I'm sending you the sentences again. (Is it incorrect to use the simple past??). Thank you.

1)Though the narrator gets frightened the captain decides to sail. (OR The captain decides to sail, despite the narrator’s fears.
2) He feels uneasy and can't sleep. So he goes upon deck at midnight. He hears a loud, humming noise.
3) All of a sudden the sea has grown and big waves has invaded the ship.
Luckily, the ship lifts from the sea and regains her right position (Or returns to her correct position?). He is struck (surprised?) to see the foaming ocean around him.
4) He soon discovers that he is the only survivor of the shipwreck together with a Swede, who has shipped with them at the moment of leaving the port. All the other members of the crew has died swept away by the sea.
5)They see the ship hasn’t been badly damaged. They sail at high speed for 5 days and nights. On the fifth day the sun gives out no light, it is very cold and extremely windy.
6) All of a sudden they see a gigantic ship nearby. The ocean current becomes stronger and rougher.
7) Their ship sinks, as it is hit by the other ship. The Swede dies and the narrator is thrown on board the unknown ship. When he sees the sailors, he soon feels a sense of fear.

1) The captain decides to sail, despite the narrator’s fears.

2) He feels uneasy and can't sleep, so he goes up on deck at midnight. He hears a loud, humming noise.

3) All of a sudden, the sea grows angry, and big waves overtake the ship. Luckily, the ship lifts from the sea and regains her right position. He is surprised to see the foaming ocean around him.

4) He soon discovers that he is only one of two survivors of the shipwreck. The other survivor is a Swede, who shipped with them just as they left port. All the other members of the crew die and are swept out to sea.

5)They see the ship isn't badly damaged. They sail at high speed for five days and nights. On the fifth day, the sun gives out no light. The weather is very cold and extremely windy.

6) OK

7) Their ship sinks when it is hit by the other ship. The Swede dies, and the narrator is thrown on board the unknown ship. When he sees the sailors, he soon feels a sense of fear.

Compare all VERY carefully to catch all the corrections, large and small.

1) The first sentence, "Though the narrator gets frightened, the captain decides to sail," is grammatically correct. However, if you want to rephrase it, you can say "The captain decides to sail, despite the narrator's fears."

To explain how to get the answer:
To determine if a sentence is grammatically correct, you can check if the subject and verb agreement is correct. In this case, "the narrator gets frightened" is in the present tense, simple past tense, which is grammatically correct. The phrase "the captain decides to sail" also follows subject-verb agreement.

2) The sentence "He feels uneasy and can't sleep, so he goes upon deck at midnight. He hears a loud, humming noise" is grammatically correct.

3) The sentence "All of a sudden the sea has grown and big waves have invaded the ship" needs some adjustments. Instead, you can say "All of a sudden, the sea grew, and big waves invaded the ship." Additionally, instead of "regains her right position," you can say "returns to its correct position." Finally, you can replace "He is struck" with "He is surprised" to improve the sentence.

4) The sentence "He soon discovers that he is the only survivor of the shipwreck together with a Swede, who has shipped with them at the moment of leaving the port. All the other members of the crew has died swept away by the sea" requires some corrections. You can rephrase it as "He soon discovers that he is the only survivor of the shipwreck, along with a Swede who had joined them at the moment they left the port. All the other members of the crew have died, swept away by the sea." Here, it is important to use past perfect tense for the action of the Swede joining the crew, and present perfect tense for the action of the crew members dying.

5) The sentence "They see the ship hasn't been badly damaged. They sail at high speed for 5 days and nights. On the fifth day, the sun gives out no light; it is very cold and extremely windy" is grammatically correct.

6) The sentence "All of a sudden they see a gigantic ship nearby. The ocean current becomes stronger and rougher" is grammatically correct.

7) The sentence "Their ship sinks, as it is hit by the other ship" is grammatically correct. However, you can rephrase "The Swede dies" as "The Swede dies," and "thrown on board the unknown ship" can be changed to "thrown onto the unknown ship." Finally, you can change "when he sees the sailors, he soon feels a sense of fear" to "when he sees the sailors, he quickly becomes afraid."