Collision risk estimates in the english channel and western approaches

AR11F

NMD

National Maritime Institute

Collision Risk Estimates in the

English Channel and Western Approaches

by

M J Barratt

Supported by the Department of Energy

through the Offshore Technology Board

OT-R- 8144

NMI R115

August 1981

National Maritime Institute

Feitham

Middlesex TW14 OLQ

Tel: 01-977 0933 Telex:263118

Lab. v.

Scheepsbouwkun

Technische Hogeschoot

Deift

- Crown Copyright 1981 OT_R_81Li+

This report is Crown Copyright but may be freely reproduced for all purposes other than advertising providing the source is acknowledged.

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National Maritime Institute

Collision Risk Estimates in the English Channel and Western Approaches

by M J Barratt

SUMMARY

This study estimates the risk of collisions with fixed structures by passing vessels, for the British Sector of the English Channel and Western Approaches. Marine traffic data was obtained from shipping surveys, radar records and reported ships' positions, to build up the distribution of traffic between

the Greenwich Meridian and 9 deg. W. Together with information on visibility, the traffic flow rates were then compared with that in the Forties field of the North Sea, to give the relative risk of collision compared with that location.

In addition, estimates of the absolute risk of collision were made, based on safety zone infringements and analogies with ship/ship and ship/light vessel collisions.

The risk of collision with fixed structures for the study areas was found to cover a wide range, being comparable with the North Sea in the far Western Approaches, but approaching 40 times greater to the south east of the Isle of Wight.

This work was commissioned by the Department of Energy Offshore Energy

Technology Board, under Project OT-F609

NNI Report R115 August 1981

COLLISION RISK ESTIMATES IN ENGLISH CHANNL AN CONTENTS

INTRODUCTION DATA SOURCES

Previous Survé

Voluntary Observer Ships Aerial. Radar photographs Isle of Wight Radar Survey

North/South Traffic in the Western Approaches Fishing Vessels

The Forties Field

Visibility

-T'pes of Vessels ANALYSIS

Correlation of traffic data Comparative R±sk prediction LigIt Vessel Analogy

Safety Zone Irifringetherits

Ship-ship c1]4sioris DISCUSSION AND CONCLUSIONS

ACKNOWLEDGEMENT REFERENCES WESTERN APPROACiES :' 1 2 2 2 2 3 3 5 6 6 7 7 7 8 9 10 :1 1

INTRODUCTION

It was required to' evaluate the risk of' cpllisions with fixed structures

by passing vessels, for the English Channel and Western Approaches,

between 0 and 9 degs west, and north of the median line between the UK. and France (fig 1) The risk was to be estimated mainly in comparative terms, ie in relation to the risk for an existing oil field, rather than absolutely Methods to be used had been developed in previous studies for the Post Office and the Department of Energy (refs.1,2).

The major part of the study therefore consists of obtaining, reliable estimates of marine traffic over the entire region, to be compared with

the known traffic from the Forties field, which was measured during

a

previous NM1 survey (ref.

3).

Allowances are, also made for the incidence of redUced visibility, and comparisons are made With the probability of collision predicted for the Forties field

DATA SOURCES

The difficulty in obtaining suitable traffic data for this study was

that although traffic surveys had been performed in the English Channel, (refs ,5),.the region beyond Land's End-was not well covered, and the

traffic was expected to be very sparse over much of the region of'

interest-. It has therefore been necessary to place considerable reliance

on the geographical distribution of reports from ships on passage

reporting weather conditions to the Meteorological Office, calibrated by

known traffic flows These have been further supplemented by radar

observations made by the RAF during training flights.

Previous Surveys

Fig 2 is taken from ref , and shows the coverage of marine traffic

in the English Channel achieved during the 1977 Anglà French. survey, which has been the most extensivéto date. Attention was mainly 'focuSsed on the - regions expected to have traffic concentrations, and in

particular the traffic separation schemes Regions near the Anglo French

median line and between the traffic schemes were less well covered.

- To some extent the gaps. have been filled in by the mid-channel survey

of.1979, and the two surveys are used to calibrate the more extensive voluntary observer Ship data..

Voluntary, Observer Ships

A proportion of the world's merchant ships report weather conditions

to meteorological organisations on a voluntary basis, and the

meteorological office has gathered an archive of these observations. The geographical distribution of the reports may be expected to be a guide

to the distribution of shipping density, but clearly some caution is

needed regarding the randomness of' the sample, which must be calibrated by survey data.

The proportion of vessels participating in the scheme is quite large, exceeding 10% for northern European countries, but most of them report far less frequently than the standard 6-hOur interval as is shown later in the report. Fig. 3 shows the distribution of reports over the region of interest, divided into 1/10 deg. rectangles. it can be seen that the density decreases, steadily towards the west and away from land.

The area to the south and east of the Isle of Wight has a heavy

concentration of traffic, and a special survey of it has therefore been made as part of this work.

Aerial Radar Photographs

A direct check on the distribution of shipping density has been obtained from photographs of radar taken by the RAF during training

flights. By arrangement it was possible to route several flights over the region needed for this study. RAF personnel plotted the positions of' vessels observed on charts, and these were used to obtain the density

distribution shown in fig. i4 The numbers of observations are of course

small, particularly in the Western Approaches, but they give a valuable' overall check on the voluntary observer ship data. For comparisOn, the

fig. 5, taken from ref. 5.

Isle of Wight Radar Survey

Because of' the dense traffic revealed by the VOS data near the Isle of Wight, and because poor visibility was known to increase up Channel,

it was decided to perform a brief radar survey of the region, within the

original cost estimates for the study A mobile radar station was set up

by ASWE at Ventnor, by courtesy. of the Civil Aviation Authority.

(Fig 6) The area of sea covered is shown in fig 7, with a radius of

approximately 32 miles from the station. Although returns were obtained from greater distances, these were beyond the horizon, and so would have excluded the smaller vessels.

The radar was run for a period of 1L days, during which time-lapse

photographs were taken of the two radar screens., offset to south-east and south-west. The photographs were taken at one frame per minute and

replayed at a few frames per second for analysis.

The numbers of vessels were counted which passed through a gate drawn

due south from the radar station at Ventnor and subdivided at 6-mile

intervals The flow distribution thus obtained is shown in fig 8, with

west- and east-bound traffic presented separately The flows are remarkably well-defined, with the traffic bet.ièen the Casquets and the Dover strait concentrated into narrow bands, and east- and west-bound

vessels well separated This point is considered further in the analysis

section.

The site chosen for the experiment was in a position to give the best

Ooverage of the concentrated traffic region, with less extensive

coverage to the west of the Isle of Wight. A check was therefore made on

traffic in this area by analysing a one month sample of movements at

Poole Harbour, which was thought likely to contribute some local

traffic. However, the numbers were small, consisting chiefly of 2 ro-ro vessels per day in each direction between Poole and Cherburg.

North/South Traffic in the Western Approaches

A notable feature of the VOS reports was an apparent concentration of' vessels travelling north and south. in the Western Approaches, at

approximately 7 deg west It was surmised that this could be due to

those vessels on voyages between the Irish Sea and the Mediterranean or the southern hemisphere,.and passing close to the Scillies. and the coast

of' Spain. . . ..

To check. on. the numbers of such vessels, Lloyd's Intelligence was asked to supply details of vessels on voyages between Irish Sea ports and locations which.would involve crossing the Western Approaches, over

a period of .one month. These are summarised in table 1, which shows a

meantraffic flow of 15 vessels/day, and a mean tonnage of 9800 dwt. The. great majority of ships were categorised as general cargo, of less than

5000 tonnes dwt. All the vessels over 0,O00 dwt were tankers, including

7 .i the range 150,000 350,000 dwt, over the one month period.

Assuming ,the mean traffic flow of 15 vessels/day was concentrated. in a band of approximately 6 miles width, would give 2 5 vessels per thile day

corresponding to an additional

2.7

reports per year for each 1/10 de.

rectangle using the calibration of fig 15 By inspection in fig 3, it can be seen that this accounts for the . bulk of the apparent north/south

,traffic stream.

Fishing Vessels

Enquiries were made at MAFF on the distribution of' sightings Of

fishing vessels This information was available for foreign vessels

only, but these were believed to comprise the great majority of offshore vessels in the English Chàhnel and Western Approaches.

Fig. 9 showe the numbers of' individual vessels sighted in each

1/k

deg. by

1/2

deg. rectangle over a one month period. While this can not be translated into traffic flows or densities, it does indicate a widely

distributed fishing activity over the Western Approaches There is a

tendency for the sightings to be in the northern half of the British part Of the Western Approaches, i.e. away from the median line with France. It would be. wrong however to draw any detailed conclusions, as

fishing patterns change both seasonally and from year to year with

changing fish stocks.

The Forties Field

The estimati9n of collision risk in absolute terms is inherently

unreliable because to date very few collisions have occurred between

offshore structures and passing traffic (ref. 2). It was therefore

decided to make the main risk estimate in comparative terms, using as the yardstick an existing oil production 'region. The Forties' field has been chosen, 'mainly bacause the traffic there is well known - as the

result of the previous NMI survey (ref. 3) Th& general traffic pattern

in the region is shown in fig. 10, and the distribution of vessels

withinlO miles of the platf'ors in fig. 11. The mean traffic flow in the region, in the absence of avoidance action, has been ca.culated as

231 ships/ 2x10 n.m. x 30 days .:39 vessels/milé.day.

-Visibility ' . .

The visibility at a given location -is known to be an important factor

influencing the numbers of collisions between ships. A fog collision

risk index (FCRI) has been devised (ref.

6),

whose value is calculated

to be proportional to the probability of collision in a given region.

DWT (l000s) Type riot known < 5 Table 1 5- 10-10 15

-k-15- 20-20 kO kO-80

80-150

150-350 >

30

Total Tanker 3 27 8 8 2 15 1 2 7 0 73 :Bulker .0 0 0 1 3 6 0 0 0 0 - 10 Container 1 1k 2 2 3 k 0 0 0 0 27 General 7 268 39 27 i k 0 . 0 0 0 357 Total 11 309 k9 38 20 29 1 _{2 7} 0 k66 Tonnage - 6kk ₃₅₉ k75 ₃₃₀ 763 50 18 1749 0 k5.59

5

We define FCRI = 1667v1 + 100v2 + 5v3

where vi = time with visual range below 200m.

v2 = between 200m. & LIkm.

v3 = more than Z km.

(the times being expressed as fractions of the total).

Fig. 12 shows the distribution of this index in the English Channel and

Western Approaches, calculated from voluntary observer ship data,

supplemented by three fixed stations (Royal Sovereign, Channel Light

Vessel and Seven Stones).

For comparison, the value for the Forties field is also given. It can

be seen that the worst visibility, at the eastern end of the region,

approximates to that at the Forties field, but that the visibility

improves steadily with distance to the west. The fixed stations give

consistently better visibility than the ship observations, and are

probably more reliable. However, the FCRI for the Forties field was

calculated from VOS data, so for comparative purposes the latter are to be used.

Types of Vessels

As a guide to the types of vessels in the region, fig. 13 gives some

representative data from the 1977 Channel survey (ref.

U.

The Isle of

Wight - Cherbourg area was chosen because it gave a large and fairly

typical sample, and also because the area was of particular interest in the present study.

The largest number of vessels was British registered, with a preponderance of dry cargo vessels. A wide spread of vessel sizes was observed, with the majority in the smallest categories.

-6

ANALYSIS

Correlation of traffic data

Of the three primary data sources, the reports from voluntary

observer ships were the most extensive, and it was therefore decided to use them as the framework for the traffic pattern, calibrated by the shipping survey data, and checked against the aerial radar results.

Fig. 114 shows the numbers of VOS ship reports plotted against the

numbers of ships observed by aerial radar, for this study and in 1979. Because of the small size of the radar sample only a coarse division was meaningful, into regions covering 1 deg. of longitude between the

latitude boundaries of data. A reasonably close correlation was

obtained, but with a tendency for the VOS reports to be relatively

greater than the aerial observations at the lowest densities. Two

possible reasons may be advanced - the very small size of the sample of aerial observations in the furthest Western Approaches, and a possible tendency of the observing ships to report more frequently in regions where there is least traffic.

Fig. 15 calibrates the VOS data by plotting the mean densities of reports against the mean traffic flow rates through a number of 'gates' used in the 1977 and 1979 traffic surveys. The agreement is reasonably good, using data from the Lizard, Start Point, Portland Bill and the region between the Isle of Wight and Cherbourg. It is also possible to

make a check on the number of voluntary observer ships actually

reporting in this region.

A traffic flow of 5 vessels/mile.day would give approximately 500

reports/year in a 1/10 deg. rectangle, if composed entirely of vessels with mean speed 114 kts., reporting every 6 hours. The corresponding rate

of reporting is in fact 5/year, indicating that about 1% of the vessels

report every 6 hours. This compares with approximately 10% of the total fleet in the reporting scheme.

The region south of the Isle of Wight is examined in more detail in

fig. 16. The VOS data for this area has been calibrated using the

previous fig. 15, and the resultant omnidirectional flow density Is

plotted against distance south of the radar station. This is compared

with the distribution of east- and west-bound flows from the radar

observations. Although the mean traffic flows agree well, at approximately 7 vessels/mile.day, it can be seen that the peaks of the

distributions are displaced. The difference is consistent with the

west-bound traffic having been displaced to the north between the period of the VOS observations and the radar survey, ie between 1977 and 1981.

The traffic pattern in the mid-channel is known to have been modified

after the Amoco Cadiz stranding, by the alterations to the traffic

separation schemes at Oussant and the Casquets to route large oil

carriers well away from the French coast, (ref. 5) and it is reasonable

to assume that the west-bound traffic is now taking a more northerly

course, to link up with the Casquets routeing scheme (fig.17). This

figure also shows in more detail the distribution of traffic flow

density south of the Isle of Wight measured during the survey, and

confirms the hypothesis that the traffic has been diverted north, on a

line between the Dover and Casquets routeing schemes.

The voluntary Observer Ship data of fig. 3 was used for the final

traffic estimate, in conjunction with the calibration of fig. 15, and

7

Wight. On this basis Fig. 18 gives smoothed contours of traffic flow

density (vessels/mile day) Three main traffic density zones may be

distinquished within British waters.

The main through traffic between Northern Europe and the South, with

flow density > 8 ships/mile.day, which is close to the Channel centre

lIne up to k deg.W.. Joining this is the crossing traffic south of the Isle of Wight.

Ships crossing the North Atlantic, passing south of the Lizard, and north-south traffic across the Western Approaches. The traffic density here is rather lower, generally in the range 6-8 ships/mile.dày.

More diffuse traffic between these 'and other regions, particularly

south of Lyme Bay,and also spreading into the North Atlantic and the

Irish Sea, with flow density -6 ships/mile.day.

This is of course a simplified picture of the traffic, bearing in

mind that the traffic distribution may change. It can be seen by

comparison with fig 1 that the areas of heavy traffic do not coincide

with the blocks under licence or on offer except in the region of the Isle of Wight.

Comparative. Risk prediction

The primary mode of risk prediction is comparison with 'the Forties field. Since the collision risk is. proportional to the product.of the traffic flow density and the FCRI,we have

relative risk flow density x FCRI /.39 x 25

Then the relative risk of collision is obtained, for the regions closest to the southern boundary of the British zone as in table 2, in, the final

section of the report Compared with the Forties field, the risk in the

English channel is greater by a factor of up to approximately LW,

reducing to a similar risk in the far Western Approaches.

Light Vessel Analogy

An absOlute value for the risk of collision can be found by analogy with light vessel collisions (refs. 1,3). A group of light"vessels in the Dover Strait and southern North Sea was used to obtain a

relationship between traffic flow rate and collision rate Over a period

of 11 years, L$ collisions occurred between ships and the N Goodwin, E

Goodwin., S Goodwin, W Hinder and Sunk Light Vessels - a mean collision.

rate of .073/year. The mean traffic flow rate 'within 1, mile of these

vessels was estimated from radar and direct observations to, be 21.

vessels/mi].e.day. The mean FCRI for the area was 27.4L Then the expected

collision rates for the English Channel and Western Approaches are

obtained as

collision rate '= flow rate x FCRI x .073 / 21.,Lt x 27.1k (See table 2)

Safety Zone Infringements

An alternative way of estimating collision risk is based upon numbers of safety zone infringements observed for . existing platforms.. The assumption is made that these rare events for passing traffic correspond to gross failures of navigation, and hence position within safety zones approaches a random distribution. Therefore

number of colliSiohs = number of inftingements x (rig+ship)dimension safety zone dimension

information supplied by the Dept. of Energy shows that during the

years 1976-80,. there have been 27 safety zone infringements at gas

platforms and 8 at oil platforms, by passing vessels During this period

there was an average of 14L gas platforms and 21 oil platforms in the

British Zone of the North Sea. Taking the significant dimensions of oil rigs,.gas rigsand vessels as.70, 30 and 10 metres respectively, with a 500 m. safety zone., the. expected risks of collision per platform are

therêfore . . . . .

Gas fields -.0.005 .1 year

Oil fields . 0.006 / year

Taking the Forties Field as a typical oil location, we can multiply

the latter risk by the relative 'risks for the English Channel and

Western Approaches, to obtain the estimates in table 2.

Ship-ship collisions

The.numbers, of collisions bètwèen ships can be used. as a guide to the number of' collisions with fixed structures if it is assumed that ships

are no more likely to strike a fixed object than another vessel Taking

the effect of a fixed structure as equivalent to an extra vessel within a given area, we can calculate the incremental effect of an extra vessel onthe.number of collisions.

It is generally assumed that the number of collisions between vessels is proportional to the number of encounters between vessels in a given

area Hence the number of collisions is proportional to the square of'

the number of vessels in the area, i.e

c.kn2

dcldn ?kn = 2cm

That is ,. the number of collisions per extra vessel or structure is twiàe the mean nümbér of collisions per vessel.

For the 1.0 years 1970-9, the N14I databank has 20 collisions recorded

in British waters of the Channel, between 0.-7deg W The mean number of

vessels in., the area, has been fOund from the. aerial surveys to be 10. Hence the mean yearly risk due to a structure or another vessel in the

area is .,

2 x 20' /(10 x.1'110)...= 0.029

From the flow rates and FCRI's previously obtained, we have mean traffic flow rate = 7 ships / mile.day

mean FCRI 2

The distribution of risk is then obtained as before in table 2.

Although the nuthber of vessels involved. in collisions was a small sample of' the total traffic, it is interesting to note that their

composition by size and type was not greatly different to that for the

mid-channel region shown in figure 13 However, they did include a

higher proportion of vessels below 500 grt (32% compared with 19%), and a higher proportion of fishing vessels (18% compared wi,th 8%).

-9

DISCUSSION AND CONCLUSIONS

Three methods have been used to make estimates of the risk of a

passing vessel colliQing with a fixed structure, _{in addition to the}

basic comparison with an existing structure.

Of these, two are based on numbers of collisions, but with moored

light vessels and other moving vessels. The third, while based on fixed

structures, uses the number of safety zone infringements, because of the lack of collision statistics for passing vessels.

It is interesting to note that the methods based on collisions are in fairly good agreement, while that based on safety zone infringements gives estimates which are several times higher. The latter may well be

in error, because of the basic assumption that the vessels passing

through the zone do so in a random manner. The collision- based estimates must carry the greater weight, although they do not refer to the correct type of target.

The following general conclusions are drawn from the study.

The English Channel and Western Approaches is a more dangerous

region for collision risk than the oil fields of the North Sea, the

relative risk approaching a factor of 140 _{to the east of the Isle of}

Wight, down to values comparible with the North Sea in the far Western Approaches.

While the available methods for absolute risk prediction are based upon analogy, and hence somewhat speculative, a probability of collision

of the order 0.1 is to be expected to the east of the Isle of Wight,

down to the order 0.01 in the Western Approaches.

Area Traffic flow

(degs.W) (/mile.day)

Table 2

Absolute risk estimates FCRI Relative L V Safety zone ship-ship

risk analogy infringements collisions

O - 1 15 25 38 .0147 .23 .065 1 - 2 12 25 _{31 .037 .19 .052} 2 - 3 8 25 21 .025 .13 .035 3 - 14 6 ₂₃ 114 _{.017 .085 .02k} 14 _{- 5} 14 22 ₉ .011 _{.055 .015} 5 - 6 2 21 14.3 .0052 .026 .0072 6 - 7 2 18 _3.7 .00145 _.023 .0062 7 - 8 6(locally) 16 10 .012 .061 .017 8 - 9 2 14 2.9 .0035 .018 .00148

10

-ACKNOWLEDGEMENTS

The National Maritime Institute gratefully acknowledges the cooperation

and assistance of the organisations which have contributed to this

study. These were Department of Energy Meteorological Office Royal Air Force

Admiralty Surface Weapons Establishment Civil Aviation Authority

Lloyd's Intelligence

Ministry of' Agriculture Fisheries and Food Poole Harbour Authority

Of the NMI staff involved, particular mention is due to Mr S C Dare, for liasori with the RAF and analysis of the airborne radar results, and Dr G R G Lewison for general advice.

The work was funded by the Department of Energy through the Offshore Energy Technology Board. The Project Officer was Mr A D Read, Petroleum Engineering Division.

11

REFERENCES

"Further evaluation of the risk of collision to sea platforms by ships in the southern Nortk Sea", NMI P1401003

"The risk of Ship/platform encounters in UK waters" NMI R39,

OT-R-7728

BátchelorK.S, Chalk R.F, and Lewison G.R.G, "Survey of shipping in the Forties field 1978", NMI R52, OT-R-7729, April 1979

.k."Study of marine traffic in the English Channel, June 1977" NMI R42 "Study of marine traffic in the mid-channel, Sept. 1979" NMI R8LI, OT-M-8002

pare S.C, and Léwison G.R.G, "The recent casualty record in the Dover Strait", NMI R68, OT-R-7962

AREAS UNDER LICENCE SEVENTH ROUND: BLOCKS ON OFFER Miles o 25 I L_ o 50 100 PCms 1?0

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DENSITY OF SHIPPING IN THE CHANNEL

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ST. MALO

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MOBILE. RADAR INSTALLATION

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FIG. 8

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20

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MILES SOUTH OF RADAR STATION

DISTRIBUTION OF TRAFFIC

7

4

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4

3 2 7 3 I I 3 8 2

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iO

SAMPLE OF FISHING VESSEL SIGHTINGS

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FIG.1O

4°

THE NORTH SEA SH'OWIN.G LOCATION OF FORTIES FIELD,

NUMBER OF PASSING SHIPS AND PROBAL.E DESTINATION

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DISTRIBUTION OF CLOSEST POINT OF APPROACH

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SAMPLE SIZE

MEAN = 41 MI

STANDARD DE

231 LE S

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FIG. 11

FOG COLLISION

RISK INDEX

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ENGLISH CHANNEL

(FCRI FOR FORTIES FIELD

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20-I:

-TYPE

(432 VESSELS)

DRAUGHT

(375 VESSELS)

SPEED (599 VESSELS)

- .- - SERV!CE SPEED (280 VESSELS)

0 5 10 15 20 25 30

35 >35 KNOTS

-J

z

LI

CHARACTERISTICS OF VESSELS iDENTIFIED IN I.O.WIGHT /CHERBOtJRG AREA

Fig.13.

16-'

14-

12-

10-LI)

_-j

LU I-n

8-I-n LU

>

6-Ij

0

4-FLAG

(41.3 VESSELS)

226

₄₅

4035

-

30-25 LU

>

20-0

o 15 10 -51

C) oo

('4

cC

c- m

(I)

0

>

0

x

xo

0

0

1979 FLIGHTS

X 198.1

_FLIGHTS

FIG. 14

5

to

Is

20

OBSERVED SHIPPING DENSITY (SHIPs/boo SQ. N

)

COMPARISON OF VOLUNTARY OBSERVER SHIP REPORTS

WITH VESSELS OBSERVED BY AIRBORNE RADAR

- 300

300

100

a

z

a

U) START POINT

0

0

200.

U)

a-I

U, In

PORTLAND BILL

O

0

a-Ui p ST KATHERINES POINT

0

LIZARD

0

25

5

.75

MEAN TRAFFIC FLOW (VESSELS/MILE DAY)

CORRELATION OF VOLUNTARY OBSERVER SHIP REPORTS

WITH TRAFFIC FLOW FROM SURVEYS

V.0.5 REPORTS

EAST BOUND. TRAFFIC

I

.-WEST BOUNb TRAFFIC

I I I I I

I.

I I 1

PRESENT TRAFFIC FLOW DISTRIBUTION

COMPARED WITH THAT DEDUCED FROM

VOLUNTARY OBSERVER SIItP REPORTS 1913-7

I I I I I I

I

I,

Ii

FIG. 16

2.0

30

MILES SOUTH OF VE.NTOR

20

15

>-4

w -J U, -J Lii

U,.

inIO

Ui

>

0

-J IL U

U-4.

I-5

510 N

50°N

49 °N -', 6°W /

/

/

I

/

/

c BREST

/

PLY MOUT 14°W GUERNSEY7 SA R K SOUTHAMPTON ALDERNEY JERSEY

CHE ' BOURO

PORTSMOUTH YE S SEL S/M IL E DAY

0-6

6-8

18

12°W 10°

LE HAVRE

DOVER DIE PP E

MAIN TRAFFIC FLOWS

ST. MALO

TRAFFIC FLOW DISTRIBUTION

1

SHIPS/MILE DAY

Mile,

? 25 0 9)0 0 50 100 Kms 00 0

TRAFFIC FLOW DISTRIBUTION COMPARED WITH STUDY AREA

ZONE I

>8

ZONE 2

6-8

ZONE 3

4-6