ARCH1EF
Lab. v. Scheepsbouwkunde
Technische Fiageschool
Delft
SERVICE-PERFORMANCE TRIALS CARRIED
OUT
IN
THE NORTH ATLANTIC ON
S.S. " CAMNDHU "
.By S. LIVINGSTON SMITH, C.B.E., D.Sc.(Eng.)Member
and R. E. CLEMENTS, B.Sc., Associate Member
29th November 1957
-SYNOPSIS.This paper describes trials carried out by the British Shipbuilding Research Association in a dry-cargo vessel under normal service conditions in the North Atlantic. The object was to study the performance of the vessel under different cOnditions in order to provide accurate data for comparing and developing
methods of analysing service performance, power allowances, etc.
An important item in work of this nature is the trials instrumentation and consequently this was given careful attention, the object being to obtain
auto-graphic records of as many items as possible. Shaft revolutions, wind speed and
direction, rudder angle, angles of roll and pitch, and ship speed by pitometer log, were all recorded autographically. It was not possible to record propeller thrust and torque autographically and for these measurements a Michell thrustmeter
and Siemens-Ford torsionmeter were used. Estimates of wave length and height during each observation were made visually and stereoscopic. photographs were
taken.
During each observation the power necessary to maintain the recorded speed was measured ; this power was higher than that necessary to maintain the same speed in calm water ; the percentage difference between these two powers has been estimated to give the percentage increase in power under the prevailing
conditions. The effect of direction of encounter has been analysed in a similar
manner. The loss of speed for a given shaft horse-power from the speed for the
same power in calm water has also been estimated for each observation. Details are given of the weather encountered, ship motions during the trials, and of the velocity distribution within the. boundary layer measured by means of the pitometer log.
It was realized that on a single round voyage of this nature, it would be quite impossible to cover all the variations of weather and condition of hull surface normally encountered in service. Conclusions reached regarding power margins
would naturally depend on the weather encountered by the vessel during the voyage and the condition of the hull. An appendix has therefore been prepared giving details of the weather encountered by the vessel during the first year of service, and a brief analysis has been made of the performance during this time from data supplied by the ship's officers.
Introduction
FOR
several years now the British Shipbuilding Research Association
has been interested in estimating the influence of various factors
on the performance of a vessel in service and determining the
powering allowances necessary to maintain the designed service speed. The purpose of the present trials was to obtain accurate service perform-ance data with which to examine methods of analysis and at the same time to determine the powering margins for the ship,For the data to be useful for research obahvaiittitthafabsitill'sis, the
differentfader
:116 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU
range as possible.
From the point of view of weather, the North
Atlantic can provide a wide variation at certain seasons of the year
The Cairn Line of Steamships, Ltd., which operate ships between thenorth-east coast of England, Scotland, and Canada, Were therefore
asked if they would co-operate by allowing trials to be carried out onthe S.S. Cairndhu. The vessel was already equipped with a thrustmeter
and a torsionmeter, and therefore it was only necessary to instal a
pitometer log to complete the major items of instrumentation.Since the effect of fouling or deterioration of the hull surface cannot be examined from one round voyage only, it was decided to carry out the trials immediately after dry-docking.
This paper presents the results obtained and the analysis of the propulsion data, together with notes on the characteristics of the ship's boundary layer and
of the motions of the Vessel. Experience gained in the analysis of these data
contributed towards the development of the method of analysing service-performance data described in a paper recently given before this Institution (1).*
1. Particulars of Vessel
The S.S. Cairndhu is a single-screw, steam-turbine driven dry-cargo vessel of
shelter-deck type with accommodation for twelve passengers. The Vessel is
owned by the Cairn Line of Steamships, Ltd., Newcastle upon Tyne, and was
built by Wm. Gray and Co., Ltd., West Hartlepool. She is designed for
service in the North Atlantic, going North about from Newcastle upon Tyne and other northern ports to Montreal and SL John, New Brunswick. The maiden voyage was made in October, 1952.
The principal dimensions are as follows
Length overall 444ft. 6in.
Length b.p. 419fL Oin.
Breadth extreme 60ft. 2f in.
Breadth moulded 60ft. Oin.
Depth moulded to upper deck 37ft Oin.
Deadweight 9,200 tons.
Gross tonnage 7,503.
Service shaft horse-power 4,650.
Service speed, loaded 13 knots.
Steam is supplied by two water-tube boilers having a working pressure of 225 lb. per sq. in.
The propelling machinery consists of a set of three steam turbines
trans-mitting power through double-reduction gearing to the propeller shaft. These
turbines develop 4,650 s.h.p. continuous running, to maintain a designed service speed of 13 knots.
The propeller dimensions are as follows :
Diameter 18ft. 9in.
Mean measured pitch 15.51ft.
Pitch ratio 0 . 83.
Blade area 1.10 sq. ft.
Blade-area ratio '0 -400.
4 blades, right handed.
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHIJ 117
The loading particulars during the trials were as follows : Departure from Grangemouth :
draughts (SW), forward 18ft. 10in.
aft 24ft 5in.
displacement 10,622 tons.
Arrival at Montreal :
draughts (SW), forward 19ft. sin.
aft 22ft. 9m.
displacement 10,319 tons.
Departure from Port Alfred : draughts (SW), forward 24ft.
aft 27ft.
displacement 13,375 tons.
Arrival at Newcastle upon Tyne : draughts (SW), forward 25ft. 10in.
aft 26ft. 10in.
displacement 13,034 tons.
2. Instrumentation
When considering the instruments to be used on these trials, it was decided that as many as possible of the records taken during each observation should be obtained autographically, firstly so that the number of records taken by each observer could be reduced to a minimum, thereby reducing the time taken for each observation, and secondly to enable a careful examination to be made of the various records after the trials.
The positions of the various instruments in the ship are showh in Fig. 1. (a) Ship Speed
From the point of vie* of the analysis of the performance data it was essential that the speed of the ship through the water should be measured as accurately
as possible. To this end a pitorneter log was fitted in the ship during dry
docking immediately prior to the voyage. The log was fitted at a position
245ft. aft of the forward perpendicular and approximately 3ft. 6in. off the
centre line on the port side. Since it is also essential that the pressure orifices
shall be clear of the bOundary layer in order to measure the true ship speed,
arrangements were made for an extra long rodmeter to be fitted. The distance
of the pressure orifices below the hull surface was measured in dry-dock and found to be 51fi in. when the rodmeter was fully extended.
The record of ship speed was transmitted to a recorder in the chart room
which indicated ship speed and integrated this speed to give distancerun.
It
was also transmitted to an autographic recorder which was specially lent by the British Pitometer Co. for the period of the trials. This recorder was used during each test run and also while boundry-layer traverses were being taken.
The pitometer log was calibrated by making a number of runs over the
Newbiggin Measued Mile. The accuracy in speed measurement was one per cent, in calm water and four per cent in rough.
During the passage from Grangemouth to Montreal a certain amount of trouble was encountered in the pitometer with faulty contacts in the electrical
circuits. As a result, no speed measurements were obtained from the log for
Observations 9 to 12 inclusive and approximate speeds were obtained from the Walker log.
118 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU
Boundary-layer traverses were taken at the beginning and end of each passage
with the vessel in calm, deep water. For this purpose, marks were scribed on
the rodmeter to ensure that the distances of the pressure orifices from thehull
surface were the same for each test. The error in measurement of these
distances was ± 1/64th in. Thrust Measurement
A Michell thrustmeter was fitted in the vessel for its mea.sured-mile acceptance trials and was retained in position for the collection of service-performance data. It was thoroughly checked immediatelY before the present trials and found to
be operating satisfactorily. The instrument was fitted to the thrust block
immediately aft of the main turbine. The accuracy of thrust measurement
in calm water was 2 per cent.° .
Power Measurement
A Siemens-Ford torsionmeter was used to measure torque in the shaft, the instrument having been in position since before the measured-mile trials.
The length of shafting on which the torsionmeter was mounted was calibrated
and found to have a modulus of elasticity of 11.82 x 106 lb. per sq. in. The accuracy of the torque measurement in calm water was 2 per cent.°
Power is proportional to torque times shaft revolutions per minute and since
every revolution of the shaft was recorded on a time base, the shaft r.p.m.
at any instant may be obtained exactly so that the accuracyof power
measure-ment in calm water was 2 per cent. Shaft Revolutions
The measurement of shaft revolutions was made with the standard B.S.R.A.
equipment for measured mile trials. By means of this equipment every
revolution of the shaft was recorded electrically against a time base. Two
contacts were fitted on the transmission shaft to the tachometer and each gave
a record once per revolution. Since every revolution was recorded on a time
base, the shaft r.p.m. at any instant was known exactly. To guard against failure of this system, the total revolutions on the counter were obtained at the beginning and end of each observation and the mean r.p.m. over this period calculated.
Ship Motions
During each observation, a continuous record was taken of the rolling and pitching motions of the vessel by means of a Sperry Roll and Pitch Recorder
which Was kindly lent by the Cunard Steamship Co. Therecorder measures
rolling and pitching movement relative to a single electrically-driven gyroscope ;
an electrically-operated time base is also incorporated. Typical samples of
records are shown in Figs. 2 to 5. Wind
Wind speed and direction relative to the ship were measured using the B.S.R.A.
equipment for Measured-mile trials. The wind vane and anemometer were
mounted side by side on a single mast on the compass platform over the
wheel-house. In order to avoid the effect of local eddies from the bridge. structure;
the mast was made as high as possible. The anemometer cups were actually
19ft. 6M. above the wheelhouse top, lift. abaft the bridge front, and 10ft off the centre line on the port side. As a check on these readings, wind speed was measured by means of a hand anemometer usually from the compass platform and a visual observation made of the direction relative to the ship.
The average relative wind speed during each observation could bemeasured
tbutvithirkivtlitia-
'editqt
VSarriaiked;t6ii:+ia..-'iteate-reeot& obtfffliiittIkV &ellViothrge 166t/Ylef iFii411dfile-or
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 119
speed was readily obtainable. This speed was later corrected using a calibration
curve for the anemometer obtained by means of wind-tunnel calibration.
(g) Sea Conditions
-The estimation of wave height was one of the most difficult observations to
make, particularly in confused seas. With practice, however, a fair degree
of accuracy was attained. It was discovered that the best method of obtaining
Wave heights was to stand looking along the wave crests and comparing the
heights with the known height of certain objects on the ship. The officer on
watch was always consulted on this matter, Wave lengths were equally difficult to estimate and were most easily estimated with reference either to the ship's
length or one's position relative to the forward or after end. This applied to
waves either ahead or astern ; for waves on the beam it was a little more
difficult but the same principle could be applied. Wave lengths have only
been quoted where the seas were fairly regular.
The frequency and direction of encounter were obtained by standing on the compass platform on the centre-line and timing the number of waves coming on
to the bow over a given period, usually five minutes. As with wave lengths,
frequencies of encounter are only given where the seas were fairly regular ; in
confused seas it was impossible to make any estimate of the frequency. As a check on the observations of sea conditions, stereoscopic photographs
were taken with a Rolleidescope camera which had a lens spacing of in. It
was not possible to make accurate measurements of wave heights by this means
without an immense amount of analysis. The purpose of taking photographs
was more as a check on the day to day consistency of the estimate of given conditions rather than an accurate measurement of those conditions.
Course
The course was obtained from the gyro-compass, the necessary corrections to be made being obtained from the officer on watch.
Rudder Angle
The rudder angle was measured using the standard I3.S.R.A. rudder-angle recorder. A continuous record of rudder angle was obtained by means of a
rod and a stiff helical spring which wasP fitted on the rudder stock. the
instru-ment was calibrated in position before the trials in order to check on any possible fault in the recording
device.-Propeller Measurenient
In order to determine the accuracy of manufacture of the propeller, it was
measured prior to fitting in the ship. The mean measured pitch was -15 -51ft.
3. Method of Recording Data
When deciding upon the time that should be taken to complete each
observa-tioh, several factors had to be taken into consideration. If the time were very
short it would be difficult to obtain a good average for the power and thriist during the observation ; also it would not be possible to estimate, the period of encounter of the waves with any degree of accuracy. On the other hand if -the period were too long, it would be difficult to maintain engine settings steady, and also weather conditions might change. Two observers were available to take the various readings and observations.
It was considered that a period of ten minutes would be suitable for each
observation. In this time continuous autographic records were taken of shaft
revolutions, ship speed, angles of roll and pitch, wind speed and direction, and
rudder angle. Wave direction and period of encounter were observed over a
period of about 5 minutes during each observation and notes made of wave height and length, air temperature, wind speed (by hand anemometer), estimated, wind direction, barometric pressure, and ship's course. In the engine-room,
120 SERVICE-PERFORMANCE TRIALS ON SS. CAIRNDHU
the total shaft revolutions on the counter were noted at the beginning and end
of each observation and the sea temperature noted. Average readings of thrust
and torque were taken at alternate half-minute intervals ; the torsionmeter and thrustmeter were therefore observed for a total of five minutes each during observation and the average obtained from ten readings over the ten minute period.
4. Sea Trials'
The purpose of carrying out these trials at sea was to study the behaviour
of the vessel under as many different conditions of weather as possible. The
main interest was to measure the performance of the vessel with a view to throwing some light on the problem of likely powering allowances in order to
maintain a given speed in service. It was therefore necessary first to measure
the propulsive performance of the vessel as accurately as possible, and second to record simultaneously all the factors likely to affect that performance.
The North Atlantic is generally accepted as being able to provide both the worst weather likely to be encountered on any sea route and also the greatest
variety. It was for this reason that the S.S. Cairndhu was chosen for these
tests. It was considered that the period late September to the end of November
was the one most likely to give the most changeable weather and at the same time it allowed a passage up the St. Lawrence before it was closed to shipping
The outward passage was from Grangemouth to Montreal with the vessel
in a moderately light condition. As will be seen from Tables 1(a) and 1(b),
the weather was mainly from ahead. On the first day, 24th October, the weather was fairly good with a slight following sea, a moderate following gale
blowing up during the afternoon and evening. During the 25th and most of
the 26th, the wind remained at Beaufort force 6 or above and the vessel was
rolling and pitching heavily at times in a rough sea. Towards late afternoon
of the 26th, the wind rose suddenly and veered to the NW. The vessel was
then rolling and pitching heavily at times in a rough, short, steep sea.
Condi-tions deteriorated still further as the evening drew on and the vessel was forced
to heave to and run at half speed into the seas. By the morning of the 27th
there was a very rough sea runnhig and the wind was force 10/11. However,
the storm abated somewhat during the day and the normal course was resumed. The 28th opened with a strong south-westerly wind and moderate sea but before noon the wind had veered NW. again, increasing in strength until at midnight it was force 9/10. As before, speed was reduced and course altered. As a result of this gale the conditions on the morning of the 29th were the worst encountered on this passage and it was during Observation 15 that the largest amplitudes of roll and pitch were recorded. The wind decreased a little during the day but increased again in the late afternoon to a moderate to
fresh gale which produced a very confused sea. During the last day out from
Belle Isle Straits, the weather conditions gradually improved until by evening the
ship was rolling and pitching easily in a moderate swell. The 31st was spent
running up the St. Lawrence in extremely good weather conditions and some excellent fine-weather data and boundary-layer traverses were obtained.
For the return voyage from Port Alfred to Newcastle upon Tyne, the vessel was fully loaded and on this occasion the weather was mainly following. The weather data for this passage is given in Tables 4(a) and 4(b). The first two days, November 12th and 13th, were _spent in the St. Lawrence in weather
conditions which were again extremely good. During the evening of the 13th
the wind freshened to force 6, increased to a moderate following gale by the 14th, and remained at or above this force until the evening of the 17th, thence to force 5/6 on the 18th. On the 19th, conditions were fairly good at the start of the day, but by mid-afternoon, the wind had increased to force 6 producing a short, moderate sea.
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 121
Observations were taken at random times throughout each day and since the vessel was not deliberately deviated from her course on any occasion for the purpose of taking records, the results represent a good cross-section of the vessel's performance during a heavy-weather winter voyage. The weather encountered was typical of the worst the Atlantic can provide and a number of vessels making the westward passage at the same time were many hours behind
schedule. As stated above, the weather on the eastward passage was following
practically all the time and in this respect was more favourable than is generally
the case. Reference to the Appendix will show that, on the average, the
weather on the eastward passage is evenly divided between ahead, abeam, and astern.
When making observations of the weather conditions it was very noticeable that the state of the sea for a given wind force agreed very closely with the descriptions given in the Beaufort Scale of Sea published in the Admiralty
Manual of Seamanship, 1951. This is a distinct asset to the ship's Officers when
making observations for their weather log. It may be seen from the tables of
weather data, however, that for head winds there is a slight tendency on their part to over-estimate the true wind speed while the reverse is true for following
winds. Exact agreement between the weather data obtained from the ship's
Jog and those of the observers cannot be expected, since the ship's data were those for the watches during which observations were taken, and did not necessarily correspond exactly to those prevailing at the time of the B.S.R.A. observations.
The wave heights for a given wind force were in fairly good agreement with those given by Donn' although on the outward passage the wind changed direction so frequently that the sea rarely had an opportunity to build up to its maximum height for the prevailing wind force. One occasion when the waves were high on the outward passage was the morning of the 29th October (Observa-tion 15) when the wind had been in the NW. for approximately 20 hours.
The highest waves were encountered on the 16th November, during
Observations 33 and 34. Prior to this, the wind had been mainly westerly for
three days, rising during the 15th to gale force. The waves were between
25ft. and 35ft. high for most of the day, with an occasional wave which
probably exceeded 40ft. Caution is advisable in quoting wave heights of this
magnitude, but on several occasions to an observer standing on the bridge when eye level was 41ft. above the still-water level, the horizon was obscured forward and aft when the vessel was lying in a trough between two waves. These waves
were fairly regular and up to 500ft. in length.
Figs. 17 to 22 are photographs of typical sea conditions. A wave of 30ft. or
over, is shown on Fig. 21. The photograph was taken from 33ft. above the
still-water level with the vessel in a trough, the wave shown coming up from
astern. It will be seen that the horizon was obscured by the wave, the true
horizon being just visible near the ship's boat.
Each of these photographs was one of a pair of stereoscopic photographs and when viewed singly it was found that the wave heights did not appear to be as high
as the estimates given in Tables 1(b) and 4(b). This is a general tendency with
two-dimensional photographs, but the agreement between the photographs and the estimated wave height was more apparent when each pair of photographs
was viewed through a stereoscopic viewer. As stated earlier,
it was not
possible to make accurate estimates of wave heights from these photographs but they served a very useful purpose in checking the consistency of estimates from day to day.
where
/1
Ls.h.p.2
(3)
i22 SERVICE-PERFORMANCE TRIALS ON S.S.. CAIRNDHU
5. Analysis of Propulsion Data (Tables 3 and 6)
Unfortunately, an accurate curve of shaft horse-power- against speed for the vessel in calm water was not available, the acceptance trials being carried out
, with the screw emerged. This was offset to a certain extent by the fact that on
both the outward and return passages fine weather was experienced in the St. Lawrence which enabled excellent fine-weather data to be obtained with the hull and the displacement the same as in the open sea. The fine-weather speed for the operating power was also obtained and used as datum for estimating speed losses under various conditions when operating at constant power.
The propulsion data together with their analysis are given in Tables 3 and 6.' When examining Table 3, it should be borne in mind that in Observations 9,
10; 11, and 1-1, speed through the water was measured by means of the Walker log and the speeds were, in consequence, subject to greater errors than the
,speeds obtained from the pitorneter log.
The analysis was carried out by two methods, one using the propeller as a measuring dynamometer, the other uSing the hull performance in terms of the
Admiralty coefficient. The power necessary to maintain the speed recorded
on each observation was measured ; this power was higher than that necessary to maintain the same speed in calm water ; the percentage difference between these powers represented the percentage increase in power under the ci:mditions prevailing at the time of the observation.
To use the propeller to, measure the increase in power necessary to maintain a given speed under given conditions, we compare the power absorption at
given , revolutions .(ko or d.h.p. /N3) and apparent slip under these conditions
.With the power, revolutions, and apparent slip in calm water in the following manner.
Let Y'=
Let suffix 1 relate to calm-weather conditions and suffix 2 relate to any other conditions.
V
Now s.h.p.i/Nia = 1'2 and N, (l
Yi
therefore s.h.p./ = Y Nis Pma (1 sair
Y2 v3
Similarly s.h.p.2 = Y2 N2 3 Pm 8 (1 sa2)
Then for similar speeds,
percentage increase in power = 1
s.h.p.2 Y8 (1 Sal)
s.h.p.2 Yi (1 Sa2)3
The apparent slip was calculated and is given in COL 7, Using the mean measured face Pitch for the propeller; the ratio s.h.p.//0 is given in Col. 19. Substitution of-These two quantities in (3), gives the percentage increase in power
recorded in Col 20. The values of Y1 and sal used in these calculations were
based on fine-weather data obtained in the St Lawrence in deep water. For
the outward passage these were taken as Observations 21, 22, and 23; for the return passage the fine-weather data was obtained from Observations 24, 25, 26 and 27.
.
... : ... (1)
A2/3 V"
AC,
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHIJ 123
Using the second Method, the porforniante of the hull under adverse Conditions was compared with its performance- in calm water by means of the Admiralty coefficient.
2/8V8
Now Admiralty coefficient = s.h.p.
where A = displacement
V ---= ship speed
s.h.p: =- shaft horsepower.
If AC, = Admiralty coefficient in calm water and AC2= Admiralty coefficient in rough water, then for calm water
s1h.p.2
and for rough water
Azis 113
s.h.P.2 = AC2
thus for a given displaceinent and speed
s.h.p.2 AC,
/1C2
In order to estimate the separate effects of wind and sea upon power, the increase in s.Ji.p. due to wind was calculated from B.S.R.A. wind tunnel data
for a similar ship. The effect of wind was related in all cases to the increase or
decrease in power relative to the still-air condition.
For each observation, two Admiralty coefficients were calculated, one the overall coefficient without any correction and the other a Coefficient. calculated on s.h.p. corrected to still-air conditions. the ratio of each of these relative to the calm-water, still.air Admiralty coefficient was calculated, the outward passage being based on Observations 21, 22, and 23 and the return on Observa-tions 24, 25, 26 and 27 as previously.
The ratio of the overall Admiralty coefficient, to that for calm water and still air, gave the combined effect of wind and sea resistance ; the ratio of the still-air Admiralty coefficient to that for calm water and still air gave the effect
of the sea alone. The difference between the two gave the effect of wind alone.
The results of these several operations are given in Cols 16, 17 and 18, It
should be pointed out that the values of s.h.p. were not corrected to a standard sea-water temperature.
As stated earlier, an accurate curve of shaft horse-Power against speed for the vessel in calm water was not available so that the variation in Admiralty coefficient with speed could not be determined. Therefore the Admiralty coefficient was assumed to remain constant with speed, this being inherent in basing the calm-water Admiralty coefficients on certain observations Generally, Admiralty coefficient increases with decrease in speed so that with loss of speed in *ayes, the assumed calm-Water Admiralty coefficient for this speed will be low with a corresponding effect upon the calculated percentage increase in
power. The effect of this will be to underestimate the increases in power by
124 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU
Even with such accurate data as were available from these trials, it was still extremely difficult to say what the powering allowance to maintain a given
service speed should be. In order to decide on this with any degree of accuracy,
it would be necessary to obtain, data over several years under all conditions of
weather. Further, another factor must be considered, namely the increased
roughness of the hull surface with fouling or deterioration of paint surface. This was a factor which could not be taken into account over the short period of the present trials and, when examining the power increases, it should be
borne in mind that they apply to the clean-hull condition only. In order to
shed a little more light on the average performance of the vessel in service, data obtained by the ship's officers during the first year of service has been analysed and discussed in the Appendix.
As far as the present trials are concerned, Figs. 6 and 7 have been prepared to give an overall picture of weather conditions and corresponding power
allowances. According to the ship's personnel, the average wave heights for
wihter in the North Atlantic are between 6ft. and 14ft., approximately, and that it is usual to encounter one or sometimes two whole gales on each passage.
In this respect the present voyage was quite typical. As one might expect,
the strength, direction, and duration of the gales had a considerable influence on the mean power for the passage as may be seen by comparing Figs. 6 and 7. Very much depends also upon the action which the mister deems necessary for the safety of the vessel, for upon this depends the direction of encounter of the vessel to the waves and also whether or not normal power may be maintained.
With the exception of Observation 9, all the records were taken with the
engines running at normal settings. It is considered, therefore, that the
behaviour of the vessel with the approach and decline of the second gale on the outward passage (Observations 12 to 16 inclusive) is more typical of performance in these conditions than Observation 9.
Before deciding upon the average increase in power during the voyage, it
should be remembered that, while the St. Lawrence is navigable,Cairndhuenjoys
the advantage of having approximately 36 hours steaming at normal -.power under what are generally good conditions. Therefore, whatever the perform-ance in the open sea, the overall average for the voyage will be reduced on
account of this. Hence two separate power increases may be considered, one
for the whole voyage, the other for the open Atlantic, which will be more typical of the runs made during the winter to St. John, New Brunswick. The
open-sea conditions may be further divided into four classes : (i) 'where the
waves encountered are between 6ft. and -14ft., and mainly from ahead for the whole passage, (ii) where one gale is encountered from ahead, (iii) where two gales are encountered from ahead, and (iv) where the seas are mainly following. In order to assist in these estimates, the power curves from Figs. 6 and 7 were replotted on a time base (Fig. 8).
For the first condition, reference to Fig. 6 will show that for Observations 4-7, 10-12, and 16-18 the waves were mainly from ahead and between 6ft. and
14ft. The average percentage increase in power for these observations was
36 per cent., the average for U.K. to Belle Isle was 29 per cent., while the average increase in power over the passage was 24 per cent.
If one gale is encountered of an intensity similar to that of the second gale on the outward passage, the average power increase in the open sea is 40 per
cent, while that for the whole passage is 33 per cent. If two gales are
en-countered the power increase will be 50 per cent, in the open Atlantic giving
Note : Belle Isle is an island at the entrance of the St. Lawrence. Father Point is the place in the St. Lawrence where river pilots embark and disembark.
A note on the weather encountered during the first year of service is given in the Appendix.
As will be seen from Figs. 6, 7 and 8 the direction of encounter had a
con-siderable influence on the performance of the ship. To emphasize this point,
Fig. 9 was prepared showing percentage increase in power against wave height
for waves mainly ahead and astern. These percentages represent the effect
of sea alone, being the total percentage increases in power after correcting to
still-air conditions. Owing to insufficient data, it was unfortunately not possible
to make similar estimates for beam seas. The likelihood of running in heavy
beam seas is, however, very small for reasons of safety.
The power increases discussed above were calculated as the percentage increase in power over that necessary to maintain the same speed in calm water. Another way of analysing the data is to estimate the decrease in speed for a given shaft horse-power from the speed at the same power in calm water. The results of this analysis are given in Fig. 10 for an average shaft horse-power
of 4,450. Here again, it will be noted that the loss of speed on the outward
passage, when the weather was mainly from ahead, is much higher than in following seas on the return passage, a point which is brought out very clearly
in Fig. 11. This diagram corresponds to Fig. 9 and shows the percentage
decrease in speed against wave height, the results having been corrected to still-air conditions.
It was considered of interest to study the efficiency of the propeller under heavy-weather conditions and also having reasonably accurate data to establish the efficiency between times of dry-docking.
The method of estimating the propeller efficiency was outlined in an earlier paper before this Institution.' The curves of krIko and efficiency to a base of ka or, for convenience in computation, 1000 d.h.p.IN3 are first obtained from
Troost's data.4 The curves for a Troost propeller of the same pitch ratio,
blade-area ratio and diameter as the ship's propeller are shown in Fig. -12.
The ship values of k7-1kQ are plotted on the diagram. Divergence between
ship results and the Troost curve may be expected due to scale effect, difference
in design and relative rotative efficiency. Despite this, however, the form of
the mean curve through the spots is the same as that for the Troost propeller and approximately one per cent. above it. The scatter of the spots is within
the limits of accuracy of the thrustmeter and torsionmeter. Then, knowing the form of the Troost curve of kTIkp and efficiency, the ship propeller efficiency curve will be of the same form only one per cent. higher.
Sea conditions increase in powerPercentage
U.K.-Belle Isle
Percentage increase in power
U.K.-Father Point
(i) Waves 6ft.-14ft. ahead .. .. 29 24
(ii) As (i) plus one gale .. .. ao 33
(iii) As (i) plus two gales .. 50 42
(iv) Following seas '10 8
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 125
for the whole passage is eight per cent., while that for the open sea is ten per
126 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU
Under adverse weather conditions the value of 1000 d.h.p. /N3 increases, so
that we move from left to right in Fig. 12. It will be seen that at the extreme.
left-hand end of the diagram, where the weather was good, the scatter of spots is quite small, the scatter increasing somewhat as weather conditions deteriorated. It may also be observed that under good conditions the propeller efficiency was approximately 0-67, the efficiency decreasing as weather intensity increased until under the worst conditions, the efficiency was 0-51 approximately.
6. Ship Motions
As may be expected from winds of such variable force and direction as were encountered, a truly regular sea was never observed. A regular wave system
may be produced in the swell remaining after the abatement of a gale. In
the present case, gales followed each other in such quick succession that the swell remaining from one gale was quickly confused by the sea produced from
a different direction by the next The only reasonably regular waves observed
were encountered after the wind had blown from a given direction for about eight hours and the seas were then in the process of building up. In conse-quence, rolling and pitching diagrams of the type that can be constructed from theoretical consideration of the ship's natural period and the period of en-counter were never obtained for more than a few minutes at a time.
The rolling and pitching motions of the ship, details of which are given in Tables 2 and 5, ' divided themselves into the following main classes :
Small oscillations of irregular period and angle. This type was
experienced in waves 3ft. to 4ft. high where the period of encounter was'
low compared with the ship's natural period. The oscillations varied in
frequency between the ship's natural period, and confused pitching
of higher frequency, the amplitude being 2 to 3 deg. It was possible.
under these conditions to obtain the natural periods' fairly accurately, and these are given below :
Natural period of pitch :
Outward 6-1 sec.
Homeward 9 sec. approx.
-Natural period of roll : .
Outward 10-2 sec.
Homeward 12-2 sec.
These natural periods are those for the vessel under way, which are not necessarily the same for the vessel when stopped.
Forced oscillations where the period of oscillation was equal to the period of encounter. This type applied chiefly to pitching motions
since the seas encolintered were generally from ahead or astern. The
nature of the resulting pitching diagram is illustrated in Fig. 5 and was experienced chiefly in the heavy following seas on the homeward passage. The waves in this instance were overtaking the vessel and the pitching
period represented the period of the waves overtaking the shiP. The
rolling in this instance was generally irregular but mostly in the natural period.
Cyclic oscillations where the angles of roll and pitch reach maximum
and minimum values at fairly regular intervals of time. This type of
oscillation occurred when the period of encounter was close to the ship's natural period and was divided into two main classes, one where the period of oscillation in each cycle was equal to the ship's natural period, the other where the ship's natural cycle appeared to be superimposed on
one of three times this period. This latter type was Only encountered
on two occasions, during pitching in Observations 10 and 12. The
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 127
during almost every observation.- As a result, violent rolls were often
encountered (as shown in Fig. 2) which built up rapidly and almost as
quickly died down again. Fig. 3 shows this type of cyclic pitching,
which occurred during Observation 6.
(d) Mixed forced and natural pitching (as illustrated in Fig. 4) which was usually encountered when the seas were fairly confused but where there
Were isolated groups of regular waves. As may be seen from this figure,
when the vessel was in confused water it tended to pitch in its own period, while when it encountered a group of regular waves the pitching
became forced.. It was this type of motion which was encountered most
frequently on both the outward and return passages, although the forced pitching was not generally as pronounced as that in Fig. 4.
The analysis of the rolling and pitching diagrams was necessarily a very complicated matter and in the absence of any really regular wave systems of varying wave lengths and height it is difficult to draw any definite conclusions
as to the behaviour, of the vessel under these conditions. It is also difficult
to draw firm conclusions from the number of observations available. However-,
it may be of interest to state the tendencies in the behaviour of the vessel which confirm the findings of previous observers (References 7 to 11) :
Maximum pitching did not necessarily occur at synchronism.
In regular waves the ship tended to pitch in the period of the waves, i.e. the pitching was entirely forced.
Pitching angle appeared to increase with period of encounter. This
should be qualified by saying that no waves which were long in relation to the ship's length were encountered with the vessel running head into
the waves. In this case the vessel would tend to follow the slope of the
wave and the resulting angle of pitch would depend upon its steepness. This type of pitching did occur, however, in following seas on the return passage, where the apparent length of the waves was long in relation to the ship:
Since the exciting forces are a function of the height of the waves encotmtired, amplitudes of pitch and roll must depend on wave height. Most of the time the vessel rolled in its natural period either at a small regular amplitude as in irregular waves of small height, or in a cyclic manner as illustrated in Fig. 2, or in the irregular fashion shown in Fig. 4. The heaving movements of the ship were not measured and in the complex rolling and pitching motions taking place it was difficult to decide at any instant
exactly how much of the movement was due to heaving alone. It can be said
with certainty, however, that the amplitude of heave was never as high on the
outward passage running into the seas as it was on the return passage. The
damping forces to heaving motion are so high that all the heaving that does
take place is forced heaving. There was no apparent increase in amplitude
at synchronism, which for the outward passage was calculated to be 6.8 sec., for the return 76 sec.
As to the yawing motion, the vessel behaved very well in seas from ahead,
astern, and on the beam. With heavy waves just abaft the bow the vessel
occasionally gave a heavy combined pitch and roll as a wave crest passed the bow, which produced a heavy yawing movement in the direction of the roll. When 'heavy seas were encountered on the quarter, a wave overtaking the stern tended to lift it, again producing a combined pitch and roll and tending to
take the stern with the wave. Here again considerable yawing occurred
although it was noticeable that no water was taken over the stern.
." rillitEblubrieiViWaPVIVaiNIVIM grAnlyffiftitile/Maige
&NM11Pl24, qrclobraqiEd*Cligallaffieliffil9glilld khinf63nrlifithi9118tIti
128 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHLJ
off the bow and the frequency of encounter close to the natural pitching period
of the ship. The waves were fairly regular and slamming appeared to increase
in intensity as the steepness of the waves increased.
Under these conditions, the rolling amplitudes were not particularly high
while the pitching motions were similar to those illustrated in Fig. 3. As shown
in this figure, the pitching motion was cyclical with the pitching amplitudes
reaching maximum or minimum values at fairly regular time intervals. The
build-up in amplitude was produced by wave crests coming on to the bow more or less in phase with the upward movement of the bow, thus increasing the
amplitude of pitch. Owing, however, to the difference in period between the
waves encountered and the pitching period of the ship, there came a time after a few oscillations when instead of the crest of a wave coinciding with the bow when in its upper position, the wave had moved aft along the ship and in its
next downward movement the bow plunged into a wave trough. This produced
the largest pitching angle in the cycle. Now, if the waves were of such steepness
that part of the keel forward was clear of the water, slamming occurred. Attempts were made to photograph the surface of the water in the vicinity of the slam and two such photographs, taken just before Observation 14 was made, are shown in Figs. 23 and 24. From these it will be seen that (a) the bow is in its lowest position, (b) a sheet of water is thrown out more or less horizontally from the point of slamming, and (c) that the slam occurs towards the after end of No. 1 hold, the position where the forward sections become fairly flat in the vicinity
of the keel. Fig. 25 shows the next wave crest coming into the bow.
After the occurrence of a slam, heavy main-hull vibration was produced in the 2-node vertical mode. The frequency was of the order of 95 to 100 c.p.m. and persisted for from 6 to 8 complete cycles.
7. Boundary-Layer Traverses
With the pitometer log installed in the ship, an excellent opportunity pre-sented itself for the measurement of flow in the boundary layer, firstly in order to determine the thickness of the boundary layer, and secondly to study the flow
within the boundary layer itself. Knowledge of the boundary layer
char-acteristics of a vessel can give useful information about the nature of the hull
surface and consequently on the skin-friction resistance of the surface. This
is particularly useful if traverses can be made at intervals between dry docking in order to relate the extent of fouling or deterioration of the hull surface with changes in flow within the boundary layer.
A roughness survey of the hull was made just before the vessel was undocked
prior to the voyage. Roughness measurements were taken on the final coat of
anti-fouling paint using a roughness gauge specially designed by B.S.R.A. for the purpose.
Boundary traverses were made on four occasions during the trials, on departure from and arrival at this country and in the St. Lawrence on the outward and return passages. On each occasion the measurements were made in deep water, with good sea conditions. No attempt was made to make traverses under bad-weather conditions 'owing to the large fluctuations in ship speed which, in the absence of a second log, could not be corrected for. Particular care was taken to ensure that the position of the measuring orifices was accurately
known. Sufficient time was also allowed during each reading to allow the
pitometer log ,to settle down, a condition which could readily be observed from the autographic recorder. In order to determine the probable fluctuation in ship speed, a record of about ten min. duration was taken but in all cases the fluctuation was less than ± 1 per cent.
The resulting mean curve of speed against distance from the hull surface
is shown in Fig. 13 for convenience, the speed at any position is expressed
SERVICE-PERFORMANCE TRIAL'S, ON S.S. CAIRNDHU 129
The generally accepted equation for the velocity in a turbulent boundary layer takes the form
V = Vmax(Y lYmaxr
where V = speed at any pOsition,
= free-stream velocity,
y = distance from surface,
= thickness of boundary layer.
It is usual to assume that y
occurs when V = 0.99 V.
This formula was developed for the flow over plane surfaces, the value of n depending upon the surface roughness, its value for smooth surfaces being
taken as The velocity distribution in the boundary layer may be affected
by the form of the vessel which will in turn affect both the thickness of the
friction belt and the velocity distribution within it. The form of the vessel
introduces a change in distribution of free-stream velocity owing to the con-traction of stream lines close to the hull surface, the effect of which must be added to the velocity distribution obtained from a plane surface in a uniform
stream. The likely effect of this potential wake has been obtained theoretically
by Harvald5 and has made itself apparent in the results of experiments con-ducted recently on a Swedish destroyer.6
In the case of 'Cairndhu, however, there appears to be sufficient parallel body forward of the position of the log to render the potential wake insignificant and, as will be seen from Fig. 13, a good approximation to the form of the velocity-distribution curve is given by the equation
V = Vmax Lvimar123 or V =- V,r (y/y)112-1.
Regarding the thickness of the boundary layer, von Karman, Baker, and Allan have given expressions for this as follows
According to von Kaman
= 0-37 L (-ffy )115
where.. L = distance from forward end (ft.), v = kinematic viscosity,
V = free-stream velocity (ft. per sec.).
This expression gives an estimated boundary-layer thickness of 21in.
According to Baker, y',,, 1.5 --- 0.022 L which gives a value for
the thickness of 19in. As will be seen from Fig. 13, the measured
boundary-layer thickness was 27in. when V/ = 0-99.
The formula y2 ± 4.0 ymax = 0.065 L, given by Allan and Cutla.nd,13
leads to a value for the thickness of the boundary layer of 29 6th. when
= 1-0.
This compares with a thickness of approximately 34th. for the ship.8. Conclusions
Ship Speed
Under very bad conditions, the speed of the vessel fluctuated considerably about the mean speed, the fluctuation amounting at times to ± 12 per cent. The mean speed was at times 25 per cent. below the corresponding still-water speed ; but despite this, as will be seen from the Appendix, the vessel maintained an average speed over the first year of 13/ knots, which compares with a
designed service speed of 13 knots. As may be expected, the speed loss in
following seas is not so high as when the seas are from ahead. This
130 SERVICE4TRFORMANCE. TRIALS ON S.S. CAIRNDHU
Shaft Horse-power
Approximate figures obtained from the power-time diagrams (Fig.. 8) show that on an average, the increase in power necessary to maintain a given speed
from the U.K. to Father Point is of the order of 25 per cent. On the winter
voyage, from the U.K. to St. John, New Brunswick, the increase Will be bettireen 40 per cent. and 50 per cent., depending upon the severity of the weather. These figures are based on the performance in the east-west direction, since
on the homeward passages the weather is usually more favourable. The
marked influence of direetion of encounter.. on increase in shaft horse-power is shown in Fig. 9.
In exarnining the propeller 'efficiency, it will be obserVed from Fig. 12 that as sh.p. /N3 increases under bad-weather conditions, the form of the lcilka curve
can be predicted from methodical-series tests on propellers. 'Thus, although
the propeller efficiency decreases in bad weather, the decrease is no greater than that for a corresponding increase in s.h.p. /Ars (or true slip) for the open-water propeller results, provided that the screw is immersed.
Ship Motions
Before reaching any definite Conclusions with regard to the ship's- Motions, a great deal more data are necessary, obtained with the Vessel running at different directions relative to the waves and with a greater range of wave height. However, the following tentative conclusions may be made :
Maximum pitching does not necessarily occur at sYnchronism.
In regular Nkaves, pitching is entirely forced. .
Pitching angle rappe,ars to increase with period of encounter.
Amplitudes of roll and pitch depend not only upon frequency of en-counter but also upon wave height.
The Vessel rolls mainly in its natural period. The natural periods of the vessel were
Natural period of pitch :
Outward 6.1 sec.
Homeward 9 sec. approx. Natural period of roll :
Outward 10-2 sec.
Homeward 12-2 sec. Boundary-Layer Traverses
The thickness of the boundary layer was 27in. and this did not appear to increase with draught. A very close approximation to the velocity distribution within the boundary layer is given by
V
=
1/84Vm Y max
General
The data obtained will be extremely valuable in establishing methods of
analysing service. performance. For this purpose it is essential that the data.
used shall be as accurate and shall cover as wide a range of conditions of weather and loading as possible. The observers were fortunate in experiencing extreshelyzniiielsvirathermqvinglfrvermnewrly
withairflanybilerftda irestliciiantadto sdmaaritvtio *WS tiOnAllitcalsaighagolgiol
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 131
Acknowledgments
The Authors express their thanks to the Council of the B.S.R.A. for permission to publish this paper.
The Cairn Line of Steamships, Ltd., are thanked for kindly giving permission for the S.S. Cairndhu to be used for these trials. Their willing co-operation and assistance, and the forbearance of the master and ship's officers towards the two representatives of the Association during the voyage, were greatly
appreciated. Thanks are due also to the British Pitometer Co. for kindly
lending the autographic speed recorder, and the Cunard Steamship Co. for the loan of the Sperry Roll and Pitch Recorder.
132 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU APPENDIX
Performance and Weather Data for First Year of Service
In order to shed further light on the question of powering allowances, a brief analysis has been made of the performance data and weather data collected
by the ship's personnel during the first year of service. The data supplied
consisted of mean daily values of power, speed, thrust and r.p.m., mean draught, average wind force and true direction, and state of sea and direction relative to the vessel.
For the present, only s.h.p., r.p.m. and speed have been analysed in such a
'manner that a mean value of Admiralty coefficient may be calculated.
The method used for obtaining the mean values of r.p.m., s.h.p., and speed
was that adopted by Lehmann 12 In this method, use is made of the "net
probability ". This method was used because it is considered to be more
useful than the arithmetic mean for handling service-performance data. In
these data, there are likely to be a few readings, representing very bad days, which
may be far removed from the general scatter of readings. If an arithmetic
mean were taken of all these, the effect of the very bad days would have an influence on the mean out of all proportion to the number of times that they
occur. Resort was therefore made to the net probability.
To use Lehmann's method, the data to be analysed were split up into regular intervals ; for example, if r.p.m. was to be analysed, the range of r.p.m.
would probably be divided into intervals of one r.p.m. Then the number of
times that the revolutions fell within each interval was noted and calculated as a percentage of the total number of observations. Hence the percentage frequency for each interval was obtained. This frequency may then be plotted
to a base of r.p.m. and a frequency-distribution curve obtained. Then, in
effect, the area of this curve was integrated and the value of r.p.m. calculated
which divided the area into two equal parts. This whole process was actually
carried out quite simply in tabular fashion as shown in Table 7 which is that for the r.p.m. on the outward passages. The curve of total percentage frequency against r.p.m. was obtained from the table and plotted on
prob-ability paper as shown in Fig. 14. Then, since this is virtually an integral curve
of the frequency distribution, the intersection of this curve with the base of 50 per cent gives the value of r.p.m. that will halve the area of the
frequency-distribution curve ; this is the most probable mean value of r.p.m.
The analysis was divided into two parts by separating the outward and
return passages. This was done because the homeward passages are nearly
always made loaded while the outward passages are made in a fairly light
condition. In this manner, more accurate mean values of Admiralty coefficient
were obtained and further, these were directly comparable with the present trial values.
The probability curves are shown in Figs. 14 and 15, from which it will be seen that the mean values of r.p.m., s.h.p., and speed are remarkably similar
for each direction. But since these diagrams relate to different mean
displace-ments, the Admiralty coefficients for the two directions are not the same. The fine-weather Admiralty coefficients were assumed to be the same as those pertaining to the present trials, namely 334 for the outward passages, 360 for the homeward passages. This assumption was based on the analysis of the performance on .fine days early in the vessel's career when the performance was found to be almost exactly the same as that under fine-weather conditions during the present trials. It should be pointed out that, under good conditions, the Walker log on board the vessel gave speeds accurate to within 2 per cent., so that estimates of Admiralty coefficient under good conditions from the
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 133
Walker log and pitometer were made in the St. Lawrence over the straight course of 93 miles, along the north side of Anticositi Island, on which,
according to the charts, there were no currents. The actual distance recorded
by the Walker, log was 94-9 miles while that for the pitometer log was 99-6
miles. Assuming the pitometer log to be 6 per cent, high, as determined by
the calibration on the measured mile, the distance travelled through the water was 93-6 miles making the Walker log reading high by less than 2 per cent.
The average Admiralty, coefficient for the outward passages calculated from Fig. 14 was 273, giving an increase in power of 22 per cent while that for the return passages was 328, representing an increase in power of 10 per cent. The agreement between these figures and those given in Table 3 was purely
fortuitous ; it merely indicated that the assumed average conditions were
not far removed from the truth.
A brief analysis of the weather encountered during the first year has also
been made and is shown diagrammatically in Fig. 16. From this it can be seen
that, for the whole year, the wind was force 8 or above on approximately 3i days per voyage, while during the winter this was increased to 6 days. On the homeward passages, the wind was equally divided between ahead, abeam, and astern, while on the outward passages the wind was ahead for half the time and abeam for one-third.
NOMENCLATURE AND SYMBOLS
A2/3 vs
AC Admiralty coefficient
s.h.p. Diameter of propeller (ft.).
d.h.p. Delivered horse-power.
e.h.p. Effective horse-power.
Advance number -, vaIND. Torque coefficient
pN2 D6
kr Thrust coefficient
pN2 D4
N Revolutions per minute.
Pm 'Mean measured effective pitch of propeller.
Torque in shaft (lb. ft.).
QPC Quasi-propulsive coefficient.
101.3 V
Sa Apparent slip = I
-NPnt
s.h.p. Shaft horse-power at torsionmeter.
Thrust of screw.
Thrust-deduction fraction. Ship speed (knots).
Va Speed of advance of propeller.
wt Wake fraction (Taylor).
Displacement (tons salt water).
134 SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU
REFERENCES
CLEMENTS, R. E., "A Method of Analysing Voyage Data." N.E.C.
Inst., 73(1956-57), p. 197.
Cpojc, R "Marine Torsionmeters and Thrustmeters." Inst. Mar.E., 63
(1951), p. 115:
1. Dow, W. L.," Meteorology." McGraw-Hill Book Co., Inc. 1951, p. 134.
twos'', L.,, " Open Water Test Series with Modern Propeller Forms." N.E.0 . Inst., 67 (1950-51), p. 89.
HARvArp, S. A., "Wake of Merchant Ships." Danish Technical Press,
Copenhagen.. 1950.
NORDSTRoM, H. V., "Full-Scale Tests with the Wrangel and Comparative
Model Tests." Swedish State Shipbuilding Experiment Tank.
Pub-lication No. 27. 1953.
NIEDERMAIR, J. C. "Ship Motions." International Conference of Naval
Architects and Marine Engineers. 1951. Trans. Inst. Nay. Archit.,
Lond., 93 (1951), p. 137.
WILLIAMS, A. J. "An Investigation into the Motions of Ships at Sea." Lly.A., 95 (1953), p. 70.
BARrixn, J. L. "The Motion of an Aircraft Carrier at Sea in relation to
the Operation of Naval Aircraft." LN.A., 95 (1953), p. 249.
Kan, J. L,
Experiments on Mercantile Ship Models in Waves." I.N.A., 64 (1922), p. 63.kinqr, J. L., Appropriate Ship Lengths for Minimum Pitching and
Maximum Seaworthiness." LN.A., 76 (1934), p. 85.
LialmAw, G. " Neue Statistische Methoden zUr AusVvertung der
Reiseergebnisse von Seeschiffen." (New Statistical Methods for
Evaluation of Service Results). Schebau, 39 (1938), pp. 221 and 238.
ALLAN, J. F. and CUTLAND, R. S., "Wake Studies of Plane Surfaces." N.E.C., 69 (1952-53), p. 245.
The wind fann and direction from the ship's log is that for the watch clueing which each observationwas taken. Obs'n No. I Date Oct. 1953 Ship's ca'ul., degrees Marin
la.ctl.knots ditccdca.Relative degrees
True wind,
Beaufort Bade duurnionTrue Air
ten4"
811201131171C
ing6.2.173e. n Ship'.log abetBy Ship's
I 24 325 8 130P 5 4 SSE. S. 50 29-84 2 24 269 18 135? 7 5 ESE. S. by E. 51 29-73 3 24 261 26 90? 7 7-8 . SE. S. 53 29-56 4 25 26,7 33 20P ' 5-6 6-7 SW. WSW. 50 29.48 s 26 297 M 90? 6 $--7 SE. S. by E. 52 6 26 255 30 50P 6 S. SSW. ao 2811 7 26 259 38 20P 6 8-9 W. NW. 38 28-69 8 26 315 52 45P 9 9-10 W. by N. NW. ss 28.86 9 27 243 54 45S 10-11 8-9 WNW. NNW. 43 29-24 10 27 195 28 95S 7-8 7-8 NW. WNW. 43 29-34 11 27 235 36 IOS 6 s WSW NW. 38 29-38 12 28 244 40 201. 6-7 6-7 SW. W. by N. 49 29.16 13 28 247 45 20S 7-8 _ 8 W W 44 29-24 14 247 - 53 40S 9 9 WNW. W. 44 29.30 15 29 255 43 IOS 7 6-7 WSW. W. 49 2E1-93 16 29 239 95 ahead 7 WSW. WSW. 47 29-93 17 29 2-31 37 SOP 6-7 7-8 SSW. SSW. 46 29-93 18 SO 246 30 20S 5 3-4 WNW. WNW. 42 29-86 19 30 246 32 10S . SW by W 39 29-79 30 . 246 21 10P 2-3 - 4 SSW. W 38 29-83 21 91 227 9 SOP 4 1-2 ENE. E 32 30-24, 2-2 31 235 14 15? ' 3-4 - E ESE. 35 30-22 23 31 248 17 70P 5 3-4 SE. ESE. 37 3015
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 135
1-36 SERVICE-PERFORMANCE TRIALS ON 5.3. CAIRNDFth
TABLE 1 (b)Weather Data : Grangemouth-Montreal, Sea Conditions
M Mtodinum height ' A - Average height. Oben No.
d=
shio's Wave Remarkssr.
by% °Frequency see oipuiat, degrees Sea 1 325 3 M 2A Astern53 Slight ace and swell
2 269 4M
3A 100 Astern ' 53
Slight sea and swell
231 . 3 A Confused sea 110 P " 53 Slight sea and swell
287 15 M
10 A
370-400 9-0
.
20 P 53 Rough sea and heavy swell
5 ' 267 10 M
8 A 88 approx.
70 P 53 Rough confused sea and swell. Cross
swells making sea yeti, confused
255 12 M
10 A
-380-420 8.8 40 P 51 Rough seas and heavy swelL Waves
fairly regular, white foam on surface
7 259 15 M
12 A
76 40P 51 High sea, heavy swell. Fairly regular
waves, extensive white foam
8 315 18 M
15 A Confused sea
40 P 49 High sea; heavy swell. Crests of waves
rolling, white foam everywhere
9 243 26 M
20 A Confused
8-0 approx. 45 P 47 ..Rough sea, heavy swell, tops blown off waves, foam on surface
10
-195 15 M
12 A Confused 126 approx.
100 S 46 Rough sea, heavy swell, sea very
confused ; white crests on wives,
much foam
ii 235 9 M
7 A Confused
12.0 approx. 90S 47 Rough sea, heavy confused swell follow-jog gales
12 244 7 M
4 A 300
6.0 20 P 44 Rough sea, moderate swell. Extensive
white tops to waves
13 247 is M
12A 350 6-5 20 S
45 High sea, heavy swell, waves very
regular
14 247 25 M
20A 350 6-5 20 S
- 44 High sea, heavy swell, fairly regular
waves
15 -155 30 M
25 A 460
6.8 20 S 42 High, steep, very rough sea and very
heavy swell, white tops everywhere, extensive foam
-18 239 15M
12 A 350
6.7 20 S 40 Rough sea, moderate to heavy swell,
waves fairly regular
17
.
11 -M
7 A Confused sm.
20 P 42 Moderate to heavy sea and swell. NW.
swell, SW..sea
18 248 8 M
5A 150-200 6-7
40 S . 45 Moderate sea and swell
19 8M
4A 150-200 74 505
44 Moderate sea and swell
20 246 3 A 100 86 40 S 43 Moderate to slight sea and swell
21 727 16-1-5 Choppy surface 35 Slight sea
--22 235 1-0-1-5 Choppy surface 39 Slight sea '
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 137
TABLE 2Ship Motions : Grangemouth-Montreal
The mks for pitch and roll given above are of double amplitude, In degrees. Oben
No.
Piteh Roll
Remarlo Pedal,
see Meaneagle Mashotimangle Period,see Mess.angle Maximumangle
1 6-1 1 2 10-3 1 2 Vessel steady
2 s I 10.5 2 3 Movement hardly discernible
3 6-5 2 2 100 2 3 Very litde movement
4 6-8 4 12 98 11 26 Rolling and pitching heavily ; shipping a
little water
S 6-6 3 7 10-5 5 10 Moderate to heavy rolling and pitching ;
shipping spay
6 6-5 4 8 10-2 5 12 Moderate to heavy rolling and pitching ;
shipping heavy spiny
7 64 4 8 94 s 12 Moderate to heavy rolling and pitching ;
shipping heavy Will
s 64 5 12 9-8 7 18 Rolling and pitching heavily ; bridge swept
by heavy spray
9 7-8 5 Is ' 104 16 38 Rolling and pitching heavily ; rolling
violently at times. Shipping seas overall
10 6.3-184 5 12 10-2 12 23 Rolling and pitching heavily ; occasional
very heavy rolls. Shipping seas overall
11 7-2 4 8 100 12 23 Rolling and pitching heavily ; occasional
very heavy rolls. Shipping seas overall
12 62-15-5 2 3 104 4 10 Rolling and pitching moderately
13 6-3 4 8 10-8 5 10 Moderate rolling, moderate to heavy
pitch-ing. Slamming occasionally
14 64 5 10 9-9 5 9 Moderate rolling, moderate to heavy
pitch-ing. Occasional .slamming
15 7-0 6 14 10-5 16 50 Rolling and pitching very heavily, violent
rolling at times ; shipping spray forward
16 64 4 10 104 19 95 Rolling and pitching very heavily, at times
violently
17 64 3 10 10.7 16 32 Rolling and pitching very heavily, occasional
violent rolls
18 6.8 3 s 10-7 11 19 Moderate to heavy rolling and pitching
19 6-7 3 6 10-1 9 18 Moderate to heavy rolling and pitching
20 67 4 4 10-3 6 15 Moderate rolling and pitching
21 0 0 0 1 Vessel very steady
22 o 1 o 1 Vessel very steady
TABLE 3-Propulsion Data:' Grangemouth-Montreal
Notes
CoL 4. Thin J is propeller thriist, Le, thrust at, thrustblOck corrected for the
'
axial componen of weight of shafting, Propeller, eta.
Col. 7. Apparent slip is calculated using mean measured pitch of 15.51 ft. Col. 8. Calculated assuming tlirtiNf-dedUctiori fraction of 022. Col. 9. dhp-=0-97 shp
Col. 12. Calculated from B.S.R.A. wind resistance data.
.
COL 13.
CoL 12 +.0.97 (CoL 10).
Col. 14. = Col. 1 - CoL 13. Oals.16, 17, 18. Calculated from mien water, still ale ahp'S of Observations
21, 22 and 23. 1:141.° . ogt, lima I ,hp )k 2
p..
eee 5 sr"'d . 4 , Ttn"" . Displace- wan, UM 8Sea tern- pas- V,
7
'App.,- ens .hp,' cant
, 8 . (I 10 ehr, qP' - dh9 II Admiralty A .Crt. 12. md ehl' IS wk., nh9 14 81111,- shp IS 80117 AC 18 Percent-age In power 17 Percent-age
irreese age°7 sea dace
18
Percent-age
Lncresse dg:t7 wind slow
18
igag.hp
20
Percent- kge,.. b' Pc.'" proitl...
N' 1 24 08.54 4422-92.5 14-7 41-0 10,610 53 ' -3-9' '3243 4289 0-756 344 -79 108. 4530 337 -1 -2 5-58 -1 2 24 13.19' .4405 92.4 - 14-8 40-6 10,600 53 -41 3236 4273 j 0.757 351 -122 -157 : 4672 338, -2 -3 5-59 -5 3 24 16-48 4319 . 91.6 141 414 10,800 53 -01 31201 4248 ' 0134 313 -27 -39 :4418 310 6 7 -1 510 ' 4 25 08-59 1363' 89-4 12-9 4343 10,580 53 81 3013 j 4231 0-712 339, ' 4023 255 42 31 ' 11 ' 8-10 46 5 25 1719 4447 911 137 42.1 10,570 53 21. 3088 4314 ! 0116 276 -38 -52 4499 273 21 22 -1 5-36 24 6 26 09-20 '4531 891 12.6 45-9 - 10,550 -51 '8.0 3098' 4395 0104 211 153 - 224 : 4307 222 58 50 8 6.40 82 7 26 13-48 4380 88.8_ 1243 44.1 '10,540 51 71 2976j 4249 0-700 218 320 472 -3908 243 53 ' .36 ' 17 6-26 57 8 26 16.46 4427! 851 11-8 18.1 10,530 49 101 3036 I 4294 0.707 177 559 815 3612 217 88 35 717 93 , 9 27 0947 1828: e3-5' 7.8, 29.0 10-510 47 20,4 1204 1773 0-680 122, 420 637 ' 1191 187 ' 172 -78 94-714 181 10 27 13-44 44247 .; .88.3 131 42.9 10510 46 .21 3048 4120 0140 264 -31 -43 .4240 282 . 26 27 , -1 : 848 30 11 27 17.14 4050 86-7 ' 13-0 42-8 10,500 47 2-2 2984 3929 0-759 260 261 355 3695 285 28 17 ' it i 1312 31 12 28 ' 09-57 4423 j, 91-3 13-2 43-7 10,480 44 ' 5-8 3097 : 4290 0-722 ' 249 362 517 3906 _282 33 18 16 -512 39 ' 13 28 '14,19 4432 , 86-6 11-6 47-5 10,480 45 1243 .2949 j 4299 0186 168 426 .640-3792 196 98 69 29 6,83 104 14 28 , 1519 4260 -841 101 481 10470 14 16-2 28371 4132 0187 145 605 909j 3351 185 128 80 ' 48 ' Zol 136 15 ' 29 09-44 4315 ., 88-2 114 45.8 10,450 42 13-9, .2796 j 4186 0168 163 354 547 3788 187 78 25 6.73 109 16 29 13.23 4448 , 88-8' 13-0 45-2 10,440 40 . 4-7 ' .3147 4315 029 234 .302 428 4020 259 42 25 14 6.23 42 17-29 16.40 4537 901 13.1 . 44-3 10,440 42 5-8 3109 4401 0-706 235' 360 52. 4011266 41 25 -16 , 6413 41 18 30 09-34 4507 1 90-4 '13.9 44-2 10,420. 45 0 3286, 4372, 0-752 282 191 2132J 4245 300 18 11 7 6-11 20 19 30 13.57 4452 90-2 131 121 10,410 44 -01 3159 ' 4318; 0.732 286 199 280; 4172 305 16 9 7 617 19 20 . SO 16-48 4430 91-5 14.1: 41-9 10,410 43 -0-2 3160 4297 0.735 299 55 77 ' 4353 305 11 9 2 , 518 13 21 31 1124 4550 934 141 -42-1 10,380 35 -2-3 3307 4414 0,749 333 -59 -69 4619 321 1 3 . -2 . 518 2 22 31 14-01 4450 924 14-8 414 10,380 '39 --44 3274 4917 0-758 343 -14 -20 j 4470- 941 -3 ' 2 -I ' 615 -2 23 31 15.58 4362 92-4 1443 40.5 10,360 41--2.7 3185 4291 0149 338 -28-394401 334 -1 0 -1 : 5-53 0
SERVICE-PERFORMANCE TRIALS ON S.S. CAIRNDHU 139
TABLE 4 (a)Weather Data : Port Alfred-Newcastle upon Tyne, Wind
The wind force and direction from the ship's log is that for the watch during which each observation was taken.
True wind,_ True
Obn Dare Ship's Relative Relative Beaufort scale direction Air Barometric No. Nov. 053 ::T.4purt% 1=. direction, 027-, pressure,
nip's By ShIP's
ollin log *ben
24 12 63 16 Ahead 1 0 1-2 ENE. Various ' 35 30-33
12 90 6 45S 4 1-2 WSW. Various 35 30.33 26 12 90 6 73S 4 1-2 WSW. Various 30-33 27 13 , W. NW. 29 30-15 13 64 11 166P . 6 , 4 WSW. . W. 30 3003 14 57 94i, 7 5-6 WNW. NW. by W. 30 29-68 -30 15 63 21 115P 7 4 W. by N. WNW. 32 2933 31 15 70 29 I26P 8 6-7 tTisitf. WNW.- 34 2942 32 15 70 31 140P 9 6-7 W. by N. WNW. 32 29.33 33 16 70 25 Astern 8 7-8 WS*. *. 39 29.83 _ 34 16 7-8 7-8 WSW. W. 40 29-83 35 1 16 80 18 144S 7 7 WSW. WS*. 30 29.83 36 17 . 85 15 1258 6-7 6 WSW. WSW. 45 29.80 37 17 87 17 134S 7 6 WSW. SW. . 45 _ 29-83. 38 18 87 13 175S 6 5 W W. . 49 30.00 39 18 84 10 131P - W. by N. W. 49 30.03 40 18 84 8 113P 5 5 WNW. W. 49 30.09 41 v 18 84 10 126P 5 W. by N. W. . 49 30.09 42 19 144 20 20S 3 _ _ 2. , SSW. S. 48 30.15- -43 19 176 25 30S 4 4 SW. SW. 53 30.15 44 19 175 33 45S 6 4-5 WSW. SW. 53 30.12
