Figure 4.1-11 illustrates the width and draft of the commercial polar-sea ships of Russia and other countries, plotted as a function of ship length. The ratio of width to length of Russian ships is concentrated in the 1:6-1:7 range, narrower than its icebreakers, which lie in the range of about 1:5. In contrast, the icebreaking commercial ships of other countries are scattered across a broad range of width/length ratios. Except for the unusually large nuclear-powered LASH ship Sevmorput, Russia's icebreaking commercial ships are no wider than the SA-15 type ship's 24m. Russia's icebreakers and icebreaking commercial ships therefore adhere to a consistent design enabling them to work together in escort operations. As Figure 4.1-11 illustrates, again with the Sevmorput as the sole exception, the draft of Russian icebreaking commercial ships is no greater than 10m. The shallow waters of the NSR impose limitations on their drafts.
4.1.3 Research and Development in Icebreaking Ships
(1) Recent achievements in icebreaking ships
Systematic research and development in the field of polar navigation has barely begun. Furthermore, the optimum conditions of the various technologies involved in icebreaking operations often depend on the condition and characteristics of the ice and the operational mode of the ship. The present maturity of ordinary ship designs is still a distant goal for icebreaking technologies. Stated in a more positive way, the room for further technological innovation is enormous, and the development and commercialization of technologies based on new approaches is continuing. Especially noteworthy is the recent progress in the design of hull forms for icebreaking ships. There are several reasons why these advances are happening now. First, researchers' understanding of the mechanical properties of ice and of the mechanisms of icebreaking are steadily deepening. Second, improved methods of gathering and analyzing data on ship structures have brought greater assurance in the area of the structural safety of novel hull forms. A further factor is the development of ice tanks and experimentation as reliable tools for testing new ship models and their effectiveness.
The primary objective of development of icebreaking hull forms is to improve icebreaking performance by reducing the resistance from ice. Because the bow form governs icebreaking behaviors, developers have proposed a wide range of bow shapes designed to minimize ice resistance. The conventional bow form of icebreaking ships is a wedge type with V-frame lines. The wedge type is widely adopted because it offers a practical tradeoff between icebreaking and hydrodynamic requirements. However, recent research has demonstrated that bows with a round stem and blunt water line provide lower icebreaking resistance.