International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 3

Number 4

December 2009

367

1 INTRODUCTION

Estimating moorings manoeuvres safety level is a

basic problem undertaken in the procedure of ma-

noeuvre planning. Captain or Pilot manoeuvring the

vessel needs to take into consideration the vertical

and horizontal restrictions of the navigating area.

During vessel manoeuvre process it is necessary to

take also into consideration other important factors

such as hydro meteorological conditions, equipment

and standard of technical maintenance of the vessel,

deck and engine crew qualifications, the condition of

navigational aids of the navigational area, the inten-

sity of vessel traffic and the quality of local Vessel

Traffic Service.

Figure 1. View of m/f “Polonia”.

Researches evaluating the level of safety moor-

ings manoeuvres of the m/f “Polonia” ferry at the

port of Ystad based on experts’ questionnaire have

been carried out. Researches of manoeuvres only

one vessel, verified during more than 10 years of

experience, at only one port give the chance to reject

influence of factors others than selected in hypothet-

ical questionnaire. Researches were conducted for

the following variables: force and direction of wind,

visibility, day and night manoeuvres. Additional var-

iable has been introduced: manoeuvres done with or

without Ferry Nautical Anti-collision System

(FNAS) – specialized equipment type of Electronic

Nautical Chart. Experts asked in questionnaire were

captains with manoeuvring experience of m/f “Polo-

nia”. Every one of them was a holder of suitable pi-

lot exemption certificate. 16 experts completed and

returned the questionnaire.

2 OBJECT AND PLACE OF RESEARCHES

Unity Line m/f ”Polonia” ferry was built in 1995 at

Norwegian Shipyard Langsten Slip & Batbyggeri

A/S in Tomfjord. She is modern passenger rail car

ferry, especially designed for Świnoujście - Ystad

service. The ferry is berthed at Ystad’s rail ferry

Stand no 4. Below are some technical and manoeu-

vre data of m/f “Polonia”:

over all length 169,9 m, breadth 28 m, GRT 29875;

4 main engines Stork-Wartsila type each 3960, kW

clutched in twos, each pair drive one of two control-

lable pitch propeller;

behind each of propeller double, Becker type flap

rudder is situated;

3 bow thrusters, 1 stern thruster, each 1600 kW

Brunwoll SPA-VP type;

summer draft 6,2 m corresponding to wind pressure

area 3250 m2;

4 navigational radars, first radar aerial is situated on

the bow, second on stern, last two are on radar mast

above wheelhouse.

Estimating Manoeuvres Safety Level of the

Unity Line m/f “Polonia” Ferry at the Port of

Ystad

A. Kowalski

Unity Line Ltd., Szczecin, Poland

ABSTRACT: Briefly characteristic of m/f „Polonia" ferry has been presented. For the port of Ystad, topo-

graphical, hydro and meteorological conditions have been described. Moorings of the “Polonia” ferry at the

port of Ystad have been discussed. Researches based on experts’ questionnaire and statistical methods of

analyses have been exemplified. Finally there are some conclusions concerning improvements of ferries ma-

noeuvres safety.

368

M/f ”Polonia” is equipped with Ferry Nautical

Anti-collision System (FNAS). FNAS is a kind of

Electronic Nautical Chart (ENC) with some function

specially designed for pilot’s passages and manoeu-

vres.

Figure 2. View of m/f “Polonia” manoeuvring controls on port

side wing.

On the bridge in a centre, main ferry controls are

located. M/f “Polonia” always berths port side for

this reason on bridge port wing additional ferry

steering and manoeuvring control equipment are lo-

cated. Main controls are joysticks of both controlla-

ble pitch propellers, coupled in one joystick which

control three bow thrusters, another one for stern

thruster, hand wheels for each main rudders with

possibility of synchronized operation. On steering

console FNAS LCD monitor is mounted. Above it is

the monitor of ship’s internal TV system with a se-

lected view of ferry area.

Figure 3. Nautical chart of Ystad and approaches.

[BA Chart, UKHO]

Port of Ystad is located on the southern Baltic

coast of Sweden. Due to its location the port is well

sheltered from northerly winds, but is fully exposed

to winds from southern directions. Force of easterly

winds is only a little reduced due to port location on

south-eastern cape. Ystad port is relatively well se-

cured from westerly winds. The inner port area has

additional protection from west by high grain silos

and port’s buildings along the western quay - Vastra

Kajen.

q y g

January

April

July

October

Figure 4. Mean values of wind occurrence form given direc-

tions for each quarter of year.

[data UKHO, BSH]

M/f “Polonia” was designed as maximum size

ferry for berthing at rail stand no 4. Then for sum-

mer draft 6,2 m, the ferry has only 0,5 m draft re-

serve. At the port water level is changing according

to the same rules as all south-western Baltic. When

strong wind is blowing from southern and south-

western directions, water level is rapidly falling

down to 1 meter below mean water level. In this hy-

dro and meteorological conditions during powerful

manoeuvres of own propellers and thrusters the shal-

low water effect is of great importance.

3 MANOEUVRING OF THE FERRY M/F

“POLONIA “ IN YSTAD

During multi year operation of the ferry, methods of

manoeuvres were standardized and optimized. Since

the ferry was properly designed for the Świnoujście

– Ystad line, for the changed hydro and meteorolog-

ical conditions manoeuvring strategy will not be

changed. Only some adjustments of settings for pro-

pellers and thrusters will be necessary.

Based on captain’s experience, some stages of

manoeuvres of m/f “Polonia” at Ystad were separat-

ed. Criteria of manoeuvres division was the goal

done on each separate stage. 8 stages for entry ma-

noeuvres and 5 for departure were obtained. The ta-

ble on figures 5.1 and 5.2 show manoeuvres division

369

placed at expert’s questionnaire including events

discriminating the stages.

Scale of difficulty and complication of manoeu-

vres can easily estimate based on the ferry speed on

each stage of mooring. When passing the outer

heads (110 m distance between heads) speed is

about 10,5 kts, in the inner heads about 7 kts. At the

beginning of slow down at the moment of reversing

the engine speed is about 5,5 kts and at this speed on

a distance of 130 m, the ferry stops and continues

left side turning. In very good hydro meteorological

conditions at wind force 0 m/s, the ferry passes con-

crete elements of ports infrastructure on the distance

of 20 – 25 m. The distances to piers and breakwaters

are reduced rapidly simultaneously with the deterio-

ration of hydro meteorological conditions.

4 EXPERT RESEARCHES OF MOORING

SAFETY

Researches were based on anonymous questionnaire

revered directly to respondents. Every respondent

received 12 sheets with relevant questions. Each

questionnaire consists of entering or departure ma-

noeuvres tables, same as on figures 5.1 and 5.2 with

place for individual answer for every stage of ma-

noeuvres and for changeable conditions of manoeu-

vres.

Consecutive stages of ferry

entering manoeuvres

Events discriminating the stages

Sea buoy Ystad

Approaches to the port

Stabilized in the line of leading lights

Outer port entry after passing

heads.

Red pole beam

Deviation on the left side of

leading lights.

Left inner head on fore beam

Turning to the left

Quay corner left beam

Continuation of turning,

commencing of stopping the

forward run

Longitudinal run stopped, stern passed

quay IV corner

Continuation of turning,

commencing of astern run

Completing of astern run

Approaching to the quay

Ferry contact with fender at the Quay

Astern run alongside

Ferry alongside at the train stand

Figure 5.1 Examples of expert’s entering questionnaire.

Consecutive stages of ferry

departure manoeuvres

Events discriminating the stages

Ferry alongside at the train stand

Unberthing, commencing the run

forward

Abeam quay corner I/IV

Turning to the port

Turning stopped

Turning to starboard

Ferry in the line of leading lights

Inner port passage

Ferry passed breakwater heads

Departure the harbour

Sea buoy

Figure 5.2 Examples of expert’s departure questionnaire.

Scale of opinion was integer number started from

1 for very easy manoeuvre to 10 for very risky ma-

noeuvre but still feasible with acceptable level of

risk. If the level of risk exceeded acceptable level

experts were asked to use mark “X” instead of inte-

ger number. Initial conditions were: day, no wind,

good visibility and manoeuvres done without sup-

port of FNAS. Next the opinion concerning the fol-

lowing conditions was estimated:

night manoeuvres;

visibility 0,2 Nm and 50m;

wind E 5 m/s, E 15 m/s, E 25 m/s;

wind W 5 m/s, W 15 m/s, W 25 m/s;

wind S 5 m/s, S 15 m/s, S 25 m/s;

manoeuvres done with support of FNAS.

Minimized to 3 levels only the wind and visibility

variable were taken into consideration. Recognized

that additional levels will generate non-sharp and

subjective component to opinions. 4 Nm suggest

good visibility. 0,2 Nm mean bad visibility – only

the nearest area around the ferry is visible, naviga-

tional marks and aids are not visible. Very bad visi-

bility 50 m – possible only a view of the water be-

low conning position. Stern and amidships are not

visible. Earlier researches reveal that critical force of

the wind for m/f “Polonia” ferry is 27 m/s. For this

reason the following has been assumed: weak wind

force as 5 m/s, strong wind 15 m/s and very strong

wind force 25 m/s. 3 directions of the wind has been

selected: W, S, E. Choice of this direction respects

not only the occurrence of the wind according to fig

4 but also exposed the port area for winds from the

selected directions.

370

5 ANALYSIS OF SELECTED RESULTS OF

RESEARCHES

For all conditions covered by 12 questionnaires, as

anticipated, no expert estimated any stage of the ma-

noeuvre “as risk that’ will exceed acceptable level”.

Once again well-calculated critical force of the wind

for m/f “Polonia” ferry – 27 m/s was confirmed.

Selected results of researches are shown on fig-

ures 6, 7, 8. For each result was calculated range of

mean safety level with 0,95 probability and passed

test of normality distribution. For each stage of ma-

noeuvres and for each variable difference of average

estimate of safety level was tested by t-test pre-test –

post-test for a standard significant level 0,05. Ac-

ceptance of zero hypothesis means no changes in

safety level opinions despite changes of visibility,

force and direction of wind, night and daytime, us-

age of FNAS. Rejection of zero hypothesis means

changes in experts’ opinion.

5.1 Entering and departure daytime manoeuvres

with restricted visibility. No wind.

Figure 6. Results of experts’ opinions for manoeuvres during

restricted visibility without the use of FNAS.

For daytime, at no wind conditions, on each stage

of manoeuvres with variable described as visibility

for every stage, zero hypothesis was rejected. For

each stage of manoeuvres, along with decreasing of

visibility deterioration of experts’ opinions concern-

ing safety level was observed. Approaching ma-

noeuvres were estimated as less safe than departure

from Ystad. Regardless of the kind of manoeuvres at

visibility reduced from 4 Nm to 50 m, 3-4 time re-

duction of estimated safety level was observed.

That’ means strong influence of restricted visibility

on manoeuvres safety.

5.2 Entering and departure daytime manoeuvres

with restricted visibility with FNAS in use. No

wind.

Figure 7.1. Results of experts’ opinions on entering manoeu-

vres in restricted visibility without FNAS compared to ma-

noeuvres with FNAS.

At good visibility of 4 Nm, the average estimate

of safety level varies from 1 to 2. Except for entry

manoeuvres no 4 and 5, the zero hypothesis was not

rejected. For 4th and 5th manoeuvres at these condi-

tions a dozen or so improvement of safety was ob-

served when FNAS was in use. This manoeuvres

was estimated as a most difficult. For the best possi-

ble hydro meteorological conditions, usage of FNAS

can also improve safety of manoeuvres.

371

Figure 7.2. Results of experts’ opinions on departure manoeu-

vres in restricted visibility without FNAS compared to ma-

noeuvres with FNAS.

For bad visibility of 0,2 Nm for manoeuvres

without FNAS, average experts’ opinions do not ex-

ceed “4”. When FNAS was in use at the same visi-

bility conditions, 50 percent in crease in safety was

observed. That was observed for all kinds of ma-

noeuvres except entry no 7 and 8 where ferry direct-

ly approaches to the quay and keeps contact with

fender moves along stand no 4. For these stages

sight distance of 0,2 Nm enables sufficient level of

visibility for execution of safety manoeuvres.

At very bad visibility up to 50 m, the most diffi-

cult stages were estimated up to “7”. For all kinds of

entering and departure manoeuvres the average safe-

ty level was improved about 50 percent when FNAS

was in use. In this circumstances average safety lev-

el does not exceed “5”.

5.3 Daytime manoeuvres. Easterly wind. Good

visibility.

Figure 8. Results of experts’ opinions on maneuvers during

easterly winds.

Average experts safety opinions for easterly wind

force 0 m/s – 5 m/s, 5 m/s – 15 m/s, 15 m/s – 25 m/s

were compared. For every stage zero hypotheses

was rejected except entering manoeuvres no 6 and 8

when compared easterly wind 0 m/s – 5 m/s. During

stage no 6 weak easterly wind not disturb manoeu-

vre. For stage 8 when ferry keeps contact with fend-

ers on quay and moves along stand no 4, the weak

opposite wind never disturbs the progress. For all es-

timated, manoeuvres at easterly wind were described

as the least safe. For the most difficult entry stages

no 4, 5, 6, 7 sometimes levels “10” appear the last

acceptable safety level. But taken this into consider-

ation only for entry manoeuvres stage no 5 average

level exceeds “9” at the easterly wind 25 m/s.

6 CONCLUSIONS

The paper presents selected results of experts’ re-

searches based on questionnaire.

By the experts’ researches, it is possible to esti-

mate of the mooring manoeuvres safety level. The

difference average of safety levels for consecutive

manoeuvres confirm the correct division entry ma-

noeuvres for 8 stages, and departure manoeuvres for

5 stages. According to results of researches, the most

dangerous manoeuvring conditions are during the 25

372

m/s wind when safety level appears “10” the last ac-

ceptable safety level. For strong winds 15 m/s and

during 50 m restricted visibility, experts’ opinions

are situated at the center of safety scale.

During any kind of restricted visibility when Fer-

ry Nautical Anti-collision System (FNAS) was in

use, improvement on safety about 50 percent was

observed. Manoeuvres done with support of FNAS

always improve safety level. Researches were con-

ducted on the ferries, where persons manoeuvring

the vessel have excellent theoretical and practical

knowledge about sailing areas. Presumably, when

the vessel is manoeuvring on the less known areas,

improvement of the safety level should be more ef-

fective.

Carrying out the experts’ questionnaire research-

es, it is possible to establish objectively hydro mete-

orological conditions for selected and satisfied ma-

noeuvres safety level. Researches may be used for

risk management at shipping companies. Additional-

ly results of researches may be used for planning

ship’s operations during extreme hydro and mete-

orological conditions.

REFERENCES

Ayyub B.M. 2001 Elicitation of Expert Opinions for Uncertan-

ity and Risks, CRC Press LLC, Boca Raton.

Gucma, S. 2001. Inżynieria ruchu morskiego. Gdańsk: Okrę-

townictwo i Żegluga.

Gucma S., Kowalski A., Doświadczalna metoda oceny zdolno-

ści manewrowych cumowania promów morskich. Interna-

tional Conference „The Role of Navigation I Support of

Human Activity at Sea – NAVSUP 2006”, Gdynia 2006.