Theory:

     Lying snugly on a velvet backing was a most beautiful model of the ship. On it was inscribed “B.I.S.N. & Co. S.S. RAJULA.” I placed the box carefully on the table. Then I threw my hands round the captain and hugged and kissed him.

     He patted my cheek and smiled as he saw me lift the box and walk happily out of his room. I proudly showed my present to everyone I met. “See what the Captain has given me. Isn’t it lovely?”

     “Yes, indeed,” was the unanimous verdict.
 
     I was the happiest person on board that day.
Explanation:
 
To Vasantha's eyes, the sculpture of the ship looked like a fantastic treasure. The gift was placed very prettily on a velvet piece of cloth inside the brown box. Vasantha didn't have any words to express her gratefulness or happiness to the captain. She kept the gift box aside and hugged and kissed him.

The captain was glad on looking at her being happy. He patted her cheek and smiled at her. He was so happy to see her carrying the gift box while leaving his room. The captain would sure not forget the timely help of the kid. After all, it was Vasantha's initiative that saved a life.

On the other side, Vasantha was displaying her gift to everyone on the ship, asking, "See what the Captain has given me. Isn't it lovely?". Everyone agreed to it. They happily replied that the gift was looking pretty. Vasantha felt her day was fulfilled. She was very happy for having saved a man's life and also for the gift she had received.
 
Meaning of difficult words:
  
S.No
Words
Meaning
1.
Snugly
In a way that is comfortable or protected 
2.
Pat
To touch someone or something with flat hands to show your kindness
3.
Indeed
In reality
4.
Unanimous Refers to a complete agreement of many
5.
VerdictAn opinion or judgement
6.
ProudFeeling happy and satisfied with what you have done
Reference:
State Council of Educational Research and Training (2018). Term-3 English Standard-7. Man Overboard - Vasantha Murthi (pp. 125-130). Published by the Tamil Nadu Textbook and Educational Services Corporation.