The correct answer is option 4. Tipu Sultan`s major interest in building ships was to establish an overseas settlement at port Basra (Iraq) under his control, similar to the European companies.

Option 1, fighting the English at sea, is not the primary reason for Tipu Sultan`s shipbuilding interests. While he did engage in conflicts with the English, his main focus wasn`t solely on fighting them at sea.

Option 2, promoting trade and commerce, is not the primary motive behind Tipu Sultan`s shipbuilding efforts. While trade and commerce may have been a secondary benefit, it wasn`t the main purpose for his shipbuilding endeavors.

Option 3, maintaining diplomatic relations with Muscat (Oman), is not the primary reason for Tipu Sultan`s shipbuilding interests. It is true that he had diplomatic relations with Muscat, but shipbuilding was not primarily aimed at maintaining these relations.

Therefore, option 4 is the correct answer. Tipu Sultan`s main interest in building ships was to establish an overseas settlement at port Basra (Iraq), which would be under his control, similar to the European companies.