Full scale tests with the WRANGEL and comparative model tests

STATENS SKEPPSPROVN1NGSANSTALT

Nr 27 _{GOTEBORG 1953}

FULL SCALE TESTS WITH THE

"WRANGEL" AND COMPARATIVE

MODEL TESTS

MEDDELANDEN

GOTEBORG 1953

11

Synopsis

The paper gives an account of full-scale towing tests with the "Wronger, a discarded

destroyer. The results are compared with values predicted from model tests and

the agreement is quite satisfactory. 'The scale effect of the appendages appears to be of little importance.

Measurements of the local friction were made at three points _{on the bottom of}

-the ship and -the results are compared on -the basis of -the "sand roughness -theory".

Wake measurements were also carried out but they did not give reliable results.

The velocity distribution in the boundary layer was measured at _{two points. The}

results were also used for calculating the local friction coefficients.

Finally, the wave profiles on ship and model were recorded and _compared..

Introduction

Since WILLIAM FROUDE'S classical full-scale resistance _{tests with}

the "Greyhound" in conjunction with model tests, very few such

investigations have been carried out., The foremost of _{these are}

Y. HIRAGA'S tests with the "Yudachi" and the recent experiments with

the "Lucy Ashton"; carried out by the British Shipbuilding_Research

Association.

The reason that so few full-scale tests of this _{type have so far.}

been carried out is, of course, that these experiments are technically very difficult to perform and involve considerable labour and_expense'.

There is now, however, a need for more such tests with ships of different types, in order to facilitate the revision of the principles

of model testing technique, which is _{at present being carried out in}

various parts of the world. The problems connected _{with frictional} resistance are of particular current interest. _{It is also known that}

full-scale tests of _{different types are in progress}

_{or are being}

contemplated in some countries.

The results of full-scale tests in the form of trial trips are

avail-able in quantity. _{These, of course, are of considerable practical}

interest and may also be of value from a theoretical point of view.

A comparison between trial trip results and those predicted by

means of present methods from model self-propulsion tests is,

how-ever, unsatisfactory due to the difficulties involved in determining

4

thrust and torque measurements are seldom available on trial trips.

Since FROUDE'S day, research in ship hydrodynamics has extended

our knowledge of the various factors affecting ship resistance and propulsion. At the same time, further light has been thrown on the

differences between these factors in the ship and model respectively and in this connection the term scale effect has been introduced. It is therefore desirable that any full-scale experiments should be

arranged not only as pure resistance tests but also, if possible, in such a way that the various components of resistance and

propul-sion (resistance of appendages, wake fraction, thrust deduction

factor etc.), can be isolated. Then, by comparing the full-scale

results with the corresponding model test results, it will be possible

to obtain some further information on the scale effect in different

cases. This is not usually possiblewith ordinary trial trips.

Plans for certain full-scale tests, designed to contribute to the

research on this subject, have been under discussion in Sweden

since 1949. Since April 1952, the plans have been under the

super-vision of a body known as the "W r an g e 1" Com m it t e e and

various proposals have been considered.

For such tests, the ship must be chosen with due regard to the particular resistance and propulsion factors which it is intended to

study; in this case, the principal aim was to carry out pureresistance

tests. It was also necessary in this case that the test ship should be selected bearing in mind the fact that some vesselmust be available

capable of towing the ship, as it was evident that towing was the

only possible method of propulsion For several reasons, it was also

considered desirable to repeat, with a ship of another type, the

measurements of local friction which G. KEMPF made on the

"Ham-burg" in 1927. Such tests, however, presuppose that the removal of portions of shell plating will be possible and that the vessel will

be available for a considerable time.

For these and other reasons it was finally decided to employ an

already discarded twin-screw destroyer named the "Wrangel". The

"Wrangel" could easily be towed at speeds up to the required

maximum by a larger destroyer. Unfortunately it was impossible to carry out propulsion tests (measuring thrust and torque) with the "Wrangel" as the engines were out of action.

After a number of pretests of different kinds, the final trials were

carried out during June and July 1953. This paper gives a brief

5

have been carried out at

the S wedish State S hi

p-building Experimental Tank in Goteborg.

The investigations were made possible by grants from funds and

from shipbuilders and shipowners in Sweden.

The R oyal

Swedish Navy and the Swedish State Tank also

A more detailed account of the activities of the Wrangel

Com-mittee is given (in Swedish) in Appendix 3; the costs of the

in-vestigations and other internal questions are also dealt with therein.

2.

Symbols and Units

Ship Dimensions

L = length on C. W. L.

B = breadth on C. W. L.

T = draught

S = wetted surface area

Am = immersed midship section area.

volumetric displacement Propeller Dimensions

propeller diameter

P = propeller pitch

Kinematic and Dynamic Symbols and Ratios

v = speed in general

resistance in general

Rn REYNOLDS number

wake fraction (TAYLoR)

weight per unit volume

= density

= kinematic viscosity

C = total friction coefficient

C f SCHOENITERE. allowance

C' = local friction coefficient

Metric units are used throughout. For q (acceleration due to gravity) the value

9.81 m/sec.= has been used.

3.

Dimensions and Particulars of the Test Ship "Wrangel"

Ship

As previously mentioned, a discarded twin-screw destroyer, the "Wrangel", was chosen as the test ship. The principal dimensions of the "Wrangel" are as follows:

=

=

6

The ship was run on the C. W. L. in every test.

The ship was built in 1918. The machinery originally consisted of two steam turbines each developing about 5500 HP and giving

the ship a maximum speed of about 32 knots.

The shell plating is rivetted and the seams are joggled. The butts

below the waterline are flush rivetted with buttstraps on the inboard

side. The thickness of plating varies from 6.5 mm at the keel to

3 mm at the ends.

The frames consist of ordinary angles rivetted to the shell and all the rivetting below the waterline is flush.

The shell plating was naturally in rather poor condition when the discarded ship was docked for the first time. Pitting and

un-evenness due to corrosion could be observed and some rivet heads

were so eroded that they had to be welded. The shell plating was

scaled with rotary machines prior to painting and all the existing

recesses were filled with composition (Semtex) and then painted in

the same way as the shell.

Two coats of paint were given, the first of Red Hand I and the

second of Red Hand III (The Red Hand Composition Co., London).

At the second docking, when the appendages had been removed,

both the old and the new shell plating were painted, firstly with

Red Hand I and then with Red Hand III. The scaling operation

was not repeated prior to this painting.

The friction plates were painted similarly.

Length on C. W L L = 69.55 m

Breadth on C. W. L

B = 6.58 m

Draught (for all trials)

T =

Displacement (with rudder), naked

= 398

with appendages V

= 401 m3

V

Block coefficient

= 0.471

LBT

Immersed midship section area Am = 9.31 m2

Am

Midship section coefficient

_BT

V

Prismatic coefficient 99 = 0.619

A.L

Wetted surface area (incl. rudder), naked

Sn = 439 m2

with appendages S = 457 m2

. m3

... .

7

The fact that it was necessary to paint the ship again when the appendages were removed meant that the condition of the hull was

not exactly the same for the tests with and without appendages.

This should be taken into consideration when assessing the results. Attempts were made to measure the roughness of the hull, but

no reliable results could be obtained due to the lack of suitable

instruments. No more precise information on the condition of the

hull can therefore be given.

Few of the "Wrangel's" superstructures were dismantled (see Figs.

2 and 3) and, since they presented a considerable area of windage, the air resistance was relatively great. The results must therefore

be corrected accordingly.

The body plan and lines of the "Wrangel" are shown in Fig. 1, while Figs. 2 and 3 illustrate the appearance of the ship during the tests (at 10 and 20 knots respectively).

It should be mentioned that the ship was carefully measured in

the dock before the

The results showed that the hull

conformed fairly accurately to the designed lines.

Models

Two models were tested. The first, which was made of paraffin wax to a scale of 1/10, was used for the model resistance and self-propulsion tests. On the ship, the appendages (shaft brackets and bossings) were not fully symmetrical; on the model, on the other hand, they were made symmetrical and similar to those on the port side of the ship. (The wake was measured on the port side.) It was

assumed that the differences were negligible.

The second model was of wood to a scale of 1/50 and was used to

study the course stability with different lengths of towline.

(Resi-stance tests were also carried out with this model.)

The model tests were carried out in a basin having a cross section 10 x 5 m2.

Propellers

The main particulars of the "Wrangel's" twin propellers were as

follows:

Diameter D = 2.170 m

Pitch (constant) P = 2.900 m

Developed blade area/disc area = 55 %

Number of blades = 3

. .

8

The starboard propeller was right-handed and the port propeller

left-handed.

Model propellers, made in accordance with the above data, were used for the model self-propulsion tests (in which the wake was

measured by means of the propellers).

4. Aims of the Investigations

Resistance tests

The main aim of the investigations was to compare the directly measured resistance of the test ship with that predicted from the

model tests.

While carrying out these pure resistance tests it was decided to take the opportunity of studying the following ancillary problems.

Scale effect of appendages

As stated above, the test ship "Wrangel" had twin screws with shaft brackets (see Figs. 1, 15 a and 20) and bossings. It therefore seemed reasonable to carry out two series of resistance tests, i. e. with the ship in two different conditions, firstly with these appen-dages in position and secondly without them. In this way the scale

effect of the appendages could be determined

The first trial series with the "Wrangel" was thus carried out

with the appendages, including the ordinary rudder. The propellers were replaced by dummy bosses and the port boss was fitted with

apparatus for measuring the wake in the plane of the propeller. In the second trial series, the ship was naked except for the rudder,

the shaft brackets and bossings having been removed (see Figs. 4 and 15b).

Local friction

It was also decided to measure the local friction at some points on the submerged hull of the test ship. Movable plates were fitted

in the bottom of the ship flush with the shell plating and the

tangential force (two components at right angles) acting on these

plates was measured.

It was necessary for the plates to be flat and they therefore had to be fitted in positions where there was little or no curvature on the bottom shell. It was also considered desirable that all the plates should, if possible, be fitted on the same streamline. Information

9 on the streamlines was obtained beforehand from streamline

experi-ments with the model (1/10 scale) at a speed corresponding to 20

knots. Wake

In order to study the scale effect of the wake of this particular ship, the wake was measured in the first series of full-scale tests

by means of current meters mounted on two radial arms on the

port dummy boss.

In the comparative model tests, the wake was measured in the usual way with the propellers and also by means of blade wheels and Pitot tubes.

Velocity distribution in the boundary layer

It was a simple matter to measure the velocity distribution in the

boundary layer in the course of the other experiments. The

measure-ments were made at two points on the bottom of the ship by means of Pitot tubes.

Wave profile

It was also considered desirable to record the wave profile on the

ship and compare it with that observed in the model tests. Trim

Steps were taken to observe the trim of the ship during each run

in order to compare it with that observed on the model.

Un-fortunately, however, the arrangements were not satisfactory and no reliable results could be obtained.

5.

Pretests

As mentioned in the introduction, the only method of propulsion available for the test ship was that of towing, the dynamometer for

measuring the resistance being fitted on the towed ship. The

excellent method employed for the experiments with the "Lucy

Ashton" was not practicable in this case, due mainly to the relatively large resistance forces which were to be expected.

The towing method is far from ideal. It must always be borne in mind that the towed ship is affected to some extent by the wake

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wake of the towline. From this point of view, therefore, the tow-line should be as long as possible.

Course stability may also be a problem with a towed ship, and it

was foreseen from the beginning that, in this case, it would be

necessary to use the rudder to maintain the course. On the other

hand, manoeuvring with the rudder has a variable effect on the

resistance.

In order to study these and other questions beforehand, the follow-ing pretests were carried out.

Using a destroyer of about the same type as the one intended as

the towing ship, the slipstream was studied by means of a patent log

trailed at different distances behind the ship. The results of this

somewhat primitive investigation indicated that from a practical point of view, the effect of the towing ship could be neglected at the lengths of towline which it had been intended to use.

A small model (scale 1/50) was employed for investigating the effect of the length of towline on the course stability. A towline length of 800-1000 m seemed to be suitable from the point of view

of course stability.

With the purpose of studying the towing method in full scale,

towing tests were carried out in October 1952 with the "Vidar", an

almost similar ship to the "Wrangel"; the "Vidar" was towed at various

speeds up to 20 knots. At the same time, the opportunity was taken

of testing a 6" nylon towline (800 m in 4 sections). For various

reasons, it had already been decided to employ such a towline. In

this series of pretests, it was hoped to study the following points:

the towing method in general,

the course stability with different lengths of towline,

the security at the turns,

the suitability of the nylon towline,

the working of the resistance dynamometer and he effect of the slipstream.

The tests were encouraging.

The nylon towline, even at the greatest length, was easy to handle

and no difficulties were experienced in paying it out or taking it in

on the towing ship; a tug assisted at these operations. A

sur-prising feature of the towline was its elasticity; it was found that it extended as much as 50 % at the highest speeds, but returned to its original length when unloaded. The effect of this extension is

11

illustrated in Fig. 5, where the photographs (taken on the final

trials) show the cable round the coupling thimble on the towing ship when unloaded and at 15 and 20 knots.

The fears on the question of the course stability turned out to

be unfounded, but the rudder on the towed ship was nevertheless necessary. Towline lengths of 400 m, 600 m and 800 m were

in-vestigated, but, as mentioned above, the true lengths during the

runs were much greater.

No difficulties were experienced when turning (see Fig. 6 from the

final trials).

The dynamometer functioned satisfactorily.

Direct observation of the water ahead of the towed ship showed

that, with the greatest length of towline, the slipstream came mostly

from the towline itself and was negligible. This can be seen from the photographs in Figs. 7, which were taken during the final trials

in June 1953.

Among other pretests, the following should be mentioned. During

1951, a prototype was made of a plate apparatus designed for

measuring the local friction. It was tested in the Goteborg Tank. After these tests, the instrumentation was altered somewhat and

then the apparatus was retested in the Tank (see Figs. 16 and 31) and

also on a small boat. On the basis of these tests, the final friction

plates (seven, including one spare) were designed and constructed.

As mentioned previously, streamline tests were carried out on a

model of the "Wrangel", in order to find the most suitable positions

for the friction plates.

6. Measured Course

A measured course in the Stockholm archipelago was chosen for the full-scale trials (see Fig. 8).

There is no tide and the course is well sheltered from the wind

and the sea. Some current was, however, to be expected and it

was therefore necessary to observe its velocity and direction; the observations were made from a boat anchored half way along the course. From the same boat, the wind velocity and direction and the state of the sea were recorded; at the same time, the water was tested and the ship was photographed on each run. The wind was also measured on the towing ship.

12

The measured course is 6.175 nautical miles in length and is

marked by beacons at a, b, c and d (see Fig. 8), dividing it into three sections as follows:

a b = 1.028 nautical miles

b c = 1.593

cd = 3.554

ad = 6.175

Bearings can be taken on posts on the shores of islands at the

northern end of the course.

The water depth, as measured by echo sounder, is shown in Fig. 9. It can be considered quite satisfactory for the ship in question, which

was run at a draught of 1.86 m. Furthermore, the spaces for turning at each end were sufficient to allow the test ship to reach full speed before entering the measured course. At 5 and 10 knots, full speed was maintained during the turns, but on the faster runs the speed was reduced when turning. The turning circles were adapted to

the speeds.

7.

Instrumentation and Test Arrangements

Resistance dynamometer

The resistance dynamometer was designed by Dr. G. GUSTAFSSON,

of the Aeronautical Research Institute of

Swe-d e n, Stockholm, assisteSwe-d by Mr. G. SCHERLING.

The principles of the dynamometer are shown diagramatically in

Fig. 10. The major part of the towing force is taken by a link a,

the deformation of which represents the force and is measured by strain gauge arrangements. The resistance changes in the gauges are transmitted to an indicating recorder (Speedomax) on a panel in the instrument compartment (see Fig. 11).

A more detailed description of the dynamometer is given in

Appendix 1 by Dr. GUSTAFSSON.

The dynamometer was placed on the main deck in way of an

opening in the stem (see Figs. 12 and 13). This point was 2.94 m above the C. W. L. (The model was tested in the same way.)

During the tests, the angles made by the end of the towline with the horizontal and with the course of the ship were measured.

The dynamometer was calibrated at the Aeronautical Research Institute of Sweden before and after the trials.

13 Nylon towline

The 6" nylon towline was divided into four parts, each 200 m

long when unloaded. These lengths could be coupled together as illustrated in Fig. 13. Fig. 13 also shows the end shackles and other arrangements (see also Figs. 5, 6 and 7).

Friction plates

The friction plates were also designed by Dr. G. GUSTAFSSON in

co-operation with Mr. G. SCHERLING.

Fig. 14 illustrates the principle of these plates. They are plane,

measuring 400 x 400 mm2, and are made of 2 mm light alloy 51ST. Each plate is movable in two directions at right-angles to each other

and parallel to the plate edges. The plate is suspended and guided by leaf springs connected to a watertight steel box-frame attached to the ship's hull (see Fig. 15 showing Plate No. 6 on the starboard side before and after the appendages had been removed). The total clearance between the plate edges and the frame is about 2 mm.

By means of a rod in the centre, the plate is also connected to and balanced by two other spring systems attached to the outside

of the frame (see the photograph in Fig. 16, taken during the

prelim-inary test in the Tank). The movements of these spring systems,

representing the tangential force on the plate, are measured by

strain gauge arrangements, one for the principal force in the

direc-tion of the streamlines and the other for the force in the lateral

direction. The plates were so placed that two edges were as nearly as possible parallel to the flow.

In Appendix 2, Dr. GUSTAFSSON gives a detailed description of

the friction plate apparatus.

The changes in the resistances of the electrical strain gauges were

transmitted to three indicating recorders (Speedomax) on the panel in the instrument compartment (see Fig. 11). One of these gave a continuous record of the principal force on Plate No. 3 (port, amid-ships). The second recorder indicated the principal force acting on each of the other plates when they were connected in turn, while the third recorder showed the lateral forces on all the plates in turn. The plates were placed in the bottom of the ship near the keel

1 1 3

at points about L

-2 L and L from the stem. For greater

certainty, the plates were duplicated, Nos. 2, 4 and 6 being on the starboard side symmetrical with Nos. 1, 3 and 5 on the port side

14

(see Figs. 18 and 26). The plates on each side were placed as nearly

as possible in the same streamline.

Each plate was calibrated in position, the longitudinal and

trans-verse force components being reproduced by means of weights acting

through cords (see Fig. 17, left side). The calibrations were carried out every day before and after the trials.

The length x in the expression for REYNOLDS number was

determined in the manner illustrated in Fig. 18.

Wake measurements

The wake measurements were made during the first series of

experi-ments, using eight right-handed current meters placed in the plane

of the port propeller (see Figs. 19 and 20). The meters were mounted

on the forward sides of two radial arms attached to the dummy

boss: four meters were mounted on each arm at radii of 300, 500,

750 and 1000 mm.

The arms could be rotated by turning the shaft. The shaft turning gear (see Fig. 21) consisted of a pneumatic drilling machine acting through a worm gear; the compressed air for the drilling machine was supplied by a compressor on the main deck. The current meter readings were recorded in the usual manner for such instruments

(see Fig. 22). The electric cables from the meters were led through the hollow shaft (see Fig. 19).

It had been intended to begin the wake measurements with the arms in the vertical position and then make five further

measure-ments, turning the shaft each time through 30'; in this way, the

wake could be measured at 48 points in the propeller disc. In the tests, however, it was found possible to alter the positions of the meters eleven times during each run; this enabled the wake at each

point to be measured twice, first with one meter and later with

the opposite meter. As all the runs were made in both directions, four records were thus obtained at each point.

When measuring the wake on a model of a single-screw ship, the result will be the same whether a right-handed or left-handed instrument (blade wheel, current meter or propeller) is used. This is due to the fact that the flow, although neither homogeneous nor

in a single direction, is symmetrical about the vertical plane through

the centreline of the instrument. With a twin-screw model, on the other hand, different results are obtained on the same side of the

15

used. In this case too the flow is not homogeneous, nor in a single direction, and furthermore the main direction of flow is not parallel to the axis of the instrument. It is an unavoidable fact, however, that the flow is not symmetrical about a plane through the centre-line of the instrument and therefore different results are obtained with right and left-handed instruments. The usual methods are

either to use both a right and a left-handed instrument on the same side of the model or to use a right-handed (or left-handed) one on each side and then take a mean of the two results.

In this case, however, the disc of the current meter is very small

compared with that of the propeller, so that the flow into the meter can

be regarded as homogeneous. It did not seem necessary, therefore, to take

measurements with similar current meters on both sides of the ship.

In the model tests, the wake was measured in the usual way by means of propellers, blade wheels and Pitot tubes.

When propellers were used, the model was driven both by

inward-turning and by outward-inward-turning screws and a mean was taken

between the results so obtained.

In the case of blade wheels, right-handed wheels were used on both port and starboard sides and again a mean value was taken. In the full-scale tests it was unfortunately found that the

connec-tions of the current meters were not strong enough and several

meters were lost at the higher speeds. Complete records could,

therefore, only be obtained at 5 and 10 knots and it was not possible

to calibrate the instruments after the tests. The meters had been

calibrated in the Goteborc, Tank before the tests.

Other troubles were also met with in the wake measurement

apparatus. It had been tested beforehand in salt water with satis-factory results, but during the tests it was found that the long

im-mersion in salt water had had an injurious effect on the instruments. The current meters were made of non-ferrous material and the blade surfaces and the bearings became corroded through electrolytic action.

The calibration diagrams, which had been obtained in fresh water prior to the tests, were probably therefore inapplicable.

Velocity measurements in the boundary layer

Pitot tubes were employed for determining the velocity distribu-tion in the boundary layer. The tests were arranged in co-operadistribu-tion

with the Svenska Ackumulator AB Jungner(SAL

Log), Stockholm, which firm supplied the necessary apparatus.

16

The tubes were lowered through two holes in the bottom shell,

1 3

one about L and the other about L from the stem (see Fig.

2

26). Two different tubes (diameter 47.5 mm) of special design were

used in each hole (see Fig. 23). The distance of the aperture in the tube from the hull could easily be adjusted from inboard (see also the right-hand side of Fig. 17).

The part of each tube projecting through the hull represented a slight addition to the ship resistance and a correction had therefore to be applied.

Measurements were taken in both the first and second series of trials and the tubes were subsequently calibrated in the Goteborg

Tank.

Arrangements for determining the wave profile

The wave profile along the starboard side of the "Wrangel" was observed from five outriggers (see Fig. 24) against a scale network painted on the ship (see Fig. 2). The "Wrangel" was also

photo-graphed under way both from the anchored boat and by other means,

but the photographs did not provide any useful information as far as the wave profile was concerned.

Other more complicated methods can, of course, be used for

determining the wave profile, but in this case it was necessary, for

various reasons, to adopt this rather primitive method. Nevertheless,

it was found reasonably satisfactory.

Similar observations were made with the model (scale 1/10).

Steering arrangements

The ordinary steam steering engine was employed and the helm

was controlled in the usual way from the bridge. The steering engine

was driven by compressed air.

Recording of the rudder angle

The rudder angle was recorded continuously on an indicating

recorder in the instrument compartment.

The rudder angle transmitter consisted of a potentiometer coupled

to the rudder stock by a thin flexible steel wire rope (see Fig. 25, a and b), carefully secured against sliding. The potentiometer was

17

Air compressor

The steering engine and the drilling machine used for turning

the port shaft were operated by compressed air. This was supplied

by a compressor with a capacity of about 4.5 m3/min. at 6 atm.

The compressor was placed on deck and was connected to a pipeline

which distributed the air to the various consumption points.

Electrical equipment

Two motor-driven 3 kW generators (115 V, A. C., 55 cycles)

provi-ded the necessary electric power. The generators were connected to a temporary cable system supplying the lights, instruments etc. Instrument compartment

The instrument panel (see Fig. 11) was fitted up in the former radio cabin and comprised the apparatus for recording resistance, local friction, rudder angle, speed etc.

8. Full-Scale Trials

General

The general arrangement of the "Wrangel", as fitted out for the tests, is shown in Fig. 26.

The Swedish destroyer "Sundsvall" acted as the towing ship. The "Sundsvall" has a displacement of 1150 tons; the machinery develops

36000 HP giving the ship a maximum speed of 39 knots (Jane's Fighting Ships, 1949-50, p. 322).

During the trials, the "Wrangel" was in contact with the

"Sunds-vall" by wireless telephone and by the usual signal flags. Telephone communication was arranged between the various measurement

posi-tions on the "Wrangel".

The date of the trials was arranged well in advance and had to be fitted in with the routine programme for the -Sundsvall". The

weather conditions on the days concerned, while certainly not ideal, were generally favourable.

Every precaution for safety was taken. The hook on the "Wrangel"

could be released from the bridge (see Figs. 12 and 13) and that on

the -Sundsvall" could also be released easily. Two motor torpedo boats were available for warning other ships and two tenderswere

also standing by. A male nurse was on board in case of accidents. 2

18

The complement of the -Wrangel" during the tests was about 20

persons, including the crew.

Trials Series I and 2

As mentioned previously, the final trials were carried out in two

series.

Series 1. In Series 1 the "Wrangel" was in her normal condition except that the propellers were replaced by dummy bosses. Measure-ments of the following items were recorded on board the test ship:

resistance of the ship, local friction,

wake,

velocity in the boundary layer,

time (speed),

log speed and

rudder angle.

The second day began with runs in two directions at about 20

knots. It had then been the intention to make two runs at 23.5

knots. The first run at this speed was commenced, but after a few minutes the towline parted in the section nearest the -Sundsvall" and the trial had to be discontinued. However, it had been possible to obtain some records of the resistance and of the local friction. Series 2. When the ship had been docked and the brackets and bossings had been removed, Series 2 was proceeded with. Except

for the wake, the same measurements were made as in Series 1.

External measurements and observations

As previously mentioned, certain observations were made from .a boat anchored half way along the measured course. They were made

at the time when the "Wrangel" passed the boat. The velocity and direction of the current and of the wind and the air and sea tempera-tures were measured. The state of the sea was observed (the Douglas scale was used) and water tests were also carried out which showed

the specific gravity to be 1.004.

As a check, the wind velocity and direction were also measured on the "Sundsvall".

The results of the various external observations are shown in

19

very low. The correction to be applied to the speed over the ground was therefore small (see Table II). The velocity component of the

current in the direction of the trial course was calculated in eachcase.

It can also be seen from Table I that the water temperature

remained very near the standard temperature of 15° C (to which

temperature the predicted model results were transferred). Although

the corrections were very small (see Table IV), all the resistance values were transferred to the standard temperature, the corrections

being based on the SCHOENHERR friction line.

Determination of time and speed

The time taken to cover the distance between one beacon and the next was determined by stop watch and marine chronometer

readings _{(As a check, the time was also measured by stop watch}

on the "Sundsvall"). As the distances involved were comparatively long, this method can be regarded as sufficiently accurate.

The speed over the ground for each section of the _{course was}

calculated from the time thus measured and, by correcting for the current, so the speed through the water was obtained. The results

are given in Table II. As can be seen from Table II, the speed varied

a little on the different sections of the course and the different

speeds were used discriminately in the analysis of the results.

The speed, as measured by means of a SAL log, was also registered

continuously on an indicating recorder in the instrument compart-ment of the "Wrangel"; this provided evidence of any mocompart-mentary

changes of speed during the runs.

9. Results

Resistance Model

The resistance of the ship, as predicted from the model test results

is shown in Fig. 27.

As previously mentioned, the model was made of paraffin wax to a scale of 1/10. The turbulence stimulator consisted of a 1 mm tripwire stretched around the model at 0.05 L from the stem. No

correction for the air resistance of the model or the extra resistance of the tripwire was applied. All the tests _{were carried out in smooth} water and the results were corrected to a standard temperature of

The calculation of the frictional resistance was made on the basis of both the FROUDE and the SCHOENHERR formulations. In the case

of the Froude method, the formula employed was basically that

decided upon at the Tank Superintendents' Conference in Paris in

1935 (the original formula has been slightly adjusted; see Publ. No.

10 of the Swedish State Shipbldg. Exp. Tank, p. 7). In applying

the Schoenherr method the usual roughness allowance of 0.0004 was

used.

In Series 1 (with appendages) the wetted surface included the

surface area of the appendages. The total resistance of the model,

including the appendage resistance, was transferred to ship scale.

The primary results of the model tests are given in Table III.

(The results obtained with the 1/50 scale model are also given in this table, although they are not dealt with further in the present

paper.)

Ship

The results obtained from the full-scale trials were corrected as

described below.

Unfortunately, no arrangements could be made to determine the wind resistance directly and it was therefore calculated by means of the formula

k --e A/1 .v2

2 r'

where Rwind wind resistance in kg,

density of air (assumed =-- 0.130 kg sec.2/m4),

Air frontal area of the ship (= 44 m2),

vr total velocity of the wind relative to the ship in misec.

The dimensionless coefficient, k1, was obtained from the formula k,

= 1.7 sin (1.5 a +

where cc angle off the bow.

This formula has been obtained using a mean of the values given

in the literature on the subject. It must, however, be admitted

that the validity of the formula in the present case may be rather doubtful, owing to the relatively large and complex superstructures.

Rwind

=

=

21

Obviously, in applying this correction for wind resistance, the air resistance is also eliminated; thus, the corrected resistance values

given are those of a ship either moving in a vacuum or having

neither superstructures nor freeboard. This fact must be borne in

mind when considering the roughness allowance.

[In order to arrive at values comparable with reality, the air

resistance, given by

Rair 1.2 vT,, (vs -a-- ship speed)

should be added. The corrected resistance would then refer to the ship in question in calm weather. In the present case,, the values of the air resistance given by this formula are:

23 kg at 5' knots

91 o » 10 »

204 » o 15 o

36,3 » 20 ]'

The resistance of the two Pitot tubes and the ordinary log tube was calculated from the formula

Epitot

1c2f d

where k2 is assumed 0.82,

(w1004

e -__- density of water ' =

_9.81

g

'

1 = length of tube (mean assumed =- 0.50 m),, d diameter of tube (= 0.0475 m),

vn, = relative velocity (assumed = 2/3 x ship speed).

The length 1 varied in the course of each run and a mean value was

therefore used.

The resistance Of the current meter arms was also determined

from the formula.

.Rams k3 v2,,

where k3 was assumed = 0.2,

,e _{102.3 kg sec.2/m4,}

1 = length of arms = 1.91 m,

b = frontal thickness = 0.035 m,

v .= 0.95 V8 (vg = ship speed in m/sec.)

=

=

=

=

2 2

(It was found that the corrections for the resistance of the Pitot tubes and the current meter arms were of rather high order. For

this reason, it would have been better to have carried out the

resist-ance trials without these appendages and then to have made separate

tests to measure the wake and the velocity distribution

in the

boundary layer.)

As mentioned above, the resistance results were corrected to a standard temperature of 15° C. The corrections, which were based on the Schoenherr friction line, were very small (see Table IV).

As stated in Section 6, the measured course is divided into three

parts. The resistance and rudder angle diagrams for each section of each run were carefully examined and results were selected and accepted only when, on the part of the run concerned, the rudder movements and consequently the resistance variations were very

small. The results of several part runs were rejected for that reason. The accepted results, most of which, as it happened, were obtained

on the last section of the run in question, are given in Table IV and are also plotted in Fig. 27.

A comparison between the full-scale test results and the values

predicted from the model test results is given in Table V and Fig.

R8 -28. The two upper diagrams in Fig. 28 show values of

Rut

where R, is the full-scale resistance and R. is that predicted on the basis of the Froude method in one case and the Schoenherr method (with a roughness allowance of 0.0004) in the other. The lower

dia-gram shows the actual value of the Schoenherr allowance, II Cf,

corresponding to the measured resistance.

In drawing any conclusions from the results of these tests, it must

be remembered that the towing method of propulsion is not ideal. It is difficult to maintain a straight course and the corrections are

always rather doubtful; furthermore, in this particular case, the

resistance dynamometer was found to be unsuitable for measuring the small forces involved at 5 knots; the model results are also

some-what uncertain at this speed.

With these reservations in mind, the following observations can

be made regarding Figs. 27 and 28.

1. The results obtained at 5 knots are doubtful and should there-fore be ignored.

23

In the case of the results from Series 2 (without appendages),

there is reasonably good agreement between the full-scale values

and the predicted values. The Schoenherr predictions seem to give closer agreement than those based on the Froude friction

values.

The results from Series 1 (with appendages) also show good

agree-ment with the predicted values, except at 10 knots. The dis-crepancy at 10 knots is probably due to an error of

measure-ment.

Two values, obtained at about 20.5 knots on run 1.4 a (towline

length 600 m unloaded) and run 1.5 cc (800 m), are shown in Fig.

27. The relative positions of these spots indicate that the effect

of the slipstream from the towing ship can, from a practical

point of

view, be neglected at the speeds in question, at

least when the length

abo we.

As mentioned previously, the calculation of the predicted values in Series 1 (with appendages) was based on the total model resist-ance. Some Tanks, in transferring the model results to full scale,

use only 50 % (or some other percentage) of the resistance of the appendages (i. e., difference in model resistance with and without appendages). But the fact that the curves for Series 1 in Fig. 28 lie above, rather than below, those for Series 2 indicates that this method would not be correct in the present case.

It

is in fact evident that the scale effect is practically non-existent

in this somewhat special case.

The lower diagram in Fig. 28 shows that, in order to correlate the actual resistance values with the model results on the basis of the Schoenherr friction line, the roughness allowance in the present case would be of the order of 0.0004 with a tendency

to decrease at higher speeds. It should be mentioned that the

corrected full-scale values then represent 'the water resistance only, without the air resistance.

In Fig. 29, the air resistance, as given by the aforementioned formula, has been added. For agreement in this case, it would

be necessary for the allowance to have a value of 0.0005

to 0.0006 with

the same tendency to decrease at higher

speeds. 3.

24

Local friction

Measurements of the local friction were made in both Series 1 and

Series 2. It may be mentioned that no differences could be observed

between the results from the trials with 600 m and 800 m towlines. Unfortunately, the instruments were not sufficiently sensitive to record accurately the very small forces exerted on the plates at 5

knots; the results obtained at this speed have therefore been excluded.

The results from Series 1 are somewhat uncertain, because the zero line on the indicating recorder paper altered, probably due to changes in temperature and humidity. The circumstances in this

respect were much better in Series 2.

The friction plates were made of non-ferrous material and this

probably gave rise to electrolytical deposits in the recesses between

the hull and the plates, which restricted the free movements of the plates. This was most noticeable in Series 2 when only Plates Nos.

1 and 5 gave reliable results.

The plates were placed so that two edges were as nearly as possible

parallel to the streamlines and it was found that in consequence

the lateral forces could be entirely neglected.

As mentioned in Section 7, the force on Plate No. 3 (port,

amid-ships) was recorded continuously, while the forces on the other

plates were each registered in turn on another indicating recorder. Each of the latter measurements was therefore quite short in

dura-tion and was used in conjuncdura-tion with the corresponding momentary ship speed, obtained from the continuous speed record.

The results are given in Table VI and Fig. 30. In the diagram, the results are presented in the form of the local friction coefficient

V X

C7 as a function of Reynolds number . The local friction

coefficient Rf I Av2, where Rf is the measured tangential

force, A is the area of the plate (0.16 m2) and v is the speed of the ship. The significance of x in the Reynolds number expression is

illustrated in Fig. 18. The values of the kinematic viscosity, v, were

taken from S. N. A. M. E.

Bulletin No. 1-2; they are given in

y 1.004 was determined by linear interpolation between the values for fresh water (y = 1.000) and sea water .(21 = 1.026).

1 + 3.59 IFC3

(Cf = total friction coefficient) taken from W. P. A. VAN LAMME, REN, *Resistance, Propulsion and Steering of Ships*, Haarlem, 1948,

p. 42. The SCHLICHTING line was obtained from H. SCHLICHTING,

»Grenzschicht-Theorie», Karlsruhe, 1951, Fig. 21,7 on p. 407. The "relative sand roughness lines" in Fig. 30 were also obtained from the latter source.

KEMPF'S results from the "Hamburg' are also plotted for

compar-ison in Fig. 30. The values were obtained from G. KEMPF, »rber den Einfluss der Rauhigkeit 'aut. den Widerstand von Schiffem,

J. S. T. G., 1937, p. 163.

Also plotted in Fig. 30 are the CI values obtained by calculation

from the curves, of velocity distribution in the boundary layer

described below.

In this connection, the pretest in the Goteborg tank with one of the friction plates may be mentioned, although it was carried out for the purpose of testing the working of the apparatus rather than for measuring C. The arrangement of the apparatus is illustrated

in Fig. 31 and the results are given in Table VII. It should be

realized that the dimensions of the plate in this case are rather large, In relation to the distance x (leading edge to centre of plate), and that

the frame was painted while the plate was unpainted. However,

with this reservation, the results are plotted in Fig. 30. The points

cover very low Reynolds numbers. .and show reasonably good agree -m ent with the reference lines.

For the sake of clarity, the results obtained have been transferred to Figs. 32, 33 and 34. Fig. 32 shows the results from Series 1, Fig. 33 those from Series 2, and Fig. 34 those obtained by calculation from the curves of velocity distribution in the boundary layer.

When examining Figs. 39, 32 and 33, it must be borne in mind

that the plates were made of very smooth material and that the

ship's hull surface was not the same in both series of tests (it had been painted twice before Series 1 and four times when Series 2

was carried out). The value of GI must depend not only on the

degree of roughness of the plate itself but also on the roughness of

the hull surface ahead of the plate.

=

25 The SCHOENHERR and SCHLTCHTING local friction lines are shown

for comparison in Fig.. 30. The SCHOENHERR line is obtained from

the formula _Cf

-Accepting the sand roughness theory for the moment, it should

be pointed out that, in the case of the local friction, the relative

sand roughness, xlk, (k, = equivalent sand grain size, assumed

constant in this case), varies between one point and another on the hull surface. Thus the spots corresponding to different values of x can be expected to lie on different sand roughness lines. In other

words, the spots will not plot on a single curve and a certain amount

of scatter is to be expected.

In Fig. 32, where the results from Series 1 are plotted, the scatter of the spots is rather confusing. As stated previously, there is some

doubt about these results, but, nevertheless, the spots do tend to arrange themselves in accordance with the roughness lines with

increasing relative roughness.

In Fig. 33, corresponding to Series 2, this tendency is more obvious.

Except for those below 1?=- 10s, the spots for x = 16.99 m show a relative roughness of about 3 x 105 and those for x = 52.78 m a value of about 8 x 105. In both cases, the values correspond to the same value of k, of about 0.06 mm. (See also Table IX, where the values of k, are of the same order.) This figure has, of course, no

absolute significance.

As mentioned previously, the values plotted in Fig. 34 have a

different origin from those in Figs. 32 and 33. For the present,

however, it is only necessary to note that the Of values are of the same order as those in Figs. 32 and 33, and that the relative posi-tions of the spots for x = 36.11 m and x = 53.23 m show the same tendency as in the other two diagrams.

Finally,

it may be said that the sand roughness theory is

apparently sound in principle and merits further study and

in-vestigation.

Wake measurements

As stated previously, the full-scale wake measurements were not

successful. Unfortunately, therefore, no information on the scale

effect of the wake in the present case could be obtained.

Apart from the lack of success in these measurements, the ship in question was not entirely suitable for studying the scale effect of the wake. In the first place, the wake fraction has a very low value

(obtained by taking the difference between figures of the same order)

and secondly the flow behind the brackets (of obsolete design)

r-

27

Very extensive and careful model tests were carried out using outward- and inward-turning propellers, blade wheels (each wheel

on both port and starboard sides in turn), and Pitot tubes for

measuring the wake. Tests were made at speeds corresponding to about 5, 10, 15, 20 and 25 knots. In every case, the readings were very unsteady, probably due to unstable flow behind the brackets.

Although they are of no special value in the present

investi-gations, a resume of the model results is given in Table VIII. The

values of the "Wake fraction, w, are in accordance with TAYLOR'S,

definition. The methods used for determining the wake fraction are

described in Publ. No. 14 of the Swedish State Shipbldg. Exp. Tank,

p. 13. In those cases where propellers have been employed, w

represents a mean between wy, (based upon thrust identity) and wQ,

(based upon torque identity).

Isowake curves have been constructed on the basis of the Pitot

tube measurements on the model. The curves for 10 knots are shown

in Fig. 35.

Some full-scale measurements were also obtained at 10. knots and,

although they are not reliable, for reasons mentioned in Section 7, isowake curves have been constructed therefrom and are shown in

Fig. 36. They have no quantitative but perhaps some qualitative

value.

Velocity distribution, in the boundary layer

The only reliable measurements of the velocity distribution in the

boundary layer were obtained in Series 2. The apparatus was not

functioning properly in Series 1 and the following, therefore, refers:

only to Series 2.

As stated previously, the Pitot tubes were placed in the bottom.

1

of the ship (see Fig., 26) at L (x = 36.11 m; x being defined in

3

Fig. 18) and L x = 53.23 m) from the stein. NO differences were

4

-noticeable between the results obtained with the two types of Pitot

tube .(see Fig. 23).

The measurements were made continuously during runs in both

directions and, since there was sufficient time for both types of

tube to be used in turn, four measurements (and more at low speeds)

28

each case, the corresponding momentary ship speed was obtained

from the continuous speed record.

Tests were made at ship speeds of about 5, 10, 15 and 20 knots.

As the speed in each group varied a little from measurement to

measurement, the results were adjusted in direct proportion to the mean speeds of 5.4, 10.1, 15.3 and 20.4 knots. The results are

plotted in Figs. 37 and 38.

1

Fig. 37 shows only the observations obtained at

L at 5.4 and

1 3

Fig. 38 shows mean curves for both L and L at all four ship

speeds.

In Figs. 39 and 40, the results are given in the form of the wake

fraction,

V, -V

W

V8

as a function of the distance from the ship's hull (v, = ship speed,

v -= observed velocity in the boundary layer relative to the ship). The most striking fact about Fig. 38 is that, at a certain distance from the hull, the observed velocity exceeds the ship's speed. This must be caused by interference from the potential flow and, in this

case, such interference could be expected. The same phenomenon is

apparent in Figs. 39 and 40, where it will be seen that w becomes

negative in the outer part of the tested region.

noted that in this region, w is obtained by taking the difference

between figures of the same order).

This aspect of the question is illustrated diagrammatically in Fig. 41, from which it will be seen that it would be more appropriate to express the wake in the form

V8 (vb HH vp)

where v, = ship speed,

vb = velocity due to friction, vp = velocity due to potential flow.

29°

Attempts have been made to calculate approximately the value of v, or rather viva, by using the comprehensive material in S. A.

HARVALD'S doctorate thesis (HARVALD, *Wake of Merchant Ships»,

Copenhagen, 1950). A very rough calculation of the potential flow at

different points on the ship's hull gave appreciable values,. The value

of vp/v, decreases, of course, at increasing distances from the hull.

The local friction coefficient 0 for a point on the hull can be

calculated, at least approximately, from a velocity distribution curve.

G. KEMPF and K. KARHAN, in their paper »Zur Oberflachenreibung des

Schiffes», J. S. T. G.,1951, p. 223,suggest a method which was applied to

the present material, but it was found to give rather doubtful results.

Another method, described by N. SCHOLZ in a paper in J. S. T. G., 1951, entitled »rber em n rationelle Berechnung des Stromungswider-standes schlanker Korper mit beliebig rauher Oberflache», has there-fore been used instead. The results are given in Table IX and plotted in Figs. 30 and 34.

The calculations were based on the curves in Fig. 38 and as stated

earlier, these curves represent the addition of the velocity due to

friction and the velocity due to potential flow. ScHoLz' method,

however, presupposes only velocity due to friction and the curves

should therefore be corrected for the potential flow. No attempt

has yet been made to introduce such corrections. Nevertheless, the results shown in Fig. 34, although not obtained on a correct basis, appear to be quite acceptable.

Ware profile

The wave profile was determined by visual observations in both the model and the full-scale tests. It is naturally difficult to make accurate observations, particularly at the bow, when the sea, as in these cases, is not quite calm. The results. should therefore, be

regarded with this in mind.

The results are shown in Fig. 42. The agreement between ship and model is not good, but the results are quite informative from a practical point of view. A certain difference in wave formation

was apparent between ship and model.

-10. Acknowledgement

As stated in the introduction, the investigations were carried out

30

author wishes to express his appreciation of the courtesy shown by the Committee in making the results available for publication. The analysis and development of the results were carried out at

the Swedish State Shipbuilding Experimental

Tank, especially to Messrs. H. BRATT, C.-A. JOHNSSON and H. LIND-GREN, for all their assistance. Thanks are also due to Mr. D.

FRASER-SMITH, B. Sc., who has assisted the author in translating the paper

from the Swedish.

References

HIRAGA, Y.: »Experimental Investigations on the Resistance of Long Planks and Ships», Trans. I. N. A., 1934.

DENNY, Sir MAURICE E.: »B. S. R. A. Resistance Experiments on the Lucy

Ashton, Part h, Trans. I. N. A., 1951.

CONN, J. F. C., LACKENBY, H. and WALKER, W. P.: d3. S. R. A. Resistance Experi-ments on the Lucy Ashto n, Part II*, Trans. I. N. A., 1953. K_Exim G.: *Neuere Erfahrungen un Schiffbau-Versuchswesem, Jah,rb. der

Schiff-bautechn. Gesellsch., 1927.

KEMPF, G.: »Vber den Einfluss der Rauhigkeit auf den Widerstand von Schiffem, Jahrb. d. S. T. G., 1937.

KEMPF, G. and KARHAN, K.: »Zur Oberflachenreibung des Schiffes*, Jahrb. d.

S. T. G., 1951.

ScuoLz. N.: *Thaer eine rationelle Berechnimg des Stromungswiderstandes schlanker

Korper mit beliebig rauher Oberflache,* Jahrb. d. S. T. G., 1951.

ScaLicErrrNG, H.: Grenzschicht-Theorie (G. Braun, Karlsruhe. 1951).

T-TARvALD, S. A.: Wake of Merchant Ships (The Danish Technical Press, Copenhagen, 1950).

8TRANDHAGEN, A. G., SCHOENHERR, K. E. and KOBAYASHI, F. M.: The Dynamic

Stability on Course of Towed Ships*, Trans. S. N. A. M. E., 1950.

APPENDIX 1

Measurement of Towing Forces

By

G. Gustafsson

The towing force was measured by means of a dynamometer

absorbing only the horizontal lengthwise component of this force

when arranged for a parallel guided setting. A drawing of the

31

The dynamometer was designed for a 45 tons load, which could be expected under very high speed towing conditions. The force indicating part of the dynamometer consists of a link fitted with

strain gauges. The gauges are coupled in a full-bridge (a Wheatstone

bridge with four active arms) and, in accordance with the wiring diagram in Fig. 44, connected to a Leeds & Northrup Speedomax Recorder equipped with a high-gain amplifier. For checking the

zero setting of the dynamometer (reading at zero loading) there was

a device for unloading the traction from the dynamometer. The

zero deviation was generally very low, but once reached a maximum

of about 225 kg; i. e. about 0.5 per cent of the maximum load. The greatest difficulty was experienced in obtaining an accurate

calibration. Calibrated weights up to a total load of 15-20 tons

were not available. A tensile testing machine of Amsler make, with

a maximum loading capacity of 20 tons, has therefore been used as loading norm. This machine was said to give load values with

an accuracy of ± 1 per cent of the applied load. The accuracy obtained with the measurements must therefore be less than the accuracy of the loading apparatus and has been estimated to be

about ± 2 per cent of the applied load. In order to reproduce the conditions prevailing during the towing tests the calibration was carried out at lower than normal temperatures and with transverse

loading.

APPENDIX 2

Measurement of the Local Friction Forces

By

Oustafsson

The water friction against the ship was measured at six places by

means of plates (400 x 400 mm2) fitted flush with the outside of the

hull below the waterline. The plates are mounted in double inner frames, which are parallel guided by means of leaf springs, so that the plates may be moved in the longitudinal direction of the ship

as well as in the transverse direction. The inner frames are connected

to outer ones, which are screwed to the hull. From the centre of

each plate, a bolt runs through a hole in the inner plate (made

32

connected to two strain gauge elements which measure the forces in the longitudinal and transverse directions respectively. By this method it is possible to calibrate the device with known weights inside the ship whenever required. Figs. 45 and 46 show the design

of the friction measuring device.

The friction plates were designed for a maximum force of 3.5 kg,

but the true forces were considerably less, due to the fact that towing at speeds greater than 23 knots could not be carried out

using the towline that was available. No appreciable forces could be detected in the transverse direction, except when the ship was

rolling.

The greatest difficulty was to select a suitable material for these

plates. The movable parts should be as light as possible, having

due regard to acceleration forces and changes in the pitching angle. For this reason, light alloy 51 ST was selected. The plates should be

thin, but at the same time rigid and this material was therefore

chosen. As this material easily corrodes in saltwater, the plates and the inner frames were anodized. The remaining parts of the device were galvanized and painted with an antifouling composition. In

spite of these precautionary measures, accelerated corrosion occurred

in the slots around the edges, whereby the movements of the plates were increasingly limited. However, as the tests were carried out shortly after launching, measurements could be recorded without

serious disturbances from this cause.

APPENDIX 3

Redogorelse for tillkomsten av WrangelfOrsiiken och

Wrangelkommittens verksamhet

Betydelsen av fullskaleforsok med fartyg av olika typer har sedan

lange stat klar for forskare Mom skeppshydrodynamiken. Sadana forsok behiivas framfor allt som stod och for verifikation av den intensiva forskning, som sedan decennier bedrivits Mom saval den

teoretiska som experimentella skeppshydrodynamiken, sarskilt i

'an-der med intresse fOr skeppsbyggeri och sjofart. Det är darvid sar-skilt frAgan om fartygs friktionsmotstand som statt i forgrunden men otaliga delproblem ha aven varit foremal for undersokningar.

33 For ett sjofartsland som Sverige är det givetvis ett nationellt

intresse att kunna lamna bidrag till sadan forslming.

I borjan av ar 1949 blev det bekant att en vid Karlskrona

orlogs-vary byggd 140 tons torpedbat skulle bogseras till GOteborg for att

dar maskinutrustas. Det lag da nara till hands att i samband med

denna bogsering fOrsiika foretaga prov av ovan antytt slag. Forslag

harom framkastades av forfattaren till foreliggande rapport, H. F.

NORDSTRoM, vid en overlaggning med marindirektoren IVAR HULT.

Overlaggningen resulterade bl. a. i en skrivelse i maj 1949 fran Sta-tens Skeppsprovningsanstalt till Kungl. Marinforvaltningen, van i

for-slag i detta syfte framlades. Samtidigt foreslogs att en kommitte

skulle bildas for forslagets realiserande. Av manga skitl kom planen

ej till utforande.

Man kan emellertid med fog saga att de forda diskussionerna

ut-gj orde upprinnelsen till de nu slutforda fullskaleforsoken med jagaren *Wrangel». Det befanns namligen, att forsok med sakerligen battre

framgang skulle kunna goras med den utrangerade jagaren *Wrangel*.

Med detta fartyg hade man full frihet att Ora alla ingrepp, som

kunde erfordras. Vidare skulle man ha en viss frihet att valja tid

for proven och aven lamplig plats.

Med denna utgangspunkt igangsattes nu utrednings- och

forbere-delsearbeten. Sedan desaa pagatt en tid bildades en provisorisk

kommitte, bestaende av direktoren ALLAN BORGSTROM,

overdirek-toren. H. F. NORDSTROM och t. f. marinoverdirektoren BIRGER

SWEN-ZEN med vilka skeppsredaren ROLF SoRmAN snart forenade sig. Som

kommittens sekreterare fungerade marindirektoren IVAR HULT.

For-beredelserna togo darefter okad fart. Dessa kravde givetvis behov

av penningmedel. Bidrag erholls fran vissa fonder. Vid

framstall-ningarna om bidrag upptradde marindirektoren HULT som kommit-tens representant.

En viktig fraga var projektering och tillverkning av speciella

instrument, erforderliga for olika planerade matuppgifter. Som rad-givare i denna fraga stallde sig professorn STIG EKELOF

till forfogande. Genom prof. EKELOFS ftirmedling inkopplades dr. G. GUSTAFSSON vid Flygtekniska Forsoksanstalten pa denna

upp-gift. Det var dr. GUSTAFSSON som pante sin medhjalpare ingenjoren

G. SCHERLING senare svarade for den slutliga utformningen av mot-standsdynamometern, friktionsmatama, rodervinkelgivaren osv. Att

proven slutligen kunde genomfOras beror till stor del pa dr. GUSTAFS-SON OCh ing. SCHERLING.

3

34

Sedan planerna alltmer fortskridit blev det klart att en mera

officiell kommitte borde skapas for att effektivt understodja och framja slutforandet av undersokningarna. En sadan kom ocksh till stand i april 1952 och kom att besta av fern ledamoter med

konter-amiralen A. G. JEDEUR-PALMGREN SOM ordforande. Som ovriga ledamoter ingingo de fyra medlemmarna i den tidigare provisoriska

kommitten. Kommitten antog namnet Wrangelkommitté n.

Som kommittens sekreterade fungerade forst marindirektoren HULT,

men dh, denne pa grund av utlandstjanst maste trada tillbaka

in-tradde davarande kaptenen DAG ARVAS som sekreterare. Kapten

ARVAS fick bl. a. planeringen av fOrforsoket med »Vidar* pa sin lott.

Sedan aven kapten ARVAS pa grund av andrad tjanstgoring mast

lamna sekreterarebefattningen overtogs denna av kaptenen N. SKAAR,

som darefter fungerat pa denna post. Kapten SKAAR har bl. a. fatt

bara den tyngsta bordan vid organiserandet av de slutliga proven

med *Wrangel*. MarindirektOren HULT har dock under hela tiden per

korrespondens eller pa annat satt statt till Wrangelkommittens for-fogande. Han har ocksa fortfarande hela tiden framtratt som kom-mittens representant infor de anslagsbeviljande korporationerna.

Utrustningen av »Wrangel* och darav betingade

konstruktionsar-beten ha utforts av Stockholms orlogsvary. Wrangelkommitten har darvid haft ett mycket valvilligt stod av chefen for

marinverksta-derna darstades, verkstadsdirektoren GOsTA HARTZELL och chefen

for varvets skrovsektion, marindirektoren B. HANSSON. Ett

bety-delsefullt konstruktionsarbete har utforts av civilingenj Oren ENGEL

GALTUNG med bitrade av ingenjoren G. ROSENDAHL For den

prak-tiska delen av utrustningen svarade forvaltaren 0. NILSSON. Apparatur och utrustning for gransskiktsmatningarna ha

tillhanda-hallits av Svenska Ackumulator AB Jungner. Bolagets foretradare,

ingenjoren B. LAGERKRANTZ, har hela tiden intagit en mycket

val-villig installning till undersokningen. Vid fOrsokens planering och

utforande lamnades god hjalp av ingenjorerna B. NITTVE och T. To-RESJo.

Wake-matningarna blevo tyvarr av olika skal en missraluiing De hade dock omsorgsfullt forberetts i intimt samrad med chefen for AB Karlstads Mekaniska Werkstads turbinlaboratorium i Kristine-hamn, civilingenjoren H. HANSSON. Kommitten star aven i tack-samhetsskuld till ingenjoren B. LINNC som ledde

medstromsmitt-ningarna under forsoken. Intresserad medverkan vid proven

.35

Bogseringen av »Wrangel» ombesiirjdes av jagaren *Sundsvall*

under befal av kaptenen T. WULFF. _{Av »Sundsvalls» besattning}

uttogs aven personal for de sjomansmassiga arbetena ,ombord pa

»Wrangel» under forsaken och sAsom handrackning vid matningarna. Forberedande bogserforsok hade tidigare, hasten 1952, utforts med

den till malfartyg ,andrade utrangerade jagaren »Vidar»..

Bogse-ringen utfordes vid detta tillfalle av jagaren »Uppland» under befa] av kaptenen N. SKAAR..

I saraband med proven forlades *Wrangel» till Harsfjaraens

'Orlogs-depa. Depachefen, kommendorkaptenen S. BJoRKLUND och

depa-officeren,, kaptenen S. OHLSSON stodde foretaget pa ett valvilligt

,satt, sarskilt genom att stalla personal till forfogande vid olika

fallen for kompletterande arbeten. Militarmeteorologeh S. ScHENcK lamnade vaderleksrapporter under forsoksdagarna.

En god del av forberedelserna har fallit pa Statens

Skeppsprov-- ningsanstalts lott. Forf. har darvid haft vardefull assistans av

civil-ingenjaren H. BRATT, som aven medverkade vid slutproven. _Vid

bearbetningen av forsoksmaterialet, som utforts vid Skeppsprov-ningsanstalten, har fortjanstfull medverkan lamnats av anstaltens

tjansteman och sarskilt av ,civilingenjorerna H. BRATT, C.-A.

JOHNS-SON Oa. H. LINDGREN.

Forsaken ha givetvis dragit avsevarda kostnader. Rakenskaperna

ro annu

Summa Kronor 252 743:

lamnas:

:Konstruktion och tillverkning av matinstrument , 42 980: 48

Linjekontroll 417: 43

'Forberedande modellforsok 30 930: 62'

Forberedande bogserforsok med »Vidal.* .: ,. 20 974: 62

))1/Vrange1s» utrustning, forflyttning,, Andring och

avrustning . . ...,,

...

Delkostnad av nylonkabel , 2,3 126: 98

Vissa kostnader i samband med forsokens genomforande.

Viss personal m m -980: 10

Bearbetning av forsoksmaterial . 27 400:

Pub heeling . . , 6000: