GENERAL OVERLOOK OF VESSEL SAFETY ON POLISH LARGEST HARBORS: GDANSK AND SWINOUJSCIE

Transcription

1 BALTIC MASTER REPORT MII part 4/4 GENERAL OVERLOOK OF VESSEL SAFETY ON POLISH LARGEST HARBORS: GDANSK AND SWINOUJSCIE This part of report is considered on navigational conditions for handling large vessels, safety of navigation, meteorological condition and other precautions. It is a first step towards detailed description of the main ports on the Baltic Sea coast. Maritime University of Szczecin

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3 This part of report is made on the partly fulfilment of the tasks executed by MUS within the BalticMaster Interreg IIIB project. BALTIC MASTER REPORT Milestone II part 4/4 This report is joint effort of Maritime University of Szczecin research team Contributors: No Name Responsibility Signature 1 Antoniewicz Marta Development of ship grounding model 2 Artyszuk Jarosław Development of ship dynamics models 3 Bąk Andrzej General models of ship energy in collisions 4 Gucma Lucjan - Team leader 5 Gucma Maciej AIS and traffic data analysis and possession 6 Gucma Stanisław Development of general risk assessment model 7 Hajduk Jerzy General navigational requirements on the Baltic Sea 8 Jankowski Stefan Geographical data analysis and its possession 9 Juszkiewicz Wiesław Radar reliability assessment 10 Pietrzykowski Zbigniew Ship-ship collision probability determination model 11 Przywarty Marcin Main programmer software implementation 12 Tomczak Arkadiusz Modeling of position fixing systems in Southern Baltic 13 Zalewski Paweł Position fixing systems operational parameters

4 Foreword This study is preliminary study for analysis of navigational safety in areas where largest Polish ports are located. This work includes all necessary factors to asses navigational risk. Such analysis is desired for further studies over Southern Baltic Area. Work shows all described above factor for two polish harbors that can handle largest vessels (with length of 200 and more): Gdansk and Swinoujscie. In further studies smaller harbors will be described. 1. Navigational conditions at passage and entrance to port of Świnoujście 1.1. PREVAILING NAVIGATIONAL AND BATHYMETRIC CONDITION Port is located at the estuary of Świna river to Pomorska Bay 53º55.0 N and 14º17.0 E. There is a water track to Szczecin port. This port is a vast reloading base for bulk cargo (including ore), containers, general cargo. There is also a huge ferry base (connections to Sweden and Denmark). Vessels of maximum length of 270 m and draught of 13.2 m can enter the port (in the case of a smaller draught the vessels up to 300 m of length can enter the port). The port encloses the water region of Świna river from the estuary of the river up to Barge Basin in Karsibór (km 10) and all the adjacent territory and water area. The entrance is shielded by two breakwaters: east of the length of 1400 m and west of 300 m. There are two turning areas in the port north one (diameter of 370 m) for vessels of 270 m long with the draught of 10 m and south one (diameter of 320 m) which is located opposite the Bosun Basin. The plan of the first three km of the waterway (the entrance to Świnoujście Szczecin ports) is shown in figure 1.1. Fig Navigational chart presenting the entrance to Świnoujście

5 The route through Pomorska Bay leads to Świnoujście port. As far as bathymetric conditions are concerned this route leading to port in Świnoujście can be divided into the following parts: 1. western entrance route to buoy N-1 (through SWIN-N) crossing the territorial German sea from the east of Rugen. Natural minimum depth of the water area, through which western entrance route is crossing, is 16.0 m (minimum depth 15.1 m ). 2. northern part of the Northern Route leading from buoy N-1 ( km) to N-2 and then to the buoys 1 2 (12.4 km). The minimum depth of 14.4 m and the width of 180 m ensure a natural depth of the area except for the section (27.8 km 31.4 km) located in the north from buoy N-3, which is a deepened route. 3. southern part of the Northern Route crossing Pomorska Bay from the buoys 1 2 (12.4 km) to the eastern breakwater head of Świnoujście port (0.0 km). It is the deepened waterway, which minimum depth is 14.3 m with the assumed width of 180 m. The minimum depth (14.3 m) and the width of waterways given above is according to the regulation of Minister of Transport and Marine Economy from the 7 th of December 1997, par. 4. The minimal depths on the sections 2 and three are determined on the basis of the bathymetric survey conducted on the 15 th of March Fig Entrance routes to Świnoujście, with marked anchorages The northern waterway is marked with the buoys and is 14,3 m deep. The entrance to the route is at buoy ŚWIN-N. Through the last part of the waterway there is a marked channel deepened to 14,3 m, with light

6 leading marks MŁYNY-GALERIOWA (170.1º) on centerline. Eastern entrance (242º) leads from the light buoy on the northern edge of shallow water, in the north from lighthouse KIKUT, to the gate marked by light buoys 4 and 3. From this point, there is an entrance to the port in the centerline of light leading marks MŁYNY GALERIOWA (170.1º) through the marked channel. On the waterway Świnoujście Szczecin as well as on the entrance route to Świnoujście there is a marking either fixed or floating. The floating marking is in accordance with IALA System (region A) EXISTING ANCHORAGE AND ANCHORING REGULATIONS There are three anchorages near the entrance to Świnoujście port (fig. 2.3). Anchorage No 1 with the depth of 9 12 m assigned for the vessels with a maximum draught to T=7 m. Anchorage No 2 with the depth of m assigned for the vessels with a maximum draught to T=11.0 m. Anchorage No 3 with the depth of m assigned for the vessels with a maximum draught to T=13.2 m PREVAILING HYDRO-METEOROLOGICAL CONDITIONS FOR DESCRIBED AREA As far as hydro-meteorological conditions are concerned that have an influence on the safety of vessels maneuvering on the waterways: current conditions, wind conditions, water level, ice conditions, temperature, pressure and humidity of air, visibility, waves Current conditions Current conditions at analyzed area are very difficult to be described and following explanation should be treated as preliminary study in this field. On the basis of existing analysis it can be assumed that: current conditions in Strait of Świna depend mostly on the character and size of the water changes and their mutual relations in Pomorska Bay and Szczeciński transgression. Wind influences the current indirectly through the influence on he state of water in the Bay, however it has little influence on the surface current; the flows in Świna Bay can have established state, or unestablished state. For the established flow there is an outbound or inbound flow in the whole sea bed. Distribution of speed changes in the river layers depends on the depth. Distributions of horizontal surface speed of the maximum average current is shown in fig The position of a current log is marked in these figures. Unestablished flows are quasi periodical and can be one-way or two-way, but because of the random character are difficult to describe. On the basis long periodic collected data completed in real conditions, by means of a hydraulic model and calculations using three dimensional numerical model, the following speed distributions were developed taking into account the possibility of their occurrence (P): Established flow - ingoing current (outflow) P = 48.5 % P = 86.3 % P = 98.0 % v = 30 cm/s v = 55 cm/s v = 85 cm/s Established flow - ingoing current (inflow) P = 48.5 % P = 86.3 % P = 98.0 % v = - 45 cm/s v = - 70 cm/s v = cm/s Unestablished flow - any direction P = 48.5 % to - 60 cm/s P = 86.3 % to - 70 cm/s

7 maximum speed that was measured, which occurred during storming backwater was approximately 180 cm/s per 1,3 km of Zbiorczy Channel. Probability of such situation occurrence is less than 1%. Fig 2.4. Inbound current parameters (Speed) in Swinoujscie Entrance (mean, max) On the examined water area there is a current log installed on the sea bed on the centerline of waterway which is on the height of the quay 6. It measures the current speed in the vertical direction with the possibility of having current value for chosen depth. Due to the fact that it is installed on the axis of the waterway indicate current speed, which does not suit maximum value of the current as far as established flows are considered. It is caused by the tideway that deflects towards southern coast direction with the outgoing current, and it deflects towards the eastern coast direction with the ingoing current. The difference between the maximum current speed and the speed in the waterway axis is 10 20%. Taking into consideration speed current distribution, the fact that values describing its size are given for Zbiorczy Channel and also the location of the current log the indications of the current log are: average maximum outgoing current in the heads 1.0 knots complies with the measurement on the current log 0.8 knots in the heads 0.7 knots average maximum ingoing current 1.3 knots complies with the measurement on the current log 1.0 knots in the heads 0.9 knots Concluding, at described area there is neither typical current at this area, nor tides. Typically changes in water level at period of 24h is slighter than 2cm Wind conditions Presented description of winds is based on the observations conducted between in Świnoujście base as it was the most appropriate place as a water area of vessels maneuvering. Analysis presented below is based on the M. Pluta s publication titled Wind conditions in the estuarial section of Odra river [Maritime Institute, Szczecin. Conference proceedings prepared for the 50 th anniversary of Maritime Institue, Gdańsk 2000], and the data from IMiGW (Meteorology and Water Management Institute) publication Environmental conditions of he South Baltic Sea Figures show the frequency of winds occurrence for the individual directions in a different quarters of the year (frequency expressed as number of days in month).

8 Mean frequency of wind direction in Swinoujscie in I third of Year N 30 NW NE W 5 0 E January February March April SW SE S Fig Average frequency of the wind occurrence from given directions for the first third of the year. Mean frequency of wind direction in Swinoujscie in II third of Year N 30 NW NE W 5 0 E May June July August SW SE S Fig Average frequency of the wind occurrence from given directions for the second third of the year. Mean frequency of wind direction in Swinoujscie in III third of Year N 35 NW NE W 5 0 E September October November December SW SE S Fig Average frequency of the wind occurrence from given directions for the third of the year.

9 An average yearly wind speed in Świnoujście is 3.9 m/s. The greatest average wind speed is in April (4,2 m/s), however it is not much different in the rest of the months (the least in August 3,5 m/s). The occurrence of strong wind (speed more than 10 m/s) is connected with the occurrence of strong low systems on the Baltic Sea. Because of this phenomenon the wind is becoming strong and of great speed, mostly from northern and northwest directions, which causes backwater and a backflow as a result. In Świnoujście strong wind has been observed for ten days of the average year, and very strong wind (more than 16 m/s) has been observed for 0,45 of the day. Maximum speed of the wind observed in Świnoujście was 22 m/s from the southern direction. In table 1.1 and in figure 1.8 frequency of strong and very strong winds is presented. Number of days in the average year in comparison to long period for the occurrence of strong and very strong wind in Świnoujście Table 1.1 Wind speed v w [m/s] Number of days v w = v w = v w = v w > Distribution of strong winds from given directions is presented in figure 1.8. Fig Number of days in the year with a strong wind in Świnoujście for all the directions Analyzing the distribution of the occurrence of strong winds it can be admitted that the wind of more than 10 m/s is the most frequent in Świnoujście from the following directions: NE N E 2.77 Days 2.53 Days 2.42 Days An average number of days without any wind and with wind of 7 Beaufort and more for the period between is shown in the figure 1.9.

10 Mean days with wind speed 7B and more; calm calm [%] number of days with wind 7B and more January February 0 March April May June July August September 0 October November December 0 Fig An average number of days without any wind and with wind of 7 B and more (from 1969 to 1999 IMiGW data) Water level Changes of the water level result in the change of under keel clearance. It also causes the difference in the conditions of shipping (different properties of vessel s maneuvering, changes of squat). The causes of the water level differences can be different. There are no tides in the system Odra Szczeciński Transgression Baltic Sea. Tidal changes on the Baltic Sea are too slight to cause significant tidal motions in the whole system. In contrast, noteworthy change of water level is observed, which is caused by the wind, backwater and pushing water by the wind. North wind causes backwater from the seaside towards the coast, causing the outflow water to the windward side of Szczeciński transgression. It results in the occurrence of current in the estuary. Average values of water level and extreme values are presented in figure 1.10 (IMiGW data). Świnoujście water level water level [mm] absolute maximum absolute minimum mean long periodical max 2000r difference from mean and long period & y.2000 Fig Extreme and average values of water levels for Świnoujście [mm] Mean sea level - 500mm

11 Strong current in the river estuary overcomes, usual, moderate water flow in the system, which apart from escape of river water, is regulated by the difference between the water intensity of Szczeciński transgression and the sea water of the Baltic Sea. Moreover, the flow in the transgression is influenced by the strong wind on the surface of the water, causing local growth and fall of water level and as a consequence water recirculation. Whilst the occurrence of strong wind the flow in Szczeciński transgression has a significant three-dimensional character, that causes strong opposition of surface and bed/bottom currents. Yearly water level in Świnoujście is shown in the table 1.2. Table 1.2 Yearly water level in Świnoujście Period Maximum sea level [m] Minimum sea level [m] (years) (A.L.) (MWL) (A.L.) (MWL) 2 5,87 0,97 4,17-0, ,27 1,37 3,94-0, ,73 1,83 3,67-1,23 A.L. Amsterdam Level reference level MWL Mean Sea Level +4,90 m A.L. An average water level in Świnoujście (data collected during many years) is + 4,90 m A.L (level of Amsterdam as a reference datum level). Since the data with extreme water level was collected from the measurements it can be assumed that they include all natural phenomena that may influence the level of hydrostatic pressure. To make the explanation about water level clear and complete it can be emphasized that the differences of water level are also significant in Mieliński and Piastowski Channels, since they cause the occurrence of strong current in both of the channels. Table 1.3 shows a statistical distribution of water level difference of Świnoujście and Piastowski Channel Estuary in comparison to Szczeciński transgression. Extreme differences of water level Świnoujście and Piastowski Channel Estuary. Positive fall means higher level in Świnoujście Table 1.3 Period (years) Positive fall [m] Negative fall [m] ,56 0,63 0,77 0,92 0,99-0,50-0,57-0,75-0,93-1, Ice conditions Icing and the occurrence of the ice on the waterway Szczecin Świnoujście is changing every year and depends a lot on present weather conditions. From the observations it can be noticed that in severe and critical conditions the first ice appears not earlier than 15 th November and disappears about the 15 th of April. Table 1.4 presents average and extreme periods of winter season. Average and extreme periods of winter season ( ) Table 1.4 Area icing period days with icing winter time days of min. mean max. min. mean max. collecting data Sea on the Swinoujscie roads Świnoujście, port without ice

12 Ice conditions change every year. For many years the of the impact of icing on the navigation/sailing has been controlled and the results of it are shown in the table 1.5. Impact of icing on the navigation ( ) Table 1.5 Area Days where navigation was difficult due to icing steel hull vessels Days where navigation was impossible due to icing min. mean max. min. mean max. Sea near the port of Swinoujscie (on the roadsanchorages) Świnoujście, port For the last 5 8 years (data from 1995) winters were gentle and the help of icebreakers was unnecessary. It is also worth mentioning that the strength of the ship hull has grown, especially of tug boats and as a consequence there is no need for the assistance of icebreakers. Usually the ice thickness 15 cm should not be a problem that cannot be overcome. Depending on the ice thickness and the occurrence of the ice on the surface, the increase of time that is required to go through the waterway Świnoujście Szczecin should be taken into account Temperature, pressure and humidity of air On the basis of a temperature analysis including an average twenty-four hour mean temperature as well as maximum, minimum and extreme values are shown on the chart below (fig. 1.11) Air temperatures in Swinoujscie temperature absolute min. temperature mean daily min, temperature mean daily temperature mean daily max. temperature absolute max. 20 [ o C] I II III IV V VI VII VIII IX X XI XII month Fig Temperatures for Świnoujście port An average atmospheric pressure from is presented in figure An average yearly pressure is 1015 hpa.

13 Mean air pressure hpa pressurehp I II III IV V VI VII VIII IX X XI XII months Fig Average values for atmospheric pressure for Świnoujście port. Relative humidity is on the level of 89% a year. Average monthly humidity is presented in figure relative humidity [%] reltive humidi I II III IV V VI VII VIII IX X XI XII month Fig Average values of relative humidity. Perimeters of humidity, air temperature and humidity can be described as moderate, and should not affect navigation in this region Visibility There is a meteorological station in Świnoujście on the analyzed area, and after 30 years of analysis it has been noticed that there were 1148 foggy days, which gives on average 38.3 days a year. The biggest number of foggy days was 65 in 1980, and the least number of such foggy days was 17 in 1966 and There are two groups of months that differ significantly as far as he frequency of fog occurrence is concerned. The first group, with high frequency, consists of months from October to April; and the second group includes months from May to September. The months in which there was the greatest number of foggy days were: November 18.2%, October and December 16.6% each. The least foggy months in Świnoujście were: July, in which foggy days were only 1.5% of the overall number of days a month and August 3.1%. Autumn is the season with the most frequent fog occurrence in Świnoujście, on average 15.7 days and in winter 12.9 days with fog. Less foggy seasons are: summer (2.9 days) and spring (6.8 days). The year during cool time has more foggy days (28.6 days), and the year during warm time has less such days (9.7 days).

14 Summing up, it can be stated that: fog is rather in autumn and winter, the earliest time of higher frequency of fog starts in Trzebież in the decade of September, and then in Świnoujście (the firs decade of October), the highest frequency of fog presence ends in the second decade of April in Świnoujście. The number of days with fog for the period between is presented in figure The presence of good visibility (>5 Mm) and low visibility (0.5 2 Mm) for the months of the year is shown in figure days with fog I II III IV V VI VII VIII IX X XI XII months frequency of occurance Fig Mean number of days with fog for given months (data ) mean visibility frequency of visibilit occurance >5Nm 60 frequency of visibilit occurance 0.5-2Nm I II III IV V VI VII VIII IX X XI XII months Fig Mean frequency occurrence of visibility >5Nm, mean frequency occurrence of visibility 0.5-2Nm (data from ) Wave conditions Wave conditions are similar as described at southern Baltic Region area (chapter 1.1.2). The mayor factor at Baltic Sea creating waves is wind. The largest waves rises during long lasting storms. Most significant wave at deep water area (anchorages and roads) is wave of height up to 1 m (max mean wave), and period in range 0 to 7s, and length of 50-80m. During stormy days wave may be of 3m, such extreme wave but only at open sea (far from land). Longest periods of waves near Swionujscie are 17s. Generally near port waves are smaller than at anchorage (and inside port waving does not occur). Winds from shore directions tends to create smaller waves than winds of direction going inshore. Largest waves were created during February after long storms of wind speed 25m/s and more.

15 Swell is not common at Baltic Sea (small depths) (only 0.5-2% of all waves). Waves can influence also water level in Swinoujscie (inflow or outflow of water.wave conditions are strongly related with sea state so proper operation procedures shall be accomplished with wind related restrictions EXISTING AND PLANED TRAFFIC ON ANALYZED AREA Existing and planned traffic Yearly intensity of merchant vessels traffic in Świnoujście port (entrance heads) between 2000 and 2005 and predicted traffic intensity between 2010 and 2020 is presented in table 1.6. It also should be emphasized that 50% account for entrance of vessels and 50% for exit of vessels. Existing and planned intensity of merchant vessels traffic in Świnoujście port in 2000, 2005, 2010 and 2020 Table 1.6 Year Number of vessels Vessels size Analysis of the vessels size entering Świnoujście port in 2000 shows the following percentage portion of vessels: 1. small vessels (L < 120 m; T < 6.1 m) 77% 2. medium vessels (L = 120 to 180 m; T = 6.1 to 8.0 m) 21% 3. large vessels (L > 180 m; T > 8.0 m) 2% where: L length over all, T draft EXISTING SYSTEMS OF TRAFFIC REGULATION (VESSEL TRAFFIC REGULATION SERVICES VTS, VTMS) AND NECESSARY CHANGES At the entrance of Świnoujście port and in the port there is a VTMS (Vessel Traffic Management Services) so called VTS. In appendix 5 there are some regulations concerning VTS EXISTING PORT REGULATIONS CONCERNING ENTERING AND LEAVING OF VESSELS AND NECESSARY CHANGES Existing port regulations determine, that entering and leaving vessels to Świnoujście port can be of maximum measurements: the overall length of 270 m, breadth of 42 m and draught of 13.2 m for fresh water. This limit of length up to 270 m and of breadth up to 42 m is caused by the entrance heads system. Appropriate simulation researches determining these safety conditions the port regulations ought to be performed in order to changed procedures and regulations for large vessels. In Świnoujście port there is a compulsory pilot service for vessels of length more than 60 m. Vessels with the draught over 11.0 must take a pilot at bouy N EXISTING TUG SERVICE, THEIR POTENTIAL AND TUG ASSISTANCE REGULATIONS AND NECESSARY CHANGES Existing port regulations determine minimum number of tugs that must be used as well as their minimum bollard pull force (table 2.9). Minimum number of tugs that must be used and their minimum bollard pull force Table 2.9

16 Overall length of a vessel (metres) Minimum number of all-in employed tugs over over over over over over Minimum bollard pull force (tonnes) For vessels over 180 m long at least one of the tugs must have an azimuth thruster or cycloid drive (Voith Schneider type) SHIP HANDLING OF LARGE VESSELS ( M LOA) IN PORT AREA At present maximum vessel entering Świnoujście port (L oa =270m, T=13.2m): 1. Boards pilots at buoy N2 or at anchorage No From buoy N2 to the pair of buoys 3 4 vessel moves with the speed of 8 knots. 3. At the buoys 3 4 fore and aft tugs of Uran type is made fast. 4. From the couple of buoys 3 4 to the entrance heads the vessel moves with the speed over 6 knots. 5. It enters the port and before mooring to the terminal pier, vessel is turned (fore heads to the entrance).

17 2. Navigational conditions at passage and entrance to port of Gdansk 2.1. PREVAILING NAVIGATIONAL AND BATHYMETRIC CONDITION Northern Port in Gdańsk is located in Gdańska Bay, in the east from Martwa Wisła estuary and at the entrance to port of Gdańsk. Geographical location: to north latitude, do east longitude. There two following basins on the area of northern port: main basin with coal, ore and LPG piers as well as fuel basins I and II with O, P, R and T oil terminals that are constructed on the extension of northern breakwater; and inside basin with north quays, southern and western. Port basins are shielded by breakwaters. There is a turning area (670 m) opposite the entrance from the fuel basin. The plan of the northern port is presented in figure 2.1. Parameters of oil piers: Pier Fig Northern Port in Gdansk plan maximum length of vessel "O" up to 150 m up to 9.6 "P" up to 300 m up to 15.0 "P" up to 300 m up to 15.0 "T" up to 350 m up to 15.0 Parameters of coal pier: Pier maximum length of vessel maximum draft of vessel Coal up to 280 m up to 15 Parameters of LPG pier: Pier maximum length of vessel maximum draft of vessel maximum draft of vessel

18 LPG up to 190 m up to 9.5 Dredging operations were conducted here for depths of 15.0m. At present a container terminal is being built in Northern Port in Gdańsk. The location of terminal and a logistic centre is shown in figure 2.2. Container terminal is an investment that started in 2004, and its first stage is planned to be finished around the second decade of Ore pier 300m LOA container vessel Northern Port Areas Container Terminal Logistics Center pipe lines Fig Plan of container terminal (Red fill presently build) The entrance waterway to Northern port has the following parameters: length = 3.2 Nm, width 350 m, depth = 17 m. The northern side of the waterway is marked by light buoys P-1, P-5, P-9, P-13. The southern part is limited by light buoys: P-2, P-6, P-10, P-14 and P-18. The waterway centerline is marked by light leading marks (light in line) in direction with the range of 7 Nm. There is a turning area with the diameter of 670 m and depth of 17 m at the end of the waterway. Detailed bathymetry of Northern Port basins is presented on a vector chart in figure 2.3. In figure 3.4 a bathymetry of entrance waterway to Northern Port is shown. Both charts illustrate the state in November 2005.

19 Fig Bathymetry of Northern Port in Gdańsk (November 2005) Fig Bathymetry of the entrance waterway to Northern Port in Gdańsk (November 2005)

20 2.2. EXISTING ANCHORAGE AND ANCHORING REGULATIONS There are two anchorages at the entrance waterway to Northern Port in Gdańsk (Fig. 2.5). Anchorage No 4 with the minimum depth of 16.5 m for bulk cargo vessels with the maximum draught up to T = 13.3 m. Anchorage No 5 with the minimum depth of 19.9 m for tankers with the draught up to T = 15.0 m. Anchorage no 5 Northern Port Fig. 2.5 Entrance waterway to Northern Port in Gdańsk with marked anchorages 2.3. PREVAILING HYDRO-METEOROLOGICAL CONDITIONS FOR DESCRIBED AREA As far as hydro-meteorological and hydraulic conditions are concerned that have an influence on the safety of maneuvering on the waterways to Northern Port and inside the basins are:

21 wind, current, visibility and fog, changes of water level, pressure and air temperature. ice conditions wave conditions Characteristic of winds The Southern Baltic Sea in a Polish zone is characterized mostly by the occurrence of winds from SW and S directions; its frequency of occurrence is 35-50%. However, barometric system is responsible for an individual situation. Presented data come from survey stations in Gdańsk (Northern Port) and Gdynia. All the data are from periods and Average wind directions depend on the season. For the first third the wind directions are presented in figure 2.6. It can be stated that there is a prevalence of southern and western wind from January to February, and in April N and NE directions are prevailing. Mean frequency of wind direction in North harbour in I third of Year N 25 NW NE 10 W 5 0 E January February March April SW SE S Fig Average frequency of wind directions in the first decade In the second third of year N to NE directions are taking dominance in May and June, and W to SW for July and August (fig. 2.7).

22 Mean frequency of wind direction in North harbour in II third of Year N 20 NW 15 NE 10 5 W 0 E May June July August SW SE S Fig Average frequency of wind directions in the second decade In the third third of the year the most frequent winds are in W to S directions which is presented in fig Mean frequency of wind direction in North harbour in III third of Year N 25 NW NE 10 W 5 0 E September October November December SW SE S Fig Average frequency of wind directions in the third decade The average number of days with the wind of 7B and with the periods of calm in percentage are shown in fig. 2.9.