The dimensioning of high power propeller systems for arctic icebreakers and icebreaking vessels (Part 3 and 4) 1

Abstract

The massive growth of arctic sea transport, planned for the coming years is associated with the application of unfamiliar propulsion equipment for icebreaking. The classical system with fixed pitch propellers, driven by electrically transmitted diesel – or steam – power, tends to make place for propulsion systems with new elements such as controllable pitch propellers and propeller nozzles.

The introduction of these new elements in very large dimensions, means that more and rather vulnerable parts will be exposed to heavy iceloads. The advantages of this kind of new equipment can only safely be utilized if its behaviour under such extreme loads can be sufficiently evaluated. Common knowledge at this stage is rather restricted, being based on the experience with a few number of installations in service. It is also clear that theoretical analysis can only partly answer the questions.

Since in the near future a considerable number of new installations for icebreaking will be put into operation, it is expected that the coming years will provide an unknown feedback of practical experience. A better understanding of the main influencing factors finally will result in strong changes in the concept of icebreaking propulsion equipment, extrapolated to large powers.

The paper describes the nature of iceloads and indicates methods to approximize the magnitude of ice impact on propeller blades and nozzles. The influence of power and propeller size is investigated. The resulting stresses are to be compared with allowable values both for a single static shock as well as dynamically in fatigue. Recommendations are given for the dimensioning of blade sections, the supporting points of nozzles and the way of determining their plate thickness. A comparison is made with the requirements of classification societies.

Part 1. Historical events and future plans.

Part 2. Discussion of Class requirements.

Part 3. A method to determine blade strength for ice operation.

Part 4. Ducted propellers in ice.