Umitaka-class submarine chaser

In this type, the navigation performance was improved and the design was rationalized based on the operational results of the preceding 1954 planned boats (Kari-class, Kamome-class). The basic design was carried out by the Ship Design Association for boats in 1954, but it was transferred from this model to the Technical Research Institute of the Defense Agency (at that time), and the plan number was K103B.^[1]

They were designed to be larger (1.4 times the standard displacement) based on the FY1954 plan, and the ship type was the same flush deck type. In the 1954 classes, the elaborate design with extremely thin plates led to an increase in man-hours, so the bow was 2.9 to 3.2 mm thick, but now it is 4.5 to 6 mm, and the area below the waterline is also 4.5 to 8 mm. Although it was thickened to millimeters, it still had a thin plate structure as a whole. In addition, in the 1954 classes, the bridge and the deck room were separated to reduce the area on the wind pressure side, but there were drawbacks such as the inconvenience of communication inside the ship in stormy weather and the inability to secure sufficient space inside the ship. Therefore, in this model, the front and rear superstructures are integrated so that it can be easily moved back and forth even in stormy weather.^[2]

Air conditioning has been introduced in some areas such as battle areas and officer's rooms, and the living quarters have been expanded (10% increase in area per person), improving livability. However, due to these factors, the center of gravity rose and the stability deteriorated, and Umitaka and Otaka were equipped with about 15 tons of fixed ballast. In addition, for the following boats, measures to lower the center of gravity were taken in sequence by reexamining including the equipment, such as changing the thickness of the upper deck (from 6 mm to 5 mm).^[2]

In addition to the wing on the bridge, only the final ship, Kumataka was equipped with the flagship equipment, so the superstructure is extended 2.5 meters to the rear to provide the headquarters general affairs room. In addition, since the 1934 boat, corrugated panels have been adopted on the side walls of the superstructure to reduce man-hours and weight.^[3][2]

As the main engine, a relatively heavy medium-speed robust diesel engine with almost the same configuration as the Kamome-class has adopted, and the 635VBU-45 type 2 manufactured by Mitsui Zosen under a license agreement with B & W in Denmark. It was equipped with a trunk-piston diesel engine with a cycle single-acting in-line 6-cylinder exhaust turbocharger. This was developed as a sister engine with half the cylinder output of the 950VBU60 type (output 6,000 horsepower) of the Ikazuchi class' Inazuma built in the previous year's plan. It is equipped with a self-reversing mechanism and is directly connected to the propulsion device. The fuel used was No. 1 A heavy oil for ordinary diesel engines.^[4]