Influence of V and U shaped fore body sections of motions and propulsion of ships in waves at ballast draught

ME DDE LAND EN FRAN

STATENS SKEPPSPROVNINGSANSTALT

(PUBLICATIONS OF THE SWEDISH STATE SHIPBUILDING EXPERIMENTAL TANK)

Nr 56 GÖTEBORG 1965

INFLUENCE OF V AND U SHAPED

FORE BODY SECTIONS ON MOTIONS

AND PROPULSION OF SHIPS IN WAVES

AT BALLAST DRAUGHT

BY

BENGT G. BENGTSSON

Complement to Publication No. 49

SCANDINAVIAN UNIVERSITY BOOKS

AKADEMIFÖRLACET-GUMPERTS . CÖTEBORG

-.----.---SCANDINAVIAN UNIVERSITY BOOKS

Denmark: MUNKSGAABD, Copenhagen Norway: UNIVERSITETSOBLAGET, Oalo, Bergen Sweden: AXADEMJFÖRLAGET-GUMPERTS, Götebo'rg SVENSKA BoKFöRLAoETfNorstedts -Bonniers, Stockholm

PRINTED IN SWEDEN BY

Synopsis

In [1]1 are described the results of tests in regular head waves at

load draught with four = 0.675 and three = 0.794 models,

which were given different degrees of U and V form in the fore

body. The tests with three of the 5 = 0.675 models have been

extended as described in this report to include also a ballast draught investigation at about 70 % of the load draught displacement. These

complementary tests were carried out in the year 1962.

The ballast draught tests were performed in the same way as those

described in [1] and included measurements of the regular waves, the model resistances and the model motions and accelerations in

the vertical, longitudinal plane.

A motion, comparison between the three models shows the general advantage of V shaped fore bodies in waves equal to or longer than

the model. This is particularily true for the acceleration forward and the heave results. For shorter waves the U shaped fore bodies seem to be advantageous. This result is in general agreement with the load draught results in [1].

The results of the resistance measurements show that the U shaped models are superior in still water and in waves shorter than the model. The clear superiority of the V shaped models in long waves as shown

in [1] was not found to be so distinct in these ballast draught tests.

1. Introduction

The results presented in this report have been obtained at the

Swedish State Shipbuilding Experimental

T a n k (SSPA) from tests, which form a close continuation of the

tests described in [1]. The tests in [1] were carried out at load draught

4

with four 3 = 0.675 models and three , = 0.794 models. It

aimed at clarifying the effect in waves of different degrees of U

and V shape in the fore body sections.

It was considered of interest to enlarge the investigation to show also the effects of reduced draught. For these continued ballast

draught tests three of the = 0.675 models were selected. They

were towed in regular head waves. Motion and acceleration ampli-tudes in the longitudinal vertical plane and mean resistances were

measured.

It is hoped that the results presented here together with the results

shown in [1] will give a fuller picture of the relative merits of U

and V shaped fore body hulls.

2. List of Symbols

The symbols have been chosen in accordance with the

recommenda-tions of the Committee on Presentation of Resistance and

Propul-sion, data presented to the Ninth ITTC, 1960, where applicable.

AM immersed midship section area

(a0) amplitude of linear vertical acceleration at point y B breadth on waterline

R

total resistance coefficient

p/2 V2 S

g acceleration due to gravity

wave height, trough to crest length between perpendiculars

length on waterline

R resistance

S wetted surface

T draught

t distance of L.C.B. forward of amidships (L1,/2)

V speed

VI VgL Froude number

AM

BT midship section coefficient

V

=

block coefficient

LBT

amplitude of pitch angle wave length, crest to crest

À/LwL wave length fraction

p density of water

A MLPP longitudinal prismatic coefficient

y volume of displacement

Subscript M refers to the model, subscript S to the ship.

3. Models, Balancing of Models

The lines and particulars of the paraffin wax models are shown in Figure 1 and Table 1. The models all have the same after body

of a moderate U section shape and fore bodies with different degrees of U and V shape. The load draught displacement, block coefficient, length etc. were constant for all models.

In these tests the models were ballasted to about 70% of the full load displacement. They were all given a draught forward of about

59% of the full load even keel draught. This resulted in slightly dif-ferring draughts aft due to the different distribution of the

displace-ment in the fore bodies. The trims by stern were about 0.017 LWL

measured between perpendiculars.

The models were all ballasted to a radius of inertia of 0.28 A 1 mm diameter trip wire was attached to all models at the

sec-tion 0.05 aft of the forward perpendicular. Rudders were also

fitted but no other appendages.

The cross section of the towing basin is rectangular with a width of 10 m and a depth of 5 m.

For more complete information on the models and the ballasting

6

Fig. 1. Sections and profile of models. After body common for all models.

Extreme V fore body sections, Model 878-A

Moderate V fore body sections, Model 1046-A (not tested in ballast)

Moderate U fore body sections, Model 877-A Extreme U fore body sections, Model 879-A

LUPI!

Table i

Particulars of Models 878-A, 877-A, 879-A

Load draught particulars for the models as tested in [1].

Radius of inertia about thwartship axis through model centre of gravity = OE25

Ballast draught particulars for the models as tested in this report.

Radius of inertia about thwartship axis through model centre of gravity 0.28 L1,1, 7

Model 878-A 877-A 879-A

Shape of sections in fore body Geometrically similar models SSPA Pubi. No 39 Extreme V 712 Moderate U 720 Extreme U 724 LWL L1, B T LWL/ LWL/B BIT ß Trim 1I3

Full scale Model Linear scale 1:36 123.00 m 120.00 m 17.00 m 7.083 m 9.750m3 5.76 7.24 2.40 0.675 0.984 0.686 0.75% aft Even keel L1,/2 3.417 m 3.333 m 0.472 m 0.197 m 0.209 m3 5.76 7.24 2.40 0.675 0.984 0.686 0.75% aft Even keel

Full scale Model Linear scale 1:36 6810 m3 0.146 m3 TFORW 4.21 m 0.117 m 8 2330 m2 1.80 m2 Trim, measured on

8

4. Measuring Equipment, Instrumentation, Wave Generation

The mean towing resistances were measured with a hanging weight

technique.

The motion amplitudes were recorded by means of two fine wires,

streched vertically from one point in the fore body and one point in the after body to low-friction potentiometers on the carriage.

The accelerations were recorded by means of linear accelerometers

mounted with their sensitive directions vertical in the still water equilibrium position of the model. Only rigid-body motions,

acce-lerations and periods were recorded.

The waves were generated by a plunger type wave maker at one

end of the basin, which could be given desired frequencies and am-plitudes of vertical oscillation. The waves were measured with a rake of contacts lowered from the carriage.

A more detailed description of the general conditions of the tests

and the measuring equipment is given in [1].

5. Comparison of the Behaviour in Waves

Resistances

A resistance comparison is shown in figure 2. As can be expected the U shaped models have superior performance in still water. They

are superior also in the shorter of the waves tested. In the longer waves no clear trend can be detected in contrast to the results in [1], where the V shaped models clearly turned out to be the best. The general tendency of the resistance curves for the models does not differ greatly between the fully loaded case in [1] and the

ballast case here. Accelerations forward

A comparison of vertical linear accelerations at the forward per-pendicular is shown in figure 3. The U shaped models have the lowest accelerations in the short waves tested whilst the V shaped models give the lowest accelerations in the long waves tested. This

conclusion seems valid over Vf VÍJLWL = 0.10, where the speeds of

interest lie. The differences are rather significant for instance at = 0.75. This general tendency of the results does not differ

0. 10 a35 o 05 ¿030 a025 o 020 . 0 15 s020 070

j--

r

005 004 003 002 5 0006 b 0006 0005 0004

Fig. 2. Total resistance coefficients CTM (ballast condition) in regular head waves

with height hw=O.O25 ''WL

---Model 878-A Extreme V fore body se5t,ons 877-A Moderate U

879-A Extreme U

---p.-- Model 878-A Extreme V far body 5057,x05 877 A Moderate U 879 A Extreme U 0006 040

IlO

0 5 70 knots V3 15 I I I I 0 005 010 015 020 0005 0074 'JO-o/o 0.024 0.020 0.016 0012 006 004 002 o k/L225 o... y'Lwi50 I/LWL= 725 5 10 knots V3 15 070 015 020 v/VgL w 9 o o /LwL-725

Fig. 3. Dimensionless amplitudes of vertical acceleration forward (ballast condition) in regular head waves at wave height h 0.025 LWL.

5 10 75 knots V5

010 075 020 025

5 10 knots V3 15

'o

Pitch amplitudes

A comparison of pitch amplitudes is shown in figure 4. The U

shape superiority in the short waves can be perceived again although

less clearly but in the longer waves the results do not generally

favour any of the extreme fore body shapes.

The fully loaded results in [1] show more clearly the advantage of V shaped sections in long waves in the higher speed interval.

Heave amplitudes

A comparison of heave amplitudes is shown in figure 5. The V shaped models are again superior in long waves and sometimes with astonishingly high amounts. The tendency in short waves is

not clear. This is the case also fully loaded in [1], where the tendency in long waves shown here is also duplicated.

General

The behaviour of the models in the ballast case tested here rather closely resembles that in the fully loaded case as far as the relative merits of the models in different waves and at different speeds is

concerned.

6. Reference

[1] BENGTSSON, BENGT G.: "Influence of V and U Shaped Fore Body Sections on

Motions and Propulsion of Ships in Waves", SSPA Publication No 49,

1962.

Acknowledgement

The author wishes to express his thanks to the Committees of

the Martina Lundgren Foundation for

Mari-time Research and the Hugo Hammar

Founda-tion

for

International Maritime Research.

Grants from these funds made this work possible.

The author wishes to extend his thanks also to Dr HANS EDSTRAND,

General Director of the Swedish State Shipbuilding

E x p e r i m e n t a I T a n k, for encouragement and support and

010 b -t, k/LwL'i0o _¡2 1.0 '- 18 k/LwL = 060 0 5 lO knots V5 15 I I I 0 005 010 0.15 _v/vPLwL 025

Fig. 4. Dimensionless amplitudes of pitch (ballast condition) in regular head waves at wave height hw0.O25 LWL.

030 020 020 b. E ° 015 010 005 020 015 b. E 070 005 ,O-... k/Lw= 075 060 050

----7

o__ 0 0 005 0/0 /LWL= 060

Eofrerne V Por body

----0-- 877 4 ModeroteU -

----

879 A Enfrente U 14 -12 = K/LWL= ¡50 -10 - . 76 -. E -14 -72 701 040 r_i 2 5 0 005 010 /LwL = 2.25 050 o---.c

b.--

-v o--11 Sec lions

Fig. 5. Dimensionless amplitudes of heave (ballast condition) in regular head waves

at wave height lOw 0.025 LWL.

15 10 knots V5 015 V/kT 025 040 -100 15 10 knots V5 075 V/V9LwL 0 5 0 005 0/0 025 14 1.2 1,0 k. 08 , 0.6 b. a6 k 0.4 02 b. b 02 b. E 01 o