be
used to produce electrical energy for all auxiliaries
inside and outside the engine room. This solution has been adopted more than once arid then under
far more difficult circumstances, i.e. for a main
engine driving a f.b.p., but obviously a complete solution could not be obtained in such cases.
Reference is made to the motor tanker "London Independence" of 34,000 t.dw. (Motorship
Octo-ber 1961) and the motor tankr "Butmah" of
33,500 t.dÑ. (Asea Zeitschrift 1959 Heft 3).The advantages aimed at are:
the ship has only one main sourçe of energy; the auxiliary generators are only used in port, so need
less maintenance and no supervision at sea; the electric current is generated in a more efficient
way and if the main engine is a diesel with cheaper fuel.
Further, cheaper and lighter fastrunning aux-iliaìy diesel engines are acceptable as they have a rather short running time.
Fig. 16. Curves of constant fuel consumption of the Dry Cargo Vessel main diesel engine shown in the diagram of constant ship speeds, Fig. 13.
It may even be that fewer auxiliary generators
are needed.
To rea1ie this conception the main- engine has
to be provided with a shaft a1teriator which
supplies all the necessary electric energy at sea.
For the turbine tanker this will amount to
600 kW, for the motor tanker 450 kW and for the dry cargo ship 250 kW. To keep a constant D.C.
voltage, in spite of a variation in rpm between 100% and 80%, well-known regulating devices
can be used.
Direct current is being less used in new ships,
however, so?itention will have to be paid to gen-erating:alternating current.
An alternator directly coupled to the main
engine will vary its frequency in accordance with -the ABC setting, i.e. from 100% to 80%.
Although some consumers such as cooling water
pùmps may vary rpm in the same way as the
main engine, others may require a constantvol-tage (light) or a constant frequency (navigational apparatus).
In any case it is a considerable complication if no current of constant frequency is available.
Besides, in case of emergency, it must always be
8000. - -g: 7586-DUD MA'X./ /
/1:
i
-II / I.J
IORNOTO 7Q5-C)P I4DE SEtTING FOR MAO, TORQUE AT,EACH SPEED
KN
CPP DESIGN PITCH ISBDE SETTIMlI
60 REvsJMINiTcAcIISPOED' 5000 -11 1OTS -
a
ß- 145 KNOTS 41i13 KNOTS3000-.1
2X0-30 ¿0 50 60 70 10 iO WO 110 120 O REVS HIN. 16000- 150X-14000 13000- 12000-- 'T'41 i/,/,¡1/ i' i tí
,/ /j
I,I/,,_
- - j , / /- C.P.P BLADE GETTINO FOR MAX, TORQUE AT EAC'H, SEE,P
-I? RUGÍS
- TN KNOTS
I
-'
/ 'j
C.P.P, DESIGN PITCH 0 BLADE SETTING / i
/j / / f i I /
u'
j
/f/
- C.P. BLADE SETTING FOR CONSTINT / i i-, __4
AT (ACH SPEED / ¡ ,naJMIN. ISSKNOIS T:::::
¿ lW
::
8000 I\
' iL KNOTS 600 -¿000. X 3000 - -C 20 -30 40 50 60 70/ 80 90 100 110 REVSJMIN: -/
-possible to switch on an auxiliary generator at once and this is only practicable with constant
frequency.
A shaft alternator will only be a coripletely
useful source of energy if it supplies A.G.of constant
frequency.
To obtain this there are,
in principle, three
methods:
Firstly the electrical method. The shaft generator generates D.C. and drives a convertor. A control
apparatus in the D.C. keeps the rpm of the con-vertor constant, so that the A.C. produced is of
constant 'frequency.
Secondly the adjustable 4ydraulic gear method. A
hydrostatic pump unit with controlled delivery drives a hydrostatic motor unit at constant rpm.
There are objections to both the electrical and
the hydraulic method mainly high initial expenses
and too low, efficiency.
Thirdly the mechanical hydraulic method. An example
is. found in the variable-ratio epicyclic gear, which
gives an efficiency of95% to 98%.
This gear may be driven from the main engine in any suitable way. If the main engine is a geared
marine turbine, the driviñg element may be the primary pinion, the secondary pinion, the main
wheel or the shafting. In the case of a diesel engine, it may be the forward end of the motor, the shafting
or any other suitable arrangement.
The variable-ratio epicyclic gear is basically a Stoeckicht gearing. However, instead of the annu-lus being a conventional stationary reaction
mem-ber, it is connected, through suitable gearing, to a hydrostatic unit. A second hydrostatic unit of
the variable-stroke
type with swash plate
iscoupled to the constant-speed output shaft of the gearing by suitable gearing.
The two units form a closed hydraulic circuit. The built-in ratio of the gearing is such, that at one predetermined speed of the input shaft,
and thus of the main engine, the output shaft,
driving the alternator, has the required number of rpm to produce A.C. of the correct frequency.
The annulus remains stationary, the gearing
works as a' normal fixed-ratio gear with high
efficiency.
For any speed of the main engine, lower or higher
than the aforesaid predetermined speed, the hy-drostatic units add to the annulus a positive or
negative speed in such a way that the output
speed remains constant.
To arrive at this, an automatic control of the
swash plate of the variable-stroke hydrostatic unit is required.
When turning the annulus, part of the power for driving the alternator is transmitted by the
hydrostatic units.
As this takes place at a relatively low efficiency,
the total efficiency of the gearing is somewhat
reduced but remains96% at the minimum as long as the speedvariation of the inputshaft is restricted
to about 20%.
7.1 The tUrbine tanker
The propulsion plant of the turbine tanker may be
equipped. as follows:
The variable-ratio epicyclic gear driving the
600 kW alternator, is coupled to one of the pinions
or to the shaft. The electric power is delivered to
the main bars of the switchboard. The latter is also
fed by the turbo generators. The cargo-oil pumps are driven by steam turbines in the usual way.
Before sailing, the turbo alternator must supply elèctric energy to make the main turbine and the ship ready for sailing.
As soon as the signal is received, the main
engine is started with the c.p.p. in "zero pitch"setting.
The engine will then take up a speed equal to
80% of the maximum rpm.
At this moment the load of the turbo generator
may be taken over by the shaft alternator, so
that the turbo generator can be stopped.
If necessary or desirable this moment may be
delayed until the vessel is at sea.
During the whole voyage only one source of energy is in use and only the main engine, is in
service, including the shaft' alternat6r and all the
consumers.
The average load of the shaft alternator 'will
then be about 500 kW.
When the ship arrives' at her destination and
during the unloading period the turbO alternator will be running again. The value of a shaft alter-nator depends on the numbçr of running hours.
The average voyage conditions of a tanker were
mentioned iñ a lecture held at the Institute of
Marine Engineers on 14-10-1958 by Commander
20
500 kW; the second plant has a c.p.p. and thus
a main turbine without an astern turbine, driving a shaft alternator with a load of 500 kW.
The steam and feed water diagrams are exactly
the same as regards feed water heating,
de-aerating, Steam airheater, steam to steamgener-ator, etc.
The calculations for both were made in the
same way. Thus a comparison between the cal-culated fuel consumptions is reliable and is in principle valid for steam diagrams compiled inanother way.
The following steam conditions are assumed: for the ship with a f.b.p.:
steam pressure at superheater outlet: 49 ata, steam temperature at superheater outlet: 455 °C,
for the ship with a c.p.p., 53 ata and 485 °C
respectively.
The 4 ata higher steam pressure and the 30 °C higher steam temperature for the c.p.p.. plant is
permissible because of the lack of sudden
tempera-ture changes in the turbine and the absence of
thermal shocks.
This slight increase of the steam condition has
no unfavourable efféct upon the safety factor of
the engine as a whole.
The result of the calculation of the specific fuel
consumptiòn is as follows:
for the installation with f.b.p. and turbo generator,
24.7 grammes per SHP/hour; for the c.p.p. and
shaft generator, 236 grammes per SHP/hour.
This represents a difference of li grammes or
a saving of 4.45%.
The saving in costs will be dealt with under 8. It may be assumed that this saving is the result of
1% saving on the astern turbine, 1.9% on the
higher steam condition and 1.55% on the moreefficient way of generating electricity.
A fùrther saving is attainable by re-heating the steam. Although only justified for high powered
ships, re-heating can be effected far more easily
and simply when úsing a c.p.p.
Manoeuvring with re-heated steam gives rise
to complications when using a f.b.p.
The expansion of the steam in the economical
ahead turbine proceeds differently in the
un-economical astern turbine and when going astern
the balance between the superheater. and the re-superheater will be disturbed.
days
at sea, nOrmal service power 225
at sea, normal service power, ballasting 15
at sea, normal service power, tank heating 20
at sea, normal service power, tank cleaning 20
at sea, at reduced powers 10
at anchorage, steam on engines (including
loading) 35
discharging cargo steam on engines 5
shut down 35
365 According to this summary the tanker is operating for 330 days out of 365, divided as follows: 290
days at sea, 40 days at anchorage, loading and
discharging cargo with steam on engines.
This níeans that during 88% of the yearly
working time the shaft alternator may be used, during which time the. turbo alternator is out of service, so needs neither supervision normain-tenance.
Naturally a saving of fuel is involved, which will be considered later.
Normally a turbine tanker has two turbo
gen-erators, one of which is .a stand-by.
If a shaft altèrnator
is installed, one turbogenerator is sufficient.
The main turbine is simpler as the astern turbine
is omitted and consequently steam supply lines
are less complex, especially as the manoeuvring
valves and the manoeuvring stand can be
dis-pensed with.
The main turbine approximates more and
more to a land-based turbine installation; as aresult more consideration may be given to the
in-stallation of a single cylinder turbine, which has
a less complicated design with fewer foundations
and fewer pipelines.
Single cylinder turbines are not at all new on
ships.
Several cross-channel ferries have been equipped
with them, and also P. and O. Liné's "Canberra".
The latter ship has a turbo-electrical propulsion
plant and her main generators are driven by
single cylinder turbines.
It has been pointed out already that the fitting
of a shaft alternator results in a saving of fuel. To
figure this out, two steam and feed water diagrams
were designed for a marine steam turbine plant
with a service output of 15,000 SHP.
The first plant has a f.b.p. and thus a main
turbine, an astern turbine and a turbo generatorof the straight condensing type with a load of
To prevent this the re-superheater will have to
be shut off or a de-superheater will have to be put into operation.
This complicates the plant and the operation.
Ifa cp.p. is fitted this difficulty is avoided as the
expansion takes place through the very same blades
whether sailing ahead or astern.
Publications on the use of re-superheating
indicate a possible saving of 5%.
An engine plant with c.pp., shaft alternator
and ABC setting may easily be controlled from the bridge, a feature that may indeed be of ad-vantage in the future application of automation.7.2 The motor tanker
The application of the c.p.p., shaft alternator and ABC setting to the diesel engine: propulsion may lead to the following arrangement.
A 450 kW shaft generator is coupled to the main
engine by a variable-ratio epicycic gear.
This shaft generator generates electrical energy for all consumers during the whole voyage.
The generated voltage is of constant frequency.
There are four cargo pump units, two consisting
of a 900 HP diesel engine coupled to a 1350 m3/hr
pump, either directly or by a gear case, and two
units as above but also coupled toa 450 kW
alter-nator. When loading or discharging in port one of the two latter units generates electricity, the
pumpside being disconnected.
The diesel engine has not got sufficient capacity
to drive both pump and generator simultaneously. The three remaining units deliver the required pump capacity of 4,000 m3/hr.
In this way both units with aiternators are
each others' stand-by in port, at sea these units are a double standby for the shaft alternator.
-When the ship leaves port one generator unit is generating electricity just as on the turbine tanker. As soon as the main engine is started, it runs at
80% of the maximum rpm and the electricity
supply can be taken over by the shaft alternator,
which from then on supplies the electric power
for all purposes during the whole voyage.
Consequently the diesel
units are not used
during the voyage and require neither
super-vision nor maintenance.
In port one of the diesel units takes over again
and, working at about half load, delivers the
electric current.
The auxiliary diesels aie only running for a
short time; they are only used at loading and un-loading and when leaving or entering port.
Consequently fast riirLning diesels may be
in-stalled which are cheaper than the type used now.
Some saving in initial cost is not the only
ad-vantage, the shaft alternator also saves fuel.
For a load of 375 kW the shaft alternator
re-quires a driving power of 550 HP.
Assuming that the variable-ratio gear has an
efficiency of 0.965 the main engine will have to deliver 570 HP to drive the shaft alternator. This
requires at a specific fuel consumptiòn of the main
engine of 154 grammes an hourly consumption of 88 kilogrammes of heavy fuel. If a 450 kW diesel generator supplies an electric output of 375 kW,
it will have a specific consumption of 172 grammes
bringing the hourly consumption to 95 kgs of
diesel oil.
The saving in cost will be dealt with under 8.
As the main engine is non-reversible the
follow-ing simplifications are evident:
Simplifications to fuel pumps, fuel cams arid starting device, omission of the manoeuvring
stand, small starting-air vessels and small air com-pressors.
The use of a cip.p., ABC setting, shaft alternator
and bridge control represents another stride for-ward on the road to automation.
Note: The use of steam from an exhaust gas boiler
is not mentioned as the possibilities are the saine for both the f.b.p. and the c.p.p.. equipped propul-sion plant.
7.3 The dry-cargo motor ship
Used on the dry cargo vessel, the c.p.p., ABC setting and shaft generator presents a somewhat
different picture although, in principle, the same
arrangement applies as for the motor tanker.
Compared with the tanker, the dry cargo shipspends more time in port and less at sea. A good
average is 150 sea days.
The power consumption in port is considerable and often decisive for the size of the diesel gen-erators. The dry cargo vessel under consideration
of 12,300 t.dw. and an engine output of 7,800 BHP eonsumes 290 kW maximum in port when loading
and discharging, and at sea 230 kW maximum
with an average at sea of 170 kW.
There are three auxiliary diesel generators each
of 180 kW.
At sea either one or two will be running, in port during loading and discharging two will be in use.
One of the diesel generators acts as stand-by at
sea as well as in port.
The engine plant using a c.p.p., ABC setting
22
A non-reversible main engine, 250 kW shaft alter-nator with an average, load of 170 kW coupled to
the main engine via a variable-ratio gear, twò
diesel generators of 180 kW each, acting as
stand-by for the shaft alternator and for use in port.
Both generators will be working when loading
or unloading. In that case there is no stand-by.
This is acceptable, as the generators are not
running during the voyage and so make few
running-hours and can easily be kept in good
condition.
The use of the shaft alternator is completely
analogous to that of described by the motor tanker and the turbine tanker.
As far as the auxiliaries are concerned the same type of fast running machines cati be considered as for the motor tanker.
If a spare generator is required during the stay
in port, three 150 kW instead of 180 kW generators
would be sufficient. Using the shaft alternator on the dry cargo vessel also results in a saving of fuel
oil. Assuming a specific consumption for the main
engine of 156 grammes heavy fuel, for the diesel
generator of 175 grammes diesel fuel and an
efficiency of 0.97 of the variable-ratio gear, thehourly consumption will be 45 kgs of diesel fuel against 41 kgs of heavy fuel. The estimated cost will be dealt with in the following chapter. The remarks made about possible simplifications to the main engine and automation in the previous chapter also apply to the dry cargo vessel.
8 Economic aspects
Especially where dry cargo vessels ate concerned, working conditions differ considerably. Besides
tramp ships which sail all possible routes, there are liners which have fixed routes, but may also
transfer to other routes under completely different
conditions.
It would be
desirable to distinguish these varying conditions. for each form of operation andto investigate the possible significance of a c.p.p. in each case.
This wou1d be 'an extremely laborious task.
Although tankers also operate under varipüs
condi-tions the pattern of operation is more limited than for other ships and so it may be possible to arrive
at a certain operation scheme. Yet an investigation
for a particular route would be of littlè value as a general standard.
Considerations of the economic aspect must be confined to a comparison of the nett initjal cost of
the c.p.p. and the possible savings. The result of this comparison is,
however, only one factor
affecting the decision on the general suitability of
the c.p.p. Unfortunately it
is not possible toexpress the effect of the c.p.p. on the operation of
the ship in exact figures. As this effect has been described in a number of publications and be-cause it is a real possibility, the savings it may
represent have been entered as queries in the
enumeration on this and next pages. In any partic-Djfferences in initial cost for the turbine tanker:
C.p.p., adjusting gear, control panel on the bridge, pitch/rpm control, propel1er shaft, no spares
Shaft alternator, 600 kW mcl. variable-ratio gear
One turbo generator irici.
piping for steam and water,
pumps and bedplate can-celled
Less complicated maui tur-bine without astern turtur-bine, manoevring valves can-celled, piping simplified
Balance, of initial cost
Extras (Dfl.) 630,000.-320,000. Credits (Dfl.) 230,000.- 80,000.-310,000.
Savings in operatiònal cost for the turbine tanker: Fuel consumption by shaft
alternator, 4.45% lower than with f.b.p. (see 7.1);
15,000 SHPduring29O days.
Price of fuel Dfl. 61/ton. . Dfl. 70,000. p. annum
Reduction in repair cost of main turbine (no thermal
shocks, no manoeuvring
valves)...
Reduction in maintenance
and repair cost of turbo
generator (only one instal-ledand-slort running time). Reduction in engine room
personnel if manoeuvring is
controlled from the bridge Reduction in damage re-pairs due to improved ma-noeuvrability and directly available astern power,
re-sulting in an improved
general safety of the ship
.
-Omission of tugs in certainports as a very low ship
speed can be maintained
530,000.-
100,000.-ular case a reasonable figure can be filled, in in-stead. It may then be concluded that the queries
items will indeed influence the final verdict on the c.p.p.
The extras and credits of the initial cost as stated below may give rise to criticism.. They are partly based on tenders, partly on estimates. Further it is
obvious that there may be considerable differences
in the initial cost of the objects of comparison, i.e. the conventional plant and the new plant.
Even if all queried items for the turbine tanker are rated at low value or at no value at all, the
saving in fuel owing to a shaft alternator still
justifies' the use of a c.p.p.
It is understood that the main turbine will be
able to deliver the additional power for the shaft alternator.
The steam boilers have a somewhat smaller
capacity for the ship with.a c.pp. but also a slightly
higher steam condition, so that an eventual price difference can only be of little importance.
Compared with the initial cost the attainable and
calculable savings for the motor tanker are less
favourable.
In a diesel plant however, some of the queried
items would probably be estimated at a hihet
value.
The economical aspect of a c.p.p. will only be
an attractif proposition for a motor tanker,
pro-vided the main motor is capable of delivering
power to the shaft alternator from the normallyavailable. output surplus.
The directly demonstrable saving for the dry cargo
motor ship hardly justifies the use of a c.p.p. As
it is not certain that. the small saving (about 1%), obtáinable by following the optimum line AB of the ABC setting will be realized 'in practice, that saving lias not been taken into account at all.
As in the case of the motor tanker the queried items may be òf süch importance that fitting a
c.p.p. would still be' advantageous.
This is again on the understanding that the
main engine can deliver the power required to drive the shaft alternator from the availableout-put surplus.
Differences in initial cost for the motor tanker:
C.p.p., adjusting gear, control panel on the bridge,
pitch/rpm control, propeller shaft, no spares
Shaft alternator, 450 kW
mcl. variable ratio gear Two 450 kW alternators can-celled mcl. electrical appa-ratus
Less complicated main engine
Cheaper auxiliary dieseis (4off.)
Smaller starting-air vessels
Smaller air compressors Balänce of initiai cost
Extras (Dfl.) 530,000.- 100,000.- 630,000.-470,000. Credits (Dfl.) 50,000.- 25,000.-45,000.' 20,000.-160,000.
Savings in operational cost for the motor tanker: Owing to electric power
supply by shaft alternator
(heavy fuel, 1,200 sec
Redw., Dfl. 68/ton) or
by auxiliary diesel genera-tor (diesel fuel, Dfl. 105.I
ton), 290 sea days on an average load of 375 kW
(see 7.2) Dif. 28,000. p. annum
Ön.luhricatihg Oil owing to "oùt of service" of auxthary
diesel engines Dfl. 3,000. p. annum
Reduction in repair cost of main engine through ab-sence of manoeuvring; less cylinder wear, etc... Reduction in maintenance, supervision and repair of auxiliary diesels (only run-fling during loading and
discharging)
Reduction in engine room
personnel if manoeuvring is
cOntrolled from the bridge Reduction in damage
re-pairs,. due to improved
ma-noeuvrability and readily available astern power re-sulting in improved general
saféty of the ship - .
Reduction in harbour tugs in certain ports as a very
low ship speed can be
24:.
Differences in initial cost for the dry cargo motor ship:
C.p.p., adjusting gear, control panel on the bridge, pitch/rpm control, propeller shaft, no spares
Shaft alternator 250 kW
One diesel generator 180 kW
cancelled ...
Less complicated main
engine...
Faster running auxiliary diesel generators (2 off.).Smaller starting-air vessels Smaller air compressors Balance of initial cost
Extras (Dfl.) .410,000.- 75,000.- 485,000.-265,000. Credits 220,000.
Savings in operational cost for the dry cargo motor ship:
9
General considerations and Conclusions
The. efficiency of controllable pitch propellers
(c.p.p.'s) for large sea-going thips, própelled
by conventional directly-coupled engines was investigated for a tanker of 32,000 tons dead-weight, 16,000 SHP, and a dry cargo vessel of
12,300 tons deadweight,
7,800 SHP. The.
efficiency and suitability by non-conventional propulsion was not considered.
The. hydrodynamical investigation was
con-ducted by the Netherlands Ship Model Basin at Wageningen, Holland.
Exteñsive model tests show:
2.1 The geometrical modification of the c.p.p.
compared with the fixed blade propeller (f..b.p.) has no harmful effect on the
propul-sion, only at smäller ship speeds the cpp. is
slightly less favourable.
2.2 As regards tankers any deviation of the pitch from the design setting causes: an increase of the absorbed DHP for each ship
speed. The dry cargo ship, however, may
achieve a slight gain in DHP when the pitch is
increased.
2.3 Pitch control for
constant naximum
propeller rpm is not acceptable as the
loss hi propulsive efficiency is too high.
2.4 The combined rpm/pitch setting gives a favourable propulsion. Between 100%
and about 80% of the maximu.iri rpm the c.p.p.
remains in the design setting and thereafter the
rpm remain constant by pitch control
(ABC-setting).
In the case of the dry cargo vessel it is even
slightly more favourable to increase the pitch by about 30 between 100% and 80% rpm.
2.5 A tanker in ballast condition does not
attain a higher maximum speed when propellçd by a c.p.p than by a f.b.p.2.6 In case of increased hull resistances, the
highest obtainable ship speed is some-what higher when a c.pp. is used.
From a hydrodynamical point
f
view nostriking or important advantages can be shown in favour of the c..p.p.
There. is however no loss .of efficiency either.
The ABC setting
is important in view of
possible simplification of the propulsionma-chinery.
The consumption characteristics of turbines and present-day diesel engines are such that,
by an i;crease of the rpm at each constant
load, they remain practically constant.
(Dfl.) 150,000.- 20,000.- 16,000.-
14,000.-Owing to elêctric power supply by shaft alternator
(heavy oil, 1,200 sec. Redw.,
Dfl. 68./ton) or
byauxil-iary diesel engine (diesel oil
Dfl. 105./ton), 150 sea
days, 170 kW average load
(see 7.3) Dfl. 7,000. 0. annum
On lubricating oil.owing to
"Out of service" of auxiliary
diesel engines Dfl. 700. p. annum
Reduction in repair cost of main engine through ab-sence of manoeuvring; less wear, etc
Reduction in maintenance, supervision and repair of oñly 2 engines instead of 3 and only running in port. Reduction in engine room
personnel if manoeuvring is
controlled from. the bridge Reduction in damage re-pairs, due to improved ma-noeuvrability and readily available astern power re-sultingin improved general
safety of vessel
Reduction in harbour tugs in certain ports as a very
low ship speed can be
The ABC setting enables a shaft alternator wlich supplies electrical energy for all
pur-poses to be connected to the main, engine.
With the aid of a variablé-ratio gear, this
shaft alternator supplies energy of constantfrequency.
Ifa sJaft alternator is fitted, only one source of enery will be in Operation at sea.
Consequently less supervision and
mainten-ance are required. Bridge control and automa-tion are facilitated. .
There is a saving in fuel which increases with the number Of days spent at sea annually.
The extra initial cost of a cp.p. is only partly
compensated by simplifications in the
propul-sion plant.
The savings iñ fuel costs älone, hówever, make
the c.p.p. worthwhile for the tanker.
For the dry cargo vessel, at least for the assumed. number Of sea days, this is doubtfuL
There are certainly factors, difficult to express in terms of money, which, may make the c.p.p.
an attractive and paying proposition These
chIefly concern reductions in the cost of
super-vision and fnaintenance of the main and auxil-iary engines Moreover there are other factors connected with the greater practical manage-. ability and general safety of vese1s equipped with a c.p.p.
