Tank and manufacturing method thereof

A manufacturing method of a tank including a liner, and an fiber reinforced plastics layer a fiber reinforced plastics layer including at least two fiber bundles alternatively formed around the outer periphery of the liner, one fiber bundle of the at least two fiber bundles having at least one hoop layer, and another fiber bundle of the at least two fiber bundles having at least one helical layer, comprising the steps of:

• winding the another fiber bundle having the at least one helical layer around a dome portion of the tank;
• positioning the another fiber bundle having the helical layer on an inner layer of the fiber reinforced plastics layer;
• increasing a tensile force onto the another fiber bundle constituting the helical layer to decrease a thickness of the another fiber bundle in a laminating direction of the fiber reinforced plastics layer;
• and
• winding the another fiber bundle having the decreased thickness compared to that of the one fiber bundle constituting the hoop layer so that the another fiber bundle becomes flatter and more even than the one fiber bundle constituting the hoop layer,
• wherein the one fiber bundle having the hoop layer being formed outside the another fiber bundle having the helical layer, and
• wherein the another fiber bundle having a smaller number of fibers than the at least one hoop layer.