Combination of Open Water and Icebreaking Performance of Ships

During a R+D-project, four different bow hull shapes with different icebreaking capabilities have been developed. One ship was optimized for open water performance, the second was provided with a typical icebreaking bow, and the third and fourth were designed to combine open water qualities with a respectable icebreaking ability.The models were tested in calm open water, in seaway and in ice. The results of the tests were used together with other data in a computer program which has been developed to compare the economic parameters of different ships on a defined route.The round trips of the vessels were simulated for every month of the year. The above mentioned ships were compared on two routes in the Baltic Sea, an area which is only partly covered with ice during a few months of the year. To compare the different ships the required freight rate (RFR) was used.In calm water the propulsion performance on loaded draft was practically identical for all tested vessels at a speed of 15 knots. In seaway the ship with the classical icebreaking bow was slightly faster than the bulbous bow versions. In level ice the vessel with conventional bulbous bow needs about 2.5 times more propulsion power than the classical ice breaking bow. In ice cake (small ice floes) the propulsion power for the tested vessels was practically identical. The question which vessel is the best for a defined route depends on many factors, e.g. environmental conditions, distance in ice covered water, availability of icebreaker assistance, time losses caused by waiting for an icebreaker, speed of the vessel on ballast draft, etc. The differences in the economy of the vessels described above are very small. The classical icebreaking bow is an economic solution when the ice conditions are heavy, the distance in ice covered water long and when icebreakers assistance are not generally available in short time.