Taxability of income earned from foreign vessel

It requires further details.

Are you earning income in the form of salary? or

Are you the owner of the vessel or what is your connection with vessel?

How many days you stayed in India in last four years & in last 10 years?

First you need to ascertain the residential status for AY-2020-21.Taxability is based on the residential status and reply to above queries..

I am not the owner of the vessel. I am earning salary and my Period of stay in India in following F.Y.are as follows;-
16-17 107 days
17-18 210 days
18-19 184 days
19-20 116 days

Though period of stay in the FY/PY -other conditions are satisfied.On an average you stay in India in FY is above 60days
and more than 365days in 4 years immediately preceding FY.
So you will be resident and you need to pay tax in India.

This answer may change in the following situations:

Further you need to check out if you are a crew member of a foreign going vessel..

Residential status for person taking employment outside India