International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 3

Number 1

March 2009

101

Navigational Safety in SPM (Single Mooring

Point) Regions

V. Paulauskas

Klaipeda University, Klaipeda, Lithuania

1 INTRODUCTION

Navigational safety in SPM regions request deep

theoretical studies and very clear understanding of

forces and moments, which influence on all the sys-

tem (SPM, FSU, Tanker, tugs), practical implemen-

tation of proper equipment and use of correct meth-

ods of navigational safety.

In case of FSU or tanker breakout (break towage-

mooring rope) between SPM and FSU or FSU and

tanker, in case of bad weather conditions, wind,

waves and current starts pushing FSU or tanker, or

both in outer forces direction and if this direction

will be to the shore or other navigational obstacles

direction, just very fast and correct actions must be

taken to solve problematic situation.

Tugs bollard pull is important for the ships,

which are using SPM in open sea for the daily op-

eration and especially for the emergency conditions

(BS6349, 2003; EAU 2004, 2006). Typical emer-

gency conditions are investigated in cases, when

FSU or tanker has technical problems and is neces-

sary to assist for the FSU or tanker in safety region.

In different situations and additionally in case of use

of FSU and tanker, hydro meteorologically condi-

tions has different influence on FCU and tanker and

it requests actions for preventing accidents or other

failure problems.

2 THEORETICAL BASIS OF THE NAVIGA-

TIONAL SHIP’S HANDLING CONDITIONS

Typical emergency conditions in SPM regions main-

ly are linked with:

− Main engine or rudder failure, weather from rea-

sonable to good;

− FSU or tanker breakout during bad weather.

Mentioned conditions are very important, because

SPM position is in open sea but very often close to

navigational obstacles (shore and shallow waters)

and it is very important to have correct and fast an-

swers regarding requested bollard pull and time

stopping drift tanker and possibilities towage tanker

or FSU away from dangerous places.

Theoretical Study was using three the main meth-

ods:

ABSTRACT: For oil and gas transportation in some places used SPM (Single mooring point) system, this is

located in the open sea and very often not so far away from the shore. Differences between the wind loads,

waves and current forces can take a place. More complicate conditions can be in case if FSU is still in ballast

and more influence has wind and waves as current and in the same time tanker in loaded position is more in-

fluenced by the current. Navigational safety ensure in SPM regions requests deep theoretical studies and very

clear understanding of forces and moments, which influence on all the system (SPM, FSU, Tanker, tugs),

practical implementation of proper equipment and use of correct methods of navigational safety. In this article

there is made analysis of possible failures and necessary actions to ensure navigational safety in SPM regions.

102

− Calculation method on basis Ship’s Theory and

Ship’s handling in complicate conditions (V.

Paulauskas, 1999);

− Simulation, used simulators, such as SimFlex

Navigator (SimFlex Navigator Simulator, 2006);

− For the checking calculations and simulation re-

sults, to use experimental results from similar

conditions, which take place on other real SPM

places (SPM accidents investigation results,

2007).

Calculations were made by methodic, presented

in references (V. Paulauskas, 1994; 1999 and 2004),

and mainly were oriented on more complicate condi-

tions, that means acting in one direction with some

angles wind, current and waves, including shallow

water effect.

Simulations were provided with equaling ships

with recalculation to concrete planning ship in bal-

last and loaded and in same way on basis mass dif-

ferences can made simulations and taken tugs forces

(bollard pull).

Experimental results were taken from similar

conditions, which were made by Author or from

known references.

Constant wind component, as example, create

forces, which can be calculate as follows (V.

Paulauskas, 1999, 2004):

)

sincos(5,0

aCayaxaC

vqSqSCF ⋅

⋅+⋅⋅⋅=

(1)

where:

−

- aerodynamic coefficient, can be taken for

such type calculations equal to 1 or can be taken

for concrete ship, which model was tested in aer-

odynamic tube, data;

−

- wind density, for the calculations can be

taken as 1,25 kg/m³;

−

- wind surface area on diametric direction;

−

- wind surface area on middle direction;

−

- wind course angle;

−

- average wind velocity.

Periodical forces can be calculated via accelera-

tion as follows:

)/2sin()/(4

τπτπ

tatF

⋅⋅⋅⋅⋅⋅=

(2)

Finally periodical force can be expressed as fol-

lows:

mFF

⋅=

, (3)

where:

− m – ship’s mass;

−

- period of wind guess;

− a – integration constant, which can be find as:

)sincos(25,0

1 ayaxaa

qSqSvCa ⋅+⋅∆⋅⋅⋅=

(4)

Maximum forces, which can create periodical

component of the wind, will be in case:

1)/2sin( =⋅⋅

τπ

, (5)

and maximum periodical forces will be in case:

max

τπ

matF

⋅⋅⋅⋅=

(6)

Waves constant and periodical forces can be cal-

culate similar as wind loads as follows:

wwxwwc

qvSCF cos5,0

⋅⋅⋅⋅⋅=

, (7)

where:

−

- waves hydrodynamic coefficient, can be

taken from [1, 2];

−

- water density;

−

- typical waves acting square;

−

- waves spreading velocity;

−

- waves course angle.

Waves periodical forces can be calculated similar

as wind periodical forces, just in formulas (2) – (6) it

is necessary to use wave’s parameters.

3 PRACTICAL REQUEST FORCES

CALCULATIONS

For the calculations is taken Suez Max tanker with

next main dimensions: DWT – 183000 tons; length

max – 274 m; length between perpendiculars – 264

m; width – 50 m; height (board) – 23,1 m; draft - 17

m (loaded); draft – 8 m (in ballast).

Suez Max ship’s other dimensions in ballast:

wind area

– 4500 m²; wind area

– 1200 m²;

underwater area

– 2100 m²; underwater area

S’y – 400 m².

Suez Max ship’s dimensions loaded: wind area

– 2300 m²; wind area

– 800 m²; underwater

area

– 4500 m²; underwater area

– 850 m².

For the assistance were taken tugs with bollard

pull 450 kN and 650 kN and were investigated FSU

or tanker breakout during bad weather and Tanker

main engine or rudder failure cases (Fig. 1).

103

Figure 1. FSU or tanker breakout during bad weather.

Theoretical calculations results in case of acting

wind and waves on loaded tanker are presented on

table 1 and figure 2.

Table 1. Wind and waves forces on the Suez Max loaded tank-

er, forces in T.

___________________________________________________

Wind Wind and Wind and Wind and Wind and

velocity, waves waves waves waves

m/s course course course course

direction direction direction direction

0º 30º 60º 90º

___________________________________________________

5 1 2 3 4

10 4 10 13 15

15 11 26 32 35

20 19 47 61 65

25 30 77 102 115

30 46 120 157 170

___________________________________________________

Figure 2. Wind and waves forces on the loaded Suez Max

tanker depends on wind velocity and waves accordantly (wind

and waves directions are the same)

In case of FSU or tanker breakout during bad

weather, especially FSU, because normally tanker

can not be moored to FSU during bad weather, very

important to find weather limitations for the planned

tugs. To turn loaded FSU or tanker, 65 T bollard pull

tug has no limitations, 45 T bollard pull tug has limi-

tations for the FSU or tanker in ballast: wind up to

18 m/s, waves up to 3,5 m.

In case of FSU or tanker breakout (break towage-

mooring rope) between SPM and FSU or FSU and

tanker, in case of bad weather, wind, waves and cur-

rent start push FSU or tanker in acting forces direc-

tion and if this direction oriented to navigational ob-

stacles, just very fast and correct actions must be

taken to solve the problem. Tugs possibilities in case

of loaded FSU or tanker are shown on fig. 2 (green

line for 65 T bollard pull tug and blue line for tug 45

T bollard pull tug).

4 REQUEST FOR NAVIGATIONAL REGION

RECEIVED BY CALCULATIONS AND

SIMULATOR TESTINGS

Request for navigational region for the tankers ma-

neuvering after breakout mooring rope in case tanker

reach some drift speed received by theoretical calcu-

lations were checked by simulator and real data from

SPM accident situations. All results were received

very similar.

Simulations were made on visual simulator with

possibility to simulate ship, tugs and sailing condi-

tions. Simulations made for the emergency condi-

tions, in case, when mooring rope has broken and

tanker reached drift speed up to 4 knots before start-

ing towage operation by tug. Simulations results for

the loaded tanker drifting in first stage before tug

started towage at the speed about 4 knots, presented

on figure 3 by 65 T bollard pull tug and for the load-

ed tanker by 45 T bollard pull tug simulation results

in the same conditions are shown on figure 4 and

towage parameters for 45 T bollard pull tad are

shown on figure 5.

104

Figure 3. Loaded tanker and 65 T bollard pull tug way for the

stopping and later towage tanker (before towage tanker drift

speed reached 4 knots): wind 20 m/s; waves 4 m, current 0,5

knots in to the same direction (to E).

Figure 4. Loaded tanker and 45 T bollard pull tug way for the

stopping and later towage tanker, on first tanker drift speed 1,5

knots: wind 20 m/s; waves 4 m, current 0,5 knots in to the

same direction (to E).

Figure 5. Loaded tanker and tug movement parameters: Time

00.00 – speed 1,5 knots; Tanker stopped by 45 T bollard pull

tug and keep practically in the same place; Towage speed at the

end of the process reaches 0,3 kn.

Calculation and simulation results were checked

with available experimental (real) results in Butinge

terminal (Lithuania), Petrol Baltic SPM (in Baltic

Sea) and in other places in which used SPM. Corre-

lation between calculation, simulation and experi-

mental results are very good and it has shown that

calculation methodology, prepared by author and

explained in this paper, can be used on first stage for

the forecasting situation to use SPM, request for

navigational region, minimal tug’s bollard pull and

other details.

5 CONCLUSIONS

1 Methodology, presented in this paper can be used

for the SPM conditions evaluation and forecast-

ing requests for navigational region, tugs bollard

pull, depends on tankers or FSU parameters.

2 Combination of the calculation methods, simula-

tion possibilities on navigational simulators and

checking by real data, could be the main way for

receiving good quality results and for preparation

of SPM work and emergency procedures.

3 In case of failure FSU or tanker engine or rudder

system, strong enough tugs can take precautions

measures in advance, stopping on navigational

region tanker drifting or FSU and towage away

from navigational dangerous places.

4 Theoretical methods are very important during

planning of SPM and navigational regions around

SPM, selection of the main elements in the re-

gion, such as minimal tug bollard pull, tugs ma-

neuverability, ways in different conditions for the

towage tanker or FSU away from navigational

dangerous regions.

REFERENCES

1. BS 6349-1: 2000 – British Standard Maritime Structures –

Part 1: Code of Practice for General Criteria (British Stand-

ard Institution, July 2003)

2. EAU 2004 : Recommendations of the Committee for Water-

front Structures – Harbours and Waterways (Ernst & Sohn,

2006)

3. Paulauskas V. 1994. Ship’s steering. Klaipeda university

publish house, Klaipeda, 164 p.

4. Paulauskas V.1999. Ship’s steering in complicate conditions.

Klaipeda university publish house, Klaipeda, 184 p.

5. Paulauskas V. 2004. Port terminals planning. Klaipeda uni-

versity publish house, 382 p.

6. SimFlex Navigator Simulator, 2006. Force Technology,

Denmark.

7. SPM accidents investigation results, 2007, (Butinge termi-

nal).