2.5 SA-15 Operation data
WP5 collected SA-15 data as to icebreaking capability and hull damages in order to calibrate the ship transit velocity simulation code developed by WP6 and refered to the service ship designed by WP4.In this chapter the icebreaking capabilities are briefly summarized. The details are refereed to WPl report(Tsoy et al.,1998).
SA-15 was the designation for the Finnish/Russian development for 15,000 ton multipurpose cargo ships whose purpose was to improve delivery of various cargoes to the ports of the western NSR on an year round basis. In total, 19 ships were built in the two shipyards, Wartsila and vallnet in Finland during the period of 1982 to 1987.The general arrangement is shown in Figure 2.5.1. The SA-15 class equipped a roll-on roll-off deck with the stern ramp to discharge cargo directly on the land fast ices off the arctic ports in the winter season. The ship was designed to meet the requirement for ULA class of Russian register of shipping to attain sufficient ice performance both in summer with independent operation and in winter period with escort by the Arktica class icebreakers.
Several innovative systems were aboard the SA-15s. An air bubbling system was adopted to reduce friction and accretion between a hull and snow/ice at low air temperature in winter, and a hull was coated with low friction paint,Inerta-160.The SA-15 power plant comprises two medium speed engines of 7.72 MW output per each at 560 revolution per minute. Fluid couplings and friction couplings were installed between the main engines and the reduction gear. The former is mainly employed in navigating in ice to protect the propulsion system from ice torque. The latter is used for open water or light ice conditions. A controllable pitch propeller with four blades was adopted to attain a quick thrust change in ice. It measures 5.6m in diameter and 0.42 in hub/blade ratio. The principal particulars of the SA-15s are listed in Table 2.5.1.
Ship speed in level ice and pack ice
Extensive tests were performed in the Yenisei Gulf at the beginning of May in 1983 as the ice trial of SA-15m/s Igarka. The tests were run to confirm the icebreaking capability in various conditions and to assess the performance of air bubbling systems. The design specifications requested continuous icebreaking capability in lm thick ice with 20cm-snow cover at a speed of l knot. Figure 2.5.2 shows the power speed relation in 0.7 to 0.8m compact level ice with 5 to 10cm thick snow covers. Figure 2.5.3 plotted the relation between speed and ice thickness at a power of 90% of the maximum continuous output.
The test showed far better icebreaking capability than the specifications and m/s Igarka recorded a minimum steady speed of 0.5 knot against l.3m thick fast level ice with 20cm snow cover. A far better velolity is obtained when transiting pack ice, and Figure 2.5.4 shows the velocity as a function of ice concentration in tenth class of ice cake.
Ship Speed in various ice conditions
In reality, an icebreaking ship encounters various ice conditions and ship operators have to estimate a ship velocity as a function of ice regime in order to predict a transit time. Figure 2.5.5 illustrates a ship velocity against mixed ice concentrations with different ice ages containing hummocking fields ranging from 1/5 to 2/5. This figure clearly demonstrates that the ship transit velocity decreases considerably when encountering the heavier the ice conditions. The severity is expressed as a function of multiples of ice concentration and its category such as ice free water, gray-white ice, first-year ice, second-year ice and multi-year ice occupies. In order to develop the ice numeral, we need the data as depicted in Figure 2.5.5