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Scientific Journals

Zeszyty Naukowe

Maritime University of Szczecin

Akademia Morska w Szczecinie

2010, 20(92) pp. 114–119 2010, 20(92) s. 114–119

Verification of probabilistic method for under keel clearance

assessment based on ships entering to Świnoujście, Szczecin

and Police ports

Weryfikacja probabilistycznej metody szacowania zapasu

wody pod stępką w oparciu o statki wchodzące do portów

w Świnoujściu, Szczecinie i Policach

Marta Schoeneich

1

_{, Sylwia Sokołowska}

2

1_{Maritime University of Szczecin, Faculty of Navigation, Institut of Marine Traffic Engineering}

Akademia Morska w Szczecinie, Wydział Nawigacyjny, Instytut Inżynierii Ruchu Morskiego 70-500 Szczecin, ul. Wały Chrobrego 1–2

2_{Maritime Office in Szczecin}

2_{Urząd Morski Szczecin, 70-207 Szczecin, Pl. Batorego 4, e-mail: sylwia.sokolowska@gmail.com}

Key words: under keel clearance, verification of the method, risk assessment Abstract

The paper presents verification of probabilistic method for under keel clearance determination. The method enables to determine the distribution of under keel clearance in several ship’s passages and in further step to assess the probability of ship’s grounding accident during the port approach. The model which uses this method is available online for authorized users and could be used for decision making process of harbour captain in everyday practice. The results of using this model could be used in risk assessment of ships entering to the ports, therefore it is possible to introduce using online model for Polish harbours workers. Research results present verification of probabilistic model, based on data from Szczecin Maritime Office and probability of touching the bottom during ships’ passages on Świnoujście–Szczecin waterway. Moreover there are presented examples of some situations when entering to the port for analyzed ships is not allowed.

Słowa kluczowe: zapas wody pod stępką, weryfikacja metody, ocena ryzyka Abstrakt

W artykule zaprezentowano weryfikację probabilistycznej metody określania zapasu wody pod stępką. Meto-da ta pozwala na określenie rozkładu zapasu wody pod stępką, a także wskazanie prawdopodobieństwa wej-ścia na mieliznę statku podczas podejwej-ścia poszczególnej jednostki do portu. Model, który korzysta z tej meto-dy jest dostępny on-line dla uprawnionych użytkowników i może być używany w codziennej praktyce przy podejmowaniu decyzji przez Kapitana Portu. Wyniki otrzymane przy wykorzystaniu modelu mogą służyć do oceny ryzyka statków, które zawijają do portu, dlatego też możliwe jest zalecenie wykorzystania modelu on-line przez pracowników polskich portów. Wyniki badań prezentują weryfikację modelu probabilistyczne-go w oparciu o dane z Urzędu Morskieprobabilistyczne-go w Szczecinie oraz prawdopodobieństwo kontaktu kadłuba statku z dnem w czasie przejścia torem wodnym Świnoujście–Szczecin. Podane są także przykłady pewnych sytu-acji, gdy wejście analizowanych statków do portu jest niedozwolone.

Introduction

Under keel clearance is the required minimum distance between the ship’s keel and the bottom of the channel. Local regulations sometimes stipulate

the under keel clearance (UKC) that a ship must maintain in their areas where pilotage may not be compulsory. The determination of minimal under-keel clearance is especially important for the port as it allows, basing the existing meteorological

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conditions and the type of vessels, to load the vessel maximally [1]. These types of ports are represented by Swinoujscie, Szczecin and Police. There are special VTS procedures for entering and leaving these ports, and precise requirements are determined by Port Regulations. Some countries introduced special program or applications for under keel clearance determination and sometimes using these programs is required.

The paper presents verification of probabilistic model for under keel clearance calculation based on data from Szczecin Maritime Office. There are ships with length more than 180 m, entering Świno-ujście, Szczecin or Police Port in years 2005–2009 analysed. Because probabilistic model of under keel clearance determination could support the decision of Port Captain, it is possibility that using online program for under keel clearance evaluation will be recommended by local Maritime Authorities.

Local regulations for Świnoujście, Szczecin and Police Port with regard to maximal vessels (Port Regulations 2002)

Świnoujście, Szczecin and Police are ports where special local regulations are in force. The basic rule says, that no vessel which are 20 m or more in length may enter or leave the port or navigate in its area without the permission of the Harbour Master or VTS. In ports where the system is mandatory, in order to obtain permission, a ves-sel shall contact the Harbour Master’s Office or VTS. The Master of each vessel, before entering or leaving a port, shall report to the Harbour Master’s Office or VTS if that system is mandatory in that place, informing them of the voyage plan as determined in accordance with the reporting system being stated, as appropriate, the pre-notification should contain i.e. LOA, beam, GT capacity, vessel type, and maximum draught in fresh water.

Following regulations concerning length and draught of ship: vessels entering and leaving the port of Swinoujscie may not exceed 270 m in length overall, 42 m breadth and 13.2 m draught in fresh water. The overall length of vessels entering and leaving the ports of Szczecin and Police may not exceed 215 m and the overall breadth may not exceed 31 m. The draught of vessels entering and leaving the port of Szczecin may not exceed 9.15 m and the overall length may not exceed 160 m. The draught of vessels entering and leaving the port of Police may not exceed 9.15 m and the overall length may not exceed 170 m. Moreover regula-tions say that, it is prohibited for vessels that are overloaded so that they exceed the draught permit-ted in the appropriate certificate to enter or leave

the port (§18). A vessel may not enter the port, navigate in or leave the port without the Harbour Master’s permission, if that vessel endangers safe navigation and operational order in the port area, and in particular when it is excessively trimmed or has a dangerous list.

For risk assessment of maximal ships entrance to the ports, modernization and optimisation of waterways in real situations (for example by VTS operators) or some kind of application could be very helpful in decision process.

Characterisation of research with using probabilistic model of UKC determination

The stochastic model of under keel clearance evaluation was presented in [2] and description and practical implementation process of developed probabilistic model of ship’s under keel clearance was explain in [3].

The main assumption of probabilistic method for UKC determination is that the model takes into account depth measurement uncertainty, uncertain-ty of draught determination in port, error of squat determination, bottom irregularity, tides and waves influence (Fig. 1). Program is capable to consider above mentioned uncertainties using distributions and their parameters.

Fig. 1. Concept of probabilistic under keel clearance determi-nation [4]

Rys. 1. Koncepcja probabilistycznej metody określania zapasu wody pod stępką

The model UKC evaluation was implemented using Python compiler and it is available “on-line” on Maritime Traffic Engineering Institute web site. Figure 2 presents form for entering parameters. It is possible to enter the basic ship and water region data.

The remaining necessary data are taken from XML file located from the server. Model under keel clearance is evaluated after running the application. The results are presented as a histogram (Fig. 3) and diagram P(UKC<0) in function of ship’s draught shows in figure 4.

Minimal dredged depth

Grounding probability Water level Draught Depth Squat V V = 0 fs(s) fh(h)

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Marta Schoeneich, Sylwia Sokołowska This type of application allows determination of

probability of ship’s hull contact with the bottom and could be helpful to assess whether large vessel are allowed or not to enter to the port. Additionally the result of method of constant clearances is pre-sented to compare it with the proposed probabilistic method. The value of this clearance is calculated in accord with “The Guidelines for Designing of Maritime Engineering Structures”.

Fig. 2. User defined data form for probabilistic model of under keel clearance (UKC)

Rys. 2. Formularz wprowadzania danych definiowanych przez użytkownika dla potrzeb omawianego modelu (UKC – zapas wody pod stępką)

Fig. 3. Example of results probabilistic model of UKC for one of ships which entered Świnoujście Port in 2009

Rys. 3. Przykładowy wynik wykorzystania modelu probabili-stycznego określania zapasu wody dla jednego ze statków, który zawinął do portu w Świnoujściu w 2009 r.

Range of research

The analysis covers a period from 2005 till 2009. Probabilistic model was used for all ships equal or longer than 180 m, which entered to ports: Świnoujście, Szczecin and Police. Parameters of

each vessel were entered together with appropriate hydro-meteorological conditions as water level and wave height, which were checked in Vessel Traffic System database.

Fig. 4. Example of decision support application result in Świnoujście

Rys. 4. Przykład wyników zastosowania modelu wspomagania decyzji w Świnoujściu

Ship’s speed conditions

On the Świnoujście–Szczecin waterway are spe-cial restrictions according to ship’s speed. Regula-tions say that vessels, sailing at maximum permit-ted speed, which generate waves that wash sea de-fences or that are capable of damaging port facili-ties or ships at berth, shall reduce speed to such extent that waves will not be generated. Maximum permitted speeds in the different Szczecin–Świno-ujście seaway stretches are given in the table 1. Table 1. Maximum speeds in the different Szczecin–Świno-ujście seaway stretches [5]

Tabela 1. Maksymalne prędkości statków na poszczególnych odcinkach toru wodnego Szczecin–Świnoujście [5]

Lp. Seaway stretch _{speed [knots]}Maximum 1 From sea anchorage to buoys No. 7–8 12 2 From buoys No. 7–8 to Gate No. 1 8 3 From Gate No. 1 to abeam of _{northern head of Chelminek island} 12 4 From abeam of northern head of _{Chelminek island to buoys No. 13–14} 8 5 From buoys No. 13–14 to abeam of _{beacon Krepa Dolna} 12 6 From abeam of beacon Krepa Dolna _{to abeam of beacon Radun Gorna} 8 7 From abeam of beacon Radun Gorna _{to Inski Nurt} 12 8 From Inski Nurt to the port in _{Szczecin and in port areas} 8

Pr oba bi lity UKC [m] P( UK C < 0 m) draught [m] 2.44% line of equal loss (↑ – not acceptable, ↓ – acceptable)

Estimated probability of grounding

Location: Świnoujście Iterations: 1000/100 Vessel type: general cargo Calculation time: 8.69147 s

Predicted under keel clearance

Location: Świnoujście mean squat: 0.22 m Iterations: 1000/100 Vessel type: bulk carrier Calculation time: 8.75063 s

PROBABILISTIC UNDER KEEL CLEARANCE EVALUATION

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It is possible that ships enter the port with the less speed but Maritime Office database has no information about it. Therefore in research ship’s speed 6 kt is taken into account.

Research results

There were 435 ships in the analysis used with the mean draught Tm = 9.03 m and standard devia-tion δTm = 2.38 m.

Mean probability of ship’s grounding on Świno-ujście–Szczecin waterway is insignificant and equal P(UKC<0) = 1.5% and mean under keel clearance of ships which entered ports is 3.25 m.

In order to make research more precise, ships with draught more than 7.5 m were chosen.

The table 2 presents number of ships and mean parameters in Szczecin, Świnoujście and Police Harbours in period 2005–2009.

Table 2 Research results in particular ports Tabela 2. Wyniki badań w poszczególnych portach

Parameter Świnoujście Szczecin Police Number of ships 167 59 67 Mean probability UKC < 0 0.04 0 0 Mean UKC [m] 2.17 2.31 1.52

Figures 5–7 present histograms mean under keel clearance of ships in years 2005–2009 according to probabilistic model.

Fig. 5. Histogram of mean UKC in Szczecin in years 2005– 2009

Rys. 5. Histogram średniego zapasu wody pod stępką dla statków wpływających do Szczecina w latach 2005–2009

In case of 59 ships which entered Szczecin Port mean probability of touching the bottom is equal 0 and the most ships have entered to the port with under keel clearance 2.5 m.

In Świnoujście for 167 ships probability that under keel clearance will be less than zero is equal 0.04 and the most ships have entered to the port with under keel clearance 1.5–2 m.

In Police Port the most ships have passages with under keel clearance 1.5 m, and the probability UKC < 0 level for 67 ships is equal 0.

The biggest number of ships entered Świno-ujście Port. The probabilistic model confirms deci-sions of Port Captain in Szczecin and Police. There are some situations in Świnoujście, where the level of safety is not acceptable according to probabilistic model, so mean probability than UKC will be less than zero is equal 4%. These cases took place in very bad hydro-meteorological conditions, so it was possible to enter for ship with smaller speed (less than 6 kt – which was used in verification).

Case study

From 167 situations when large ships entered Swinoujscie port, 18 cases were not accepted by probabilistic model. For analyzed ships mean pro-bability when under keel clearance will be less than zero is equal 0.358 and the model not allowed for safety enter for particular ship.

Szczecin 0 5 10 15 20 25 0 0,5 1 1,5 2 2,5 3 3,5 4 More Mean UKC [m] N u m b e r o f s h ip s

Fig. 6. Histogram of mean UKC in Świnoujście in years 2005–2009

Rys. 6. Histogram średniego zapasu wody pod stępką dla statków wpływających do Świnoujścia w latach 2005–2009

Fig. 7. Histogram of mean UKC in Police in years 2005–2009 Rys. 7. Histogram średniego zapasu wody pod stępką dla statków wpływających do Polic w latach 2005–2009

0 5 10 15 20 25 30 35 -0,5 0,5 1,5 2,5 3,5 4,5 5,5 6,5 7,5 Mean UKC [m] N u m b e r o f s h ip s Police 0 5 10 15 20 25 30 35 40 45 0 0,5 1 1,5 2 2,5 3 More Mean UKC [m] N u m b er o f sh ip s

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Marta Schoeneich, Sylwia Sokołowska

Because all of these cases took place in very bad hydro-meteorological conditions (strong breeze), analysis of introduce change ship’s speed and wave height was carry out. Figure 8 and 9 present model results for ship which entered Świnoujscie Port in October 2006. According to the model of under keel clearance at the water level equals 501 and wave height 1,5 m analyzed ship cannot enter Świnoujście Port. In figures model results depend-ing on ship’s speed and wave height are presented.

In this case wave height has more influence on probabilistic model than ship’s speed change.

The table 3 presents a wave height influence for exemplary ship with parameters L = 224.9 m, T = 13.18 m and water level 529.

Analysis of ship’s speed change to point at absence of assent for entrance to the port at low water level (about 450). Even if ship’s speed is equal 1 w the model has not allowed for safety entrance to Świnoujście Port (Fig. 10).

Table 3. Research results for wave height influence Tabela 3. Wyniki badań wpływu wysokości fali

Wave height [m] Probability (UKC < 0) [%]

1.5 82 1.25 70.4 1 52.8 0.75 33.5 0.5 18.5 0.25 5.9 a) b)

Fig. 8. Results of UKC model for ship with L = 246.88 m and T = 12.8 m for wave height 0.5 m and ship’s speed 2 w (a) and 3 w (b) Rys. 8. Wyniki modelu UKC dla statku o L = 246,88 m i T = 12,8 m dla wysokości fali 0,5 m i prędkości statku 2 w (a) i 3 w (b)

a) b)

Fig. 9. Results of UKC model for ship with L = 246.88 m and T = 12.8 m for wave height 0.6 m and ship’s speed 2 w (a) and 3 w (b) Rys. 9. Wyniki modelu UKC dla statku o L = 246,88 m i T = 12,8 m dla wysokości fali 0,6 m i prędkości statku 2 w (a) i 3 w (b)

Pr oba bi lity UKC [m] UKC [m] UKC [m] Pr oba bi lity Pr oba bi lity Pr oba bi lity UKC [m]

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Conclusions

The possibility to accommodate big draft vessels without any danger to navigation safety is still actual problem.

Mean probability level of touching the bottom during ships’ passages with length over 180 m in years 2005–2009 in Świnoujście–Szczecin water-way equals 0.015.

Wave height change has more influence for calculated probability UKC < 0 than ship’s speed change.

The model confirms decisions which were made by Port Captains or VTS operators in Szczecin and Police Port. After validation and improvement wave module is intended to be used probabilistic model in Maritime Office employees’ everyday decision making practice.

References

1. www.transportweekly.com/pages/en/news/articles/56060/ 2008

2. GUCMA L.: Risk Modelling of Ship Collisions Factors with Fixed Port and Offshore Structures. Maritime University of Szczecin, Szczecin 2005.

3. SCHOENEICH M.: Probabilistic method and decision support system of ship’s under keel clearance evaluation in en-trance to the ports. International Symposium on Electronics in Transport, Ljubljana 2008.

4. GUCMA L.,SCHOENEICH M.: Probabilistic Model of Under Keel Clearance in Decision Making Process of Port Captain. Monograph-Advances in Marine Navigation and Safety of Sea Transportation TransNav’2007, Gdynia 2007. 5. Port Regulations STANDING ORDER No. 4 Director of

the Maritime Office in Szczecin of 17th September 2002.

a) b)

Fig. 10. Results of UKC model for ship with L = 225 m and T = 12,8 m for wave height 0 m and ship’s speed 1 kn; a) histogram of underkeel clearance, b) diagram P(UKC < 0) in function of ship’s draught

Rys. 10. Wyniki modelu UKC dla statku o L = 225 m i T = 12,8 m dla wysokości fali 0 m i prędkości statku 1 w; a) histogram zapa-su wody pod stępką, b) wykres P(UKC < 0) w funkcji zanurzenia statku

Pr

oba

bi

lity

UKC [m]

Estimated probability of grounding

Location: Świnoujście Iterations: 1000/100 Vessel type: bulk carrier Calculation time: 2.83215 s

draught [m]

line of equal loss (↑ – not acceptable, ↓ – acceptable

2.44% P( UK C < 0 m)