Table 5: Maximum recorded measurements. Run
Frame gauge 83
157 168 75
157 Channel Description End first Mode Test Truster angle Ice conditions
Power setting forward aſt
P10.5cSO P48eSC P47eSO
S12.5cSO P47eSC
straight line turning
manoeuvring straight line turning
aſt aſt
bow aſt aſt
combinator combinator combinator combinator combinator
anti-clockwise 25 deg same directions change of direction - fwd in thicker level ice anti-clockwise 25 deg same directions
channel edge level ice
55 33
55 75
55 75
channel edge level ice
55 33
100 75
100 75
Plate gauge 157 95
157 157 61
Longitudinal members 83 57
161 183 83
P48cPL P7cPL
P47ePL P48cP3
P12.5dPL
P10.5dL P10.5dL P10.5dL P7dL P7cL
turning turning
turning turning
straight line
straight line manoeuvring manoeuvring manoeuvring straight line
aſt aſt
aſt aſt aſt
aſt aſt aſt aſt aſt
combinator constant rpm
combinator combinator constant rpm
combinator moving from level ice into channel
combinator combinator combinator
navigation in slightly deformed ridged ice then level ice return to port short time in level ice
channel edge 55 100 100
anti-clockwise zig zag
anti-clockwise anti-clockwise
25 deg same directions
15 deg different directions
25 deg same directions 25 deg same directions
level ice level ice
level ice level ice level ice
channel edge
33 35
33 33 30
55
75 60
75 75
100 100
75 60
75 75 45
100
The trials Te trials took place between 13 February and the 16 February, 2010, and numbered some 182 trial runs. Te ice trials were carried out in the vicinity of Lumparn depending on selected ice conditions during the trials. For most of the trials, the vessel navigated
astern and just below the load waterline of 4.1m. Te vessel also had a slight trim by the stern, with the typical draughts of 3.92, 4.02 and 4.12 taken from the ship’s measurement system and checked visually to give approximate agreement when at port and during ice measurements. Te azimuth propulsion units were both
operating in the pushing mode: that is, with the hub forward and propeller aſt, during all of the runs. Te approximate propeller tip submergence was a minimum and maximum of 1.3cm and 3.7cm respectively from the waterline at the aſt end with the forward end approximately 20cm deeper. The pitch and engine rpm operate in
combination to develop the thrust required on demand. However, when navigating in ice, it is preferred to maintain the engine rpm at a high level. Therefore, during the trials the runs were made using the
The Naval Architect April 2011
combinator and maintaining a constant rpm value with variations in pitch. Te modes were then varied with different forward and aſt thruster combinations. Tese combinations were undertaken for
straight line navigation and while turning using preset angles of thrusters, 25 and 15degs, both with the thrusters operating in different directions and operating in the same directions. During turns, the ship’s speed was established at the preset combination mode and then the turn was made. Tis approach was adopted for all turns except turning on the spot with the thrusters at 90degs. In addition, a zigzag manoeuvre was carried out, principally for the channel ice tests due to the confined width of the channels while turning. The
sequence and combination of
trial runs was determined on the basis of ice conditions, the available navigation conditions and time. In addition, a number of general manoeuvring measurements were recorded while the ship was navigating between runs.
Ice and weather conditions During the open water trials there was only
a light to moderate wind present, typically 10 to 12knots. Te wave state was also light to moderate. Tere were some ice floes present; however, these were avoided during the runs. The winter season of 2009-2010 was
considered an average winter based on the ice extent, with some severe ice conditions due to significant ice driſt and movement in localised areas; for example, off the Swedish coast at the south of Bothnia Bay. Te maximum ice extent was reached in March. Te ice conditions in the Ålands, therefore, presented an ideal opportunity for the ice trials. Te ice conditions encountered during
the trials were recorded periodically between runs, depending on the variation/ change in conditions, trials sequence and location. It may also be noted that there was very little ice pressure, since there were few ice ridges. Te level ice thickness ranged from 15cm
to 40cm, with an average of 28cm for all of the days. During the first day of ice trials the ice thickness changed 7cm, while the following days experienced slightly larger variations of 10cm and 20cm respectively. Channel breadth typically ranged
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