Tonnage tax option for shipping companies permits special income computation with a prolonged lock in and expanded vessel eligibility. A voluntary tonnage tax scheme allows qualifying Indian companies that own qualifying ships (and, from the later effective date, qualifying inland vessels) to compute income from ship operations under a special tonnage regime with separate accounts; election carries a prolonged lock in and re entry restriction, and such tonnage income is excluded from MAT computation. Qualifying ships/inland vessels must meet net tonnage, registration and valid certification requirements and several vessel categories and extended fishing use are excluded. The operator definition covers ownership and various charter arrangements but excludes long term bareboat charters out.