Icebreakers have been sailing for some 120 years. At first only slightly more powerful than ordinary commercial vessels, in the early years icebreaker propulsion systems consisted of steam engines connected to a propeller. Marine diesel engines later began to replace steam engines in tandem with advances in electric equipment technology.
The first diesel-electric icebreakers were built in the 1930s, and have since become the standard solution for this kind of vessel. In the 1970s and 80s, the main focus of development work was the electric drive itself. Development of mechanical devices like controllable pitch (CP) propellers and geared propulsion drives (Z-drives) as progressing at the same time. Smaller AC motors allowed for new thinking, with podded drives coming on the scene in the early 1990s.
Today, the full range of traditional fixed-pitch propellers is available, as well as CP propellers with conventional shaftlines, mechanical Z-drives/azimuth thrusters, and podded drives, all powered by electric motors. Hybrid design solutions have also been developed, employing podded drives combined with conventional shaftlines.
Most of the focus in development work to date has been on creating more powerful devices to break thicker ice. However, there is also a need for smaller devices for ships operating in restricted waters like rivers, lakes, and coastal zones.
This paper will first discuss the development of icebreakers in general, then concentrate on conditions surrounding the development of smaller vessels.