As a result of this basic design work, research focused on development of a ship with the main particulars described in Table 4.1-5. This ship is conceived as a multipurpose icebreaking freighter for navigation of the coastal waters of the NSR (and some inland rivers). The ship is longer than that of the SA-15 class but has a shallower draft, although its displacement will be roughly the same. The design specifications mandated continuous icebreaking capability in 1.2m thick ice at a speed of 3 knots, more powerful than the SA-15s. In terms of the propulsion system, both conventional propellers and duct propellers were tested. To determine the hull form of the ship with these main particulars and obtain definite data on the performance of the ship in ice and open water, three types of bow (A, B and C) and two types of stern (a, b) were designed, and the corresponding models were prepared for testing. Their bow and stern forms are exhibited in Figure 4.1-17. Their features are given below.
Bow A: Conventional icebreaker bow form with rather simple V-frame lines
Bow B: Spoon bow with more convex frame lines than A
Bow C: Bow form with more concave frame lines at the load waterline than A
Stern a: Mariner stern with moderate U-frame lines
Stern b: U-frame lines accentuated near the bottom
Model tests were conducted with various combinations of the above bows and sterns.
These combinations are indicated below by letter: for example, a ship that combines bow A with stern a is given the designation A-a. The combinations of the two propulsion systems are indicated CP for conventional propeller and NP for nozzle propeller, so that ship design A-a is further divided into A-a (CP) and A-a (NP).
In the tank tests, the work was divided among the Ship Research Institute (SRI) the Ministry of Transport, NKK Corporation (NKK) and Mitsubishi Heavy Industries, Ltd. (MHI). For the model tests, models were prepared for each of the above ship types on a scale of 1:36 and tested in turn by each of the three agencies above. The sizes of the ice model basins of each agency and their mechanical properties of the model ice are summarized in Table 4.1-6. SRI, NKK and MHI conducted the following tests:
