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SSPA SWEDEN AB – YOUR MARITIME SOLUTION PARTNER
2 (12) SSPA Report No.: RE40146881-01-00-A
Contents
1 Introduction ............................................................................................................. 3
2 Method ....................................................................................................................... 4
3 Full scale measurements – m/s Emsmoon .................................................... 5
Vessel particulars .................................................................................................................................................. 5 3.1
Measurement set-up ............................................................................................................................................ 6 3.2
4 Collected resistance measurements 2013/2014 ........................................ 7
Brash ice channel measurements .................................................................................................................. 7 4.1
Open water resistance reference measurements ................................................................................... 9 4.2
5 Collected ice measurements 2013/2014 .................................................... 10
6 References .............................................................................................................. 12
SSPA SWEDEN AB – YOUR MARITIME SOLUTION PARTNER
3 (12) SSPA Report No.: RE40146881-01-00-A
1 Introduction
For efficient, redundant and not least safe winter navigation in the northern Baltics the interaction between the Finnish-Swedish ice class, available ice breaker assistance and current ice conditions are of great importance. During the most severe winter months the strength and capability of the merchant vessels needs to be adequate to ensure the maritime safety and low environmental risks. However, in the beginning and end of the winter season or during mild winters less ice strengthen and special purpose built vessels may be better suited for efficient operation.
The ice class rule notations are based on an ice going performance criteria of 5 knots in a newly broken brash ice channel with various brash ice depths depending on ice class notation. For the highest ice class; IA Super a consolidated ice layer of 0.1m is added to the broken brash ice thickness.
To address the constant changing ice condition, have an efficient winter navigational infrastructure and still ensure high safety the ice class restrictions has been inferred and are used during the winters.
In connection with the current ice/weather conditions and traffic situation different ice class restrictions are decided for different areas and ports.
The ice class restrictions thereby rely on the performance of merchant vessels with a certain ice class to maintain high safety, low environmental risks and efficient infrastructure. The correctness of the performance compared to ice class notation are thus of great importance.
One cornerstone in the performance of ice strengthen vessels are, except from hull form and sufficient displacement, the installed main engine output power. The minimum power requirement of the Finnish-Swedish ice class rule is based on needed power to overcome the added brash ice channel resistance in the above mentioned channels. The added resistance is determined either through calculations or through ice model tests.
During the last years the results from calculation of minimum output power requirements and results from ice model testing have diverged and full scale data compared to calculated and possibly model tests have been asked for.
Focus in this investigation is on added brash ice channel resistance. Comparisons between full scale measurements and calculations are to be made.
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2 Method
To gain more knowledge and investigate the added brash ice channel resistance full scale measurements are collected and compared with the added resistance equation of the rules, RCH. The equation is a function of vessel size, hull shape, ice class and brash ice thickness.
The full scale measurements are performed in several different brash ice thicknesses, ice conditions and ice qualities. The ice conditions, channel width, thickness, passage frequency etc. are monitored and measured before the vessel passes the reference channel where the resistance measurements are collected.
The full scale total resistance is determined through propeller shaft torque measurements followed by propeller thrust calculations. Added brash ice channel resistance is isolated through calculation aided by open water reference tests with the same corresponding speed as for the total resistance.
The measurements are compared and evaluated against calculated added brash ice channel resistance, RCH, according to the Finnish-Swedish ice class rules.
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3 Full scale measurements – m/s Emsmoon
Added brash ice channel resistance measurements have been collected in cooperation with Ahlmark Lines on-board the general cargo vessel m/s Emsmoon. The vessel represents very well an average vessel trading in the northern part of the Baltics, both regarding size and ice class. This is also shown in a previous research project [1] which included a traffic analysis.
Measurement equipment was installed on the vessel and as the vessel called suitable ports on its regular route in the north of Sweden measurements was collected. A certain part of the port approach channel was chosen, ice conditions were measured and the vessel reduced its speed to about 5 knots during passage of the controlled part.
Vessel particulars 3.1
Table 1 - General information and principal dimensions m/s Emsmoon
General information Principal Dimensions
Type General cargo carrier DWT all told 6250 t
Built: 2000 DWT cargo capacity 6000 t
IMO 9213894 Loa 111.74 m
Call sign V2BN3 Beam 14.95 m
Flag AG Draft 6.38 m summer
Built 2000 GT/NT 4563/2613
Classification BV I3/3/E, ice class 1A Speed Abt. 14 knots
Figure 1 - Reference vessel m/s Emsmoon
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Measurement set-up 3.2
The full scale measurements were collected with the SSPA in house data collecting system. Measured and stored variables are listed in Table 2 below.
Table 2 - Measured variables in the datalogger system.
Variable Unit Comment
Latitude deg, min
Longitude deg, min
Speed over ground, SOG knots
Course over ground, COG deg
Heading, HDG deg
Rudder angle deg Positive to port
Propeller pitch %
Propeller rpm min-1
Torque, Propeller shaft kNm
Power, Propeller shaft kW Calculated
Pitch motions Deg Positive bow-up
Roll motions deg Positive to port
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4 Collected resistance measurements 2013/2014
In this chapter collected measurements during the mild winter of 2013/2014 is briefly presented. Complete analysis of the measurements will be presented in the final report of the project.
Brash ice channel measurements 4.1
Unfortunately only one measurement point in very light ice conditions was collected. An attempted was made to include a second point however the ice conditions was judged to be too light.
The measurement point was collected during departure, in ballast condition, from Haraholmen the 26th of February 2014. Time series and pictures are presented below. Presentation of corresponding ice conditions are found in chapter 5.
Figure 2 Measurement area close to Haraholmen, Piteå.
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Figure 3 Measured propeller shaft torque and speed over ground.
Table 3 Average figures, Haraholmen.
Average torque 32.5 [kNm]
Average speed 5.3 [kn]
Figure 4 Visualisation of channel, aft of vessel.
0 100 200 300 400 500 60020
25
30
35
40
45
Brash ice channel, Haraholmen 2014-02-26
Time [s]
Sh
aft T
orq
ue
[kN
m]
0 100 200 300 400 500 6004
4.5
5
5.5
6
6.5
Sp
ee
d [kn
]
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Open water reference measurements 4.2
To be able to calculate the resistance component associated with brash ice channel resistance (RCH) from the ice resistance measurements, e.g. presented in 4.1, open water reference measurements are needed. The goal was to collect speed-power curves in calm and deep water for both loaded and ballast condition. During 2013/2014 the ballast condition reference was collected which is presented below.
Figure 5 Propeller shaft torque vs. speed over ground.
Table 4 Measured open water torque.
SOGavg. [kn] Torqueavg. [kNm]
1.2 13.2
1.3 15.1
3.9 17.7
7.8 29.9
10.3 47.3
13.0 75.1
13.5 88.1
2 4 6 8 10 12
20
30
40
50
60
70
80
Open water reference 2014-04-05
Speed [kn]
Sh
aft T
orq
ue
[kN
m]
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5 Collected ice measurements 2013/2014
The project aim is to monitor and analyse the growth and fate of a specific approach channel during the winter season.
In 2013/2014 a weather station and a web camera were installed on the northern shore of Skelleftehamn harbour. The first entrance of m/s Emsmoon to Skelleftehamn in thin ice was video filmed on January 31st. However the ice melted and moved out from the harbour area on February 18th. Despite some cold spells in March only drifting floes were observed for the rest of the winter. A picture from the web camera 2014-02-25 is shown in Figure 6.
Figure 6 Ice conditions in Skelleftehamn 2014-02-25.
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Ice conditions Haraholmen 2014-02-25 5.1
Ice measurements corresponding to the ship resistance measurement described in section 4.1 is presented below.
Measurement of ice conditions in the ship channel south of Haraholmen.
Level ice on both sides of the ship channel could be classified as columnar ice with a thickness of 45-50 cm. The crystal bonds were partly melted and the upper surface was covered with 5-10 cm snow and hard slush, see Figure 7 (left).
Table 5 Position, time and temperature.
Position: 65°10.6 N, 021°36.0 E
Time: 2014-02-25, 12.00-13.30
Temp: +4°C, sunny, light wind
The broken channel was about 30 m wide with a straight interface between loosely floating ice blocks and the level ice. Typically the ice blocks were rounded with 40 cm depth and 40-60 cm width. In average the depth was 40 cm along the center line with a gradually increasing depth to 80-110 cm along the edges. The largest ice blocks were 100-150 cm in diameter measured at the waterline with a depth of 90 cm. The channel was covered by 20 cm drift snow that was mixed with ice and water when the channel was broken. Ice distribution behind m/s Valkyria in the measured section as well as the chosen measuring section of the ship channel as in section 4.1 is shown in Figure 7 (right).
Figure 7 Left:Vertical edge of the landfast ice outside Haraholmen. Right: Ice block distribution behind tug boat Valkyria.
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6 References
1. Westerberg, 2014: EEDI and Finnish-Swedish ice class rules, Impact study and operational aspects, SSPA Report RE40136554-01-00-B.
2. Trafiksäkerhetsverket, 2010. Isklassföreskrifter och tillämpning av dem. Sjötrafikföreskrift, TRAFI/31298/03.04.01.00/2010. Trafiksäkerhetsverket, Helsingfors. (Authors comment, i.e. Finnish-Swedish Ice class rules)
3. Krav på isklass och tonnagestorlek, 2013, http://www.sjofartsverket.se/sv/Sjofart/Isbrytning/Isklasser--krav/ Authors comment: General ice class restrictions, downloaded 2013-09.
